Pallets for supporting workpieces and automatic adjustment of pallet workpiece support members

Abstract: A pallet having adjustable support members for automatically adjusting the distance between two support members (13,15) for carrying workpieces (17) of different dimensions. The support members are mounted on guides (12) that are fitted to pallets (10) that travel on conveyor transport systems for automatic production/assembly lines. The support members have locking means that frictionally secure the support members in place on the pallet and can be unlocked for movement along the guide. A releasably securing means on the pallet has a first condition which causes the guide to contact the support members to secure frictionally the support members to the pallet and a second condition which permits the support members to be moved.

Description: This invention relates to improvements in pallet conveyor production line systems including pallets that have support members that are adjustable for carrying workpieces of different dimensions, and particularly to a pallet that is adapted to carry different sized workpieces and apparatus and methods for the automatic adjustment of the distance between support members of such pallets. Pallet conveyor systems are used in automatic production lines where workpieces are to be subjected to a sequence of operations at successive workstations. A workpiece that is to be assembled, machined, or operated on is placed on support members that are mounted on a pallet. The pallet is set upon a moving conveyor belt that will advance the pallet and the workpiece to a series of workstations that perform the sequence of desired operations to complete the production cycle. A plurality of pallets carrying a like plurality of workpieces are typically used. The pallets are frictionally driven by the conveyor. As a workpiece is brought to a workstation, the pallet is stopped and the workstation operation is performed. While stopped, the pallet may continue to rest on the moving conveyor in sliding contact, or may be lifted off the moving conveyor belt. Depending on the desired operation, the workpiece may be worked upon while resting on the support members of the pallet, or it may be removed from the support members, worked upon, and then returned to the support members. At the conclusion of the operation, the pallet is released or placed back on the belt to advance to the next workstation. The pallets thus move asynchronously, i.e., pallets upstream of a stopped pallet will advance until they are stopped behind a stopped pallet while the conveyor continues to advance, individually or in sets or groups, and accumulate in order to wait their turn at the workstation. Alternately, the pallets may move synchronously with respect to one another. Pallet conveyor production lines are adapted for performing the same operations on workpieces that belong to the same family of workpieces and require the same machining operations, even though the workpieces may differ in certain dimensions. It is known to provide the workstations with automatic adjustment devices that can receive workpieces of different dimensions and adjust for the differences in order to perform properly the desired operation. However, to maximize efficiency of production, workpieces are usually grouped and processed in sets according to the uniformity of certain dimensions. This minimizes the amount of changing-time and thus increases the rate of through-put of finished parts. One of the problems with conventional pallet conveyor systems is that the support members on the pallets are manually adjusted for the dimensions of the particular workpieces for the production cycle. Conventional pallets have mechanical connecting links or fasteners that must be manually loosened so that the support members can be moved, and then refastened to secure the workpiece support members to the pallet in the proper location to support a workpiece. Thus, to change production from a set of workpieces having one uniform dimension to another, either the pallets must be adjusted while the pallets are advancing on the conveyor line or while pulled off the conveyor line. Alternately, the pallets may be replaced with a second set of pallets that are pre-adjusted for the dimensions of the next set of workpieces. Consequently, changing from one set of workpieces to another requires a significant slowdown or down-time in production. Another problem with conventional production lines is that the manual adjustment procedure allows for error in the settings used from one pallet to the next. Consequently, the workpieces are not always properly or uniformly carried during the production cycle, which may result in differences in the quality of the finished products. Summary of the Invention It is therefore an object of this invention to increase the efficiency of pallet conveyor production lines by rapidly and accurately adjusting the workpiece support members to the dimensions of the workpiece to be carried. It also is an object to provide for substantially the same spacing for the support members of pallets that are to carry workpieces of a set or group having certain uniform dimensions. It is another object of this invention to provide an in-line support member adjustment apparatus and method that will not slow or interrupt production for workpiece change-over. It is another object of this invention to provide a pallet with a locking means having a release mechanism that can be used to lock support members in place and easily unlocked to permit movement of the support members. It is another object of this invention to provide a pallet with adjustable support members mounted on a guide wherein the support members are held securely in place against the pallet by the guide and wherein the guide can be temporarily moved away from the pallet to permit movement of the support members therealong. It is another object of this invention to provide a pallet with adjustable support members mounted on a guide and to provide a positioning unit for engaging the pallet to translate the support members to their desired locations. It is a further object to determine the location of the support members relative to a predetermined location and, if necessary, to move the support members to the desired locations for a selected workpiece. Document EP-0348715 discloses an apparatus for automatically adjusting the distance between two support members for carrying workpieces of different dimensions. The support members are mounted on guides that are fitted to pallets that travel on conveyor transport systems for automatic production assembly lines. The support members have locking means that frictionally secure the support members in place on the pallet and can be unlocked for movement along the guide. The pallet disclosed in the above document comprises a plate having a first surface and a second surface; an elongated guide member; and first and second support members for supporting the selected workpiece, said first and second support members being mounted for movement along said guide member. According to this invention instead, the above pallet is further