Technical Field

The invention relates to a transfer system for transporting work pieces in a press, comprising a transfer rail having a plurality of grippers for gripping the work pieces and a linear mechanism attachable to a press frame of the press for linearly moving the transfer rail with respect to the press frame. The invention further relates to a press, in particular to a press line or multiple-die press, to a method for transporting work pieces in a press and to the use of an articulated robot for transporting work pieces in a press.

Background Art

An important step of the manufacture of components made of sheet metal is the forming step. Sheet metal parts are formed in a press, such as a hydraulic, hydroforming, mechani¬ cal, electrical or pneumatic press, typically including an upper die and a correspo nding lower die. The dies are moved against each other, and thereby the work piece arranged in the work space between the dies is formed. The form of the dies determines the impact on the work piece and therefore the resulting form. Usually, a succession of forming steps using differently shaped dies is necessary until the desired form of the sheet metal part is obtained. To perform these steps in an expedient way, a plurality of presses is arranged successively to form a press line, or a press is employed that includes a plurality of die pairs. On one hand, the capacity of the press line or multiple-die press is determin ed by the capacity of the press, i. e. the time required for carrying out one forming operation. On the other hand however, the capacity significantly depends on the efficiency of the transport of the work pieces from one press station to the next one. It is therefore important to employ a fast transfer system for automatically transporting work pieces from one press station to the next one.

Most presses feature a press frame that supports the lower and upper dies of the press as well as corresponding drives and gears. The work pieces are transferred through a continuous window of the press frame, along a main transfer direction. For this purpose, a transfer system comprising a transfer rail having a plurality of grippers for gripping the work pieces is provided. The work pieces may be gripped by magnetic or suction tools or by grippers that engage with matching recesses or protrusions of the work pieces or of holders attached to the work pieces. Often, such transfer systems are arranged withiin the window of the press, i. e. substantially on the inner side of the press frame.

However, in the case of small window dimensions there is not enough space for arranging the transfer system within the window and therefore the main portion of the system has to be arranged on the outer side of the press frame. Only the transfer rail runs inside the press window and only a small part of the support of the transfer rail enters the window from the outside of the press. As an example, the "gullWing" transfer system of Gϋdel

pressAutomation, Langenthal, Switzerland is specially adapted for new or retrofit press applications with small window dimensions. This system features a horizontal transfer rail running parallel to the main transfer direction which is attached to the press frame by serial kinematics, comprising in serial progression from the press frame to the transfer rail a swivel axis parallel to the main transfer direction, a vertical linear axis parallel to the main transfer direction, a first horizontal linear axis perpendicular to the main transfer direction and a second horizontal linear axis parallel to the main transfer direction. With respect to the press frame, the transfer rail is linearly moved along the main transfer direction by the second horizontal linear axis. The swivel axis exclusively serves for tipping up the whole system clear of the press, e. g. for allowing access to the bolster for changeover.

The "gullWing" system features an elaborate construction which is well adapted for heavy work pieces and fast dynamics. However, due to its complexity, the construction is rather costly.

Summary of the invention

It is the object of the invention to create a transfer system pertaining to the technical field initially mentioned, that is adapted to small dimensions of the press window and that is of a simple construction.

The solution of the invention is specified by the features of claim 1. According to the invention, the transfer system features an articulated mechanism for carrying the transfer rail, the articulated mechanism comprising at least three parallel swivel axes, whereby the articulated mechanism is attached to the linear mechanism such that it is linearly moveable with respect to the press frame.

Articulated mechanisms are widely used and cost-effective. They allow for a simple construction of the inventive transfer system. Furthermore, articulated mechanisms allow for a very precise control, the repeatability of such mechanisms may be of the order of 0.1 mm. In the case of presses with small window dimensions, the linear mechanism and the main part of the articulated mechanism may be arranged on an outer side of the press

frame, whereby only the transfer rail and the foremost part of the articulated mechanism to which the transfer rail is attached enter the press window. The three parallel swivel axes of the articulated mechanism allow for arbitrarily moving the attachment point of the transfer rail in a plane that is perpendicular to the three axes. At the same time, the orientation of the transfer rail and its grippers in said plane may be as well arbitrarily chosen. The degree of freedom of the linear mechanism must not run in said pl ane such that by means of the linear mechanism movements of the attachment point leading outside of said plane are enabled.

