translation and definition "mallet, hammer", Dictionary English-English online. mallet, hammer. Example sentences with "mallet", translation memory. tmClass. Hand tools and implements (hand-operated), in particular sledgehammers, mallets, hammers, chipping hammers, shovels, spades, pickaxes, axes, hatchets, picks, axes. tmClass. Hand tools, hand-operated, in particulra files, jig-saws, mallets (hammers), nail nippers, pickaxes (hand tools), knives (hand tools), screw extractors, tongs, spanners, trowels. Giga-fren. The springiness of ash was extremely useful in the handles. ‘Use a ball-peen hammer or a block of wood and a nail hammer to knock the tool head out of the ferule on the handle.’ ‘They would also have used tools such as planes, axes, adzes, draw knives, wedges, knives, chisels, hammers, mallets, awls, gouges, and spoon augers (a type of drill).’ ‘To drill through the tile you will need a hammer, a nail set, an electric drill and a masonry bit a little larger than the diameter of the screws you use.’. The Tier 2 hammer was short lived. Now it is time to upgrade to Tier 3!!! Hopefully the video helped!! If it did, please like, comment and sub!! Thank you!!. At Polaroid Corporation for ten years, he designed cam- eras, related mechanisms, and mallet hammer definition 5d automated machinery. Download PDF. Unlike the structured "engineering textbook" problems, which most students are used to, there is no right answer "in the back of the book" for any real design problem. Your bicycle is a simple example of a kinematic system that contains a chain drive to provide torque multiplication and sim- ple cable-operated linkages mallet hammer definition 5d braking. Since the book's first printing, Profs. The origin of the wheel and axle is not definitively known.

Drilling rigs are used to bore holes in the earth to obtain water or oil. Oil wells, water wells , or holes for geothermal heating are created with large drilling rigs.

Some types of hand-held drills are also used to drive screws and other fasteners. Some small appliances that have no motor of their own may be drill-powered, such as small pumps, grinders, etc. Some forms of drills have been used since the Pre-History, both to make holes in hard objects or as fire drills. Drills powered by electriciy or more rarely, compressed air are the most common tools in woodworking and machining shops.

Electric drills can be corded fed from an electric outlet through a power cable or cordless fed by rechargeable electric batteries. The latter have removable battery packs that can be swapped to allow uninterrupted drilling while recharging.

A popular use of hand-held power drills is to set screws into wood, through the use of screwdriver bits. Drills optimized for this purpose have a clutch to avoid damaging the slots on the screw head.

Most electric hammer drills are rated input power at between and watts. For much of the 20th century, attachments could commonly be purchased to convert corded electric hand drills into a range of other power tools, such as orbital sanders and power saws, more cheaply than purchasing dedicated versions of those tools.

As the prices of power tools and suitable electric motors have fallen such attachments have become much less common. Early cordless drills used interchangeable 7. Over the years battery voltages have increased, with 18 V drills being most common, but higher voltages are available, such as 24 V, 28 V, and 36 V.

This allows these tools to produce as much torque as some corded drills. Common battery types of are nickel-cadmium NiCd batteries and lithium-ion batteries , with each holding about half the market share.

NiCd batteries have been around longer, so they are less expensive their main advantage , but have more disadvantages compared to lithium-ion batteries. NiCd disadvantages are limited life, self-discharging, environment problems upon disposal, and eventually internally short circuiting due to dendrite growth. Lithium-ion batteries are becoming more common because of their short charging time, longer life, absence of memory effect , and low weight.

Instead of charging a tool for an hour to get 20 minutes of use, 20 minutes of charge can run the tool for an hour in average. Lithium-ion batteries also hold a charge for a significantly longer time than nickel-cadmium batteries, about two years if not used, vs. The hammer action of a hammer drill is provided by two cam plates that make the chuck rapidly pulse forward and backward as the drill spins on its axis.

Because the combined mass of the chuck and bit is comparable to that of the body of the drill, the energy transfer is inefficient and can sometimes make it difficult for larger bits to penetrate harder materials such as poured concrete.

The operator experiences considerable vibration, and the cams are generally made from hardened steel to avoid them wearing out quickly. A typical application for a hammer drill is installing electrical boxes, conduit straps or shelves in concrete.

The rotary hammer also known as a rotary hammer drill, roto hammer drill or masonry drill. Generally, standard chucks and drills are inadequate and chucks such as SDS and carbide drills that have been designed to withstand the percussive forces are used. These heavy bits are adept at pulverising the masonry and drill into this hard material with relative ease.

Some styles of this tool are intended for masonry drilling only and the hammer action cannot be disengaged. Other styles allow the drill to be used without the hammer action for normal drilling, or hammering to be used without rotation for chiselling. In Richard Trevithick designed a steam-driven rotary drill, also the first drill to be powered by steam.

This is accomplished through a piston design, rather than a spinning cam. Rotary hammers have much less vibration and penetrate most building materials.

They can also be used as "drill only" or as "hammer only" which extends their usefulness for tasks such as chipping brick or concrete. A typical application for a rotary hammer drill is boring large holes for lag bolts in foundations, or installing large lead anchors in concrete for handrails or benches. A drill press also known as a pedestal drill, pillar drill, or bench drill is a style of drill that may be mounted on a stand or bolted to the floor or workbench.

Portable models are made, some including a magnetic base. Major components include a base, column or pillar , adjustable table, spindle, chuck, and drill head, usually driven by an electric motor. The head typically has a set of three handles radiating from a central hub that are turned to move the spindle and chuck vertically.

A drill press is typically measured by its "swing", calculated as twice the distance from the center of the chuck to the closest edge of the column. Thus, a tool with 4" between chuck center and column edge is described as an 8" drill press. For most drill presses—especially those meant for woodworking or home use—speed change is achieved by manually moving a belt across a stepped pulley arrangement.

