System and method for positioning a workpiece support frame in the proper position within a processing or assembly station of a manufacturing plant

Abstract

A system for positioning a workpiece holder frame (2) in a suitable position within a processing or assembly station of a manufacturing plant comprises a stationary support structure (9) arranged on two sides of the working area (A) of the processing or assembly station, and a carriage (8) for carrying the workpiece holder frame (2) along a transfer line (L) inside the working area (A). The stationary support structure (9) arranged on the two sides of the working area holds vertically movable support members (10) positioned and configured to engage and lift the workpiece holder frame (2) held by the carriage (8) in order to move the workpiece holder frame (2) away from the carriage (8) and to vertically position the workpiece holder frame (2) at a predetermined vertical height (Z) when the carriage is stopped at the working area. The vertically movable support member (10) includes at least three spherical supports (10) spaced apart from one another and each including a sphere (12) freely rotatable in any direction around its own center. The workpiece holder frame (2) has a plurality of flat lower engagement surfaces (7) that are respectively engaged by the spherical supports (10) such that when the workpiece holder frame (2) is raised to the predetermined vertical height (Z), the workpiece holder frame (2) can float in any horizontal direction above the freely rotatable spheres (12) of the spherical supports (10). There are also auxiliary centering members (22) connected to at least two of the fixed support structures (9), vertically movable and spaced apart from one another, said auxiliary centering members cooperating with engaging elements (6) protruding downwards from the workpiece holder frame (2) so as to position the workpiece holder frame (2) in an appropriate position along two mutually perpendicular horizontal directions (X, Y) and with regard to a rotation of the workpiece holder frame in the horizontal plane.

Description

[Technical Field]

[0001] The present invention relates to a system and method for positioning a workpiece holder frame in an appropriate position within a processing or assembly station of a manufacturing plant.

[0002] In this specification and in the claims that follow, the term "workpiece" is used in a general sense to denote any part, structure, subassembly of a structure, component, or group of components that must undergo processing and / or assembly operations within a station of a manufacturing plant. For example, the invention is applicable to stations for assembling battery packs for powering electric traction motors in electric vehicles. However, the invention is equally applicable in other fields, such as in the field of assembly stations for automobile bodies or subassemblies thereof. [Background technology]

[0003] In processing or assembly stations of the type indicated above, it is often necessary to be able to carry out operations in both automatic and manual modes, with the intervention of an operator who must be able to work in ergonomic and completely safe conditions. This requirement often makes it difficult to use systems for moving and positioning workpieces within the processing station, thereby reducing or even preventing accessibility from all sides of the workpiece being processed. Conversely, in applications of the type indicated above, it is essential to reduce as much as possible the distance between the part that needs to be processed and the area that can be walked by the operator. Furthermore, the facilities provided for supporting and positioning the workpieces in the correct position must not create obstacles for the operator. At the same time, when a processing station must operate in fully automatic mode, the step of positioning the workpiece within the processing station must be carried out (in any case) with great precision, yet in a relatively short time.

[0004] Another need that arises in applications of the type described above is to be able to easily and quickly adapt the processing stations to each new application or product model, thanks to the use of flexible handling systems.

[0005] As indicated, conventional handling systems such as ground conveyors, "lift and move" systems or motor-driven roller beds involve the use of fixed floor structures that prevent operators from reaching the part being machined from all sides. Other systems, such as overhead conveyors, involve the use of support frames (in all cases) that free up floor space but also impede access to the workpiece and are expensive.

[0006] Finally, all known prior art solutions have the drawback of not being able to flexibly adapt to the introduction of new models in production or to changes in the layout of the plant and the routing of the production lines.

[0007] Also known are manufacturing systems in which manual and automated operations are performed at separate stations, with the consequent disadvantage that a transport system must be provided to carry the workpieces from the automated station to the manual station, or vice versa, which involves the introduction of non-value-added operations with associated costs and the use of additional equipment.

[0008] [Objective of the Invention] The object of the present invention is to overcome the above drawbacks.

