Illustrated Sourcebook of Mechanical Components Part 12 pps

Mechanisms 22-71 Rocking arm w 4 PIN WHEEL. Pallet A is about to unlock escape 'wheel. Pin will give a push to pallet A while slid- ing down impulse surface. As pendulum continues to swing, pallet B will stop pin, thus locking escape wheel. After pendulum reverses direction and swings toward dead center, pallet B releases wheel and receives an impulse from pin. 5 LANTERN WHEEL. Escape wheel is stopped when pin hits plate A of pallet, attached to rock- ing arm. As arm swings to right, pin pushes against impulse surface of plate until pin is clear. Escape wheel then turns freely until pin is stopped by plate B of pallet. Arm starts back toward left, re- ceiving impulse from pin until latter clears plate. 6 MUDGE'S LEVER. As balance wheel swings coun- terclockwise (I), the ruby pin enters fork of lever and pushes it to the right. The lever releases tooth of escape Wheel, which starts turning and gives a tiny push (2) to impulse surface of pallet A. This is transmitted to balance wheel through fork and ruby pin. Balance wheel continues rotating counterclockwise (3) while lever swings to righr and pallet B stops the escape wheel by engaging tooth. When balance wheel reaches ita hairspring's limit, it reverses direction and reenters fork (4). Ruby pin pushes lever to left, and receives impulse when escape wheel starts to move. Balance wheel continues clockwise until it reaches opposite limit of its hairspring. Lever continues moving to left until it again stops escape wheel (6) and awaits return of ruby pin. Another view of Mudge's Iever is given in (6). This escapement is very precise because of the small portion of each half-cycle that escape wheel and balance wheel are in contact. Friction drag is at a minimum. 22-72 7 More Escapement Another selection of these ingenious mechanical components for use in control systems. Federico Strasser 1 CYLINDER. Tooth of escape wheel and cyl- inder (balance-wheel shaft) are shown in sevea positions. Tooth has been locked (1) and is about to enter cycle. Tooth is providing im- pulse (2) by sliding action along cylinder lip. Escape wheel is locked while cylinder rotates clockwise (3) to its limit (4), then starts back (5). As tooth starts forward, impulse is again imparted (6) to cylinder lip. Second tooth is locked (7) during period of backswing. 3 HIGH-SPEED DOUBLE RATCHET. Same principle as in 2, but used with a small-mass pendulum. Speeds to 50 beats per second can be obtained. Escape 2 DOUBLE RATCHET. Two escape wheels are mounted on a common axis and pinned together so teeth are aligned with a half-pitch distance be- tween them. Drawing shows pendu- lum in its extreme left position, with its impulse surface locking a tooth of the escape wheel A. As pendulum starts to right, escape wheels start to turn, imparting a push to the pendu- lum. As it approaches its extreme right position, pendulum again stops the escape wheels, by engaging a tooth on wheel B, then receives a second impulse as it starts toward the left. €scope fl Ld wheels Pu/iet ’ surface Mechanisms 22-73 Po//ef surface 4 THREE-LEGGED. The three teeth of es- cape wheel work alternately upon top and bottom pallets. Top pallet is shown being driven to right. When tooth clears pallet, escape wheel will turn until tooth engages bottom pallet. When pendulum slide starts back toward left, bottom pallet will receive push from escape wheel, until tooth clears pallet. wheel 5 DUPLEX. Single pallet of balance wheel is shown receiving impulse from pin of escape wheel. As balance wheeI rotates counterclock- wise, tooth of escape wheel clears notch, per- mitting escape wheel to turn clockwise. Next tooth of escape wheel is stopped by balance wheel until balance wheel reaches limit, re- verses direction, and pallet swings back to po- sition shown. Escapement receives but one impulse per cycle. Impulse sur fuce 6 STAR WHEEL. Dead-beat escapement in which pallets alternately act upon diametrically opposed teeth. Illustration shows balance in extreme clockwise position with escape wheel locked. Balance starts turning counterclockwise, releasing escape wheel. At other extreme, pallet B locks escape wheel for a moment before direction of balance is again reversed and Pallet E Pu//.t A fkupe wheel @ push is imparted. Bu/mce k + 7 CHRONOMETER. As balance wheeI turns counterclockwise, jewel A pushes flat spring B and raises bar C. Tooth clears jewel D and escape wheel turns. A tooth imparts push to jewel E. As jewel A clears flat spring, jewel D re- turm to position and catches next tooth. On return of balance wheel (clockwise), jewel A passes flat spring with no action. Thus, escapement receives a single im- pulse per cycle. 