The inventive transfer system may be used in an inventive method for transporting work pieces in a press, comprising th e steps of

a) positioning the transfer rail in a first position, such that a work piece to be transported is seizable by a plurality of the grippers attached to the transfer rail;

b) seizing the work piece by actuating the grippers;

c) lifting the transfer rail together with the work piece by moving along a I inear axis of the linear mechanism and/or by moving around at least one swivel axis of the at least three swivel axes of the articulated mechanism;

d) transferring the work piece by moving the transfer rail along a main transfer direction by moving the articulated mechanism and/or the linear mecha nism;

e) lowering the transfer rail together with the work piece by moving the linear mechanism and/or the articulated mechanism; and

f) releasing the work piece by actuating the grippers of the transfer rail.

In first preferred embodiments of the invention, the linear mechanism comprises a horizontal linear guide attachable to the press frame, in such a way that its linear degree of freedom runs parallel to the main transfer direction of the press. Thereby, the linear mechanism allows for linearly moving the articulated mechanism together with the transfer rail in a direction parallel to the main transfer direction. The remaining degrees of freedom needed for the transfer rail are provided by the articulated mechanism. The linear guide

may e. g. be a rail on which a carriage is linearly movable, a slide bearing or a spindle guide.

In the case of a horizontal linear degree of freedom running parallel to the main transfer direction, the at least three swivel axes are preferably oriented parallel to the horizontal linear guide. Therefore, the swivel axes allow for arbitrarily moving the foremost end of the articulate mechanism in a vertical plane perpendicular to the main transfer direction. Together with the linear mechanism, the transfer rail is arbitrarily movable (within certain limits imposed by the actual construction of the mechanisms). At the same time, the orientation of the transfer rail and its grippers within said vertical plane may be arbitrarily chosen, in particular a change of orientation of the transfer rail caused by swiveling motions around the two swivel axes furthe r away from the transfer rail may be compensated by the third, foremost swivel axis. For example, this allows for retaining a horizontal orientation of the transfer rail and its grippers, while moving the transfer rail vertically or horizontally, in a direction perpendicular to the main transfer direction.

Alternatively, the swivel axes are oriented incli ned to the horizontal linear guide. In this case, it is still possible to move the transfer rail as needed in a transfer process in a press by combining linear motions along the horizontal linear guide and swiveling motions around the three axis. However, in the case of inclined swivel axes the linear motion along the main transfer direction is not decoupled from the movements in the plane perpendicular to the swivel axes, and therefore swiveling actions to move the transfer rail vertically or horizontally, across the press, have to be compensated by corresponding linear movements along the horizontal guide.

Advantageously, the horizontal linear guide is attachable to the press frame in a position above the work space of the press, and the artic ulated mechanism is attached to the linear guide in a suspended position. This arrangement avoids obstructions of the lateral openings of the press frame, thereby allowing for easy access to the dies and tools within the press.

Alternatively, the horizontal linear guide is attac hable to a base portion of the press frame, and the articulated mechanism is supported on the linear guide.

In second preferred embodiments of the invention, the linear mechanism comprises a vertical linear guide attachable to the press frame, such that the articulated mechanism attached to the linear mechanism is linearly movable in a vertical direction. Furthermore, the at least three swivel axes are oriented parallel to the vertical linear guide. Arranged like this, the swivel axes allow for arbitrarily moving the foremost end of the articulate mechanism, to which the transfer rail is attached, in a horizontal plane. Together with the linear mechanism, the transfer rail is arbitrarily movable (within certain limits imposed by the actual construction of the mechanisms). At the same time, the orientation of the transfer rail and its grippers within said horizontal plane may b>e arbitrarily chosen, in particular a change of orientation of the transfer rail caused by swiveling motions around the two swivel axes further away from the transfer rail may be compensated by the third, foremost swivel axis. For example, this allows for retaining a horizontal orientation of the transfer rail and its grippers, while moving the transfer rail horizontally.

Again, the linear guide may e. g. be a rail on which a carriage is I inearly movable, a slide bearing or a spindle guide.

Preferably, two linear mechanisms with vertical linear guides are attachable to two supports of the press frame. A first articulated mechanism is attached to the first of said linear mechanisms, and a second articulated mechanism is attached to the second of said linear mechanisms. The transfer rail is attached to both the first articulated mechanism and the second articulated mechanism. Attaching the transfer rail to two separate articulated mechanisms, preferably near opposite ends of the transfer rail, ensures stable support of the transfer rail and facilitates the handling of heavy work pieces. Furthermore, the two linear guides may be attached to two vertical supports at opposite ends of the press or press station.