[0009] In particular, one object of the present invention is to provide a system and method for positioning a workpiece holder frame within a processing or assembly station that can be used for stations that can operate in both fully automatic and manual modes while ensuring accessibility to the workpiece for the operator from all sides.

[0010] Another object of the present invention is to provide a system and method of the above-identified type that makes it possible to properly position a workpiece in a processing station in a highly accurate manner and within a significantly reduced time.

[0011] Another object of the present invention is to provide a system and method of the type set out above that has high flexibility characteristics in terms of easy adaptation to new applications and / or the introduction into the manufacture of new products and / or changes in the layout of the manufacturing plant and / or the routing of the manufacturing line.

[0012] It is yet another object of the present invention to provide a system and method of the type set forth above that can be implemented using simple and low-cost means. Summary of the Invention

[0013] In order to achieve one or more of the above objects, the object of the present invention is to a processing or assembly station having a work area and fixed support structures on either side of said work area; a carriage configured to carry a workpiece holder frame along a line inside the working area; a workpiece holder frame held on the carriage, the workpiece holder frame being configured to hold a workpiece in a predetermined position relative to the workpiece holder frame; Equipped with the fixed support structures disposed on the two sides of the working area carry vertically movable support members positioned and configured to engage and lift the workpiece holder frame carried by the carriage stationary within the working area to move the workpiece holder frame away from the carriage and vertically position the workpiece holder frame at a predetermined vertical height (z); the vertically movable support member includes at least three spaced apart spherical supports, two of which are disposed on opposite sides of the working area, each of which includes a sphere that is freely rotatable in any direction about its center; the workpiece holder frame has a plurality of flat lower engagement surfaces positioned and configured to be respectively engaged by the spherical supports such that the workpiece holder frame can float in any horizontal direction above the freely rotatable spheres of the spherical supports when the workpiece holder frame is raised to the vertical height (z); and there are also vertically movable, spaced-apart auxiliary centering members connected to at least two of the fixed support structures, the auxiliary centering members being configured to cooperate with engaging elements projecting downwardly from the workpiece holder frame to position the framework piece holder along two mutually perpendicular horizontal directions (X, Y); The system: an actuator device for controlling the movement of the spherical support and the auxiliary centering member independently of each other; and an electronic controller programmed to control the actuator device so that, when the carriage carries a workpiece holder frame to the working area, the spherical supports are raised and engage the workpiece holder frame to raise it to the required vertical height (Z), while the auxiliary centering members are simultaneously raised to only partially engage the cooperating engagement elements when the workpiece holder frame reaches the required vertical height (Z), and then the auxiliary centering members, taking advantage of the fact that the workpiece holder frame can float in any horizontal direction above the freely rotatable spheres of the spherical supports, continue their upward movement until they fully engage the corresponding engagement elements of the workpiece holder frame in order to center the frame with a predetermined orientation in the two horizontal directions (X, Y) and with respect to rotation in the horizontal plane until they reach a vertical position of full engagement of the corresponding engagement elements; a workpiece holder frame positioning system for positioning a workpiece holder frame in an appropriate position within a processing or assembly station of a manufacturing plant, the system also comprising:

[0014] The present invention also relates to a method implemented by the system described above.

[0015] Further features and advantages of the invention are set out in the dependent claims. [Brief explanation of the drawings]