characterised in that: said guide member is releasably secured to said pallet to secure said support members at said selected dimensions; and each of said first and second support members has a first bearing surface for contacting the first surface of the pallet and a second bearing surface so that the second bearing surface is disposed between said releasable guide member and the first surface of the pallet and the first bearing surface is disposed proximate to the first pallet surface; and in that the pallet further comprises means for releasably securing the guide member to said pallet, comprising first means for exerting a first force to urge the first bearing surface of the support members in contact with the first pallet surface to secure frictionally the support members to the pallet; said means for releasably securing the guide members to the pallet further comprising second means for exerting a second force applied to counteract the first force to translate the first and second bearing surfaces relative to the guide member and the first surface of the pallet. In one embodiment, each support member may have an associated releasable securing means, which may be secured to the support member or to the pallet. In a preferred embodiment, the pallet may have one or more releasably securing means in fixed locations for locking and unlocking one or more support members. In one embodiment, the guide is configured with a contacting surface extending along the length of the guide and the first and second support members are adapted to be mounted on the guide so that a portion of each of the first and second support members is disposed between the guide contacting surface and the pallet. The guide contacting surface may be flat, concave, convex or any other appropriate configuration. In this embodiment, the means for releasably securing the first and second support members to the pallet or guide includes a spring member connecting the pallet and the guide. The spring member has a preselected biasing force for urging the guide toward the pallet so that the guide contacting surface contacts portions of the first and second support members to hold frictionally the first and second support members in place on and to the pallet in the first condition. More than one spring member located at different positions along the guide may be used. In a preferred embodiment, the guide is configured with an elongated smooth plow extending out from and along the length of the guide and the first and second support members are adapted to be mounted on the guide so that the guide plow extends at least partially over a portion of the first and second support members. The biasing force exerted by the spring member may be adjusted. The means for releasably securing the support members also is adapted to have an unloaded condition wherein an external force acting on the spring member in opposition to the biasing force reduces the frictional forces holding the support members in place so that the support members may be moved along the guide and pallet manually or by an automatic positioning unit. This external force thus places the pallet in the second condition so long as the force is maintained. A preferred embodiment of the spring member includes a pin, a cap and a spring wherein the pin passes through an aperture in the pallet surface, one end of the pin is secured to the guide. The other end of the pin extends through the pallet aperture beyond the other side, the spring is mounted over the pin on the other side of the pallet and the cap is secured to the pin so that the spring is in compression between the cap and the pallet surface and the guide is biased towards the pallet. In a more preferred embodiment, the pallet has a plate surface, the elongated guide has a T-shaped cross section having a top cross member and a stem base and is arranged with the stem portion proximate to the top surface of the pallet plate surface and the cross member is adapted contact a portion of each support member. The releasably securing means includes a pin passing through an aperture in the pallet plate having one end attached to the stem of the T and the other end extending out the other side of the pallet surface plate, and the spring member is mounted over the pin on the other side of the pallet plate surface and restrained between the pallet surface plate and a cap that is secured to the end of the pin. Each of the support members has a corresponding receptacle or aperture, preferably T-shaped, adapted to receive a length of the guide cross member and to slide along the guide. Thus, the spring member exerts a biasing force which causes the cross member of the T to contact portions of the support members to urge the support members against the pallet surface. The support members may be provided with an opening or a slot so that the support members can be moved along the the guide and will thus not be stopped by the releasably securing means for holding the guide to the pallet. Another embodiment of the invention includes a release means for placing the pallet in the second condition so that the support members can be translated to desired positions. In one embodiment, the release means includes means for applying an external force to the means for releasably securing the first and second support members so that the support members may be translated. In an embodiment wherein the releasably securing means is a spring or resilient means, the release means preferably includes an actuator or air cylinder or the like adapted for contacting the spring means in opposition to the biasing force to reduce the forces locking the support member in place. More preferably, the release means includes a pushrod adapted to contact and push the cap or pin connected to the stem of a T-shaped guide with sufficient force to counteract the spring biasing force and optionally to overcome that force and move the guide relative to the pallet surface. In accordance with another embodiment of this invention, there is provided a system for the automatic adjustment of the distance between two workpiece support members of pallets to adjust for the different dimensions of the workpieces to be operated on by a given pallet conveyor production line. In this aspect, the invention concerns a pallet having support members and a first condition and a second condition as described above and a positioning unit for translating the support members when the pallet is in the second condition. The positioning unit may include and control operation of the release means for placing the pallet in the second condition. Preferably, the positioning unit includes one means for translating for each support member on the pallet. In one embodiment of the positioning unit, the means for translating includes means for contacting the support members and moving the support members when the pallet is in the second condition to desired locations for a selected workpiece to be supported by the support members. One embodiment of the contacting means includes an extendable sleeve or pushrod having a contacting surface for contacting a support member. In this embodiment, each contacting