Drive unit

Abstract

A drive unit for driving a stroke motion of a moving frame is provided. The drive unit comprises a first actuation device for performing a rapid stroke motion, a second actuation device for performing a working stroke motion, and a control device. The first actuation device includes a mechanically driven actuator. The second actuation device includes a hydraulically driven linear actuator. The mechanically driven actuator and the hydraulically driven linear actuator are coupled to each other so as to move as a unit. The control device controls the first actuation device and the second actuation device.

Description

[0001] DESCRIPTION

[0002] Title of the invention

[0003] Drive unit

[0004] Technical field to which the invention relates

[0005] The present invention relates to drive unit for driving a stroke motion, to a machine, in particular a pressing machine, bending machine, or punch machine comprising the drive unit, and to a method for operating the drive unit.

[0006] Indication of background art

[0007] Drive units for driving a stroke motion are used for a wide variety of applications and purposes, such as presses, bending machines or punching machines. In the context of such applications, the drive units are designed to drive a stroke motion of a moving frame holding a corresponding tool dependent on specific working cycles. Namely, a rapid stroke motion of high speed at low force and a working stroke motion of low speed at high force. The rapid stroke motion is used when the moving frame and the tool are moved to and removed from a workpiece, which requires high speed but low force. The working stroke motion is used during forming or machining the workpiece, which requires low speed but high force.

[0008] Conventionally, hydraulic drive units utilizing a hydraulic cylinder for driving the stroke motion are used in the above-mentioned applications. To meet the different requirements of the rapid stroke motion and the working stroke motion, at least two hydraulic cylinders having different piston surfaces are provided. In particular, a hydraulic cylinder having a relatively large piston surface is used for the working stroke motion requiring high force at low speed, and a hydraulic cylinder having a relatively small piston surface is used for the rapid stroke motion requiring low force at high speed. In order to make the design of such hydraulic drive units less complex and to ensure smooth interaction between the hydraulic cylinders, various designs of hydraulic circuits have been proposed in the prior art, for example in EP 2 480 405 Bl, EP 2 637 852 Bl, and DE 10 2021 121 461 Al.

[0009] However, with the continuing demand to reduce cost, maintenance, and energy consumption to improve the efficiency of the overall machine employing such drive units, there is still a need to reduce the complexity of such drive units while offering excellent operating characteristics.

[0010] Technical problem to be solved

[0011] In view of the above, it is the object of the present invention to provide a drive unit for driving a stroke motion having reduced complexity while offering excellent operating characteristics.

[0012] Disclosure of the invention

[0013] The object is achieved by a drive unit having the features of independent claim 1. A machine, in particular a pressing machine, bending machine or punch machine comprising the drive unit is subject-matter of claim 14. A method for operating the drive unit is subject-matter of claim 15. Further advantageous developments are set out in the dependent claims.

[0014] According to the invention, the drive unit for driving a stroke motion of a moving frame comprises a first actuation device for performing a rapid stroke motion, a second actuation device for performing a working stroke motion, and a control device. The first actuation device includes a mechanically driven actuator. The second actuation device includes a hydraulically driven linear actuator. The mechanically driven actuator and the hydraulically driven linear actuator are coupled to each other so as to move as a unit. The control device is configured to control the first actuation device and the second actuation device. That is, according to the invention, two different technologies are combined for driving the stroke motion. The first actuation device including the mechanically driven actuator can be used to perform the rapid stroke motion that requires high speed at low force. This allows to size and select low power motors to drive the mechanically driven actuator as high force is not required. In addition, a gear ratio can be reduced to reach the required high speed. The second actuation device including the hydraulically driven linear actuator can be used to perform the working stroke motion that requires low speed at high force. This also allows to size and select low power motors to drive the hydraulically driven linear actuator as high speed is not required. The amount of hydraulic fluid required to drive the hydraulically driven linear actuator can be reduced to a minimum.

[0015] According to the invention, the efficiency, high accuracy, and low noise characteristics of the two different technologies are combined. Compared to the conventional hydraulic solutions, the complexity of hydraulic circuits can be reduced by eliminating the need for additional tanks and pre-fill valves. Furthermore, the power installed can be reduced.

[0016] For performing the rapid stroke motion, the control device may be configured to control the first actuation device so as to drive the stroke motion, and the second actuation device so as to follow the stroke motion driven by the first actuation device while generating minimum resistance.