[0016] One embodiment of the present invention will now be described, given by way of non-limiting example only, with reference to the accompanying drawings, in which: [Figure 1] 1 is a perspective view of a processing station using a system according to the present invention; [Figure 2]FIG. 2 is a side view of a detail of FIG. 1 on an enlarged scale. [Figure 3] FIG. 2 is a plan view of a detail of FIG. 1 on an enlarged scale. [Figure 4] 1 is a perspective view of a carriage used in a system according to the present invention, with a workpiece holder frame held above the carriage; FIG. [Figure 5] FIG. 2 is a perspective view of an example of a workpiece holder frame used in a system according to the present invention. [Figure 6] FIG. 6 is a perspective view from below of the workpiece holder frame of FIG. 5. [Figure 7] 2 is a perspective view of fixed support units disposed on one side of the working area of the station of FIG. 1, which are vertically movable independently of one another and are provided with spherical support members and auxiliary centering members; FIG. [Figure 8] FIG. 8 is a partial plan view of the unit of FIG. 7. [Figure 9] 1. FIG. 4 is a perspective view of another stationary unit disposed on one side of the work area of the station of FIG. 1, including a vertically movable sphere support member. [Figure 10] FIG. 10 is a front view showing spherical support members disposed on two sides of the station's working area in engagement against the lower engagement surfaces of the workpiece holder frame. [Figure 11] FIG. 10 is a front view showing spherical support members disposed on two sides of the station's working area in engagement against the lower engagement surfaces of the workpiece holder frame. [Figure 12] FIG. 10 is a front view showing stationary structures disposed on either side of the working area, with each auxiliary centering member in engagement with a corresponding engagement element held by the workpiece holder frame. [Figure 13] FIG. 10 is a front view showing stationary structures disposed on either side of the working area, with each auxiliary centering member in engagement with a corresponding engagement element held by the workpiece holder frame. [Figure 14]1. A perspective view of an additional fixed unit arranged on one side of the working area of the station of FIG. 1, which holds a stopping device for stopping the carriage at a predetermined position within the working area of the processing station. DETAILED DESCRIPTION OF THE INVENTION

[0017] In FIG. 1, the number 1 indicates (as a whole) a system for moving and positioning a workpiece holder frame 2 within a working area A of a processing or assembly station.

[0018] As indicated above, in this specification and in the claims that follow, the term "workpiece" is used in a broad sense to refer to any part, structure, subassembly of a structure, component, or group of components intended to undergo processing and / or assembly operations within a station of a processing plant. The accompanying drawings do not show workpieces or components held by workpiece holder frames 2, nor do they show automated or manual equipment intended to operate on the workpieces. These aspects fall outside the scope of the present invention, which instead specifically refers to a system for moving the workpiece holder frame and positioning it within a work area. In the specific case of the illustrated example, the system according to the present invention is designed for application in a processing station for assembling battery packs for powering the electric traction motors of electric vehicles. However, the system would equally apply to any other type of product and operation, including assembly operations of automotive structures or subassemblies thereof.

[0019] As already indicated, the system according to the invention is suitable for use in a particularly advantageous manner on processing or assembly stations which can operate both in fully automatic mode and in (at least partially) manual mode, the system being characterized in that the workpieces arranged in the working area are easily accessible from all sides to operators who have to intervene in the working area.

[0020] 5 and 6 of the accompanying drawings show two perspective views of an example of a workpiece holder frame 2 that can be used in a system according to the present invention. In this example case, the frame 2 has a structure made up of, for example, metal elements welded and / or bolted together, and includes a plurality of upper support surfaces 3, locating pins 4 and locating brackets 5 for supporting and locating workpieces, components or assemblies in precise positions relative to the workpiece holder frame 2. The workpiece holder frame 2 further comprises two engagement elements 6 in the form of pins with conical tips projecting downwardly from side supports 60 of the workpiece holder frame 2, spaced apart in the longitudinal direction of the frame, on the same side of the workpiece holder frame 2 and adjacent the front and rear ends thereof, respectively. The function of the engagement pins 6 will become clear below.

[0021] With further reference to the illustrated example, the workpiece holder frame 2 also has four supports 70 that protrude downwardly from the frame 2 and define lower engagement surfaces 7 (FIG. 6) whose function will also become apparent below. In the case of the illustrated example, two supports 70 are provided on two sides of one end of the workpiece holder frame 2 and two supports 70 are provided on two sides of the opposite end of the workpiece holder frame 2.