surface may be adapted to interconnect temporarily with its associated support member so that, after contact is made, the pushrod can be further moved in either direction to place and release the support member at the desired location. In another embodiment of the positioning unit, the contacting means includes a first pair of pushrods having a range of motion including a rest position and a fully extended position that are adapted to extend from their rest positions to their fully extended positions thereby to move the first and second support members, in the second condition, from their positions on the pallet to a reference location associated with the fully extended positions, and a second pair of pushrods having a range of motion including a rest position corresponding to the reference location and a fully extended position corresponding to the rest positions of the first pair of pushrods, the second pair of pushrods being adapted to move from their rest positions at the reference location to contact and move the first and second support members to their respective desired locations. Each pair of pushrods may move in the same direction or in an opposite direction and the respective first and second pairs have opposite motions. For example, the first pair of pushrods may be configured to move the first and second support members inwardly towards each other to their innermost positions and the second pair of pushrods move the support members apart to their desired locations. The second pair of pushrods may be precisely controlled by for example, a precision actuator that moves the pushrods directly to locations that move and place the support members at their precise desired locations. For another example, the advance of the second pair of pushrods may be halted by a pair of arresting blocks, fixed in place on a ruled guide at positions that will leave the support members at their desired locations. The location of the arresting blocks on the ruler may be manually set by an operator, or controlled automatically by a precisely controlled motor. Optionally, the positioning unit includes control means for actuating the release means to place the pallet in the second condition for moving the support members and again to return the pallet to the first condition after an adjustment is made. The control means may be operated either before the support members are contacted or before the members are moved. In a preferred embodiment, the means for translating includes (1) means for contacting the support members (2) means for determining whether or not the support members are in the desired locations for the selected workpiece, and (3) means for moving the support members relative to each other to the desired locations for the selected workpiece. In this embodiment, the means for contacting may be an extendable sleeve or pushrod having a contacting surface adapted to interconnect temporarily with its associated support member where it stops. The pushrod is connected to a linear measurement transducer such as a potentiometer. In operation the pushrod is moved from an initial rest position until the contacting surface contacts a support member. The distance travelled is measured by the potentiometer which provides a signal corresponding to the location of the pushrod and, hence, the support member. The detected location is compared to the desired location. If a support member needs to be moved, the associated contacting surface is adapted to engage the support member and the pushrod is moved to move the support member to the desired location where the support member is released. Another embodiment of the translating means includes (1) means for contacting the support members, (2) means for determining whether or not the support members are in the desired locations for the selected workpiece, and (3) means for moving one or more of the support members to the desired locations in response to the determination made by a determining means. One embodiment of the determining means comprises a microprocessor device for comparing a signal corresponding to a measured distance or location of a support members to a desired location for a selected workpiece and indicating whether or not support member must be moved and if so, to where. In this embodiment, the moving means includes (1) reset means for translating the support members to respective reset or reference locations at predetermined locations on the pallet guide, for example, at one end of the extreme ranges of motion of the support members such as the innermost position for the first and second support members, and (2) locating means for translating the support members from their reset or reference locations to the desired locations for the selected workpiece. Preferably, the contacting means and the reset means may be the same element, for example, a pushrod having a contacting surface. In this embodiment, the locating means are precisely controlled to translate the support members independently to any of an infinite number of positions within their extreme ranges of travel. In contrast, the pushrod for contacting the support member and moving them to the reference locations innermost positions need not be precision controlled so long as contact is initially made while the pallet is in the first condition. Also included in the system of the invention is a means for moving the pallet and positioning unit into and out of engagement so that when the pallet and positioning unit are in engagement, the means for releasably securing the support members and the release means may become engaged whereby the pallet is placed in the second condition so that the means for translating can translate one or both of the first and second support members along the guide relative to one another to the selected or desired locations, and so that when the pallet and the positioning unit are out of engagement the means for releasably securing and the release means may be disengaged whereby the first and second support members are maintained in the first condition in a fixed position relative to one another and the guide on the pallet. For example, an engagement device may be provided which is a lifting means for raising and lowering the pallet between a lower position resting on the conveyor of the conveyor line and a higher position above the conveyor line. The higher position is adapted to bring the pallet into contact with the positioning unit as described herein. For another example, the engagement device may lower the positioning unit onto a pallet. For another example, the engagement device may move the positioning unit and the pallet horizontally relative to each other. In these embodiments, the release means may be a part of the lifting means, a part of the positioning unit, or a separate element disposed proximate to the pallet during the time the pallet and positioning unit are engaged. In an alternate embodiment of the positioning unit, the contacting means includes a movable carriage that is adapted for engaging and interconnecting with a support member, and a drive means for translating the carriage so that when the pallet and positioning unit are