Some drill presses add a third stepped pulley to increase the number of available speeds. Modern drill presses can, however, use a variable-speed motor in conjunction with the stepped-pulley system. Medium-duty drill presses such as those used in machine shop tool room applications are equipped with a continuously variable transmission. This mechanism is based on variable-diameter pulleys driving a wide, heavy-duty belt.

This gives a wide speed range as well as the ability to change speed while the machine is running. Heavy-duty drill presses used for metalworking are usually of the gear-head type described below. Drill presses are often used for miscellaneous workshop tasks other than drilling holes.

This includes sanding, honing, and polishing. These tasks can be performed by mounting sanding drums, honing wheels and various other rotating accessories in the chuck. This can be unsafe in some cases, as the chuck arbor, which may be retained in the spindle solely by the friction of a taper fit , may dislodge during operation if the side loads are too high.

A geared head drill press transmits power from the motor to the spindle through spur gearing inside the machine's head, eliminating a flexible drive belt. This assures a positive drive at all times and minimizes maintenance. Gear head drills are intended for metalworking applications where the drilling forces are higher and the desired speed RPM is lower than that used for woodworking.

Levers attached to one side of the head are used to select different gear ratios to change the spindle speed, usually in conjunction with a two- or three-speed motor this varies with the material. Most machines of this type are designed to be operated on three-phase electric power and are generally of more rugged construction than equivalently sized belt-driven units. Virtually all examples have geared racks for adjusting the table and head position on the column.

Geared head drill presses are commonly found in tool rooms and other commercial environments where a heavy duty machine capable of production drilling and quick setup changes is required. In most cases, the spindle is machined to accept Morse taper tooling for greater flexibility. Larger geared head drill presses are frequently fitted with power feed on the quill mechanism, with an arrangement to disengage the feed when a certain drill depth has been achieved or in the event of excessive travel.

Some gear-head drill presses have the ability to perform tapping operations without the need for an external tapping attachment. This feature is commonplace on larger gear head drill presses. A clutch mechanism drives the tap into the part under power and then backs it out of the threaded hole once the proper depth is reached. Coolant systems are also common on these machines to prolong tool life under production conditions.

A radial arm drill press is a large geared-head drill press in which the head can be moved along an arm that radiates from the machine's column. As it is possible to swing the arm relative to the machine's base, a radial arm drill press is able to operate over a large area without having to reposition the workpiece. This feature saves considerable time because it is much faster to reposition the machine's head than it is to unclamp, move, and then re-clamp the workpiece to the table.

The size of work that can be handled may be considerable, as the arm can swing out of the way of the table, allowing an overhead crane or derrick to place a bulky workpiece on the table or base. A vise may be used with a radial arm drill press, but more often the workpiece is secured directly to the table or base, or is held in a fixture. Power spindle feed is nearly universal with these machines and coolant systems are common.

Larger-size machines often have power feed motors for elevating or moving the arm. The biggest radial arm drill presses are able to drill holes as large as four inches Radial arm drill presses are specified by the diameter of the column and the length of the arm.

The length of the arm is usually the same as the maximum throat distance. The radial arm drill press pictured to the right has a 9 inch diameter and a 3 foot long arm. The maximum throat distance of this machine would be approximately 36", giving a maximum swing of 72" 6 feet or 1. A magnetic drill is a portable machine for drilling holes in large and heavy workpieces which are difficult to move or bring to a stationary conventional drilling machine.

It has a magnetic base and drills holes with the help of cutting tools like annular cutters broach cutters or with twist drill bits. There are various types depending on their operations and specializations, like magnetic drilling cum tapping machines, cordless, pneumatic, compact horizontal, automatic feed, cross table base etc.

Mill drills are a lighter alternative to a milling machine. Although they are light in construction, they have the advantages of being space-saving and versatile as well as inexpensive, being suitable for light machining that may otherwise not be affordable. Drills are used in surgery to remove or create holes in bone ; specialties that use them include dentistry , orthopedic surgery and neurosurgery. The development of surgical drill technology has followed that of industrial drilling, including transitions to the use of lasers, endoscopy , use of advanced imaging technologies to guide drilling, and robotic drills.

Drills are often used simply as motors to drive a variety of applications, in much the same way that tractors with generic PTOs are used to power ploughs, mowers, trailers, etc. Drilling capacity indicates the maximum diameter a given power drill or drill press can produce in a certain material.

It is essentially a proxy for the continuous torque the machine is capable of producing. Typically a given drill will have its capacity specified for different materials, i. For example, the maximum recommended capacities for the DeWalt DCD cordless drill for specific drill bit types and materials are as follows: [20].

You must examine the designs and decide on a score for each. The scores are then multiplied by the weighting factors which are usually chosen so as to sum to a convenient number such as 1 and the products summed for each design. The weighted scores then give a ranking of designs.

Be cautious in applying these results. Remember the source and sub- jectivity of your scores and the weighting factors! There is a temptation to put more faith in these results than is justified.

After all, they look impressive! They can even be taken out to several decimal places! But they shouldn't be. You can then make a more informed decision as to the "best" design.

Detailed Design This step usually includes the creation of a complete set of assembly and detail drawings or computer-aided design CAD part files, for each and every part used in the design. Each detail drawing must specify all the dimensions and the material specifications nec- essary to make that part.

From these drawings or CAD files a prototype test model or models must be constructed for physical testing. Most likely the tests will discover more flaws, requiring further iteration. This usually involves the construction of a prototype physical model. A mathematical model, while very useful, can never be as complete and accu- rate a representation of the actual physical system as a physical model, due to the need to make simplifying assumptions.

Prototypes are often very expensive but may be the most economical way to prove a design, short of building the actual, full-scale device.

Prototypes can take many forms, from working scale models to full-size, but simplified, representations of the concept. Scale models introduce their own complications in re- gard to proper scaling of the physical parameters. For example, volume of material var- ies as the cube of linear dimensions, but surface area varies as the square.