Preferably, the movements of the first articulated mechanism and the second articulated mechanism are synchronized by an external control system, such as an electronic control system for the entire press or a central control system for the transfer system. The control system ensures that the articulated mechanisms (and preferably as well the linear mechanisms) are synchronously actuated. Note, that in the case of two vertically movable articulated mechanisms holding a single transfer rail it is not required to actively control

the rotational position of the third swivel axis, adjacent to the transfer rail. This is because the orientation of the transfer rail with respect to a vertical axis is predetermined by the positions of the two attaching elements of the articulated mechanisms.

Alternatively, especially in cases where heavy work pieces are not to be processed, the transfer rail is attached to a single articulated mechanism, preferably in a central region of the transfer rail.

Advantageously, the at least three swivel axes are constructed and arranged such that the articulated mechanism may be swiveled out clear of the press. Thereby, the articulated mechanism is removed from the vicinity of the lateral openings of the press frame and therefore the dies and tools within the press may be more easily accessed. Furthermore, in the case of a horizontal linear mechanism the transfer rail may be swiveled out clear of the press together with the articulated mechanism if the length of the transfer rail does not exceed the corresponding dimensions of the lateral opening. Additionally, the three swivel axes allow for positioning the transfer rail in a position outside of the press which is convenient for maintenance or tool exchange, especially in the case where the three swivel axes are parallel to the main transfer direction.

Preferentially, the articulated mechanism comprises an automatic coupler for coupling the transfer rail. This allows for easy and efficient tool change, in particular in cooperation with feeders or robots for providing the transfer rail to be changed. The couplers may be actuated electrically, hydraulically or pneumatically. They are preferably controlled by an external control system, such as an electronic control system for the entire press or a central control system for the transfer system.

Alternatively, the transfer rails are manually attached to and released from the articulated mechanism.

Preferably, the articulated mechanism is constituted by a robot arm of an articulated robot having at least three parallel swivel axes. Articulated robots are widely available, therefore the inventive transfer system may be assembled from a few stock items, which reduces the system's cost. Often, usual articulated robots feature more than three swivel axes

because they are intended for rather complex handling operations. For example, the articulated robots of the roboFlex series of Gϋdel AG, Langenthal, Switzerland, feature six axes of motion, out of them one linear axis, three parallel swivel axes and two further rotational axes. While such robots are useable in the context of the invention, for transporting work pieces in a press, in principle articulated robots of a simpler construction, having only three parallel swivel axes, suffice. The linear mechanism may be an integrated axis of motion of the robot or it may be provided separately. Similarly, the drive for the linear mechanism may be arranged at the linear guide, at a carriage running along the linear guide, carrying the articulated mechanism, or at the articulated mechanism itself. Finally, using an articulated robot allows for employing existing robot control systems.

Alternatively, the articulated mechanism may be a dedicated mechanism which is not based on existing articulated robots.

Advantageously, the articulated mechanism comprises

a) a base attached to the linear mechanism;

b) a first arm attached to said base via a first of said swivel axes;

c) a second arm, a first end of which is attached to said first arm, via a second of said swivel axes, and a second end of which is attached to the transfer rail, via a third of said swivel axes;

d) a first drive for actuating a swiveling motion of said first arm with respect to said base, around said first swivel axis;

e) a second drive for actuating a swiveling motion of said second arm with respect to said first arm, around said second swivel axis;

f) a third drive for actuating a swiveling motion of the transfer rail with respect to said second arm, around said third swivel axis.

Preferably, the first drive is attached to the base, the second drive is attached to the first arm and the third drive is attached to the second arm. This allows for simultaneously minimizing the masses to be moved while preserving constructional simplicity by avoiding complex transmissions. The drives may be supplied with energy (electricity, hydraulic or pneumatic pressure) e. g. by cable drag chains.

Alternatively, only two drives are provided for actuati ng movements around swivel axes and the movement around the third swivel axis is mechanically synchronized to the movements around the two other swivel axes in such a way that the orientation of the transfer rail is preserved, e. g. by sort of a parallelogram linkage for the attachment point of the transfer rail. The mechanical synchronization is automatically provided in cases where the transfer rail is supported by two articulated mechanisms.