[0022] In the illustrated embodiment example (FIGS. 1 and 3), the workpiece holder frame 2 is carried along line L through the working area A by a carriage 8, which is shown in FIG. 4 with the workpiece holder frame 2 held above the carriage. The carriage 8 and workpiece holder frame 2 are configured such that the engagement pin 6 and the flat engagement surface 7 (FIG. 6) of the workpiece holder frame 2 are accessible from below (in all cases) even when the workpiece holder frame 2 is disposed above the carriage 8. The carriage 8 can be moved in one direction or another along line L as required for each specific application.

[0023] In the case of the illustrated example, carriage 8 is a simple, manually operated carriage comprising a frame 80 mounted on wheels W (in the example shown, the front wheels pivot and the rear wheels have fixed axles). Again, in the case of the illustrated example, carriage 8 is intended to be moved by a small tractor T with manual or motor-assisted operation driven by an operator who pulls or pushes it along a line L. The operator moves carriage 8 until it is brought to working area A, where the system according to the invention lifts (in a manner described below) the workpiece holder frame 2 away from carriage 8 and places it in a precise position both in the vertical direction Z and along two mutually perpendicular horizontal directions X, Y, and with respect to rotation in the horizontal plane. Once an operation (manual and / or automatic) has been carried out within the working area on the workpiece thus positioned in place, the system according to the present invention lowers the workpiece holder frame 2, with the workpiece held thereon, above the carriage 8, after which the operator moves the carriage along the line L out of the working area and towards the subsequent station in the plant.

[0024] Of course, the manually operated carriage shown in the accompanying drawings may be replaced by any other type of manually operated or motorized carriage, in particular it may be replaced by an AGV (Automated Guided Vehicle) or an AMR (Automated Mobile Robot).

[0025] In order to lift the workpiece holder frame 2 when the carriage 8 is within the working area A, the system according to the invention comprises a plurality of (four in the example) stationary structures 9 arranged on two sides of the working area A (FIGS. 1, 3). In the case of the example described herein, the stationary structures 9 are of the type shown in FIG. 7 or of the type shown in FIG. 9. In both cases, each stationary structure 9 comprises a vertically movable support member 10 positioned and configured to engage and lift a workpiece holder frame 2 carried by a carriage 8 stationary within the working area. Each support member 10 is constituted by a spherical support of any type known per se and comprises a casing 11 from which protrudes upwards a metal sphere 12 which is supported within the casing 11 in such a way that it can rotate freely in any direction around the centre of the sphere.

[0026] The structural details of the spherical support 10 will not be described or illustrated herein, since they can be produced in any known manner and, taken alone, do not fall within the scope of the present invention. In both the case of a fixed structure 9 of the type shown in FIG. 7 and the case of a fixed structure 9 of the type shown in FIG. 9, the spherical support 10 is rigidly connected to a slide 14 that is vertically movable on one or more guides 15 and is mounted above a bracket 13 that projects therefrom. The vertical movement of the slide 14 is controlled by a servo-controlled electric motor 28 via a mechanical transmission of any known type. In the illustrated application example (see FIGS. 12 and 13), the transmission comprises a belt transmission 281 and a worm screw device 282. Referring to FIGS. 7 and 9, the air brake device 16, which is active when the electric motor is stationary in its working position, is also coupled to the servo-controlled electric motor 28.

[0027] In the case of the illustrated example, the guide 15 for the vertical movement of the slide 14 is held by a slide 17 slidably mounted on a horizontal guide 18 oriented perpendicular to the longitudinal direction of the line L, the horizontal guide 18 being mounted on a base plate 19 intended to be rigidly connected to the plant floor by chemical or mechanical anchors 20. The movement of the slide 17 along the guide 18 is driven by an air cylinder 21.

[0028] The fixed structures 9 of the type shown in Figures 7 and 8 are also provided with auxiliary centering members 22 which are vertically movable and which are intended to cooperate with respective engagement pins 6 (Figure 6) protruding from the bottom of the workpiece holder frame 2.