Heat transfer to the environment may be proportional to surface area, while heat generation may be proportional to volume. So linear scaling of a system, either up or down, may lead to behavior different from that of the full-scale system. One must exercise caution in scal- ing physical models. You will find as you begin to design linkage mechanisms that a simple cardboard model of your chosen link lengths, coupled together with thumbtacks for pivots, will tell you a great deal about the quality and character of the mechanism's motions.

You should get into the habit of making such simple articulated models for all your linkage designs. TESTING of the model or prototype may range from simply actuating it and ob- serving its function to attaching extensive instrumentation to accurately measure dis- placements, velocities, accelerations, forces, temperatures, and other parameters. Tests may need to be done under controlled environmental conditions such as high or low tem- perature or humidity.

The microcomputer has made it possible to measure many phe- nomena more accurately and inexpensively than could be done before. Production Finally, with enough time, money, and perseverance, the design will be ready for pro- duction. This might consist of the manufacture of a single final version of the design, but more likely will mean making thousands or even millions of your widget.

The dan- ger, expense, and embarrassment of finding flaws in your design after making large quantities of defective devices should inspire you to use the greatest care in the earlier steps of the design process to ensure that it is properly engineered.

The design process is widely used in engineering. Engineering is usually defined in terms of what an engineer does, but engineering can also be defined in terms of how the engineer does what he or she does. Engineering is as much a method, an approach, a process, a state of mind for problem solving, as it is an activity. The engineering ap- proach is that of thoroughness, attention to detail, and consideration of all the possibili- ties.

While it may seem a contradiction in terms to emphasize "attention to detail" while extolling the virtues of open-minded, freewheeling, creative thinking, it is not. The two activities are not only compatible, they are symbiotic.

It ultimately does no good to have creative, original ideas if you do not, or cannot, carry out the execution of those ideas and "reduce them to practice. For example, to do a creditable job in the de- sign of anything, you must completely define the problem. If you leave out some detail of the problem definition, you will end up solving the wrong problem.

Likewise, you must thoroughly research the background information relevant to the problem. You must exhaustively pursue conceptual potential solutions to your problem.

You must then ex- tensively analyze these concepts for validity. And, finally, you must detail your chosen design down to the last nut and bolt to be confident it will work. If you wish to be a good designer and engineer, you must discipline yourself to do things thoroughly and in a log- ical, orderly manner, even while thinking great creative thoughts and iterating to a solu- tion.

Both attributes, creativity and attention to detail, are necessary for success in engi- neering design. Design methodology is the study of the process of designing. One goal of this research is to define the design process in suffi- cient detail to allow it to be encoded in a form amenable to execution in a computer, us- ing "artificial intelligence" AI. Dixon[6] defines a design as a state of information which may be in any of several forms It may be partial or complete.

It ranges from a small amount of highly abstract information early in the design process to a very large amount of detailed information later in the process sufficient to perform manufacturing. It may include, but is not limited to, information about size and shape, function, materials, marketing, simulated performance, manufacturing processes, toler- ances, and more.

Indeed, any and all information relevant to the physical or economic life of a designed object is part of its design.

He goes on to describe several generalized states of information such as the requirements state which is analogous to our performance specifications. Information about the physical concept is referred to as the conceptual state of information and is analogous to our ideation phase.

His feature configuration and parametric states of information are similar in concept to our detailed design phase. Dixon then defines a design process as: The series of activities by which the information about the designed object is changed from one information state to another. Axiomatic Design N. Suh[7] suggests an axiomatic approach to design in which there are four domains: customer domain, functional domain, physical domain, and the process domain.

These represent a range from "what" to "how," i. He defines two axioms that need to be satisfied to accomplish this: I Maintain the independence of the functional requirements.

The first of these refers to the need to create a complete and nondependent set of perfor- mance specifications. The second indicates that the best design solution will have the lowest information content i. Others have earlier referred to this second idea as KISS, which stands, somewhat crudely, for "keep it simple, stupid.

The interested reader is referred to the literature cited in the bib- liography to this chapter for more complete information. Unlike the structured "engineering textbook" problems, which most students are used to, there is no right answer "in the back of the book" for any real design problem.

Some solutions will be better than others, but many will work. Some will not! There is no "one right answer" in design engineering, which is what makes it interesting. The only way to determine the relative merits of various potential design solutions is by thorough analysis, which usually will include physical testing of constructed prototypes. Because this is a very expensive process, it is desirable to do as much analysis on paper, or in the computer, as possible before actually building the de- vice.

Where feasible, mathematical models of the design, or parts of the design, should be created. These may take many forms, depending on the type of physical system in- volved. In the design of mechanisms and machines it is usually possible to write the equations for the rigid-body dynamics of the system, and solve them in "closed form" with or without a computer.

Accounting for the elastic deformations of the members of the mechanism or machine usually requires more complicated approaches using finite difference techniques or the finite element method FEM.

Even robots must This slow author had to be programmed by a human. Human factors engineering is the study of the human- ask for an explanation, machine interaction and is defined as an applied science that coordinates the design of which was: "The answer is devices, systems, and physical working conditions with the capacities and requirements not in the back of the of the worker.

The machine designer must be aware of this subject and design devices to book. We often see reference to the good or bad ergonomics of an automobile interior or a household appliance.

A machine de- signed with poor ergonomics will be uncomfortable and tiring to use and may even be dangerous. Have you programmed your VCR lately, or set its clock? There is a wealth of human factors data available in the literature. Some references are noted in the bibliography. The type of information which might be needed for a machine design problem ranges from dimensions of the human body and their distribu- tion among the population by age and gender, to the ability of the human body to with- stand accelerations in various directions, to typical strengths and force generating abili- ty in various positions.

Obviously, if you are designing a device that will be controlled by a human a grass shortener, perhaps , you need to know how much force the user can exert with hands held in various positions, what the user's reach is, and how much noise the ears can stand without damage.

