GB2039236A - Multiple station transfer machines - Google Patents

Abstract

Work-carrying pallets move along transfer rails (6) from station to station and are located, i.e., brought into registry, at each station and clamped in place for a work operation by a pallet registry which has single energy storage means (30) which operates both a locating pin (14) and a clamp-actuating lever (66, 68) sequentially through a master lever (18) and an interconnecting mechanism (46 to 64). A common release mechanism (44) underlies the stations and is operable to act against the energy storage means (30) to effect release of the locating pin and the clamp (16) while pallets are moving between stations. The clamp-actuating lever (66) has a reaction portion (74) which bears against the housing (2) to apply a reaction force to the housing along axis A1 and a clamping portion (78) which applies a clamping force to the clamp (16) along axis A2 parallel to and close to axis A1. <IMAGE>

Description

SPECIFICATION Improvements in multiple station transfer machines The invention relates to multiple station transfer machines for use in automation equipment using multiple work-carrying jigs which are moved to various stations, and more particularly to a registry mechanism by which the jig can be clamped in place forthe initiation and completion of a particular machining operation.

In some types of automatic workpiece processing, workpieces are located and clamped in jigs or pallets, which are progressively transferred from station to station of a multiple station transfer machine on slide rails or the like. In each station, these jigs or pallets are accurately located and clamped by a mechanism referred to as a pallet registry.

Pallet registries of a variety of types have been in use in industry for many decades. Several such registry mechanisms are shown in United States Patents, Nos. 2,672,675; 2,673,386; 3,155,217; 3,571,872; and 3,968,869. As a broad generalization, these and others can be categorized into two types: a first type, in which each registry is operated by one or more hydraulic cylinders, and a second type in which multiple registries are ganged together and operated by a single power source such as a cylinder or suitable mechanical device.

Registries of the first type, which are self-powered, employ locating pins and clamps which may be mechanically interlocked or operated by separate cylinders and are characterized by having relatively large movement capability of the clamping members for the pallet.

Registries of the second type, in which a group of registries is actuated by a single power means, are characterized by having the locating pins directly actuated by the common power means, while the clamp members are actuated by, or through, elastic members such as relatively low work output springs and the clamp member movement ranges are therefore relatively small. Accordingly, the amount of wear which can be tolerated on the clamp members and/or the associated clamp surface on the pallets is very small. Stated another way, a small amount of wear on either the clamp members or the associated clamp surface of the pallet will create a large change in the clamping force or even no clamping force at all.When the clamp surface of the pallet consists of one side of a horizontal plate member, known as a pallet foot, and the opposite side of the foot is the sliding surface on which the pallet slides from station to station, as is generally the case, then wear on this pallet foot slide surface and/or wear of the associated fixed rail further magnifies the problem of variable clamp force, or zero clamp force, due to wear. The aggregate wear on the slide rails, pallet foot, pallet clamp surface, and the clamp member greatly affects the clamp force because of the small amount of available clamp member movement.

When the aggregate wear exceeds this clamp member movement, the clamp force drops to zero.

It is an object of this invention to provide a pallet registry which can be so designed that a group of registries may be ganged together and operated by a single power means while providing a clamp member movement of significantly greater range than those of present designs.

In prior registry designs, the clamp members are generally actuated by wedges, either straight line or circular, or screws, which are low efficiency mechanisms. Low efficiency refers to the fact that the work (force times distance) output from the mechanism is much less than the work into the mechanism, the loss being due to friction. Not only does the friction detract significantly from the theoretical force output of a wedge or screw mechanism, but variations in friction cause larger changes in the force output than such variations make in higher efficiency mechanisms.

It is an object of this invention to provide a pallet registry which can be so designed that the clamping force is transmitted from a power source to the clamp members through high efficiency mechanisms, such as simple levers, pivots, and rolling contacts.

In prior registry designs, the reactive loads, due to the clamping forces, on the locating and structural components of the registry appear as significant bending loads thereon.

It is another object of this invention to provide a registry which can be so designed that the bending loads due to clamping are primarily confined to members whose deflection does not affect the accuracy of pallet location, and in which the bending loads imposed on the locating and structural components of the registry are minimized to achieve lower deflections per unit of clamping force.