interconnected and the pallet support members are in the second condition, movement of the carriage will move the support member of the pallet along the guide accordingly. In a preferred embodiment, the carriage has a bushing that is adapted to interconnect with a pin protruding from a support member. In an alternate embodiment, the positioning unit comprises one releasing means, carriage, and bushing means for each support member so that when the pallet and positioning unit are engaged, each support member is released and engaged by a corresponding bushing and the support members can be adjusted simultaneously or independently. The positioning unit may comprise only one carriage and bushing so that only one support member is moved at a time. In this embodiment, moving more than one support member would require multiple cycles under the positioning unit. Alternately, the positioning unit may have one carriage, the carriage having two bushings that are spaced apart, whereby one support member is engaged and adjusted by one bushing and the other support member is engaged and adjusted by the other bushing. In operation, adjustment of the support members in accordance with one embodiment of the invention is carried oat as follows. The positioning unit including contacting means, determining means and moving means is placed at a convenient location, preferably in-line with the production line, more preferably prior to where the workpiece is first placed on the pallet. The pallet is advanced below the positioning unit and raised from its lower position to the higher position by a lifting means such as an air cylinder. When the pallet is in position the contacting means of the positioning unit makes contact with the support members. The determining means determines the locations of the support members and compares them to the desired locations for the selected workpiece to be supported by the pallet. If the determined locations match the desired locations, no change is made to the pallet support members and the pallet is lowered or returned to the conveyor and advanced to receive the selected workpiece. If the determined locations do not match the desired locations, then the release means engages the means for releasably securing the support members thereby placing the pallet in the second condition. The moving means then contacts one or more of the support member to be moved and translates them to the desired locations. Alternately, the release means could be activated as soon as contact is made or before contact is made so long as contact will not translate the support members. In the embodiment wherein the contacting means includes a pushrod and the moving means includes a reset means (which is the pushrod) and a locating means, each pushrod is first translated to contact its associated support member. If the support members are not at the desired locations, then the release means is actuated to place the pallet in the second condition and the pushrods are further translated to translate the support members to their respective reset or reference locations and then fully retracted to their rest positions, i.e., the outermost locations in their range of motion. The locating means are then actuated to translate the support members to the desired locations. Thereafter, pallet is returned to the first condition and the conveyor line to receive the selected workpiece. The embodiment of the positioning unit having a carriage for engaging and interconnecting with a support member operates as follows. At about the same time (or before or after) the pallet is brought into contact with the positioning unit, the carriage of the positioning unit makes contact with and engages a portion of the support member, thereby interconnecting the positioning unit carriage and the support member of the pallet. The release means is actuated to place the pallet in the second condition and the drive means of the positioning unit is then actuated to move the carriage, and hence, the support member, to the position associated with the particular dimensions for the workpiece that is to be placed on the pallet. Once the support member is in the proper location, the drive means is stopped and the pallet is lowered. The carriage and the support members and the release means respectively disengage. The pallet is thus placed in the first condition and lowered to the conveyor. The positioning unit drive means for moving the support members to the desired locations may comprise a motor, preferably a stepper motor, that can rotate a screw mechanism with precise control to advance or retract a member such as an arm, a pushrod (or sleeve) or a carriage along the screw to an infinite number of intermediate positions with in a range of extreme positions. Alternately, the drive means could operate a linear motion device with precise control to advance or retract a pushrod or carriage to an infinite number of intermediate positions within a range of extreme positions. Thus, the drive means permits precise automatic adjustment of the support members for a large number of workpieces having certain uniform dimensions. It also provides for consistent positioning from pallet to pallet for identically dimensioned workpieces. Computer control of the drive means enhances the automation and precision of operation. The pallet of the present invention also may be equipped with a means for lifting the work piece rapidly, to take it to a workstation for operation, and subsequently return the workpiece to the pallet. This device reduces the amount of time required to perform the operation at the workstation as compared to the time required for the workstation to perform the operation while the workpiece is held by the pallet. A microprocessor may be conventionally used to control the alignment and movement of the various elements of the apparatus, to identify the dimensions of the workpiece and the prior position of the support members, and to control the positioning unit movements. Thus, the modified pallets and the positioning unit of the present invention provide for rapid, accurate and repeatable adjustments of workpiece support members, whether successive workpieces are of the same or different dimensions. Brief Description of the Drawings The above and other objects and advantages of the invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts through out, and in which: FIG. 1 is a front elevated perspective, exploded view of a first embodiment of the pallet of the present invention; FIG. 2 is a front view of an assembled pallet taken along line 2 - 2 of FIG. 1 ; FIG. 3 is a side view taken along line 3 - 3 of FIG. 2 ; FIG. 4 is a side sectional view taken along line 4 - 4 of FIG. 2 ; FIG. 5 is a side sectional view taken along line 5 - 5 of FIG. 2 ; FIG. 5 a is an enlarged view of a portion of FIG. 5 ; FIG. 6 is front view of a pallet and positioning unit of the present invention; FIG. 7 is a side sectional view taken along line 7 - 7 of FIG. 6 ; FIG. 8 is a side sectional view taken along line 8 - 8 of FIG. 6 ; FIG. 9 is a front elevated perspective, exploded view of a second embodiment of the pallet of the present invention; and FIG. 10 