If your device will carry the user on it, you need data on the limits of acceleration which the body can tolerate. Data on all these topics exist. Much of it was developed by the government which regularly tests the ability of military personnel to withstand extreme environmental conditions. Part of the background re- search of any machine design problem should include some investigation of human factors. Many engineering students picture themselves in professional practice spending most of their time doing calculations of a nature similar to those they have done as students.

Fortunately, this is seldom the case, as it would be very boring. Actually, engineers spend the largest percentage of their time communicating with others, either orally or in writ- ing. Engineers write proposals and technical reports, give presentations, and interact with support personnel and managers. When your design is done, it is usually necessary to present the results to your client, peers, or employer. The usual form of presentation is a formal engineering report.

Thus, it is very important for the engineering student to develop his or her communication skills. You may be the cleverest person in the world, but no one will know that if you cannot communicate your ideas clearly and concisely. In fact, if you cannot explain what you have done, you probably don't understand it your- self. To give you some experience in this important skill, the design project assignments in later chapters are intended to be written up in formal engineering reports.

Informa- tion on the writing of engineering reports can be found in the suggested readings in the bibliography at the end of this chapter.

The most common in the United States are the U. The author boldly suggests with tongue only slightly in cheek that this unit of mass in the ips system be called a blob bl to distinguish it more clearly from the slug sl , and to help the student avoid some of the common units errors listed above.

Blob does not sound any sillier than slug, is easy to remember, implies mass, and has a convenient abbreviation bl which is an anagram for the abbreviation for pound Ib. Besides, if you have ever seen a garden slug, you know it looks just like a "little blob. However the student must remember to divide the value of m in Ibm by gc when substituting into this form of Newton's equation. Thus the Ibm will be divided either by This is sometimes also referred to as the mks system.

Force is derived from Newton's law, equation 1. When converting between SI and u. The gravitational constant g in the SI system is ap- proximately 9. The principal system of units used in this textbook will be the U. Most machine design in the United States is still done in this system.

Table shows some of the variables used in this text and their units. The inside front cover contains a table of conversion factors between the U. S, and SI systems. The student is cautioned to always check the units in any equation written for a prob- lem solution, whether in school or in professional practice after graduation. If properly written, an equation should cancel all units across the equal sign.

If it does not, then you can be absolutely sure it is incorrect. Unfortunately, a unit balance in an equation does not guarantee that it is correct, as many other errors are possible. Always double-check your results. You might save a life. Then we will investigate the analysis of those and other mechanisms for their kinematic behavior.

Finally, in Part II we will deal with the dynamic analysis of the forces and torques generated by these moving machines. These topics cover the essence of the early stages of a design project.

Once the kinematics and kinetics of a design have been determined, most of the concep- tual design will have been accomplished. What then remains is detailed design-sizing the parts against failure. The topic of detailed design is discussed in other texts such as reference [8]. Machine Design: An Integrated Approach.

For additional information on the history of kinematics, the following are recommended: Artobolevsky, I. Brown, H. Five Hundred and Seven Mechanical Movements. Erdman, A. Ferguson, E. Freudenstein, F. Kinematic Synthesis of Linkages. McGraw-Hill: New York, pp. Nolle, H. Developments after Developments up to Spatial Synthesis and Optimization. Reuleaux, F. The Kinematics of Machinery, A.

Kennedy, translator. Dover Publications: New York, pp. Strandh, S. A History of the Machine. For additional information on creativity and the design process, the following are recommended: Alger, J. Creative Synthesis in Design. Allen, M. Morphological Creativity. Altschuller, G. Creativity as an Exact Science. Gordon and Breach: New York. Buhl, H. Creative Engineering Design. Fey, V. Gordon, W. Haefele, W. Creativity and Innovation.

Van Nostrand Reinhold: New York. Harrisberger, L. Osborn, A. Applied Imagination. Scribners: New York. Pleuthner, W. Soh, N. The Principles of Design. Oxford University Press: New York. Taylor, C. Widening Horizons in Creativity. Von Fange, E. Professional Creativity. For additional information on Human Factors, the following are recommended: Bailey, R.

Burgess, W. Petrocelli Books. Clark, T. The Ergonomics of Workspaces and Machines. Taylor and Francis. Huchinson, R. New Horizons for Human Factors in Design.

McGraw-Hill: New York. McCormick, D. Human Factors Engineering. Osborne, D. Ergonomics at Work. Pheasant, S. Salvendy, G. Handbook of Human Factors. Sanders, M. Human Factors in Engineering and Design. Woodson, W. Human Factors Design Handbook. For additional information on writing engineering reports, the following are recommended: Barrass, R.

Scientists Must Write. Crouch, W. A Guide to Technical Writing. The Ronald Press: New York. Davis, D. Elements of Engineering Reports. Chemical Publishing Co. Gray, D. Information Resources Press: Washington, D. Michaelson, H.

Nelson, J. Writing the Technical Report. It will also present some very simple but powerful analysis tools which are useful in the synthesis of mechanisms. The system's DOF is equal to the number of indepen- dent parameters measurements which are needed to uniquely define its position in space at any instant of time. Note that DOF is defined with respect to a selected frame of reference.

Figure shows a pencil lying on a flat piece of paper with an x, y coordi- nate system added. If we constrain this pencil to always remain in the plane of the pa- per, three parameters DOF are required to completely define the position of the pencil on the paper, two linear coordinates x, y to define the position of anyone point on the pencil and one angular coordinate 8 to define the angle of the pencil with respect to the axes.

The minimum number of measurements needed to define its position are shown in the figure as x, y, and 8. This system of the pencil in a plane then has three DOF. Note that the particular parameters chosen to define its position are not unique. Any alternate set of three parameters could be used. There is an infinity of sets of parameters possible, but in this case there must be three parameters per set, such as two lengths and an an- gie, to define the system's position because a rigid body in plane motion has three DOF.