In a press, in particular a press line or multiple-die press, the inventive transfer system may be employed in various ways. Firstly, a single transfer system may be arranged at one side of the press, carrying a usual transfer rail which grips the work pieces on one of their lateral sides or which features a cross-bar that extends across the press. In the case of heavier work pieces, two transfer systems may be arranged across the press, each of them carrying a separate transfer rail for simultaneously gripping the work pieces on two opposite sides. Finally, the two transfer systems arranged across the press may both be attached to a cross-bar which extends across the press and which grips the work pieces from above, e. g. by means of suction or magnetic tools. This arrangement is particularly advantageous in the case of heavy work pieces or if it is required that the work pieces are gripped in a central region, close to the longitudinal axis of the press.

Other advantageous embodiments and combinations of features come out from the detailed description below and the totality of the claims.

Brief description of the drawings

The drawings used to explain the embodiments show:

Fig. 1 A front view of a first embodiment of a n inventive transfer system, featuring a horizontal linear guide;

Fig. 2 a side view of the transfer system of Fig. 1 ;

Fig. 3A-D side views of different positions of the articulated mechanism of the transfer system of Fig. 1 during the tra nsfer process;

Fig. 4 a front view of a second embodiment of an inventive transfer system, featuring vertical linear guides;

Fig. 5 a top view of the transfer system of Fig. 4;

Fig. 6A-D top views of different positions of one of the articulated mechanisms of the transfer system of Figs. 4, 5 during the transfer process;

Fig. 7 a top view of a rest position of one of the articulated mechanisms of the transfer system of Figs. 4, 5.

In the figures, the same components are given the same reference symbols.

Preferred embodiments

Figure 1 is a schematic illustration of a front view of a first embodiment of an inventive transfer system, featuring a horizontal linear guide. A. multiple-die press 1 features a press frame 2 comprising vertical posts 3, 4 supporting the upper dies 5 and the corresponding drives and gears arranged in a housing 6. Note, that the construction of the press 1, which has a substantially rectangular footprint, is symmetrical, i. e. across the press another pair of vertical posts are arranged for supporting the upper dies 5 and the housing 6. The four vertical posts define a substantially rectangular work space. The lower dies 7 are supported on a floor-based press bed 8. The dies 5, 7 and the corresponding mechanisms for moving the upper dies 5 are as such known in the field of press technology and are not shown in detail. Along a main transfer direction 9 a sequence of corresponding upper and

lower dies 5, 7 are provided, on opposite sides of a press window 10 in which work pieces are formed in a plurality of forming steps.

The work pieces are transported from a die pair to the next adjacent die pair by a transfer system 100. The transfer system 100 comprises a linear mechanism 1 10, an articulated mechanism 130 and a transfer rail 150 attached to the articulated mechanism 130. The linear mechanism 1 10 features a horizontal bar 1 1 1 that is arranged at the outer side oϊ the press frame 2 in a vertical position above the work space for forming the work pieces between the upper dies 5 and the lower dies 7. The horizontal bar 1 1 1 is attached to the two lateral vertical posts 3, 4 by corner profiles 1 12, 1 13. It has a substantially square profile and features a horizontal guide rail 1 14 constructed along its lower surface. A carriage 1 15 featuring a drive 1 16 is horizontally running along the guide rail 1 14 (linear axis J ₁ ).

The articulated mechanism 130 is attached to the carriage 1 15 and features three paralle-l swivel axes J ₂ , J ₃ , J ₄ is described in more detail in connection with Figure 2, which is a schematic illustration of a side view of the transfer system of Figure 1, in a plane that is perpendicular to the main transfer direction 9 of Figure 1. Figure 2 again illustrates the press 1 with the press frame 2, the upper dies 5, the housing 6 for the drives and gears fo r the upper dies 5 and the press bed 8 supporting the lower dies 7. Visible in Figure 2 is one of the vertical posts 3 to which the horizontal bar 1 1 1 of the linear mechanism 1 10 is attached by means of the corner profile 1 12. The transversal width of the linear guide rail 1 14 attached to the lower surface of the horizontal bar 1 1 1 is slightly larger than the width of the horizontal bar 1 1 1 such that the rail protrudes from the horizontal bar 1 1 1 on its outer as well as on its inner transversal side.

