www roymech co uk

7/22/2019 Www Roymech Co Uk

1/4

Disclaimer: The information on this page has not been checked by an independent person. Use this information at your own risk.

ROYMECH

Click arrows to page advertsClick arrows to page adverts

Shigley's MechanicalEngineering Des...

Budynas Buy New

Privacy Information

HomeMachine_Parts_Index

MechanismsMechanisms

More details on Mechanism design are to be found in the links below the table

IntroductionIntroduction

A mechanism considered to be an assembly of mechanical items designed to achieve a specific purpose within a machine. There are clearly an infinite number ofmechanisms available but the notes and links are concentrating on the specific ones as listed below. For specific information on linkages please refer..Linkages

Motion Control Using ComputersMotion Control Using Computers

The notes below relate generally to mechanical methods for providing relative motion and forces. There is an increasing tendency to produce motions using servohydraulic systems and stepping motors under the control of digital computers. Although the mechanism design often requires creativity and a high level of analysisthe final product is often low priced and provides reliable, efficient, predictable performance. However a mechanism is generally made to perform a fixed operation,reliably and predictably. Computer controlled motions can be continuously monitored and if necessary modified. If the output motion is changed from a harmonicmotion to a periodic square wave motion or a sawtooth motion then changing the control parameters for a computer controlled system is often very convenient. If alarge number of systems have been developed then the cost of modifying the software or firmware is much less than modifying a large number of mechanisms..

Although the motions of many of high technology machines and computer systems are being controlled by computers. The need for mechanisms is also increasing inconsumer goods e.g. mechanisms in consumer goods, toys, lifting equipment, vehicles, aircraft, industrial machines, gardening implements,etc etc etc... ......

Classification Of Mec hanismsClassification Of Mec hanisms

There are many methods of classifying mechanisms. The following list is a functional list based on the type of motion required. This list is based on that provided inTheory of Machines and Mechanisms ..Uicker, Pennock, ans Shigley. The notes below are low level descriptions. Over time additional notes will be included...Fordetailed analysis and synthesis please refer to the books listed in the book section of this site.

1. Snap-Action Mechanisms2. Linear Actuators3. Fine Adjustment Mechanisms4. Clamping Mechanisms5. Location Devices6. Ratchets7. Escapements8. Indexing Mechanisms9. Swinging or Rocking Mechanisms

10. Reciprocating Mechanisms11. Reversing Mechanisms12. Couplings and Connectors13. Sliding Connectors14. Stop Pause and Hesitation Mechanisms15. Curve Generators16. Straight Line generators17. Tracing Mechanisms

Snap Action MechanismsSnap Action Mechanisms

Snap action mechanisms are also called toggle and bi-stable mechanism are widely used for components for simple toggle switches to clamps. A typical togglemechanism is shown below...

Linear ActuatorsLinear Actuators

Stationary Screws with rotating nutsThis group include machine tool traversing mechanisms, jacks, valve drives etc etc.These mechanism essentially convert rotary motion to linear motion. High mechanical advantages can result from components which are convenient to design and

engineer. The output motions and forces are very easy to evaluate for the input forces.

Stationary Nuts with with rotating screwThis group includes power screw actuators, valve drives, jacks. The characteristics of this group is essentially the same as the group with stationary screws androtating nuts

Single and double acting hydraulic and pneumatic cylindersThis is a massive group including positioning cylinders, rams jacks . The motions and forces are very easy to calculate..The motion involves convertion of potentialenergy in fluid to kinetic energy of the motion of the component moved by the cylinder

NanoPWM servo driveswww.acsmotioncontrol.com

PWM drives replacing linear drives in high precision applications

converted by Web2PDFConvert.com
http://www.web2pdfconvert.com/?ref=PDFhttp://www.web2pdfconvert.com/?ref=PDFhttp://www.roymech.co.uk/Useful_Tables/Mechanics/Linkages.htmlhttp://www.roymech.co.uk/Useful_Tables/Cams_Springs/Machine_Parts_Index.htmlhttp://www.roymech.co.uk/index3.htm


2/4

Fine adjustment mechanismsFine adjustment mechanisms

A fine adjusting mechanism is primarily used for control where small movements are required resulting from larger movements of the input. The variations of this groupinclude screws, differential screws, gears, cams.etc etc. A typical method of providing small output rotations from input motions is shown below.. One rotation of theinput shaft will result in a linear motion of the carriage of 0,5mm..