Hold it above your desktop and move it about. You now will need six parameters to define its six DOF. Any rigid body in three-space has six degrees of freedom. Try to identify these six DOF by moving your pencil or pen with respect to your desktop. The pencil in these examples represents a rigid body, or link, which for purposes of kinematic analysis we will assume to be incapable of deformation.

This is merely a con- venient fiction to allow us to more easily define the gross motions of the body. We can later superpose any deformations due to external or inertial loads onto our kinematic motions to obtain a more complete and accurate picture of the body's behavior. But re- member, we are typically facing a blank sheet of paper at the beginning stage of the de- sign process. We cannot determine deformations of a body until we define its size, shape, material properties, and loadings.

Thus, at this stage we will assume, for purposes of initial kinematic synthesis and analysis, that our kinematic bodies are rigid and massless. In three-dimensional space, there may be rotation about any axis any skew axis or one of the three principal axes and also simultaneous translation which can be resolved into components along three axes. In a plane, or two-dimensional space, complex motion be- comes a combination of simultaneous rotation about one axis perpendicular to the plane and also translation resolved into components along two axes in the plane.

For simplic- ity, we will limit our present discussions to the case of planar kinematic systems. All other points on the body describe arcs about that center. A reference line drawn on the body through the center changes only its angular orientation. Pure translation all points on the body describe parallel curvilinear or rectilinear paths.

Complex motion a simultaneous combination of rotation and translation. Any reference line drawn on the body will change both its linear position and its angular orientation. Translation and rotation represent independent motions of the body.

Each can ex- ist without the other. If we define a 2-D coordinate system as shown in Figure , the x and y terms represent the translation components of motion, and the e term represents the rotation component. Linkages are the basic building blocks of all mechanisms. We will show in later chapters that all common forms of mechanisms cams, gears, belts, chains are in fact variations on a common theme of linkages.

Linkages are made up of links and joints. A link, as shown in Figure , is an assumed rigid body which possesses at least two nodes which are points for attachment to other links. Binary link - one with two nodes. Ternary link - one with three nodes. Quaternary link - one with four nodes. A joint is a connection between two or more links at their nodes , which allows some motion, or potential motion, between the connected links. Joints also called ki- nematic pairs can be classified in several ways: 1 By the type of contact between the elements, line, point, or surface.

Reuleaux [1] coined the term lower pair to describe joints with surface contact as with a pin surrounded by a hole and the term higher pair to describe joints with point or line contact. However, if there is any clearance between pin and hole as there must be for motion , so-called surface contact in the pin joint actually becomes line contact, as the pin contacts only one "side" of the hole.

Likewise, at a microscopic level, a block sliding on a flat surface actually has contact only at discrete points, which are the tops of the surfaces' asperities.

The main practical advantage of lower pairs over higher pairs is their better ability to trap lubricant between their enveloping surfaces. This is especially true for the rotating pin joint. The lubricant is more easily squeezed out of a higher pair, nonenveloping joint. As a result, the pin joint is preferred for low wear and long life, even over its lower pair cousin, the prismatic or slider joint.

Figure a shows the six possible lower pairs, their degrees of freedom, and their one-letter symbols. The revolute R and the prismatic P pairs are the only lower pairs usable in a planar mechanism. The Rand P pairs are the basic building blocks of all other pairs which are combinations of those two as shown in Table A more useful means to classify joints pairs is by the number of degrees of free- dom that they allow between the two elements joined.

Figure also shows examples of both one- and two-freedom joints commonly found in planar mechanisms. Figure b shows two forms of a planar, one-freedom joint or pair , namely, a rotating pin joint R and a translating slider joint P. These are also referred to as full joints i. These are both contained within and each is a limiting case of another common, one-freedom joint, the screw and nut Figure a.

Motion of either the nut or the screw with respect to the other results in helical motion. If the helix angle is made zero, the nut rotates without advancing and it becomes the pin joint. If the helix angle is made 90 degrees, the nut will translate along the axis of the screw, and it becomes the slider joint.

Figure c shows examples of two-freedom joints h1gherpairs which simultaneously allow two independent, relative motions, namely translation and rotation, between the joined links.

Paradoxically, this two-freedom joint is sometimes referred to as a "half joint," with its two freedoms placed in the denominator. The half joint is also called a roll-slide joint because it allows both rolling and sliding.

A spherical, or ball-and-socket joint Figure a , is an example of a three-freedom joint, which allows three independent angular motions be- tween the two links joined. This ball joint would typically be used in a three-dimensional mechanism, one example being the ball joints in an automotive suspension system. A joint with more than one freedom may also be a higher pair as shown in Figure c. Note that if you do not allow the two links in Hgore c connected by a roll-slide joint to slide, perhaps by providing a high friction coefficient between them, you can "lock out" the translating At freedom and make it behave as a full joint.

This is then called a pure rolling joint and has rotational freedom AD only. A cornmon example of this type of joint is your automobile tire rolling against die road, as shown in Figure e.

In normal use there is pure rolling and no sliding at Ibis joint, unless, of course, you encounter an icy road or become too enthusiastic about accelerating or cornering. If you lock your brakes on ice, this joint converts to a pure sliding one like the slider block in Figure b. Friction determines the actual number of freedoms at this kind of joint.

It can be pure roll, pure slide, or roll-slide. To visualize the degree of freedom of a joint in a mechanism, it is helpful to "men- tally disconnect" the two links which create the joint from the rest of the mechanism. You can then more easily see how many freedoms the two joined links have with respect to one another.

Figure c also shows examples of both form-closed and force-closed joints. A form-closed joint is kept together or closed by its geometry. A pin in a hole or a slider in a two-sided slot are form closed. In contrast, a force-closed joint, such as a pin in a half-bearing or a slider on a surface, requires some external force to keep it together or closed.