The carriage 1 15 is running on the linear guide rail 1 14 by means of rolls 1 17 supported on the protruding portions of the guide rail 1 14. Drive pinions 1 18 are pressed against a rack arranged on the lower surface of the guide rail 1 14, opposite to the rolls 1 17. The drive pinions 1 18 are driven by drive 1 16 in order to move the carriage 1 15 along the horizontal bar 1 1 1. The drive 1 16 comprises an electric motor which is fed by a cable drag chain which is as such known from prior art and which is not displayed in the Figures for the benefit of lucidity. The cable drag chain may e. g. run in a suitable profile arranged on top

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of the horizontal bar 1 1 1. Thereby, the transfer system 100 and the lateral openings to the press window 10 are not obstructed.

The carriage 1 15 features an upper portion 1 19 featuring the rolls 1 17 and drive pinions 1 18 as well as a lower portion 120 to which the drive 1 16 is attached and which features - as part of the articulated mechanism 130 — an axle 131 which is oriented horizontally, parallel to the horizontal bar 1 1 1 and therefore parallel to the main transfer direction. The axle 131 is coupled to a drive 132 (see Figure 1), attached to the lower portion 120 of the carriage 1 15, for actuating movements around the axle 131, corresponding to the first swivel axis J ₂ . A first arm 133 of the articulated mechanism 130 is rotatably supported on the axle 131. A drive 134 comprising a nother electrical motor is attached to an upper portion of the first arm 133, coaxial with the first swivel axis J ₂ . Its movements are transmitted to an axle 135 situated near the lower end of the first arm 133, e. g. by means of a belt or shaft drive, in order to actuate movements around the axle 135 corresponding to the second swivel axis J ₃ . A second arm 136 of the articulated mechanism 130 is rotatably supported on said axle 135. Again, a drive 137 (see Figure 1) with an electrical motor is attached to the portion of the second arm 136 supported on the axle 135 of the first arm 133. The movements of the drive 137 are transmitted to another axle 138 situated near the other end of the second arm 136 (again e. g. by a belt or shaft drive). Thereby movements around the axle 138 are actuated, corresponding to the third swivel axis J ₄ . An attaching element 139 for the transfer rail 150 is rotatably supported on the axle 138 of the second arm 136.

The transfer rail 150 features a longitudinal rod 151 and a plurality of grippers 152 that feature suitable grip means (not displayed) for the work pieces to be transported, such as magnetic or suction tools or other elements that are suitable for gripping the work pieces. The transfer rail 150 and/or the grippers 152 may feature additional (rotational or translational) degrees of freedom such that gripping of the work pieces is facilitated or such that the orientation of the work pieces may be changed during the transfer process.

Figures 3A-D are schematic side views of different positions of the articulated mechanism of the transfer system of Figure 1 during the transfer process. The Figure 3A displays a starting position where the transfer rail 150 is situated in a lowered position outside the

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actual work space between the upper and lower dies 5, 7. The work piece 1 1 to be transported (which may be a single work piece, a plurality of work pieces or one or several pallets for holding the actual work pieces) is located on the lower die 7. Starting from the displayed position, the transfer rail 150 is moved horizontally towards the center of the press 1. For this purpose, the first arm 133 of the articulated mechanism 130 is rotated counter-clockwise around the first swivel axis J ₂ . To compensate the vertical movement of the transfer rail 150 effected by the rotation of the first arm 133 the second arm 136 of the articulated mechanism 130 is rotated clockwise around the second swivel axis J ₃ .

The Figure 3B displays the situation in which tri e gripper 152 of the transfer rail 150 has engaged with the work piece 1 1 (or with a contact piece attached to the work piece 1 1, respectively). The transfer rail 150 is still in a lowered position and has reached its innermost position needed during the displayed transfer process. However, in principle the transfer system 100 is capable of positioning the transfer rail 150 in positions that are far more inside the press, which is necessary if the work pieces to be transported have a width that is much smaller than the width of the press 1.

Next, the second arm 136 of the articulated mechanism 130 is rotated counter-clockwise around the second swivel axis J ₃ in order to lift the transfer rail 150. At the same time, the first arm 133 is rotated counter-clockwise around the first swivel axis J ₂ to compensate lateral movements. Furthermore, the attaching element 139 is rotated clockwise around the third swivel axis J ₄ such that a change of orientation of the transfer rail 150 due to the rotation of the second arm 136 is compensated, i. e. the orientation of the transfer rail is preserved.