Clamping MechanismsClamping MechanismsTypical clamping mechanisms include toolmakers clamps, G clamps, screw clamps, clamps based on cams. Clamps result from lever actions, screw forces, togglemotions..The two important factors in the engineering of a clamp is the method of applying a high force and the method of retaining the force after removal of the inputmotion...

Toolmakers Clamp G Clamp

Toggle Clamp

Cam Clamp

Horizontal In-Line ToggleClamp Vertical Toggle Clamp

Location DevicesLocation Devices

Location devices often involve positioning and centralising of the component being located. Jigs and fixtures are used widely in industry for locating items prior tomachining or assembly..

RatchetsRatchets

A ratchet is used to ensure that the motion of the output device is only allow in one direction even though the input motion may be in either direction or ocillatory.Refer to Links below

Ratchet Notes.

EscapementsEscapements

Escapements are used for to control continuous motion to produce a highly controlled step motion at a fixed rate. Escapements are used for mechanically drivenclocks. When used with clocks the escapement controls the spring driven clock mechanism such that it moves in regulated steps controlled by a pendulum or anoscillating arm . Refer to Links below

Escapement Notes.

Indexing Mec hanismsIndexing Mec hanisms

Indexing mechanisms generally converts a rotating,rocking or oscillatory motion to a series of step movements of the output link or shaft. Indexing mechanisms areuseful for counters and machine tool feeds. Refer to Links below

Indexing Notes.

Swinging Or Rocking MechanismsSwinging Or Rocking Mechanisms

This type of mechanism produces a swinging or rocking motion of a link. The motion is generally less than 360oand is an oscillatory motion.

Rocking/ Oscillatory Mechanism Notes.

Reciprocating MechanismsReciprocating Mechanisms

Reciprocating straight line motion is most generally completed using pneumatic, hydraulic, and electric linear actuators. Reciprocating motion is also achieved usingrack and pinion, and cams. Historically a number of machines have been operated very successfully using specially developed mechanisms.

Reciprocating Mechanism Notes.

Reversing MechanismsReversing Mechanisms

It is comparatively easy to obtain reversing motion using pneumatic, hydraulic, levers and gears methods.

Reverse Linear Motion Using 2-Racks and a Pinion Reverse Rotational Motion using 2 PinionsReverse Linear Motion using Links

A mechanism capable of delivering output motion in either direction can also be achieved using pneumatic and hydraulic systems with appropriate direction controlvalves. A lever or gear type system would require the use of some type of clutch. Some two-way clutches which connect one output shaft to one of two drive shaftsrotating in the opposite directions can result in a direction reversal of the output shaft without stopping the drive shaft. This, of course assumes no problems due toinertia.

http://www.web2pdfconvert.com/?ref=PDFhttp://www.web2pdfconvert.com/?ref=PDFhttp://www.roymech.co.uk/Useful_Tables/Cams_Springs/Reciprocating.htmlhttp://www.roymech.co.uk/Useful_Tables/Cams_Springs/Rocking.htmlhttp://www.roymech.co.uk/Useful_Tables/Cams_Springs/Indexing.htmlhttp://www.roymech.co.uk/Useful_Tables/Cams_Springs/Escapements.htmlhttp://www.roymech.co.uk/Useful_Tables/Cams_Springs/Ratchets.html


3/4

Rotational Couplings / ConnectorsRotational Couplings / Connectors

Transmitting motion between parallel, coaxial, intersecting and skewed shafts is achieved using mechanical coupling systems. There are a wide range of differentdesigns of couplings. The basic simple design of coupling is used to transmit rotary motion in both directions between two co-axial shaft. The design of thesecouplings is based on the torque to be transmitted, the speed, and the degree of misalignment..

The available range of gear designs can be used to connect shafts of virtually any relative orientation. Gears not only allow the transfer of rotation but also directionand speed.