is a front view of an assembled pallet taken along line 10-10 of FIG. 9 . Detailed Description of the Invention Referring to FIGS. 1-8 the first embodiment of this invention comprises a pallet 10 and a positioning unit 11. Pallet 10 includes a plate 9 attached to a base 1 that is adapted for contact with a pair of conveyor belts 2 for transport between workstations. Base 1 and plate 4 have respective holes that are at least in part superimposed to form an aperture 4 through pallet 10. Pallet 10 also includes a guide 12 which is mounted to plate 9, and support members 13 and 15 which are slidably mounted on guide 12. In the discussion that follow, two support members are described which have a substantially similar construction and which are mirror images of each other. Accordingly, the discussion will at times refer to both support members in the distributive, i.e., element A and B, where A corresponds to an element of one support member and B corresponds to the same element of the other support members, and at other times only with respect to one of the support members. It is to be understood, however, that in alternate embodiments, more than two support members that are similar in construction could be used. Support members 13 and 15 have respective support arms 14 and 16 that are adapted to support a workpiece 17. In the preferred embodiment, workpiece 17 comprises an armature for an electric motor and the production line machines armatures. Referring to FIGS. 1 and 4 - 5 , guide 12 is an elongated member. Two pins 21 are secured to the guide 12, preferably by a threaded connection, and preferably with one pin being located near each end of guide 12 . Pins 21 pass through respective bores 22 in plate 9 and extend into respective receptacles 23 in base 1. The ends of pins 21 in receptacles 23 are threaded. Springs 25 are mounted over pins 21 in receptacle 23 and nuts 26 are threaded over the ends of pins 21 in the receptacles, thereby securing springs 25 between plate 9 and nuts 26. Springs 25 cause pins 21 to urge guide 12 towards plate 9. The tension of springs 25 may be selected by screwing nuts 26 on pins 21 to preload the biasing force urging guide 12 toward pallet 10. Springs 25 are preferably discoidal springs of conventional construction capable of exerting an appropriate biasing force. In the preferred embodiment, a biasing force of approximately 20 Kg (44 pounds) has been found to be appropriate. When more than one releasably securing means is used the total force is equally shared by each means, i.e., for two discoidal springs spaced apart, each spring would provide approximately 10 Kg (22 pounds) of force. Support members 13 and 15 have respective slide blocks 30 and 40, bearing surfaces 32 and 42, bearing surfaces 34 and 44, and bearing surfaces 36 and 46. Referring to FIGS. 1 and 4-5 , slide blocks 30 and 40 include a housing adapted to fit over a length guide 12 in a loose fitting manner as described below. The interior configuration of the slide sections is preferably a female complement of the male structure of guide 12. Slide blocks 30 and 40, and bearing surfaces 32, 34, and 36 and 42, 44 and 46 are preferably long and wide enough to contact a length of guide 12 or pallet plate 9 to be stable in its intended retention and sliding functions. Bearing surfaces 32 and 42 are adapted to contact an opposing bearing surface on plate 9. When the pallet is in the first condition, springs 25 act on guide 12 to hold bearing surfaces 32 and 42 of support members 13 and 15 against plate 9 with sufficient force that friction will prevent support members from moving along guide 12 or plate 9 whether or not the support members are supporting a workpiece. It is to be understood that the frictional force must be sufficient to prevent unintended and inadvertent movement of the support members as a result of being in the conveyor production line assembly environment and subjected to vibrations, accelerations, decelerations, turning corners, repeated loading and unloading of workpieces and certain other anticipated forces applied parallel to the guide axis. Appropriate frictional forces are in the range of approximately 6,8 Kg (15 pounds) for each support member. The base of guide 12 may or may not be in contact with pallet plate 9 in the first condition. When the pallet is in the second condition, bearing surfaces 32 and 42 may slide across plate 9, whether or not surfaces 32 and 42 are in contact with plate 9 during such movement. Bearing surfaces 34 and 44 are adapted to contact guide 12. When the pallet is in the first condition, the forces exerted on guide 12 by springs 25 urges guide 12 against bearing surfaces 34 and 44 which forces in turn cause bearing surfaces 32 and 42 to contact frictionally plate 9. When the pallet is in the second condition, surfaces 34 and 44 may slide across or along guide 12 whether or not surfaces 34 and 44 are in contact with guide 12 during such movement. Bearing surfaces 36 and 46 are adapted to contact the top surface 28 of guide 12 which is preferably a bearing surface. When the pallet is in the first condition, surfaces 36 and 46 are preferably not in contact with top surface 28 of guide 12. When the pallet is in the second condition, surfaces 36 and 46 may be in contact with surface 28 of guide 12 and are adapted for sliding therealong during movement of the support members. In the preferred embodiment, guide 12 has a T-shaped configuration including a stem area 50 having a vertical axis, a cross member area 52 having a horizontal axis attached to stem 50, and a pair of protrusions 54 extending from the ends of cross member 52, and slide blocks 30 and 40 of support members 13 and 15 each have a pair of protrusions 31 and 41 that interfit with corresponding guide protrusions 54. Cross member 52 includes top surface 428 opposite stem 50. Protrusions 54 each include bearing surfaces 56 which are beveled at an angle relative to the axis of stem 50 preferably between 0 and 90° and more preferably at about an acute angle of approximately 20° relative to the vertical axis of stem 50. Slide portion protrusions 31 and 41 also have bearing surfaces 38 and 48 which are disposed on opposite sides of stem 50 of guide 12 and which may or may not be beveled relative to the stem axis. Beveled surfaces 56 are thus adapted to contact bearing surfaces 34 and 44 of support members 13 and 15 to hold frictionally support members 13 and 15 against guide 12 and plate 9 in the first condition. To place the pallet in the second condition so that the support members 13 and 15 may be moved, an external force is applied to each of pins 21 (or nuts 26 depending upon which element is presenting to the release means) sufficient to counteract the biasing force of springs 25 so that the friction between the bearing surfaces of plate 9, guide 12 and support member slide portions 30 and 40 is sufficiently reduced that support members can be manually or automatically pushed across and along guide 12 and plate 9 to desired locations. Preferably, such an external force is equal to the biasing force, although it could be slightly greater than or less the biasing force. Thus, when