The present invention resides in a registry mechanism for clamping pallets at a work station of a multiple station transfer machine in which workpieces are located and supported in pallets and in which said pallets are moved in sequence through said machine, said registry mechanism comprising a registry frame, a pallet clamp movably mounted in said frame and having a first portion to engage a pallet in a clamping relationship with one face of a relatively rigid section of said frame and a second portion to receive a clamping force to move said first portion into said clamping position, said second portion being located on the opposite side of said frame section from said first portion, and a mechanical means to cause engagement of said clamp with said pallet, which means comprises a clamp-actuating lever having a reaction fulcrum portion, at which said lever is pivoted to said frame for transmission of a reaction force along a first axis, and having a second fulcrum portion to contact said second portion of said clamp to transmit thereto the clamping force along a second axis, said reaction fulcrum portion on said clamp-actuating lever being positioned to contact said frame on a face of said rigid frame section opposite said one face and said second axis being substantially parallel to and disposed closely to said first axis, whereby said reaction force substantially places said rigid frame section in compression between said pallet and said reaction fulcrum, thereby minimizing the reactive bending moment applied to said registry frame by said clamp.

In present registry designs of the second type, in which multiple registries are operated by a single power means, the locating pins in each registry are directly actuated by that power means. Therefore, a slight mislocation of a pallet in any given registry will cause the entire power means to stall or break a component in the offending registry, since all the force generated by the common power means is concentrated on the offending registry.

It is, therefore, a secondary feature of this invention to provide a pallet registry which can be so designed that several registries are operated by a common power source, butthe locating pins, as well as the clamp members, are independently actuated by individual internal elastic members when the common power source is operated.

In a preferred embodiment of the present invention, one or more locating pins are slidably mounted in said frame to engage corresponding locating holes in said pallet, and said mechanical means provides inter-connections between energy storage means provided on said frame and said locating pin and between said energy storage means and said clamp actuating lever, to sequentially engage the locating pin in a locating hole in the pallet and then clamp the pallet to the registry frame, external power means being interconnected with said mechanical means to actuate said clamp actuating lever to retract the clamp from the pallet and thereaf thereto disengage the locating pin from the locating hole in the pallet against said energy storage means.

In many prior registry designs, the transfer system operates above and through the pallet registry.

Therefore, from a maintenance standpoint, in order to remove or replace a registry, it is necessary first to remove the transfer system, or parts of it, which increases the work and time required for maintenance.

It is another secondary feature of this invention to provide a pallet registry which can be made in two independent sub-assemblies which are mounted to the machine bed on each side of a substantially central transfer system, and one side or the other or both sides of the registry can be removed or replaced on the machine bed without removing the transfer system.

The invention is further described, by way of example, with reference to the drawings, in which :- Figure 1 is a schematic force diagram showing the forces on a simple wedge acting with friction, Figure 2 is a graph showing the efficiency of wedges acting with friction, Figure 3 is a plan view of a registry mechanism of the present invention, Figure 4 is a vertical section taken on line 4-4 of Figure 3, Figure 5 is a vertical section taken on line 5-5 of Figure 3, Figure 6 is a vertical section taken on line 6-6 of Figure 3, Figure 7 is a schematic elevation of an intercon necting mechanism for a group of registries, Figure 8 is a partially schematic exploded isometric view of a registry mechanism, Figure 9 is a section through an alternative spring cartridge mechanism, and Figure 10 is a section through a second alternative spring cartridge mechanism.

As background for the terms "high efficiency" mechanisms and "low efficiency" mechanisms, which are used throughout this description, the efficiency of a mechanism will be defined as the ratio of the work out to the work in, where work is used in the normal sense of force times distance. The effi-' ciency of a mechanism is therefore Efficiency Output Force x Output Distance Input Input Force x Input Distance High efficiency mechanism are those having an efficiency of 85% or higher, while low efficiency mechanisms have an efficiency of less than 85%. Of the basic or fundamental types of mechanisms, those with high-efficiency are pivots, levers, gears and rolling contact mechanisms, while wedges and screws are considered as low efficiency mechanisms.The loss of efficiency of any mechanism is attributable to friction, ignoring such relatively minor factors as lubricant churning orwindage.

Therefore, in high efficiency mechanisms, losses due to friction are quite small, 15% or less; while in the low efficiency mechanisms of a wedge or screw, the friction losses are 15% or more - generally much more. Furthermore, with the low efficiency mechanisms, not only is much of the output work reduced by the frictional losses, but the inevitable inconsistent nature of the frictional variations causes a high degree of inconsistency of the output work. Since the relationship of output distance to input distance is fixed by the fixed mechanical interrelationship of a given mechanism, and the distance portion of the ratio is therefore fixed, loss of efficiency is reflected as a loss of output force, and, in the case of low efficiency mechanisms, as an inconsistency of output force as well as a loss thereof.