[0029] In the case of the illustrated example, the auxiliary centering member 22 is of a type known per se and includes a casing 23 within which are mounted a plurality of freely rotatable rollers 24 that are radially arranged around the central vertical axis of the centering member 22, are mounted so as to be freely rotatable around their respective axes, and are all arranged in the same horizontal plane perpendicular to said central vertical axis. In a manner known per se, the rollers 24 define between them a central space Y that is configured and sized to receive each engaging pin 6 following lifting of the auxiliary centering member 22 relative to the corresponding pin 6. Each pin 6 has a conical tip that favors engagement of the centering member 22 around the pin 6, even when the centering member 22 has a central vertical axis that is not initially perfectly aligned with the corresponding vertical axis of the pin 6.

[0030] 7 and 8, in the illustrated example, the centering member 22 is held by a bracket 25 protruding from a slide 26 slidably mounted on a guide 27, which is again held by the slide 14 that holds the spherical support 10 in the illustrated example. Thus, in this embodiment, activating the actuator 28 results in synchronized vertical movement of the spherical support 10 and the auxiliary member 22. When the actuator 28 is deactivated, the vertical movement of the spherical support 10 is suspended, but the vertical movement of the slide 26 holding the centering member 22 can be controlled by an actuator assembly 100 that includes a pneumatic actuator with a rod locking device.

[0031] 1 and 3, on one side of the working area A, there are provided two stationary structures 9 of the type shown in FIGS. 7 and 8, each equipped with a spherical support 10 and an auxiliary centering member 22, while on the other side of the working area A (shown in the lower part of FIG. 3), there are two stationary structures 9 of the type shown in FIG. 9, each equipped with only a spherical support 10. Thus, in this example, four spherical supports are provided, two on each side. Theoretically, if the actual weight of the workpiece holder frame, the workpiece, and the machining forces are applied within an imaginary triangle whose three vertices are the contact points between the spherical supports 10 and the supports 70, then with two supports arranged on opposite sides of the working area A, only three spaced-apart spherical supports 10 may be sufficient to support the workpiece holder frame 2 at the required vertical height Z.

[0032] Again, in the case of the illustrated example, two centering members 22 are instead provided, disposed on the same side of the working area A and spaced longitudinally from each other.

[0033] 6, one of the engagement pins 6 protruding from the bottom of the workpiece holder frame 2 has opposite flattened sides 6A symmetrical about its own axis, so that when that pin 6 engages with a respective centering member, it properly positions the frame 2 in the horizontal direction Y transverse to the longitudinal direction of the frame and acts as an anti-rotation feature for the other pin. The other pin 6 protruding from the bottom of the frame 2 (i.e., the pin closest to the viewer in FIG. 6 ) instead has a perfectly circular cross-section, so that when it engages with a respective centering member 22, it properly positions the frame 2 in the two mutually perpendicular horizontal directions X and Y. The simultaneous engagement of the two pins 6 in each centering member results in proper positioning of the workpiece holder frame 2 along the two mutually perpendicular horizontal directions X and Y and with respect to rotation of the frame 2 in the horizontal plane. The servo-controlled electric motor 28 and actuator 100, which constitute the actuator device for the vertical movement of the spherical support 10 and the centering member 22 (in the example shown), are controlled by an electronic and electro-pneumatic control unit E (schematically shown in FIG. 7) according to a predetermined program to perform the functions described herein below.

[0034] When the carriage 8 is stopped within the working area A, the workpiece holder frame 2 is lifted and moved away from the carriage 8 by the spherical supports 10, which engage with the respective lower flat surfaces 7 of the workpiece holder frame 2 (FIG. 6). The lifting is achieved by the electronic control unit E activating the electric motor 28 coupled to the fixed structure 9 for controlling the vertical movement of the slide 14. FIGS. 10 and 11 show the state in which the spherical supports 10 engage with the respective lower flat surfaces 7 of the workpiece holder frame 2.