the releasably securing means exerts a force of 20 Kg (44 pounds) to hold the guide against the support members in the first condition, the release means applies a force of 20 Kg (44 pounds) opposite to the biasing force to place the pallet in the second condition. In the preferred embodiment, the pallet and guide are manufactured from metal such as steel and the support members are manufactured from a plastic material such as nylon or delrin containing approximately 20% glass. Accordingly, the forces exerted by the releasably securing means and the release menas may be adjusted to provide sufficient control over movement of the support members without introducing excessive wear of the materials in sliding contact. An external force may be applied by a release means as described below or manually using an appropriate tool. In the latter regard, a notch (not shown) may be provided between one end of guide 12 and plate 9 for receiving a lever device such as a crowbar which can be used to pry guide 12 a distance away from plate 9 to permit movement of support members 13 or 15 manually. Slide blocks 30 and 40 of support members 13 and 15 are mounted on guide 12 with a loose mechanical fit. The mechanical tolerances are in the range of 0.1 to 0.2 mm such that the narrowest of the gaps between the surfaces is approximately 0.1 mm between bearing surfaces 38 and 48 of blocks 30 and 40 and the opposite sides of stem 50 of guide 12. This tolerance a permits movement of support members 13 and 15 along guide 12, more particularly movement guided by stem 50, when the pallet is in the second condition without derailing the support members. Referring to FIGS. 9 and 10 , in an alternate embodiment the means for releasably securing guide 12' to pallet 10' is a combination of a single pin 21', spring 25', and nut 26' arranged in the same manner as described above in connection with the embodiment depicted in FIGS. 1 - 8 . In this alternate embodiment, a means for preventing rotation of guide 12 when the pallet is in the second condition is provided. For example, a pair of locating pins 29 are secured to guide 12', preferably threadably interconnected, and adapted to pass through corresponding bores 29A in plate 9' of pallet 10'. Pins 29 are adapted for reciprocation in bores 29A and are provided to maintain guide 12' properly oriented on pallet 10' when pallet 10' is in the second condition. Pin 21' is preferably located under the center of mass of guide 12' to accommodate better the different torques that support members 13' and 15' will exert on pin 21' as the support members are moved along guide 12' within their extreme ranges of motion. In the preferred embodiment, workpiece 17 is suspended over aperture 4 during transport. Aperture 4 allows the passage of a lifting means through the aperture to lift workpiece 17 off pallet 10 from below to a workstation or off the production line. Workpiece 17 is supported on support members 13 and 15 on v-shaped seat members 60 and 70. Referring to FIGS. 1 , 4 - 5, and 9 , v-shaped seat members 60 and 70 are releasably connected to arms 14 and 16 of support members 13 and 15. V-shaped members 60 and 70 include, in addition to the v-shaped seat section for receiving a workpiece 17, resilient guide means 64 and 74. Each guide means includes a pair of resilient flanges 69 separated by a space 79. Space 79 is preferably in the range of from about 2.0 to about 4.0 mm. Support member arms 14 and 16 respectively contain cut-out portions (see, e.g., cut-out 72 on FIG. 1 ) a receptacle for receiving resilient guide means (see guide means 74, FIG. 1 ) of v-shaped members 60 and 70. The dimensions of the cut-outs are selected so that the resilient guide means will be frictionally retained in the cut-outs. More particularly, the distance between the outermost surfaces of a pair of flanges 69 is greater than the corresponding dimension of the receptacles. Thus, when inserted, paired flanges 69 will be compressed and frictionally retained in the cut-outs. Flanges 69 may be further provided with bosses on their respective outward side for interfitting with corresponding notches in the cut-outs (see, e.g., notches 73 in cut-out 72). This will facilitate centering and retention of v-shaped seat members 60 and 70 in support members 13 and 15 for precise adjustment of the v-shaped seats relative to the desired locations of their respective support members. One advantage to using v-shaped seat members having resilient guide means frictionally interconnected with the support members is that it provides for rapid replacement of the v-shaped seat members when worn members need to be replaced or different seat members are to be used. For example, seat members may be of different shapes and sizes to accommodate different workpiece configurations, such as armature shaft diameters, shaft lengths, and overall armature dimensions. The resilient members thus save time and money in reducing down time for changing the seat members. Referring to FIGS. 6 -8 , a release means 100 is depicted. Release means 100 is adapted for contacting the means for releasably securing the support members to the pallet to place the pallet in the second condition. There is preferably one release means 100 for each releasable means. For example, in the aforementioned preferred embodiment of pallet 10 having each means for releasably securing the support members to the pallet 10 include spring 25 confined between plate 9 and nut 26 and around pin 21 to urge the support member against plate 9, each release means 00 is adapted for contacting one of pin 21 or nut 26 and compressing spring 25, thereby conteracting the biasing force and reducing the forces exerted by guide 12 on support members 13 and 15. Thus, actuation of release means 100 places pallet 10 in the second condition so that the support members may be translated. Such a release means 100 is preferably a linear actuator which may be an air cylinder having a pushrod. It is to be understood that release means 100 may be associated with (1) the pallet conveyor line in that they are stationary and the pallets are manipulated into position relative to the release means, (2) a positioning unit and relatively moved into position proximate to the pallet as the pallet and positioning unit are moved into engagement (not shown) or (3) each pallet in that it is a part of the pallet. Referring to FIGS. 6 - 8 , positioning unit 11 includes pushrods 130 and 140 having contact surfaces 138 and 148 for respectively contacting portions 135 and 145 of support members 13 and 15, and arms 152 and 162 having contact surfaces 158 and 168 for respectively contacting portions 154 and 164 of support members 13 and 15 as described below. Pushrods 130 and 140 are respectively connected to air cylinders 134 and 144. These cylinders advance and retract the pushrods. Positioning unit 11 also includes linear measurement transducers 132 and 142, preferably linear potentiometers, which are respectively connected to pushrods 130 and 140 by brackets 133 and 143. Thus, as cylinders 134 and 144 advance and retract pushrods 30 and 140, the distance of the pushrods from a predetermined rest