This is quantitatively illustrated by the drawing of a simple wedge, shown in FIGURE 1, operating with friction. From an excellent derivation of such a wedge with friction on pages 126 and 127 of Brandt's "Vectorial Mechanics" (John Wiley & Sons, Copyright 1930), the ratio of the input force Ptothe output force Cl is shown to be

where: a = wedge angle, 0 = friction angle at wedge interface, 01 = friction angle of driving wedge, 02 = friction angle of driven wedge, and the friction angles are the arc tangents of the.

respective coefficients of friction.

By making the reasonable assumption that the three friction angles are identical, i.e., 02 = 01 = 0, and by inverting equation (1) to give the ratio of output force to input force:

The output force Q is noted as QF to define it as the output force when friction is present in the system.

This same equation can be used to determine the output force, Qo, when the friction is assumed to be zero in which case the angle O is zero. Therefore, the ratio of the output force To to the input force P under conditions of zero friction is:

The efficiency of a wedge with friction is the ratio of the output force with friction to the output force without friction or

This can be found by dividing equation (2) by equation (3) which gives:

The efficiency of a wedge versus the coefficient of friction for a sampling of representative wedge angles is shown in FIGURE 2.It is clearthatthese efficiencies are very low in general, and, for a representative situation using a 150 wedge and a coefficient friction of .15, the wedge efficiency is only 43%.

Furthermore, it can be seen that variations in the coefficient of friction due to variations in lubrication, surface wear, etc. cause large changes in an already low efficiency.

Screws may be considered as circular wedges having a low wedge or helix angle. Indeed this makes them self locking. Screws generally have efficiencies which approximate or are lower than the 50 wedge angle curve of FIGURE 2.

The primary objective of this brief analysis of wedges and screws is to quantitatively demonstrate the relatively low efficiency of such mechanisms.

With large amounts of input force available, this deficiency is of little disadvantage, but when a group of mechanisms is to be operated by a single power source, the mechanism efficiency is of some importance.

For this and other reasons, the embodiment of the invention described below uses no screws or wedges to generate the clamping force. An other important reason for using only high efficiency mechanisms, such as levers and pivots, is that variations in friction have much less effect on the clamp force, and, therefore, much more consistent clamp forces are obtainable.

A plan view of the registry mechanism is shown in FIGURE 3. This is comprised of two identical housings 2 mounted on a machine bed 4. The space between the housings 2 is available for passage of the transfer bar which indexes the pallets from station to station. For some applications, the two identical housings 2 may be inter-connected into a single unit without affecting the performance of the registry.

The mechanism enclosed within either housing 2 is identical with the mechanism enclosed in the other housing 2; each is operated by a push rod, operated by a bellcrank system within the machine frame to be described in connection with FIGURE 7. Two advantages accrue from the use of two separate housings 2 which together comprise a complete registry. The two housings 2 may be mounted on the machine bed with increased separation to accommodate larger pallets; and either housing 2 may be removed for maintenance or replacement without disturbing the transfer system. Furthermore, the use of a vertical push rod for actuation further facilitates such ease of interchange. Each housing 2 constitutes a frame for the registry.

Referring to FIGURE 3, parallel transfer rails 6 are mounted to the top of the housings 2. It is on these fixed transfer rails 6 that the pallets slide from one registry to the next by actuation of a transfer bar.

Four foot members 8, mounted on the underside of a pallet 10 (FIGURE 6), contact and are supported by the transfer rails 6. Holes 12 in two ofthe palletfoot members 8 can be engaged by vertically moving locator pins 14 to establish pallet location; and four vertically moving clamp members 16 can exert downward force on the upper faces of the pallet feet 8, to clamp them to the transfer rails 6.

The details of the operating mechanism for the locator pins 14 and clamp members 16 are shown in the longitudinal sections in FIGURES 4 and 5, and the transverse section FIGURE 6, while the entire mechanism is shown in expanded isometric view in FIGURE 8.

Referring to FIGURE 4, a master lever 18 is pivoted on a shaft 20 mounted in the housing 2. This master lever directly actuates the locator pin 14 through a spherical sector 22 which engages a cylindrical hole 24 in the locator pin 14. An offset portion 26 of the master lever 18 is engaged by the nosepiece 28 of an elastic energy cartridge 30 through a wear pin 32.