This force could be supplied by gravity, a spring, or any external means. There can be substantial differences in the behavior of a mechanism due to the choice of force or form closure, as we shall see. The choice should be carefully considered. In linkag- es, form closure is usually preferred, and it is easy to accomplish.

But for cam-follower systems, force closure is often preferred. This topic will be explored further in later chap- ters. Figure d shows examples of joints of various orders, where order is defined as the number of links joined minus one. It takes two links to make a single joint; thus the simplest joint combination of two links has order one.

As additional links are placed on the same joint, the order is increased on a one for one basis. Joint order has significance in the proper determination of overall degree of freedom for the assembly. We gave def- initions for a mechanism and a machine in Chapter 1.

With the kinematic elements of links and joints now defined, we can define those devices more carefully based on Reu- leaux's classifications of the kinematic chain, mechanism, and machine.

A mechanism is defined as: A kinematic chain in which at least one link has been "grounded," or attached, to the frame of reference which itself may be in motion. A machine is defined as: A combination of resistant bodies arranged to compel the mechanical forces of nature to do work accompanied by determinate motions.

By Reuleaux's definition [1] a machine is a collection of mechanisms arranged to transmit forces and do work. He viewed all energy or force transmitting devices as ma- chines which utilize mechanisms as their building blocks to provide the necessary mo- tion constraints.

We will now define a crank as a link which makes a complete revolution and is piv- oted to ground, a rocker as a link which has oscillatory back andforth rotation and is pivoted to ground, and a coupler or connecting rod which has complex motion and is not pivoted to ground. Ground is defined as any link or links that are fixed nonmov- ing with respect to the reference frame.

Note that the reference frame may in fact itself be in motion. We need to be able to quickly determine the DOF of any collection of links and joints which may be suggested as a solution to a problem. Degree of free- dom also called the mobility M of a system can be defined as: Degree of Freedom the number of inputs which need to be provided in order to create a predictable output; also: the number of independent coordinates required to define its position.

At the outset of the design process, some general definition of the desired output motion is usually available. The number of inputs needed to obtain that output mayor may not be specified. Cost is the principal constraint here. Each required input will need some type of actuator, either a human operator or a "slave" in the fonn of a motor, sole- noid, air cylinder, or other energy conversion device.

These devices are discussed in Section 2. These multiple input devices will have to have their actions coordinated by a "controller," which must have some intelligence. This control is now often provid- ed by a computer but can also be mechanically programmed into the mechanism design. There is no requirement that a mechanism have only one DOF, although that is often desirable for simplicity.

Some machines have many DOF. For example, picture the num- ber of control levers or actuating cylinders on a bulldozer or crane. See Figure I-lb p. Kinematic chains or mechanisms may be either open or closed. Figure shows both open and closed mechanisms. A closed mechanism will have no open attachment points or nodes and may have one or more degrees of freedom. An open mechanism of more than one link will always have more than one degree of freedom, thus requiring as many actuators motors as it has DOF.

A common example of an open mechanism is an industrial robot. An open kinematic chain of two binary links and one joint is called a dyad. The sets of links shown in Figure a and b are dyads. Reuleaux limited his definitions to closed kinematic chains and to mechanisms hav- ing only one DOF, which he called constrained. A multi-DOF mechanism, such as a robot, will be constrained in its motions as long as the necessary number of inputs are supplied to control all its DOF.

Degree of Freedom in Planar Mechanisms To determine the overall DOF of any mechanism, we must account for the number of links and joints, and for the interactions among them. The DOF of any assembly of links can be predicted from an investigation of the Gruebler condition.

In Figure c the half joint removes only one DOF from the system because a half joint has two DOF , leaving the system of two links connected by a half joint with a total of five DOF. In addition, when any link is grounded or attached to the reference frame, all three of its DOF will be removed. Multiple joints count as one less than the number oflinks joined at that joint and add to the "full" 11 category. The DOF of any proposed mechanism can be quickly ascertained from this expression before investing any time in more detailed design.

It is interesting to note that this equation has no information in it about link sizes or shapes, only their quantity. Figure a shows a mechanism with one DOF and only full joints in Bossing Mallet Hammer Definition Youtube it. Figure b shows a structure with zero DOF and which contains both half and mul- tiple joints. Note the schematic notation used to show the ground link. The ground link need not be drawn in outline as long as all the grounded joints are identified.

Note also the joints labeled "multiple" and "half' in Figure a and b. As an exercise, compute the DOF of these examples with Kutzbach's equation.

Degree of Freedom in Spatial Mechanisms The approach used to determine the mobility of a planar mechanism can be easily ex- tended to three dimensions. Each unconnected link in three-space has 6 DOF, and any one of the six lower pairs can be used to connect them, as can higher pairs with more freedom. Grounding a link removes 6 DOF. This leads to the Kutzbach mobility equation for spa- tiallinkages: where the subscript refers to the number of freedoms of the joint.

We will limit our study to 2-D mechanisms in this text. There are only three possibilities. If the DOF is positive, it will be a mechanism, and the links will have relative motion. If the DOF is exactly zero, then it will be a structure, and no motion is possible.

If the DOF is negative, then it is a preloaded structure, which means that no motion is possible and some stresses may also be present at the time of assembly. Figure shows examples of these three cases. One link is grounded in each case. Figure a shows four links joined by four full joints which, from the Gruebler equation, gives one DOF. It will move, and only one input is needed to give predictable results.

Figure b shows three links joined by three full joints. It has zero DOF and is thus a structure. Figure c shows two links joined by two full joints. It has a DOF of minus one, making it a preloaded structure. In order to insert the two pins without straining the links, the center distances of the holes in both links must be exactly the same. Practical- ly speaking, it is impossible to make two parts exactly the same. There will always be some manufacturing error, even if very small.