[0017] For performing the working stroke motion, the control device may be configured to control the second actuation device so as to drive the stroke motion, and the first actuation device so as to follow the stroke motion driven by the second actuation device while generating minimum resistance.

[0018] The control device may be configured to control the first actuation device in a closed-loop position control or a closed-loop speed control.

[0019] The control device may be configured to control the second actuation device in a closed-loop force control. The second actuation device may further include a hydraulic pump controlled by the control device and driving the hydraulically driven linear actuator.

[0020] The hydraulic pump may be an electrically driven hydraulic pump.

[0021] The first actuation device may further include an electric motor controlled by the control device and driving the mechanically driven actuator.

[0022] The first actuation device may further include a hydraulic motor controlled by the control device and driving the mechanically driven actuator.

[0023] The hydraulic motor of the first actuation device may be driven by the hydraulic pump of the second actuation device.

[0024] The first actuation device may comprise a bypass fluid path including an on-off valve controlled by the control device. The bypass fluid path may connect an inlet port and an outlet port of the hydraulic motor bypassing the hydraulic pump.

[0025] The mechanically driven actuator may be an actuator comprising one of a gearbox, a roller screw, an inverted roller screw, a balls screw, rack and pinion, a crank rod, and a nonlinear mechanical lever, or any combination thereof.

[0026] The mechanically driven actuator may be a mechanically driven linear actuator.

[0027] The hydraulically driven linear actuator may be a hydraulic cylinder.

[0028] The second actuation device may comprise a bypass fluid path including an on- off valve controlled by the control device. The bypass fluid path may connect an inlet port and an outlet port of the hydraulic cylinder bypassing the hydraulic pump. Further benefits and advantages of the present invention will become apparent from the following detailed description of at least one exemplary embodiment for carrying out the present invention with reference to the accompanying drawings.

[0029] Brief description of drawings

[0030] In the drawings:

[0031] Figure 1 illustrates a schematic diagram of a drive unit according to a first embodiment of the present invention.

[0032] Figure 2 illustrates a schematic diagram of a drive unit according to a second embodiment of the present invention.

[0033] Figure 3 illustrates a schematic diagram of a drive unit according to a third embodiment of the present invention.

[0034] Figure 4 illustrates a schematic diagram of a drive unit according to a fourth embodiment of the present invention.

[0035] Description of at least one way of carrying out the invention

[0036] First embodiment

[0037] A first embodiment of the present invention is described below with reference to figure 1.

[0038] As it is shown in figure 1, the drive unit 1 comprises a first actuation device 100 and a second actuation device 200. Additionally, the drive unit 1 comprises a control device, which is not illustrated in the figures.

[0039] The drive unit 1 drives a stroke motion of a moving frame 2. In particular, the drive unit 1 causes the moving frame 2 to reciprocate in a working direction. The moving frame 2 can be part of a machine for press applications such as metal forming, punching, bending forming, sizing press, powder metal presses, horizontal or vertical mold closing applications. According to the specific type of press application, an appropriate tool or mold cover can be coupled to the moving frame 2 so as to reciprocate with the moving frame 2. The first actuation device 100 comprises an electric motor 110 and a mechanically driven actuator 120.

[0040] The electric motor 110 may be of any suitable type, such as an electric servomotor (synchronous permanent magnet, asynchronous or reluctance).

[0041] The mechanically driven actuator 120 may be a mechanically driven linear actuator 120. According to the present embodiment, the mechanically driven actuator 120 comprises a screw 121 and a nut 122 connected to a sliding rod 123. The screw 121 is rotated by the electric motor 110. A transmission of the torque from the motor to the screw may be realized by a suitable gearbox, belt, chain, etc. or combination of these. The nut engages with the screw to reciprocate as the screw 121 rotates. The nut 122 is connected to a sliding rod 123 which reciprocates with the nut 122 as a unit, thereby performing a stroke motion. In the following, the mechanically driven actuator 120 is referred to as a screw actuator 120.