The elastic energy cartridge 30 is comprised of a sleeve 34 which is flanged at one end 36 to bear against the housing 2. Mounted within the sleeve 34 is a compression spring 38, which bears on one end against the partially closed end of sleeve 34 and at its other end bears against a head 40 formed on the end of a pull rod 42; the other end of pull rod 42 is threaded in and locked to nosepiece 28. The compression spring 38 is preloaded to a large degree during assembly prior to attachment of the nosepiece 28; or prior to attachment of the head 40 to the pull rod 42. It will be noted that even though the spring 38 operates in compression, the action of the entire cartridge is in tension, acting between the flange 36 and the nosepiece 28. This exerts a clockwise turning moment on the master lever 18 about pin 20.It will also be noted that the movement of pull rod 42 to the right is limited to the distance determined by nosepiece 28 which will contact the closed end of sleeve 34, at which position there is still considerable preload on spring 38. The preload is accomplished by an external assembly fixture of standard design which may be as simple as an arbor press to compress spring 38 during assembly. The practical advantage of using a preloaded spring cartridge is that it can be handled as a simple package during assembly of the registry, while still retaining the advantages of preload; this results in a more nearly flat force curve during the working stroke of the cartridge 30.

As noted above, the tensile force of the cartridge 30 exerts a clockwise moment on master lever 18 and extends the locating pin 14 upward into engagement with pallet foot member 8. This clockwise motion of master lever 18 also causes engage ment of the clamp members 16 as will be described.

The locating and clamping is accomplished entirely by the force and movement generated by the cartridge 30, to reach the position shown in FIGURE 4.

The end of the master lever 18 opposite the spherical sector 22 is recessed to mate with a cylindrically ended push rod 44 which is externally actuated as will be described. A slot 46 is also formed into this side of the master lever 18. This slot 46 is engaged by a pin 48 mounted on an arm 50 which is attached to a torque tube 52 that rotates on a shaft 54 mounted in the housing 2.

Referring to FIGURES 5 and 8, the torque tube 52 also has mounted on it a clamp drive arm 56, which, at its outboard end is connected by pin 58 to clamp link 60. At its other end, the clamp link 60 is connected by pin 62 to an equalizing link 64, at or near its midpoint. Each end of equalizing link 64 is connected to clamp levers 66 and 68 by pins 70 and 72.

Clamp levers 66 and 68 are symmetrically disposed about the longitudinal centerline and actuate two identical clamp mechanisms, only one of which need be described.

The clamp lever 66 has rigidly mounted to it a cylindrical convex member 74 which contacts a bearing pad 76 mounted in the housing 2. On the opposite side of clamp lever 66 is mounted a second cylindrical convex member 78 which makes area contact with a slipper member 80 whose upper surface is concave to mate with convex member 78. The lower side of slipper member 80 is convex at right angles to the upper concave surface. This lower convex surface of slipper member 80 mates with a concave surface 82 of clamp member 16. As can be seen in FIGURE 6, the clamp member 16 is a "C" shaped member whose upper inboard surface 84 contacts and clamps the pallet foot member 8 to the slide rail 6; the clamp member 16 is mounted in the housing 2 through a resilient bushing 86 which permits adequate movement of clamp member 16.

FIGURE 8 is a partially schematic isometric drawing and is intended only to indicate the functional relationship of the mechanism members. The housing 2 is completely deleted, and various members slightly altered for drawing simplicity and the slippers 80 are omitted completely to more clearly show the lever action of the clamp levers 66 and 68.

It will be noted (FIGURE 5) that the contact line between the convex member 74 and reaction pad 76 is on axis A1 and that the effective axis of the bearing between the convex member 78 and the slipper 80 is along the axis A2, which is the clamp axis. In effect, the clamp lever 66 acts as a simple lever having a fulcrum with respect to the housing 2 on axis A1, an output movement on axis A2, and an input movement on the axis of pin 70. It can be seen that there is a considerable force magnification or leverage from the downward force of pin 70 to the downward force on the clamp member 16, which is transmitted as a clamp force on the pallet foot member 8 by surface 84. Yet this force magnification is achieved with a simple lever which is a "high efficiency" mechanism.

The clamp action of the clamp lever 68 is the same as that of the clamp lever 66 except that its operation is symmetrically opposite. Substantially equal downward forces for clamping are applied by pins 70 and 72 on the clamp levers 66 and 68 by the equalizing link 64 which is pulled downward by link 60 due to a counterclockwise torque on torque tube 52 and arm 56. This counterclockwise torque on torque tube 52 is generated by arm 50 (FIGURES 4 and 8), and pin 48 which is forced downward by slot 46 in master link 18 due to the clockwise torque exerted on this master link 18 by the spring cartridge 30.

It can be seen that the force generated by the spring cartridge 30 is transmitted to the pins 70 and 72 (FIGURES 5 and 8) by simple high efficiency levers such that the work (force times distance) delivered by spring cartridge 30 is decreased only slightly by friction when it appears at pins 70 and 72, and, due to the high efficiency of the clamp levers 66 and 68, when it appears as a clamp force at surface 84 on pallet foot member 8.