Figure 3C displays the situation after the transfer rail 150 has been lifted into its upper position. It is this position in which the work piece 1 1 is transferred along the main transfer direction by actuating the linear mechanism 1 10. After the linear transport, the transfer rail 150 is again lowered in order to deposit the work piece 1 1 on the next adjacent lower die 7. For this purpose, the second arm 136 is rotated clockwise around the second swivel axis J ₃ and the first arm 133 is rotated clockwise around the first swivel axis J ₂ . The orientation of the transfer rail 150 is preserved by simultaneously rotating the attaching element 139 counter-clockwise around the third swivel axis J ₄ . Please note, that depending

on the form and size of the work piece 1 1 and of the dies 5, 7 the lowering of the transfe r rail 150 may start before the linear transport along the horizontal bar 1 1 1 has finished, in order to speed up the transfer process.

After the work piece 1 1 has been deposited on the lower die 7, as shown in Figure 3D, the transfer rail 150 is again horizontally retracted from the press 1. This is achieved by rotating the first arm 133 of the articulated mechanism 130 clockwise around the first swivel axis J ₂ . Again, to compensate the vertical movement of the transfer rail 150 effected by the rotation of the first arm 133 the second arm 136 of the articulated mechanism 13O is rotated around the second swivel axis J ₃ , this time counter-clockwise.

After linearly returning the articulated mechanism 130 to its start position by means of the linear mechanism 1 10 the situation displayed in Figure 3A is reached again, such that the next transfer step may be effected as soon as the forming step is finished. Note that a plurality of work pieces are generally simultaneously transported by the transfer process, engaged by different grippers 152 of the transfer rail 150 (or arranged on a common holder or pallet).

Figure 4 is a schematic illustration of a front view of a second embodiment of an inventive transfer system, featuring vertical linear guides.

The multiple-die press 1 corresponds to the press described in connection with the first embodiment of the invention (Figures 1-3). Again, it features the press frame 2 comprising vertical posts 3, 4 (and another two posts across the press) supporting the upper dies 5 and the corresponding drives and gears arranged in the housing 6. The lower dies 7 are supported on the floor-based press bed 8. Along the main transfer direction 9 a sequence of corresponding upper and lower dies 5, 7 are provided, on opposite sides of a pres s window 10 in which the work pieces are formed in a plurality of forming steps.

The work pieces are transported from a die pair to the next adjacent die pair by a transfer system 200 that comprises two linear mechanisms 210.1, 210.2, two corresponding articulated mechanisms 230.1, 230.2 and a transfer rail 250 attached to both the articulated mechanisms 230.1, 230.2. In contrast to the first embodiment, the linear and

articulated mechanisms 210.1 , 230.1; 210.2, 230.2 are constituted by two stock articulated robots (such as the roboFlex series of Gϋdel AG, Langenthal, Switzerland) having six axes (one linear axis and five rotational axes) J ₁ -J ₆ . Note that both the first embodiment described above may as well be equipped by stock articulated robots (featuring at least the four needed axes) and the second embodiment may be equipped by dedicated linear/articulated mechanisms as described in connection with the first embodiment.

The linear mechanisms 210.1 , 210.2 feature vertical bars 21 1.1 , 21 1.2 that are arranged at the outer side of the press frame 2 by means of booms 221.1 , 221.2. These booms 221.1 , 221.2 are attached to the vertical posts 3, 4 by corner profiles 212, 213 and hold the vertical bars 21 1.1 , 21 1.2 in a suspending manner, in positions that are diagonally outside the vertical posts 3, 4 with respect to the main transfer direction 9 as well as with respect to the transverse direction (see also Figure 5). The vertical bars 21 1.1 , 21 1.2 have a substantially square profile and feature vertical guide rails 214.1, 214.2 constructed along their transversally inner surface (see Figure 5). Carriages 215.1 , 215.2 featuring drives 216.1, 216.2 run vertically along the guide rail 214.1, 214.2 (linear axis J ₁ ). The articulated mechanisms 230.1, 230.2 are attached to the carriages 215.1 , 215.2 and feature three parallel swivel axes J ₂ , J ₃ , J ₄ . The height of the linear mechanisms 210.1 , 210.2 is chosen such that the transfer rail 250 attached to the articulated mechanisms 230.1 , 230.2 is vertically displaceable in the press window 10. The articulated mechanisms 230.1 , 230.2 are constructed and arranged reversed left to right with respect to each other and described in more detail below, in connection with Figure 5.