[0042] The term "mechanically driven" means that a movement / reciprocation of the mechanically driven actuator is caused mechanically, i.e. by parts that are in physical contact with each other, such as gears, racks, screws, belts, chains, crank rod, nonlinear mechanical lever, etc. In particular, the term "mechanically driven" is to be understood as distinguishing the mechanically driven actuator from other types of linear and non-linear actuators in which the reciprocation is not caused mechanically but, for example, by fluid pressure differences in different fluid chambers of the actuator, as in the case of a hydraulic cylinder ("hydraulically driven") or a pneumatic cylinder ("pneumatically driven").

[0043] Accordingly, the mechanically driven actuator 120 is not limited to the abovedescribed screw actuator 120, but can be designed to combine different drive and transmission arrangements and solutions, such as gearbox, roller screw, inverted roller screw, ball screw, rack and pinion, crank rod, or non-linear mechanical lever. The second actuation device 200 comprises a further electric motor 210 driving a fluid pump 230 and a hydraulically driven linear actuator 220. The fluid pump 230 supplies hydraulic fluid to the hydraulically driven linear actuator 220 via a hydraulic circuit path 240. The hydraulically driven linear actuator 220 may be a double acting hydraulic cylinder with two fluid inlet-outlet ports. The hydraulic cylinder 220 comprises a piston 221, a piston rod 222, and two fluid chambers separated by the piston 221.

[0044] The hydraulic circuit path 240 includes a bypass fluid path 250 directly connecting the two inlet-outlet ports of the hydraulic cylinder 220. The bypass fluid path 250 is provided with an on-off valve 260 which is controlled by the control device. Depending on the state of the on-off valve 260, the bypass fluid path 250 selectively connects the two inlet-outlet ports of the hydraulic cylinder

[0045] 220 so as to short-circuit the inlet-outlet ports and to bypass the fluid pump 230.

[0046] When the on-off valve 260 of the bypass fluid path 250 is in a closed position and the fluid pump 230 is driven by the electric motor 210, a pressure difference is generated between the two fluid chambers, which applies a force to the piston

[0047] 221 causing the piston 221 and the piston rod 222 to reciprocate.

[0048] The sliding rod 123 of the screw actuator 120 is coupled to the piston rod 222 of the hydraulic cylinder 220 so as to move as a unit. In particular, both the sliding rod 123 and the piston rod 222 are coupled to the moving frame 2. Thus, reciprocation of one of the sliding rod 123 and the piston rod 222 is transmitted to the moving frame 2 and to the other of the sliding rod 123 and the piston rod 222.

[0049] An exemplary operation of the drive unit 1 according to the first embodiment is described in the following.

[0050] At the start of a work cycle, the drive unit 1 is in an initial position, which corresponds to a standby position of the drive unit 1. In the initial position of the drive unit 1, the sliding rod 123 of the screw actuator 120 and the piston rod 222 of the hydraulic cylinder 220 are fully retracted. Normally, the initial position of the drive unit 1 corresponds to a state of the machine utilizing the drive unit 1 where a corresponding tool or mold cover attached to the moving frame 2 is retracted from the workpiece or a mold cavitiy is open.

[0051] In the initial position, the control device actuates the electric motor 110 of the first actuation unit 100 so as not to rotate but to apply a holding torque to the screw actuator 120. Alternatively, a suitable braking mechanism controlled by the control device can be used to prevent reciprocation of the actuators 120 and 220 so as to maintain the initial position as long as no stroke motion is demanded.

[0052] In addition, the electric motor 210 of the second actuation unit 200 is not actuated by the control device and the on-off valve 260 is in the closed position. Thus, fluid is not supplied to any of the two inlet-outlet ports of the hydraulic cylinder and the piston rod 222 remains in the retracted position.

[0053] When a corresponding input signal is received from the control device demanding a stroke motion, e.g. when the machine is operated by an operator, the control device first actuates the drive unit to perform a rapid stroke motion. The rapid stroke motion serves, for example, to quickly approach a tool to a workpiece or a mold cover to a mold, which requires low force at high speed.

[0054] The rapid stroke motion is mainly driven by the first actuation device. The control device actuates the electric motor 110 of the first actuation device 100 so as to extend the sliding rod 123. In particular, the electric motor 110 is actuated to generate a torque to rotate the screw and thereby move the nut and the sliding rod in the extension direction.