Stated another way, there is a large mechanical advantage in force transmittal from the spring cartridge 30 to the clamp surfaces 84, and this is only slightly less than the movement ratio of spring cartridge 30 to that of the clamp surfaces. It is well known that for a 100 /O efficient mechanism (and as can be derived by rearranging equation 1) that: Input Movement ~ Output Force Output Movement input Force Therefore, for a system of simple levers and pivots, with a minimum work loss due to friction, this force ratio will be only slightly less than the movement ratio.

Referring again to FIGURE 5, the outboard end of lever 66 (and symmetrically opposite lever 68) is formed into a cylindrical extension 88 which fits into a resilient bushing 90 supported by the housing 2.

The two resilient bushings 88 are made of neoprene or the like, and it is their function to establish the left to right position (FIGURE 5) of levers 66 and 68 and equalizing link 64, yet permit sufficient float to allow a true rolling contact between convex member 74 and reaction pad 76 when the clamp forces are being reacted by this fulcrum interface. To further permit a true rolling contact at this same interface, the holes in levers 66 and 68 and/or the corresponding holes in equalizing link 64 for pins 70 and 72 are slightly elongated or made oversize.

The underside of the clamp member 16 is supported by a resilient bushing 92, also made neoprene or the like. This bushing 92 permits downward movement of the clamp member 16 during clamp ing, absorbs deflections in the clamp member 16 during its deflection under clamp loads, and provides the return force on the clamp member 16 during unclamping, as is to be described.

It will be noted from FIGURE 5 that the fulcrum axis A1 is only slightly displaced from the clamping axis A2. This accomplishes two important things: it provides a large mechanical advantage in generating the clamp force as previously described; and it generates a very small reactive bending load in the housing 2. This small bending load in the housing 2 in turn minimizes the reactive deflections therein, which is significant when high accuracy is required.

It will be noted from FIGURE 6 that the clamp force applied to the clamp member 16 by the clamp lever 74 through the convex member 78 and slipper 80 is directly in line with the clamp surface 84, on clamp axis A2. This, of course, is what dictates the "C" shape of the clamp member 16. This clamp member 16 will deflect due to the clamp forces it is transmitting, but, because of its mounting into the housing 2 through the resilient bushings 86 and 92, deflection of the clamp member 16 causes negligible loads on the housing 2.

In essence then, this clamping system creates the theoretically most nearly perfect system to minimize deflection of the housing 2 due to the clamp forces.

The largest load on the housing 2 due to the clamp forces is an almost pure compressive load which is experienced as a reactive load between the reaction pad 76 and the support rail 6.

It can be seen from the above mechanism description that the locating pins 14 are extended and the clamp members 16 exert their clamp force on the pallet foot members 8 due to the elastic work of the spring cartridge 30 which produces a clockwise movement and exerts a clockwise force for clamping on the master lever 18. The force and movement for unclamping and withdrawal of the locating pins 14 is provided by a common external system. As shown in FIGURE 7, machine beds 4 are connected together in a series by spacers 100 to form the centre section of a transfer machine. On each of these machine beds 4 are mounted two registry mechanisms 2, or a single registry if the two mechanisms are interconnected in a single housing. Only three machine beds 4 are shown; it will be understood that there are as many such machine beds as there are stations in the machine.It will also be understood thatthere may exist idle (non working) stations interposed between the working stations, which may or may not contain a registry for the pallet, or they may contain registries having only locating pins with the clamp portions of the registries omitted.

Within each machine bed 4, underthe position of the registry, isjournalled a shaft 102; on each such shaft 102 is mounted an actuator link 104. The other ends of links 104 are pivotally connected together by tie rods 106 equal in length to the corresponding distance between shafts 102. One of the links 104 is pivotally connected by a connecting rod 108 to a crank arm 110 through a crankpin 112; this crank arm 110 is mounted to the output shaft 114 of a gear reducer 116. An electric motor 118 in turn drives the gear reducer through belts and pulleys 120. It can be seen that as the motor 118 drives the gear reducer 116, the crank arm 110 causes the links 104 to oscil late about shafts 102 in substantially parallel motion.

The crank arm 110 position shown in FIGURE 7 has the links 104 attheirapproximate mid-stroke position. When the crank arm 110 is at the 9 o'clock posi tion related to the center of the shaft 114, referred to as the top dead center position, all links 104 are in their most clockwise position relative to shafts 102.

When the crank arm 110 is at the 3 o'clock position relative to the shaft 114, referred to as the bottom dead center position, all links 104 are in their most counterclockwise position relative to their shafts 102.