22-74 Desi n Hints for Mechanical Sma P I Mechanisms How to avoid close tolerances, and otherwise improve parts, where accurate assembly is necessary. Federico Strasser High accuracy 4 Easily machifled1 Wrong c1 Right Wrong 63 Right HOLD-DOWN COVER for bearing should have a take-up gap between the cover flange and the bearing box. BUSHING FACE i5 much eabier to nia- chine than the huh of a large part such as a flywheel or heavy gear. Wrong Grooved pin -, I DOVETAILED parts that are to be a tight fit are best provided with a slot and grooved pin where d equals b/3 to b/4. SMOOTH-BORED HOUSINGS shown on right let one hearing move when shaft length changes hecause of expansion, Mechanisms 22-75 ~ymmefrico/ weights ( rcover opfiono/ \ I I i Section A-A SYMMETRICAL WEIGHTS give even braking action when they pivot outward. Entire action ran be enclosed. SHEETMETAL BRAKE providec larger braking arca than previous design. Opera- tion is thiic more eve11 and cooler. Brake disk I __._ ffof SDTiOUS . . . . . . ___ I Speed odjusimenj THREE FLAT SPRINGS carry weight% that pro,idr hdhe forre upon rotation. Ihvice ran be provided with adjustment. TYPICAL GOVERNOR action of swing- ing weights is utilized here. As in the pre- vious device, adjustment is optional. ILLUSTRATED SOURCEBOOK of MECHANICAL COMPONENTS SECTION 23 LINKAGE 8 Basic Push-Pull Linkages 23-2 5 linkages for Straight-line Motion 23-4 10 Ways to Change Straight-Line Direction 23-6 9 More Ways to Change Straight-line Direction 23-8 Shape of Pin-Connected Linkages 23- 10 Seven Popular Types of Three-Dimensional Drives 23- 1 2 Transmission Linkages for Multiplying Short Motions 23- 16 Power Thrust Linkages and Their Applications 23-1 8 Toggle Linkage Applications in Different Mechanisms 23-20 When Linkages Need Harmonic Analysis 23-22 Four-Bar Linkages and Typical Industrial Applications 23-26 Four-Bar Power Linkages 23-28 5 Graphic Methods for Designing Four-Bar Linkages 23-34 Four-Bar Linkage Proportions 23-45 Linkage 23-3 ROTARY-ACTUATED LINKAGE gives opposite direction of motion and can be obtained by using 3-bar linkage with pivot point of middle link located at midpoint of arm length, Disk should be adequately strengthened for heavy loads. THIS ROTARY-ACTUATED linkage for straight-line 2-direction motion has rotary driving arm with a modified dovetail open- ing that fits freely around a flat sheet or bar arm. Driven arm reciprocates in slot as rotary driving arm is turned. Driving /For driving in _- same direction SAME-DIRECTION MOTION is given by this rotary-actuated linkage when end arms are located on the same sides; for opposite-direction moxion, locate the arms on opposite sides. Use when a crossover is required between input and output. ,/Fixed pivot Driving arm, , EQUALIZING LINKAGE here has an equalizing arm that balances the input force to two output arms. This arrange- ment is most suitable for air or hydraulic systems where equal force is to be exerted on the pistons of separate cylinders. link D-drive . . . results when linkage arms are arranged as shown here. Output-link point describes a path re- sembling the letter D, thus it contains a straight portion os part of its cycle. Motion is ideal fot quick engagement and disengagement before and after a straight driving-stroke. Example, thc intermittent film-drive in movie-film projectors. Linkage Four-bar linkage . . . produces approximately straight-line motion. This arrangement provides motion for the stylus on self-registering measuring instruments. A compara- tively small drive-displacement result; in n long, almost-s!raight line. 23-5 The "Peaucellier cell" . . . was first solution to the classical problem of generating a straight line with a linkage. Its basis: within the physical limits of the motion, AC x AF remains constant. Curves described by C and F are, therefore, inverse; if C describes a circle that goes through A, then F will describe a circle of infinite radius-a straight line, perpendicular to AB. The only requirements are: AB=BC; ADzAE; and CD, DF, Ff, EC are all equal. The linkage can be used to generate circular arcs of large radius by locating A outside the circular path of C. Linkage 23-7 Guides Pivots odd supporf 1 - - Connecting rod 11 Inclined bearing-guide Matching gear-segments Single connecting rod (left) is relo- cated (right) to get around need for extra guides Friction Drives Belt, steel band, or rope around drum, fastened to driving and driven mem- bers; sprocket-wheels and chain can replace drum and belt Gears Rocks, )I[ Rocks, Racks and coupled pinions (can be substituted by friction surfaces for low-cost setup) Linkage 23-9 - Sliding wedge is similar to previous example but requires spring-loaded follower; also, low friction is less essential with roller follower. Offset driver actuates driven member by wedge action. Lubrication and low coefficient of fric- tion help to allow max offset. Pneumatic cylinder / 3 Fluid coupling is simple, allows motion to be transmitted through any angle. Leak problems and accurate piston-fitting can make method more expensive than it appears to be. Also, although action is reversible it must always be a compressive one for best results. Pneumatic system with two-way valve is ideal when only two extreme positions are required. Action is irreversible. Speed of driven member can be adjusted by controlling input of air to cylinder. I Auxijliary switches\, Solenoids and two-way switch are here arranged in analogous device to previous example. Contact to energized solenoid is broken at end of stroke. Again, action is irreversible. sw"ch' Y [...]