[0035] The upward movement of the slide 14 is automatically stopped by the control unit E when it detects that the workpiece holder frame 2 has reached a predetermined vertical height Z. It should be noted that in this state, the workpiece holder frame 2 is completely released from the carriage 8 and can float in a horizontal plane above the spherical support 10 due to the free rotation of the spheres 12. In this state, the workpiece holder frame 2 is safely held (in any case) above the spherical support 10, because simultaneously with the lifting movement of the spherical support 10, the electronic unit E also commands the vertical lifting movement of the two centering members 22 so that, when the workpiece holder frame 2 reaches the predetermined height Z, the centering members 22 have already begun to engage with the conical tips of the respective engagement pins 6. Starting from this state, the spherical support 10 remains at the vertical height reached, while the centering members 22 continue their upward movement until they abut and fully engage with the respective engagement pins 6. This additional upward stroke of the centering members 22 relative to the engagement pins 6 results in the proper positioning of the workpiece holder frame 2 along the two mutually perpendicular horizontal directions X and Y, and with respect to rotation in the horizontal plane. This centering movement occurs thanks to the floating ability in the horizontal plane provided by the spherical supports 10. When the centering members 22 reach the vertical position of full engagement with the pins 6, their movement is naturally stopped. In this state, the workpiece holder frame is correctly positioned in its position within the working area, and a cycle of machining and / or assembly operations can be initiated on the workpieces held by the frame 2, both in cases where these operations are performed by fully automatic equipment and in cases where these operations are partially performed manually by an operator.

[0036] Thanks to the above-described configuration of the system according to the invention, the operator has access to the working area A. During the cycle of automatic operation, the carriage 8 can remain in position within the working area or can be moved to make the working area even more accessible for carrying out manual operations.

[0037] Another advantage of the system according to the invention, as shown, is that it can be easily adapted when introducing new applications or new products into production, or in the case of changes in the path of the production line, and also for processes that require alternating between automatic or semi-automatic stations requiring the entire system of FIG. 3 and purely manual stations where the presence of the carriage 8, workpiece holder frame 2, and tractor T is sufficient. The ability to translate the slides 17 of the fixed structures 9 in the transverse direction allows these structures to be easily adapted to various configurations of workpiece holder frames. Furthermore, the fixed structures 9 can be easily disassembled and reassembled at various positions along the length of the line, and again adapted to various configurations of workpiece holder frames 2. Of course, the possibility of envisaging each of the structures 9 being mounted on a slide that is movable in the length of the line is not excluded in any way, in order to make the adjustment of the position of the structures 9 in the length of the line automatic.

[0038] When the cycle of operations on the workpiece held by frame 2 is completed, frame 2 can be lowered back onto carriage 8 by controlling the downward movement of spherical support 10 and centering member 22. Once frame 2 is placed on top of carriage 8, the carriage can be moved to carry frame 2, together with the workpiece held thereon, out of working area A and sent to a subsequent operation in the manufacturing process.

[0039] Preferably, within the working area A there is also present a stop device 29 provided with a cushioned stop member 30 intended to cooperate with the carriage 8 or the workpiece holder frame 2 held on the carriage 8, in order to provide a correct positional reference within the working area A along the longitudinal direction. In particular, a stop block or pad 101 (Fig. 14) defines a fixed stop position for the carriage or workpiece holder frame; to avoid any reverse movement of the carriage, there is present an anti-reverse device consisting of a chamfered movable bar 102 which is free to rotate about an axis 103. This bar 102 can only be pulled down from the carriage in the direction of travel of the carriage itself, but it prevents reverse movement of the carriage by returning the bar to its rest position due to the weight of the bar or a return spring.

[0040] The bar 102 interacts with the carriage and engages the lower portion 81 of the carriage (FIG. 4).

[0041] The backstop 102 , stop pad 101 and cushioned stop member 30 are all mounted on a slide 104 which slides against a guide 106 and is operated by a pneumatic actuator 105 .

[0042] Before the carriage reaches the stop position, the stop device 29 is advanced toward the center of the carriage's translational axis into the work area to capture the carriage during its movement. After the carriage has stopped, to allow the carriage to leave the work area, the stop device 29 moves back away from the center of the carriage translational axis, allowing the carriage to freely exit the work area.