Each link 104 also has mounted on it two links 122 at approximately right angles to the link 104 to serve as a bell crank. At the outboard end of the links 122 is pivotally connected a push rod 44 which contacts the master lever 18 of a registry mechanism (FIGURE 4).

All the registry mechanism master levers 18 are driven counterclockwise in unison as the crank arm 110 rotates from the 3 o'clock position to the 9 o clock position, through the clockwise rotation of links 104 and 122 serving as a bell crank on shafts 102, the result being an upward movement of push rods 44.

Within each registry mechanism, the counterclockwise rotation of master lever 18 retracts the locating pin 14 (FIGURE 4); extends the spring cartridge 30 by compressing spring 38, thereby storing work therein; and rotates the arm 50 on torque tube 52 clockwise through pin 48 in slot 46.

The clockwise rotation of torque tube 52 (FIGURE 5) causes arm 56 to raise link 60 through pin 58 and this raises equalizer link 64 through pin 62. The clamp lever 66 rotates counterclockwise about its fulcrum pivot on axis A1 and the resilient bushing 92 lifts the clamp member 16 to provide clearance between the surface 84 (FIGURE 6) and the pallet foot 84. The withdrawal of ail locating pins 14 and the lifting of the clamp members 16 is accomplished, therefore, by the rotation of the crank arm 110 from the 3 o'clock position to the 9 o'clock position; this also stores work in the spring cartridges 30. It will be noted that the direction of rotation of crank arm 110 is immaterial.

To accomplish the extension of the locator pins 14 and the engagement of the clamp members 16, the crank arm 110 rotates from its 9 o'clock position to its 3 o'clock position with the direction of rotation again immaterial. As a result, all push rods 44 move downward. This allows the spring cartridges 30 to rotate the master levers 18 clockwise.

During approximately the first two thirds of this motion, the locating pins 14 are extended while the clamp members move through the clearance space before contacting the pallet foot members 8. After the clamp members 16 contact the pallet foot mem bers 8, some slight additional rotation of a master lever 18 takes place to compensate for the deflections of the clamp members 16 and the other mem bers in the lever system as well as for the slight lost motions that occur at all the pin connections.

The exact point or position at which each registry mechanism develops full clamp force also depends on the various dimensional errors and wear on all mechanism members including the pallet foot members 8 and slide rails 6 which are subject to progressive and not necessarily uniform wear. But within a very wide range of such wear, each spring cartridge 30 and clamp mechanism will clamp a pal let with a substantially uniform amount of force. As each mechanism reaches its full clamp force and the mechanism reaches equilibrium, the spring car tridge 30 stops moving and the force generated is balanced out by the forces generated by the clamp surfaces 84, which, because of the high efficiency mechanisms employed, are far more reproducible than with wedges or screws.

The equilibrium full clamp position may vary from registry to registry because of the wear factors noted above. As each registry reaches its own equilibrium position, its master lever 18 stops rotating, but its associated push rod 44 will continue to move downward for its full stroke. A gap, variable from one registry to the next, and which may vary even in a given registry from pallet to pallet, will develop between the top of the push rod 44 and its recessed contact surface on master lever 18. This is of no consequence since it will be closed on the next unclamp upward movement of the push rod 44.

In essence, therefore, all clamps and locating pins are driven by the external power system to a common returned position, but the locating pins 14 are extended and clamps are actuated by an internal elastic power system, namely, the spring cartridges 30, whereby each registry mechanism can find its own equilibrium position independent of the other registries.

In an illustrative practical situation, the working stroke of the spring cartridge 30 will be 1 1/4 inches with a force output of 800 Ibs. A total work output of 1000 Ib. in. is therefore achieved. The total clamp member movement is .060 inches; since the work output is equally divided between two clamp members, the theoretical force generated at each clamp member is 1000/2/.060 = 8333 Ibs. The practical force which is reached is 7500 Ibs. at each clamp member. The total theoretical stroke of each clamp member, which is .060", is divided as follows:.035" clearance to theoretical pallet foot upper surface when clamp members are fully raised; .010" deflection of clamp member, and internal linkage members, and aggregate lost motions; and .015" unused stroke or "to go" which is available to compensate for pallet foot and slide rail wear.Stated another way, .015" total wear can be tolerated on the pallet feet or slide rails while still maintaining substantially constant clamping by the registry mechanism. This is severalfold greater than can be tolerated by present registries.