Thus you may have to force the second pin into place, creating some stress in the links. The structure will then be preloaded. You have probably met a similar situation in a course in applied mechanics in the form of an indeterminate beam, one in which there were too many supports or constraints for the equations available. Both structures and preloaded structures are commonly encountered in engineering. In fact the true structure of zero DOF is rare in engineering practice.

Even simple structures like the chair you are sitting in then their interconnection are often preloaded. Since our concern here is with mechanisms, we will concentrate on is impossible. Order in this context refers to the number of nodes perlink, i. The value of number synthesis is to allow the exhaustive determination of all possible combinations of links which will yield any chosen DOF. This then equips the designer with a definitive catalog of potential linkages to solve a variety of motion control prob- lems.

As an example we will now derive all the possible link combinations for one DOF, including sets of up to eight links, and link orders up to and including hexagonal links. For simplicity we will assume that the links will be connected with only full rotating joints. We can later introduce half joints, multiple joints, and sliding joints through link- age transformation.

First let's look at some interesting attributes of linkages as defined by the above assumption regarding full joints. Hypothesis: If all joints are full joints, an odd number of DOFrequires an even number of links and vice versa. Proof: Given: All even integers can be denoted by 2m or by 2n, and all odd integers can be denoted by 2m - I or by 2n - 1, where n and m are any positive integers.

The number of joints must be a positive integer. There are other examples of paradoxes which disobey the Gruebler criterion due to their unique geometry. The designer needs to be alert to these possible inconsistencies.

Isomers in chemis- try are compounds that have the same number and type of atoms but which are intercon- nected differently and thus have different physical properties. Figure a shows two hydrocarbon isomers, n-butane and isobutane. Note that each has the same number of carbon and hydrogen atoms C4HlO , but they are differently interconnected and have different properties. Linkage isomers are analogous to these chemical compounds in that the links like atoms have various nodes electrons available to connect to other links' nodes.

The assembled linkage is analogous to the chemical compound. Depending on the particular connections of available links, the assembly will have different motion properties. The number of isomers possible from a given collection of links as in any row of Table is far from obvious.

In fact the problem of mathematically predicting the number of iso- mers of all link combinations has been a long-unsolved problem. Many researchers have spent much effort on this problem with some recent success. See references [3] through [7] for more information. Dhararipragada [6] presents a good historical summary of iso- mer research to Table shows the number of valid isomers found for one-DOF mechanisms with revolute pairs, up to 12 links.

Figure b shows all the isomers for the simple cases of one DOF with 4 and 6 links. Note that there is only one isomer for the case of 4 links. An isomer is only unique if the interconnections between its types of links are different. That is, all binary links are considered equal, just as all hydrogen atoms are equal in the chemical analog.

Link lengths and shapes do not figure into the Gruebler criterion or the condition of isomer- ism. The 6-link case of 4 binaries and 2 ternaries has only two valid isomers.

These are known as the Watt's chain and the Stephenson's chain after their discoverers. Note the different interconnections of the ternaries to the binaries in these two examples. The Watt's chain has the two ternaries directly connected, but the Stephenson's chain does not.

There is also a third potential isomer for this case of six links, as shown in Figure c, but it fails the test of distribution of degree of freedom, which requires that the overall DOF here 1 be uniformly distributed throughout the linkage and not concentrat- ed in a subchain. This creates a truss, or delta triplet. Thus this arrange- ment has been reduced to the simpler case of the fourbar linkage despite its six bars.

This is an invalid isomer and is rejected. It is left as an exercise for the reader to find the 16 valid isomers of the eight bar, one-DOF cases.

If we now relax the arbitrary constraint which restricted us to only revolute joints, we can transform these basic linkages to a wider variety of mech- anisms with even greater usefulness.

There are several transformation techniques or rules that we can apply to planar kinematic chains. This will create a multiple joint but will not change the DOF of the mechanism.

A multiple joint will be created, and the DOF will be reduced. Figure 2-lOa shows a fourbar crank-rocker linkage transformed into the fourbar slider-crank by the application of rule 1.

It is still a fourbar linkage. Link 4 has be- come a sliding block. The Gruebler's equation is unchanged at one DOF because the slid- er block provides a full joint against link 1, as did the pin joint it replaces. Note that this transformation from a rocking output link to a slider output link is equivalent to increas- ing the length radius of rocker link 4 until its arc motion at the joint between links 3 and 4 becomes a straight line.

Thus the slider block is equivalent to an infinitely long rocker link 4, which is pivoted at infinity along a line perpendicular to the slider axis as shown in Figure 2-lOa. The first version shown retains the same motion of fourbar linkage are the slider as the original linkage by use of a curved slot in link 4. The effective coupler replaced by prismatic.

Also, pler. The second version shown has the slot made straight and perpendicular to the slid- if three revolutes in a four- er axis. The effective coupler now is "pivoted" at infinity. This is called a Scotch yoke bar loop are replaced with and gives exact simple harmonic motion of the slider in response to a constant speed in- prismatic joints, the one put to the crank.

Link 3 has been removed and a half joint substituted for a full pinned links together as joint between links 2 and 4. This still has one DOF, and the cam-follower is in fact a one. This effectively fourbar linkage in another disguise, in which the coupler link 3 has become an effec- reduces the assembly to a tive link of variable length. We will investigate the fourbar linkage and these variants of threebar linkage which should have zero DOF.

But, a delta triplet with Figure 2-lla shows the Stephenson's sixbar chain from Figure b p. It is one DOF-another Gruebler's paradox. The two triangular subchains are obvious. Just as the fourbar chain is the basic building block of one-DOF mechanisms, this threebar triangle delta triplet is the basic building block of zero-DOF structures trusses. A dwell is a period in which the output link remains stationary while the input link continues to move.

There are many applications in machinery which require intermittent motion. The earn-follower varia- tion on the fourbar linkage as shown in Figure 2-lOc p. The design of that device for both intermittent and continuous output will be ad- dressed in detail in Chapter 8.