Figure 5 is a schematic illustration of a top view of the transfer system of Figure 4, in a horizontal plane that is in a height above the booms 221.1, 221.2 of the transfer system 200. The upper dies and the corresponding housing are not displayed for clarity of the illustration. Visible are the press bed 8 supporting the lower dies 7, as well as the vertical posts 3, 4 supporting the linear mechanisms 21O.1, 210.2 by means of booms 221.1, 221.2 attached to the vertical posts 3, 4 by corner profiles 212, 213. In the following, we discuss one of the two linear/articulated mechanisms 210.1, 230.1; 210.2, 230.2. As remarked above, the other just corresponds to a mi rror image of this one.

The width of the linear guide rail 214.1 attached to the inner surface of the vertical bar 2 1 1.1 is slightly larger than the width of the vertical bar 21 1.1 , such that the guide rail 2 14.1 protrudes from the vertical bar 21 1.1 on its left as well as right side. The carri age 2 15.1 is running on the linear guide rail 214.1 by means of rolls 217.1 co-operating v/vith drive pinions 218.1 pressed against a rack arranged on the inner surface of the guide rail 2 14.1, opposite to the rolls 217.1. The drive pinions 218.1 are driven by drive 216. 1 in order to move the carriage 215.1 up and down along the vertical bar 21 1.1. The d rive 2 16.1 comprises an electric motor which is fed by a cable drag chain which is as such known from prior art and which is not displayed in the Figures for the benefit of lucidity. The cable drag chain may e. g. run in a suitable vertically oriented profile arranged outside or behind the vertical bar 21 1.1. Thereby, the transfer system 200 and the lateral openings to the press window 10 are not obstructed.

The carriage 215.1 features an outer portion 219.1 featuring the rolls 217.1 and drive pinions 218.1 as well as an inner portion 220.1 to which the drive 216.1 is attached and which features - as part of the articulated mechanism 230.1 - a vertically oriented axle 231.1. The axle 231.1 is coupled to a drive (arranged on the bottom side of the inner portion 220.1 and therefore not visible in Figure 5) for actuating movements around the axle 231.1, corresponding to the first swivel axis J ₂ . A first arm 233.1 of the articulated mechanism 230.1 is rotatably supported on the axle 231.1. A drive 234.1 comprising a nother electrical motor is attached to the upper side of an outer portion of the first arm 233.1, coaxial with the first swivel axis J ₂ . Its movements are transmitted to an axle 235.1 situated near the inner end of the first arm 233.1, e. g. by means of a belt or shaft drive, in order to actuate movements around the axle 235.1 corresponding to the second swivel axis J ₃ . A second arm 236.1 of the articulated mechanism 230.1 is rotatably supported on said axle 235.1. Three drives 237.1, 240.1, 241.1 with electrical motors are attached to the outer end of the second arm 236.1. The movements of one of the drives 237.1 are transmitted to another axle 238.1 situated near the other end of the second arm 236.1 (again e. g. by a belt or shaft drive). Thereby, movement around the axle 238.1 is actuated, corresponding to the third swivel axis J ₄ . An attaching element 239.1 for the transfer rail 250.1 is rotatably supported on the axle 238.1 of the second arm 236.1. The other two drives 240.1, 241.1 attached to the second arm 236.1 are used for actuating two other

swivel axes of the articulate robot, that are not used in the context of the transfer system 200, namely an axis (J ₅ ) which is coaxial with the second arm 236.1 , allowing for rotating an inner section of the second arm 236.1 with respect to the outer section of said second arm 236.1, and an axis (J ₆ ) that is coaxial with the attaching element 239.1, allowing for rotating an end piece of the attaching element 239.1 with respect to the base piece of the attaching element 239.1.

The transfer rail 250 attached to both the articulated mechanisms 230.1 230.2 again features a longitudinal rod 251 and a plurality of grippers 252 that feature suitable grip means (not displayed) for the work pieces to be transported such as magnetic or suction tools or other elements that are suitable for gripping the work pieces.

Figures 6A-D show schematic top views of different positions of one of the articulated mechanisms of the transfer system of Figures 4, 5 during the transfer process. The Figure 6A displays a starting position where the transfer rail 250 is situated in a lowered position outside the actual work space. The work piece 1 1 to be transported (which may be a single work piece, a plurality of work pieces or one or several pallets for holding the actual work pieces) is located on the lower die 7. Starting from the displayed position, the transfer rail 250 is moved horizontally towards the center of the press 1. For this purpose, the first arm 233.1 of the articulated mechanism 230.1 is rotated clockwise around the first swivel axis J ₂ , and at the same time the second arm 236.1 of the articulated mechanism 230.1 is rotated counter-clockwise around the second swivel axis J ₃ . The orientation of the transfer rail 250 is preserved by slightly rotating the attaching element 239.1 clockwise around the swivel axis J ₄ .