In FIGURE 7, the connecting rod 108 is shown connected to the link 104 which is at the end of line of multiple links 104; it will be understood that by placing the gear reducer 116 off to one side or the other of the line of interconnecting links 106, the connecting rod 108 can be connected to any one of the intermediate links 104. It will be further understood that the entire motor gear reducer crank drive system can be replaced by any other type of suitable prime mover capable of moving the links 104 through their required angular range. This includes a simple fluid actuator attached to one or the other of links 104, or links 106. It will be noted that the links 104 are significantly longer than the links 122, approximately 5 times longer as shown in FIGURE 7.

The reason for this length ratio is to reduce the forces in links 106, as compared to the forces in the push rods 44; this is, of course, compensated for with a longer stroke in links 106 as compared to the stroke of push rods 44, in exact proportion to the force reduction. Aforce reduction in links 106 is advantageous because it reduces the amount of reactive force which must be supplied by the spacers 100; which reactive forces are cummuiative along the length of the machine. A large stroke of the interconnecting links is also desirable, because the deflections, lost motions and cummulative wear are more tolerable with a large stroke than with a small one.

The spring cartridge shown in FIGURE 4 utilizes a coiled wire spring operating in compression.

Another type of spring cartridge is shown in FIGURE 9; in this design, the elastic element is comprised of a stack of disc springs, also referred to as Belleville washers. Referring to FIGURE 9, a pull rod 130 is connected to the nosepiece 28 (as in FIGURE 4); the other end of pull rod 130 is formed into a head 132. A stack of disc springs 134 is concentrically positioned and preloaded on the pull rod 130 between the head 132 and an internal flange 136 on a sleeve 138; the other end of sleeve 138 has an external flange 140 mounted in the housing 2. Each disc spring 134 is a conical shaped washer, which in compression becomes more nearly planar. A stack of disc springs 134, as in FIGURE 9, is generally to be preferred over a more conventional wire coil spring because a larger amount of work or energy can be stored in a given volume.

An alternative design for the spring cartridge, while still using disc springs, is shown in FIGURE 10.

Here, the stationary sleeve 142 is screwed to a mounting disc plate 144 through a stud 146; the disc 144 is mounted to the housing 2. The other end of the sleeve 142 is formed into an external flange 148.

Disc springs 150 are stacked on the outside of the sleeve 142 and bear against the flange 148.

At the other end of sleeve 142, this stack of disc springs 150 is preloaded against a shouldered washer 152. The washer 152 is held in place by a thin flat keeper 154 which extends across a diameter of the washer 152 passing through two long longitudinal slots 156 in the sleeve 142 and also passing through a slot 158 in a pull rod 160. At its other end, the pull rod 160 mounts the nosepiece 28. It can be seen that the tensile load in pull rod 160 is transmitted by the keeper 154, acting as a beam, into a compressive load on the stack of disc springs 150. As the pull rod 160 moves through its stroke, as determined by the mechanism, the keeper 154 remains loaded against the righthand side of slot 158 in pull rod 160, but the keeper 154 moves freely through the clearance slots 156 in sleeve 142.

Referring to FIGURES 5 and 6, it will be recalled that the resilient bushing 92 is utilized to returnithe clamping member 16 to its unclamped and clearance position upon release of the clamp force generated by lever 66. It will be understood that alternative elastic return systems can be used to accomplish this same return force. A short stack of disc springs can be utilized in place of bushing 92. A simple conventional wire coil spring can also be used to return the clamp member 16.

In connection with FIGURE 7, one embodiment of an external mechanism, suitable for actuating the push rods 44 vertically upward, was described.

Another means for accomplishing these same motions is to mount a long torque tube longitudi nallythrough the machine beds, suitablyjournalled therein, which oscillates through a small angle on a horizontal axis. At each station an arm is fastened to the torque tube and the outboard end of each arm drives a vertically moving push rod 44 through a pivot connection. The torque tube in turn is driven by a suitable arm, connecting rod, and eccentric or the like. It can be seen that two torque tube assemblies are required, one to operate the push rods on one side of the registry line and a second to drive the push rod on the other side of the registry line.

Still another approach to operating the registries with a single external mechanism requires no push rods. A downwardly extending arm can be added to each master lever 18. The lower outboard ends of these extensions can then be connected together by links driven by a mechanism as in FIGURE 7, to operate all the master lever extensions and registries in synchronism.