position, i.e., their outermost position in their range of motion, can be monitored and measured using the respective linear measurement transducers 132 and 142. More particularly, the potentiometers produce a signal correlated to the amount of extension of the potentiometer which signal can be converted into a measurement of distance from the rest position. Air cylinders 134 and 144 and linear measurement transducers 132 and 142 are connected to frame 105 of the positioning unit. Positioning unit 11 also includes arms 152 and 162 which are suspended from slides 150 and 160, which in turn are mounted on threaded rods 151 and 161. Rods 151 and 161 are mounted in bearings 153 and 163 in frame 105 and preferably are axially aligned in parallel to each other and to the axis of guide 12 of a pallet having support members 13 and 15 to be adjusted. Rods 151 and 161 are connected to drive means 156 and 166 by a conventional pulley and belt arrangement 155 and 165. Drive means 156 and 166 are preferably conventional DC motors having encoders so that rods 151 and 161 can be independently rotated to locate arms 152 and 162 precisely at any desired location along the axis of rods 151 and 161 respectively. Preferred motors include the aforementioned model R220 manufactured by Parvex. The DC motors are preferably conventionally controlled by a microprocessor. In operation, positioning unit 11 is initially at a rest condition wherein pushrods 130 and 140 are disposed at one end of their extreme range of motion, preferably as far apart as possible, and arms 152 and 162 are disposed at one end of their extreme range of motion, preferably as close together as possible. A pallet 10 is brought into proximity to positioning unit 11. Positioning unit 11 is provided with a plurality of rods 110, for example, three rods (only one rod is shown in FIGS. 7 - 8 ), spaced apart to contact pallet 10. Rods 110 provide a stop to fix the pallet in the proper location and planar orientation relative to the positioning unit for the automatic adjustment operation. Once the pallet is in the desired position, cylinders 134 and 144 are actuated to advance until contact surfaces 138 and 148 respectively contact the outer portions 135 and 145 of support members 13 and 15 of pallet 10. The cylinders provide a gas pressure of about 2 to 3 atmospheres to advance the contact surfaces to contact the support members. It is to be understood that the cylinders are independently actuated and the contact surfaces of the pushrods may not contact their respective support members simultaneously. When contact is made, linear transducer devices 132 and 142 provide respective signals corresponding to the distance of the support members from the rest position of the corresponding pushrod. These values are processed by the microprocessor in order to determine the locations of the support members. The determined locations are then compared to the desired locations for the selected workpiece 17 that is to be supported by the pallet, which workpiece specification is separately provided to the microprocessor. The microprocessor then determines whether or not the support members are in the desired locations. If they are, then the pallet is disengaged from the positioning unit and returned to the production conveyor line to receive the selected workpiece. If the support members are not in the desired locations, in the preferred embodiment, release means 100 are actuated to place the pallet in the second condition by compressing springs 25, and optionally urging guide 12 away from pallet plate 9, and cylinders 134 and 144 are further independently actuated to advance pushrods 130 and 140 to the other end of their respective extreme ranges of motion, i.e., as close together as possible. For this operation, the cylinders provide a gas pressure or force of about 5 to about 6 atmospheres to move the support members. Thereafter, pushrods 130 and 140 (and associated potentiometer means 132 and 142) are fully retracted to their respective rest positions. This action translates support members to reference locations c and c' where they are maintained in position proximate to, if not in contact with, arms 152 and 162. In this embodiment, each time support members are to be adjusted they are first translated to the reference locations c and c' which corresponds to a minimum distance between support members. Following moving the support members to reference locations c and c', DC motors 156 and 166 are driven independently under the control of the microprocessor to rotate threaded bars 151 and 161 to arms 152 and 162 to contact portions 154 and 164 of support members 13 and 15 and to translate the support members in opposite directions along guide 12 to their desired locations on pallet 10. Once the support members are in the desired position, release means 100 are actuated to withdraw and release pins 21 or nuts 26 so that guide 12 presses support members 13 and 15 against pallet plate 9 to maintain the support members fixed in place, thereby returning pallet 10 to the first condition with the support members in the adjusted desired locations. In a preferred embodiment, air cylinders 134 and 144 exert a first force that is less than the frictional force holding the support members 13 and 15 in place when the pallet is in the first condition, and a second force that is greater than the frictional force, if any, holding the support members 13 and 15 to pallet 10 when the pallet is in the second condition. In a preferred embodiment, each release means 100 is operated to raise pin 21 and guide 12 a distance sufficient to remove the predominant frictional force acting on support members 13 and 15 as a result of the force exerted by spring 25. In addition, the tolerances between guide 12 and the interior of slide portions 30 and 40 of the support members are loose so that the motion of guide 12 is substantially confined within portions 30 and 40. Thus, the distance that the guide is raised is preferably not so great that (1) the top of guide 12 contacts the support members or (2) the guide raises support members 13 and 15, more particularly bearing surfaces 32 and 42, an appreciable distance from plate 9 for example, less than approximately 3mm. This distance is preferably minimized so that any waste materials found in the environment of an armature machining production line does not become interposed between the support members and the pallet, and so that movement of the support members along the guide will push any such waste materials out of the way. Pallet 10 may include an aperture adapted to permit a piston type lifting device for lifting workpiece 17 from pallet 10 to a workstation, and then to lower the workpiece back to its rest position for transport. Alternately, the workstation may include gripper means for grasping the workpiece from above to transfer the workpiece to and from the workstation. One skilled in the art will appreciate that the present invention can be practiced by other than the described embodiments, which are presented for purposes of illustration and not of limitation, and the present invention is limited only by the claims which follow.