Belt drives can also be used to couple shafts together. The method can accomodate various relative shaft positions and can be designed such that the relative shaftpositions can vary as rotation is taking place.

Chain drives provide more positive coupling than belt drives but are not as positive as gear drives..

Typical couplings based on simple link systems are shown below. These methods are limited in the power that can be transmitted and the evenness of the output

shaft motion.

Universal Coupling

Realeaux Coupling

Sliding ConnectorsSliding Connectors

Sliding connectors are used when one slider is used to drive another slider. The normal problem is that the sliders operate on the same plane but in differentdirections..Different methods of solving this problem include.

1. Using Rigid links between the slider with pivot points on the sliders2. Joining the sliders with belts, chains or guided chains- push_pull chains3. Fastening racks to each slider and mechanically joining the sliders using gears4. Using Rigid links between the slider with pivot points on the sliders5. Using Flexible drive systems6. Using hydraulic cylinders.

Simple sliding linkage coupling Simple sliding coupling using Rack & Pinions

Stop and Dwell MechanismsStop and Dwell Mechanisms

The most obvious example of this type of mechanism is that used to control the valves on and internal combustion engine. The valve has to open, remain open for afixed part of the cycle, close, and remain close for a fixed part of the cycle. The solution for this type of mechanism is to use of cam controlling the motion of the valvestem.

Indexing mechanisms as described in the indexing section can often provide stop and dwell motions.

Curve GeneratorsCurve Generators

The four bar chain can be used to generate an infinite range of curves by adjusting the two fixed pivot points and the lengths of the links. The curves generated bythe free pivot points are obviously circles with radii = to the length of the links to the adjacent fixed pivot points. The motion of points along the coupler between thetwo free pivot points is however complex and variable.

The modern method of developing curve motion is to use Numerical control methods combined with hydraulic, or electronic servo drives. There are howeveropportunities for using direct mechanical systems for low cost components.

Straight Line GeneratorsStraight Line Generators

The clear obvious method of developing a straight line motion is to use a machined slideway. The obvious alternative method is to use computer controlled electric orhydraulic drive systems. However in the early days of the engineering industry these options were not available and methods of generating straight lines usinglinkages were developed. These systems all resulted in approximate straight lines but they were generally sufficient for the requirements.

Whitworth StraightLine Mechanism

Roberts Straight < Chebychev

http://www.web2pdfconvert.com/?ref=PDFhttp://www.web2pdfconvert.com/?ref=PDF


4/4

Line Mechanism Straight Line Mechanism

Path Following Mech ananismsPath Following Mec hananisms

The pantograph (ref figure below) is a linkage mechanism that is used to trace the movement of a point at a larger or small scale. Movement of point p is copied bymovement of point p'. The geometric requirement of the pantagraph linkage are that the links a,b,c & d form an equal sided parallelogram.

Links to Mechanism Design

1. Brock Eng. (Virtual mechanisms)...Excellent Notes and Graphics2. D& T Online ..A review of various types of mechanisms3. Four-Bar Linkage Analysis and Synthesis ..A site with web based applets4. Mechanisms ..A site with lots of useful moving graphics for simple mechanisms5. Introduction to Mechanisms ..Lots of very useful reference notes6. Animated indexing Mechanisms ..Provides clear understanding of operations

This Page is being develop edThis Page is being develop ed

HomeMachine_Parts_Index

Send Comments to Roy Beardmore

Last Updated 23/01/2013

Linear Drive

Linear Motor

Mechanisms

http://www.web2pdfconvert.com/?ref=PDFhttp://www.web2pdfconvert.com/?ref=PDFhttp://www.roymech.co.uk/email.htmlhttp://www.roymech.co.uk/Useful_Tables/Cams_Springs/Machine_Parts_Index.htmlhttp://www.roymech.co.uk/index3.htm#Tableshttp://www.mekanizmalar.com/menu_index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/http://www.technologystudent.com/cams/camdex.htmhttp://iel.ucdavis.edu/chhtml/toolkit/mechanism/fourbar/http://www.dtonline.org/apps/menu/app.exe?2&6&0http://www.brockeng.com/mechanism/

www roymech co uk

Documents