Other pure linkage dwell mechanisms are discussed in the next chapter. This is also a transformed fourbar linkage in which the coupler has been replaced by a half joint. The input crank link 2 is typically motor driven at a constant speed. The Geneva wheel is fitted with at least three equis- paced, radial slots. The crank has a pin that enters a radial slot and causes the Geneva wheel to turn through a portion of a revolution.

When the pin leaves that slot, the Gene- va wheel remains stationary until the pin enters the next slot. The result is intermittent rotation of the Geneva wheel. The crank is also fitted with an arc segment, which engages a matching cutout on the periphery of the Geneva wheel when the pin is out of the slot.

This keeps the Gene- va wheel stationary and in the proper location for the next entry of the pin. A Geneva wheel needs a minimum of three stops to work. The maximum number of stops is limited only by the size of the wheel. The arm pivots about the center of the toothed ratchet wheel and is moved back and forth to index the wheel. The driving pawl rotates the ratchet wheel or ratchet in the counter- clockwise direction and does no work on the return clockwise trip.

The locking pawl prevents the ratchet from reversing direction while the driving pawl returns. Both pawls are usually spring-loaded against the ratchet. This mechanism is widely used in devices such as "ratchet" wrenches, winches, etc. This mechanism is anal- ogous to an open Scotch yoke device with multiple yokes. It can be used as an intermit- tent conveyor drive with the slots arranged along the conveyor chain or belt. It al 'r;an be used with a reversing motor to get linear, reversing oscillation of a single slotte, put slider.

Even with the limitations imposed in the number synthesis example one DOF, eight links, up to hexagonal order , there are eight linkage combinations shown in Table p.

In addition, we can introduce another factor, namely mechanism inversion. An inversion is created by grounding a different link in the kinematic chain. Thus there are as many inversions of a given linkage as it has links.

The motions resulting from each inversion can be quite different, but some inver- sions of a linkage may yield motions similar to other inversions of the same linkage. In these cases only some of the inversions may have distinctly different motions. We will denote the inversions which have distinctly different motions as distinct inversions.

Figure previous page shows the four inversions of the fourbar slider-crank linkage, all of which have distinct motions. Inversion 1, with link 1 as ground and its slider block in pure translation, is the most commonly seen and is used for piston en- gines and piston pumps.

Inversion 2 is obtained by grounding link 2 and gives the Whitworth or crank-shaper quick-return mechanism, in which the slider block has complex motion. Quick-return mechanisms will be investigated further in the next chapter. Inversion 3 is obtained by grounding link 3 and gives the slider block pure rotation. Inversion 4 is obtained by grounding the slider link 4 and is used in hand op- erated, well pump mechanisms, in which the handle is link 2 extended and link 1 pass- es down the well pipe to mount a piston on its bottom.

It is upside down in the figure. The Watt's sixbar chain has two distinct inversions, and the Stephenson's sixbar has three distinct inversions, as shown in Figure The pin-jointed fourbar has four distinct inversions: the crank-rocker, double-crank, double-rocker, and triple-rocker which are shown in Figures and It also appears in various disguis- es such as the slider-crank and the earn-follower.

It is in fact the most common and ubiquitous device used in machinery. It is also extremely versatile in terms of the types of motion which it can generate. Simplicity is one mark of good design. The fewest parts that can do the job will usu- ally give the least expensive and most reliable solution. Thus the fourbar linkage should be among the first solutions to motion control problems to be investigated.

The Grashof condition [8] is a very simple relationship which predicts the rotation behavior or rotat- ability of a fourbar linkage's inversions based only on the link lengths. This is called a Class I kinematic chain. If the inequality is not true, then the linkage is non-Grashof and no link will be capable of a complete rev- olution relative to any other link.

This is a Class II kinematic chain. Note that the above statements apply regardless of the order of assembly of the links. That is, the determination of the Grashof condition can be made on a set of unassembled links. The motions possible from a fourbar linkage will depend on both the Grashof con- dition and the inversion chosen.

The inversions will be defined with respect to the short- est link. Ground the shortest link and you will get a double-crank, in which both links piv- oted to ground make complete revolutions as does the coupler. Ground the link opposite the shortest and you will get a Grashof double-rocker, in which both links pivoted to ground oscillate and only the coupler makes a full revolu- tion.

At these change points the output behavior will become indeterminate. The linkage behavior is then unpredictable as it may assume either of two configurations. Its motion must be lim- ited to avoid reaching the change points or an additional, out-of-phase link provided to guarantee a "carry through" of the change points. See Figure c. Figure p. The two crank-rockers give similar motions and so are not distinct from one another.

Figure a and b shows the parallelogram and antiparallelogram configurations of the special-case Grashof linkage. The parallelogram linkage is quite useful as it ex- actly duplicates the rotary motion of the driver crank at the driven crank. One common use is to couple the two windshield wiper output rockers across the width of the wind- shield on an automobile.

The coupler of the parallelogram linkage is in curvilinear trans- lation, remaining at the same angle while all points on it describe identical circular paths.

It is often used for this parallel motion, as in truck tailgate lifts and industrial robots. The antiparallelogram linkage is also a double-crank, but the output crank has an angular velocity different from the input crank. Note that the change points allow the linkage to switch unpredictably between the parallelogram and anti parallelogram forms every degrees unless some additional links are provided to carry it through those positions.

This can be achieved by adding an out-of-phase companion linkage coupled to the same crank, as shown in Figure c. A common application of this double par- allelogram linkage was on steam locomotives, used to connect the drive wheels togeth- er. The change points were handled by providing the duplicate linkage, 90 degrees out of phase, on the other side of the locomotive's axle shaft. When one side was at a change point, the other side would drive it through.

The double-parallelogram arrangement shown in Figure c is quite useful as it gives a translating coupler which remains horizontal in all positions.

Wood Carving Machine Ebay Job Bottom Mount Ball Bearing Drawer Slides Example