Claims: A pallet (10) for carrying a workpiece (17) having selected dimensions in a pallet conveyor line comprising: a plate (9) having a first surface and a second surface; an elongated guide member (12); first and second support members (13, 15) for supporting the selected workpiece, said first and second support members being mounted for movement along said guide member; the device being characterised in that: said guide member (12) is releasably secured to said pallet to secure said support members (13, 15) at positions corresponding to said selected dimensions; and each of said first and second support members has a first bearing surface (32, 42) for contacting the first surface of the pallet and a second bearing surface (34, 44) so that the second bearing surface is disposed between said releasable guide member (12) and the first surface of the pallet and the first bearing surface (32, 42) is disposed proximate to the first pallet surface; and in that the pallet further comprises: means (21,25,26,100) for releasably securing the guide member (12) to said pallet, comprising first means (25) for exerting a first force to urge the first bearing surface (32, 42) of the support members in contact with the first pallet surface to secure frictionally the support members to the pallet; said means (21, 25, 26, 100) for releasably securing the guide members (12) to the pallet further comprising second means (100) for exerting a second force applied to counteract the first force to translate the first (32, 42) and second (34, 44) bearing surfaces relative to the guide member (12) and the first surface of the pallet. The pallet of claim 1 wherein the guide further comprises an elongated plow (54) extending along and from the guide to contact the second bearing surfaces of the first and second support members (13, 15) when said first means (25) exerts said first force. The pallet of claim 1 wherein the guide (12) further comprises an elongated member having a T-shaped cross section including a stem (50) and a cross member (52), each of the first and second support members further comprises an aperture, said second bearing surface (34, 44) being inside the aperture, the first and second support members (13, 15) being mounted to for movement along the guide so that the guide cross member section (52) is disposed inside the support member apertures whereby, when said first means (25) exerts said first force, the cross member section contacts the second bearing surface (34, 44) of the support members to urge the first bearing surface (32, 42) of the support members in contact with the first pallet surface to secure frictionally the support members to the pallet. The pallet of claim 3 wherein the cross member section (22) has an axis and further comprises a first end and a second end, each of the first and second cross member ends having protrusions (54) including a third bearing surface (56) at an acute angle in the range of from about 60 to about 80 degree relative to the axis of the cross member section (52), said third bearing surfaces (56) being adapted for contacting the support members to secure frictionally the support members to the guide (12) and the first pallet surface. The pallet of claim 1 wherein said first means (25) comprise a spring member (25) connecting the guide and the pallet; and said second means (100) for exerting a second force comprise a linear actuator means. The pallet of claim 5 wherein the pallet further comprises an aperture (22) extending through the first and second pallet surfaces and wherein said first means (25) of said releasably securing means further comprise a pin (21) and a cap (26), the pin passing through the aperture in the plate and having a first end attached to the stem (50) of the guide and a second end extending beyond the second plate surface, the cap (26) being attached to the second end of the pin (21) so that the spring member (25) exerts the first force between the cap and the second surface of the pallet. The pallet of claim 6 wherein the pin (21) is further adapted for reciprocation in the pallet aperture (22) in response to the second force, said reciprocation moving the guide relative to said first plate surface. The pallet of claim 7 wherein the spring member (25) is a discoidal spring surrounding the pin (21), the second end of the pin is threaded, and the cap (26) further comprises a nut wherein the first force exerted by the spring may be selected by rotating the nut on the second end. The pallet of claim 8 wherein the pallet further comprises means (29) for preventing the guide from rotating about the pin (21) when the securing means is in the second condition. The pallet of claim 1 wherein said guide (12) is provided with two opposite ends each having a respective releasably securing means. The pallet of claim 1 wherein each of the first and second support members further comprises respective first and second receptacles (64, 74), each receptacle having a depth and width, the apparatus further comprising a first seat member and a second seat member (60, 70) for carrying the selected workpiece therebetween, the members being adapted to interfit frictionally in the respective receptacles. The pallet of claim 11 wherein each of the members further comprises a first and a second flange (69) extending generally in parallel and in superposition from the seat, the flanges being paired and having inner surface and outer surfaces, each pair of said first and second flanges being separated by a space (79), resilient, and having outer surface spaced apart a distance that is greater than the width of the receptacle so that inserting the flanges into the receptacle provides a frictional fit. The pallet of claim 12 wherein each of said outer flange surfaces further comprise a boss and wherein each of said receptacles further comprise a notch whereby the flange bosses interfit with a receptacle notch (73) to fit properly the seat members.

Inventors: LOMBARDI MASSIMO, SANTANDREA LUCIANO, LOMBARDI, MASSIMO, SANTANDREA, LUCIANO
Applicants: AXIS SPA, AXIS S.P.A.
Application year: 1991
Main classification: B23Q7
IPC codes: B23P19, B23P21, H02K15, B65G17, B65G35, B23Q7