... positions of a four-bar linkage (AI &-A4 e, a r e chosen; the properties of the pole triangle ) and of the circle point curves of points at infinity of the coupler a r e used Y The path of the tracer point obtained has four precision points AI d Three coplonor positions of o plane systemlocation of the center points of system points at infinity Three coplonor positions of a plane systemlocation of three... thc velocity of the change of position of tlic in~tantancouscenter, the angle between the tangcnt to the centrodes at the instantancous center and the my COP V, the velocity of point C of the moving system, I = CP, and ro = COP The vclocity of any point of the moving , ,)stem, for instance, velocity V of the midpoint M of AB, is arbitrarily selected, and V determined The fixed centrode of the trammel... gcncrating line of the conchoid Point C then describes an approximately straight-line path in the vicinity of the apex of the conchoid, and is used as tracer point To summarize characteristics of tlic above linkagcs, the path of the tracer point of the symnictrical linkages, Figs 4, 6 and 7, has an infinite rachis of curvature In tlic linkagcs of Figs 1, 2, 3 and 8, the corresponding radius of curvature... two pair of poles whose indices have one common digit-for example, P"-P, P*'-Pand drawing a circle through each pair of poles such that the radii of these circles are proportional to the distance bctwcen the poles of a pair; the points of intersection of the two circles, Ale, Ala, are points of the focal curve The radius of the crank circle associated with each center point, and the location of the congruent... 5, the amplitudes of the first harmonics are given in the C, column as: el = 0.309774; = 0.023573; e = 0.00400 radians , Ratio of higher harmonics to the 1st harmonic can also be obtained from the d, column For example, Ratio of amplitude of 2nd to 1st: (a,) = 0.079326 = 7.9% Ratio of amplitude of 3rd to 1st: (d,) = 0. 0129 13 = 1.3% The significance of these values depends upon the particular design... through M The centers of curvature, A,, Bo, of the path of these two points are selected as the fixed pivots of the cranks, and they are determined as previously The velocity V, is equal to velocity V, The path of points A and B are cycloids whose radius of curvature niay be calculated as follows: p = 4r sin 0 / 2 ; where r is radius of the rolling circle, and e is its angle of rotation The cycloidal... curvature C of the point C on the trammel is selectccl as the second fixed pivot Point A is then the tracer point The center of cuniature C, of point C must lie on a line through C and the instantaneous center of rotation P of AB which is found as Mie intersection of the normals through A and B to y and x respectively The radius of curvature CC can be calculated, or solved grap1iically by the tire of Euler-Savary's... the intersection of lines P1Al with ala and P'lB1 with bIz respectively The intersection point P of the lines ' , A'.A2 and B'.B, determines the corresponding instantaneous center of A2B2.PtZrepresents one point of the locus z of all possible instantaneous centers of system position EPA& for which the iiistantaneous center of system position EIAIBl lies on line nl The intersection point of this curve... point of x and y, as center, and OP = t, the length of bar AB as raI dius; the moving centrode is the circle K through P and 0, with M, the midpoint of AB as center and t / 2 as radius The velocity V, is determined from the consideration that the motion of the bar is equivalent to rolling of the moving centlode on the fixed centrode V, is therefore the velocity of this rolling inotion, of tlic point of. .. associatcd poles constitute opposite sidcs of a rhombus, the focal curve degenerates into the diagonals m, m of this rhombus and they are perpendicular to one another 44 Construction of Linkage by Use o f Center Point Curve Consisting of Two Straight Lines 8 23-4 1 Tliis is another csample of the use of the simplified shape of the centerpoint curve for the design of a linkage As in the precccling example, . TYPICAL GOVERNOR action of swing- ing weights is utilized here. As in the pre- vious device, adjustment is optional. ILLUSTRATED SOURCEBOOK of MECHANICAL COMPONENTS SECTION 23 LINKAGE. column. For example, Ratio of amplitude of 2nd to 1st: (a,) = 0.079326 = 7.9% Ratio of amplitude of 3rd to 1st: (d,) = 0. 0129 13 = 1.3% The significance of these values depends. harmonics of a given motion are used in the determination of the significance of resonant speeds and the corresponding inertia forces, which are proportional to the second derivative of