Figure 6B displays the situation in which the grippers 252 of the transfer rail 250 have engaged with the work piece 1 1 (or with a contact piece attached to the work piece respectively). The transfer rail 250 is still in a lowered position and has reached its innermost position needed during the displayed transfer process. However, in principle the transfer system 200 is capable of positioning the transfer rail 250 in positions that are far more inside the press, which is necessary if the work pieces to be transported have a width that is much smaller than the width of the press 1.

Next, the transfer rail 250 is lifted into its upper position by actuating the linear mechanism 210.1. Following this, the second arm 236.1 of the articulated mechanism 230.1 is rotated clockwise around the second swivel axis J ₃ in order to move the transfer rail 250 along the main transfer direction 9 . In order to preserve the transversal position of the transfer rail 250, the first arm 233.1 is at the same time rotated clockwise around the first swivel axis J ₂ . The attaching element 239.1 is rotated counter-clockwise around the third swivel axis J ₄ in order to compensate its change of orientation due to the simultaneous clockwise rotations of both the arms 233.1 , 236.1. Note, that it is not necessary to actively control the rotation around the third swivel axis J ₄ because the respective orientation of the transfer rail 250 is already defined by the positions of the two attaching elements 239.1 of the two articulated mechanisms 230.1.

Figure 6C displays the situation after the transfer rail 250 has reached its end position with respect to the main transfer direction 9. Now, the transfer rail 250 is lowered by the linear mechanism 210.1 in order to deposit the work piece 1 1 on the next adjacent lower die 7. Please note, that depending on the form and size of the work piece 1 1 and of the dies the lowering of the transfer rail 250 may start before the transport along the main transfer direction 9 has finished, in order to speed up the transfer process.

After the work piece 1 1 has been deposited on the lower die 7, the transfer rail 250 is again horizontally retracted from the press 1. This is achieved by rotating the first arm 233.1 of the articulated mechanism 230.1 counter-clockwise around the first swivel axis J ₂ and by rotating the second arm 236.1 clockwise around the second swivel axis J ₃ . At the same time, the attaching element 239.1 is rotated counter-clockwise around the third swivel axis J ₄ .

After the situation displayed in Figure 6 D has been reached, the transfer rail 250 is returned to its start position by simultaneously rotating the first arm 233.1 counter¬ clockwise around the first swivel axis J ₂ and rotating the second arm 236.1 clockwise around the second swivel axis J ₃ . The orientation of the attaching element 239.1 is preserved by clockwise rotation around the third swivel axis J ₄ .

Figure 7 is a schematical top view of a rest position of one of the articulated mechanisms of the transfer system of Figure 4. To return the articulated mechanism 230.1 in its rest position the transfer rail is first separated from the attaching element 239.1. Preferably, this is done automatically employing automatic couplers for the transfer rail. After the separation, the first arm 233.1 as well as the second arm 236 A are both rotated counter¬ clockwise around the first swivel axis J ₂ and the second swivel axis J ₃ respectively. Thereby, the articulated mechanism 230.1 is removed from the press window 10 and its spatial extensions in the main transfer and opposite directions. This allows for unhampered access to the dies of the press 1.

As a matter of course, the technical details of the discussed embodiments may be modi¬ fied without leaving the scope of the invention, e. g. the construction and arrangement of the linear and articulated mechanisms as well as of the transfer rail may be modified. Furthermore, the inventive conveyor system is appropriate for press lines as well as for multiple-die presses of different press widths, lengths and distances. A press or a press line may be equipped with a plurality of serially arranged transfer systems.

The transfer system may be integrated into a variety of press configurations, e. g. independent of the arrangement of the support for the upper dies or of the press bed. The inventive conveyor system is suited for retrofitting of existing press lines or multiple-die presses as well as for integration into newly built appliances. The transfer system is not only suitable for transporting work pieces from a press station to the next adjacent press station but can as well be employed for transporting work pieces from an initial feed station to a first press, to or from an intermediate deposit station or from a final press to a delivery stack or further conveyor.

In summary, it is to be noted that the invention creates a transfer system that is adapted to small dimensions of the press window and that is of a sim pie construction.