[0043] Of course, the details of construction and the embodiment may vary widely from those described and illustrated, without prejudice to the principles of the invention and without departing from the scope of the invention. In particular, the invention includes a system such as that set out in the appended claim 1, in which instead of a carriage any other known type of transport device is provided.

Claims

1. 1. A system for positioning a workpiece support frame in an appropriate position within a processing or assembly station of a manufacturing plant, comprising: a processing or assembly station having a work area and fixed support structures on either side of said work area; a carriage configured to carry a workpiece holder frame along a line within the working area; a workpiece holder frame held on the carriage, the workpiece holder frame being configured to support a workpiece at a predetermined position relative to the workpiece holder frame; Equipped with the fixed support structures disposed on two sides of the working area carry vertically movable support members positioned and configured to engage and lift the workpiece holder frame carried by the carriage to move the workpiece holder frame away from the carriage and position the workpiece holder frame at a predetermined vertical height when the carriage is stationary in the working area; the vertically movable support member includes at least three spaced apart spherical supports, two of which are disposed on opposite sides of the working area, each of which includes a sphere that is freely rotatable in any direction about its center; the workpiece holder frame has a plurality of flat lower engagement surfaces positioned and configured to be respectively engaged by the spherical supports such that the workpiece holder frame can float in any horizontal direction above the freely rotatable spheres of the spherical supports when the workpiece holder frame is raised to the vertical height; and and each auxiliary centering member is coupled to at least two of the fixed support structures and is vertically movable and spaced apart from one another, the auxiliary centering members being configured to cooperate with engaging elements projecting downwardly from the workpiece holder frame to position the workpiece holder frame along two mutually perpendicular horizontal directions and with respect to rotation in a horizontal plane; The system: an actuator device for controlling the movement of the spherical support and the auxiliary centering member independently of each other; and an electronic controller programmed to control the actuator device such that when the carriage carries a workpiece holder frame to the working area, the spherical support is raised and engages with the workpiece holder frame to raise it to the predetermined vertical height, while the auxiliary centering members are simultaneously raised to only partially engage with the cooperating engagement elements when the workpiece holder frame reaches the predetermined vertical height, and then the auxiliary centering members continue their upward movement until they fully engage with the corresponding engagement elements of the workpiece holder frame by virtue of the workpiece holder frame being able to float in any horizontal direction above the freely rotatable spheres of the spherical support in order to position the workpiece holder frame in an appropriate position in the two horizontal directions perpendicular to each other and with respect to rotation in the horizontal plane; The system also includes:

2. the engagement elements of the workpiece holder frame are in the form of pins having a circular cross section and a conical tip, protruding downward from a support of the workpiece holder frame and positioned on the same side of the workpiece holder frame, respectively adjacent to two opposite ends of the workpiece holder frame; and 2. The system of claim 1, wherein the two auxiliary centering members cooperating with the engagement pins are carried by two fixed structures disposed on the same side of the working area, each defining a centering opening configured to receive a respective one of the engagement pins.

3. the plurality of flat lower engagement surfaces of the workpiece holder frame are in a single theoretical horizontal plane, and the freely rotatable spheres of the spherical support at the top of the spherical support are all tangent to the single theoretical horizontal plane; The system of claim 1 , whereby said freely rotatable spheres simultaneously engage said plurality of flat lower engagement surfaces when said workpiece holder frame is raised.

4. the plurality of flat lower engagement surfaces of the workpiece holder frame are in a plurality of horizontal planes spaced apart from one another, and the freely rotatable spheres of the spherical support at the top of the spherical support are in contact with theoretical horizontal planes spaced apart from one another by distances corresponding to the distances between the planes of the plurality of flat lower engagement surfaces of the workpiece holder frame; 4. The system of claim 3, whereby said freely rotatable spheres simultaneously engage said corresponding flat lower engagement surfaces when said workpiece holder frame is raised.

5. 5. The system of claim 3 or 4, wherein the electronic controller simultaneously controls the actuator devices coupled to a fixed structure to move the workpiece holder frame vertically while maintaining a horizontal orientation of the workpiece holder frame.