Claims (13)

1. A registry mechanism for clamping pallets at a work station of a multiple station transfer machine in which workpieces are located and supported in pal lets and in which said pallets are moved in sequence through said machine, said registry mechanism comprising a registry frame, a pallet clamp movably mounted in said frame and having a first portion to engage a pallet in a clamping relationship with one face of a relatively rigid section of said frame and a second portion to receive a clamping force to move said first portion into said clamping position, said second portion being located on the opposite side of said frame section from said first portion, and a mechanical means to cause engagement of said clamp with said pallet, which means comprises a clamp-actuating lever having a reaction fulcrum por tion, at which said lever is pivoted to said frame for transmission of a reaction force along a first axis, and having a second fulcrum portion to contact said second portion of said clamp to transmit thereto the clamping force along a second axis, said reaction fulcrum portion on said clamp-actuating lever being positioned to contact said frame on a face of said rigid frame section opposite said one face and said second axis being substantially parallel to and dis posed closely to said first axis, whereby said reac tion force substantially places said rigid frame sec tion in compression between said pallet and said 'reaction fulcrum, thereby minimizing the reactive bending moment applied to said registry frame by said clamp.

2. A registry mechanism as claimed in claim 1 in which said clamp comprises a "C" shaped member having a body extending transversely of said rigid frame section opposite sides thereof, said first clamp portion comprising a first extension extending transversely to said clamp body on one side of said frame section, said second clamp portion compris ing a second extension extending transversely to said clamp body on the opposite side of said frame section and substantially co-planar with said first extension, said first and second clamp portions lying on said second axis to which said clamp body is substantially parallel.

3. A registry mechanism as claimed in claim 1 or 2 wherein said clamp is mounted on said frame by resiliently distortable means whereby deflections in the clamp impose negligible loads on the frame.

4. A registry mechanism as claimed in claim 1,2 or 3 in which said lever is mounted in said frame by resiliently distortable means to locate the lever in position.

5. A registry mechanism as claimed in any of claims 1 to 4 wherein said reaction portion of said lever is adjacent one end thereof, and power means for pivoting the lever is operative upon the opposite end thereof, said second fulcrum portion being located intermediate the opposite ends of the lever but substantially closerto said reaction portion than to the end connected to the power means.

6. A registry mechanism as claimed in any preceding claim in which one or more locating pins are slidably mounted in said frame to engage corresponding locating holes in said pallet, and in which said mechanical means provides interconnections between energy storage means provided on said frame and said locating pin and between said energy storage means and said clamp actuating lever, to sequentially engage the locating pin in a locating hole in the pallet and then clamp the pallet to the registryframe, external power means being interconnected with said mechanical means to actuate said clamp actuating lever to retract the clamp from the pallet and thereafter to disengage the locating pin from the locating hole in the pallet against said energy storage means.

7. A registry mechanism as claimed in claim 6, in which said mechanical means includes a master lever pivotally mounted in said frame and having four interconnections which include a first connection to said locating pin, a second connection to said energy storage means, a third connection to said external power means, and a fourth connection to said clamp-actuating lever.

8. A registry mechanism as claimed in claim 7 when dependant from claim 5 including a pair of said clamps and a pair of said clamp actuating levers symmetrically disposed, in which said fourth connection of said mechanical means comprises an intermediate lever pivotally mounted in said frame and in turn pivotally connected to one end of a link means which, at its other end, is pivotally connected to the approximate midpoint of an equalizing lever which, at each of its ends, is pivotally connected to a respective one of the two clamp-actuating levers at the end thereof remote from the reaction portion.

9. A registry mechanism as claimed in claim 6,7 or 8, in which said energy storage means comprises a first elongate member, a second elongate member slidably mounted in said first elongate member, an elastic spring means mounted between said elongate members, and means limiting the relative travel between said elongate members, whereby said elastic spring means cannot achieve a fully relaxed position, and whereby the working stroke of said energy storage means is between a partially deflected posi tion of said elastic spring means and an even greater deflected position of said elastic spring means.

10. A plurality of registry mechanisms, each as claimed in any preceding claim, in which said registry mechanisms are mounted on a machine bed and wherein a shaft is mounted in the machine bed below each registry mechanism, a bellcrank is jour nalled on each of said shafts and has a short arm with an outboard end spaced from said shaft and a long arm, a push rod interconnects the outboard end of each short arm of said bellcranks and said mechanical means of each registry mechanism, and means are arranged below said registry mechanisms to interconnect and drive said multiple long arms of said bellcranks.

11. A multiplicity of registry mechanisms as claimed in claim 10 in which said interconnecting and driving means comprises a drive means connected to one of said long arms of said bellcranks to oscillate said bellcrank about said shaft, and a multiplicity of links interconnecting one or more long arms of said bellcranks, whereby all said long arms of said bellcranks oscillate in unison.

12. A registry mechanism constructed and adapted to operate substantially as herein described with reference to and as illustrated in the drawings.

13. A multiple station transfer machine having a plurality of registry mechanisms, each as claimed in any preceding claim.