6. 3. The system of claim 2, wherein one of the engagement pins has a circular cross section with two opposite flattened faces such that it cooperates with each of the auxiliary centering members to properly position the workpiece holder frame in a horizontal direction transverse to the longitudinal direction of the workpiece holder frame, while the other engagement pin has a circular cross section and cooperates with each of the auxiliary centering members to properly position the workpiece holder frame in both of the mutually perpendicular horizontal directions and with respect to rotation of the workpiece holder frame in a horizontal plane.

7. 3. The system of claim 2, wherein each of the auxiliary centering members comprises a set of freely rotatable rollers radially disposed about a central vertical axis, the axes of which all lie in the same theoretical plane perpendicular to the central vertical axis.

8. 2. The system of claim 1, wherein each of the spherical supports and each of the auxiliary centering members is held by a bracket protruding from a vertically movable slide driven by a servo-controlled electric motor, the vertically movable slide being slidably mounted on guides held by the supports, the supports being further in the form of a slide slidably mounted on guides in a base plate of a fixed structure in a horizontal direction transverse to the longitudinal direction of the line.

9. the brackets holding the auxiliary centering members are slidably mounted vertically on guides held by the vertically movable slides holding the respective spherical supports; 9. The system of claim 8, whereby activation of the actuator device controlling the vertical movement of the vertically movable slide holding the spherical support also results in simultaneous movement of the auxiliary centering member coupled to the vertically movable slide, while when the actuator device of the vertically movable slide holding the spherical support is stopped, the actuator device controlling the vertical movement of the vertically movable slide holding the auxiliary centering member can be activated to continue vertically moving the auxiliary centering member after the spherical support is stopped at the predetermined vertical height.

10. The system of claim 1 , wherein the carriage is selected from a manual traction carriage, a towable carriage having a motor-driven tractor, a motor-driven carriage, an AGV, or an AMR.

11. 1. A method for positioning a workpiece holder frame in an appropriate position within a processing or assembly station of a manufacturing plant, comprising: a processing or assembly station is provided having a work area and fixed support structures on either side of the work area; a workpiece holder frame is transported along a transfer line within the working area by carrying the workpiece holder frame on a carriage, the workpiece holder frame configured to support a workpiece at a predetermined position relative to the workpiece holder frame; the fixed support structure on two sides of the working area is provided with vertically movable support members positioned and configured to engage and lift the workpiece holder frame carried by the carriage so as to move the workpiece holder frame away from the carriage and position the workpiece holder frame at a predetermined vertical height when the carriage is stationary within the working area; the vertically movable support member includes at least three spaced apart spherical supports, two of which are disposed on opposite sides of the working area, each of which includes a sphere that is freely rotatable in any direction about its center; the workpiece holder frame has a plurality of flat lower engagement surfaces positioned and configured to be respectively engaged by the spherical supports such that when the workpiece holder frame is raised to the vertical height, the workpiece holder frame can float in any horizontal direction above the freely rotatable spheres of the spherical supports; and at least two of the fixed support structures are also coupled to respective vertically movable, spaced-apart auxiliary centering members configured to cooperate with engaging elements projecting downwardly from the workpiece holder frame to position the workpiece holder frame along two mutually perpendicular horizontal directions and with respect to rotation in a horizontal plane; and when the carriage carries a workpiece holder frame to the working area, the spherical support is raised to engage with the workpiece holder frame and lift it to the predetermined vertical height, while the auxiliary centering members are simultaneously raised to partially engage with the cooperating engagement elements when the workpiece holder frame reaches the predetermined vertical height, and then the auxiliary centering members continue their upward movement until they fully engage with the corresponding engagement elements of the workpiece holder frame by virtue of the auxiliary centering members being able to float in any horizontal direction above the freely rotatable spheres of the spherical support until they reach a vertical position of full engagement with the cooperating engagement elements in order to position the workpiece holder frame in an appropriate position in the two horizontal directions and with a predetermined orientation with respect to rotation in the horizontal plane. method.

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