[0055] At the same time, the control device actuates the on-off valve 260 to switch from the closed position to the open position. The open on-off valve 260 allows the fluid to flow between the fluid chambers via the bypass fluid path 250 with low resistance. This allows the piston rod 222 to extend readily by following the stroke motion caused by the extension of the sliding rod 123. The control device may additionally actuate the electric motor 210 of the second actuation device 200 to drive the fluid pump 230 in a direction to facilitate the flow of the fluid between the fluid chambers. This allows the resistance applied by the hydraulic cylinder to the rapid stroke motion driven by the first actuation device 100 to be reduced to a minimum.

[0056] The rapid stroke motion is followed by a working stroke motion. The change from the rapid stroke motion to the working stroke motion is triggered, for example, when a tool or a mold cover approaches a workpiece or a mold to a threshold distance, or by operator input. The working stroke motion serves, for example, to process the workpiece with the tool or to compress the mold, which requires high force at low speed.

[0057] The working stroke motion is mainly driven by the second actuation device 200. The control device terminates the actuation of the electric motor 110 of the first actuation device 100 to terminate the drive of the rapid stroke motion. The on- off valve 260 is actuated to switch to the closed position. The electric motor 210 of the second actuation device 200 is actuated to drive the fluid pump 230. The fluid pump 230 generates a pressure difference between the two fluid chambers of the hydraulic cylinder 220 applying a force to the piston 221 so as to further extend the piston rod 222.

[0058] At the same time, the control device may additionally actuate the electric motor 110 of the first actuation device 100 to drive the first actuation device 100 so as to follow the movement of the second actuation device 200. In particular, the first actuation device 100 is controlled so that the sliding rod 123 follows the stroke motion of the piston rod 222. This allows the resistance applied by the screw actuator 120 to the working stroke motion driven by the second actuation device 200 to be reduced to a minimum.

[0059] When the working stroke motion has been completed, that is, when processing of the workpiece or molding has been completed, the moving frame 2 is retracted from the workpiece or the mold towards the initial position. Normally, to retract the moving frame 2, the rapid stroke motion is performed by the drive unit 1 as described above, but in the opposite direction, that is, away from the workpiece or the mold. The reversal of the stroke motion is achieved by reversing the drive direction of the electric motor 110. Thus, the sliding rod 123 and the piston rod 222 are retracted to the initial position together with the moving frame 2 and the work cycle is completed.

[0060] In specific circumstances the first and second actuation devices 100, 200 could cooperate together controlled by the control device. For example, the first actuation device 100 is controlled in a closed-loop position control and / or a closed-loop speed control, while the second actuation device 200 is controlled in a closed-loop force control. That is, the pressure in the fluid chambers of the hydraulic cylinder 220 of the second actuation device 200 is controlled in the way to unload a resistance force seen by the screw actuator 120 of the first actuation device 100.

[0061] Second embodiment

[0062] A second embodiment of the present invention is described below with reference to figure 2.

[0063] The second embodiment differs from the first embodiment in the type of motor driving the first actuation device 100. Instead of the electric motor 110, a hydraulic motor 170 is provided to rotate the screw 121 of the screw actuator 120.

[0064] The hydraulic motor 170 is supplied with hydraulic fluid by the fluid pump 230 of the second actuation device 200 via a hydraulic circuit path 140 of the first actuation device 100. The hydraulic circuit path 140 of the first actuation device 100 is provided in parallel with the hydraulic circuit path 240 of the second actuation device 200. As shown in figure 2, in order to selectively supply hydraulic fluid to one of the hydraulic circuit paths 140, 240, each hydraulic circuit path 140, 240 is provided with respective on-off valves in the respective supply and return paths. These on-off valves are actuated by the control device to actuate the first actuation device 100 by supplying fluid to the hydraulic motor 170 or the second actuation device 200 by supplying fluid to the hydraulic cylinder 220.

[0065] The hydraulic circuit path 140 of the first actuation device includes a bypass fluid path 150 directly connecting an inlet port and an outlet port of the hydraulic motor 170. The bypass fluid path 150 is provided with an on-off valve 160 which is controlled by the control device. Depending on the state of the on-off valve 160, the bypass fluid path 150 selectively connects the inlet port and the outlet port of the hydraulic motor 170 so as to short-circuit the inlet and outlet ports and to bypass the fluid pump 230.

[0066] When the on-off valve 160 of the bypass fluid path 150 is in a closed position, the fluid pump 230 is driven by the electric motor 210, and fluid is supplied to the hydraulic circuit path 140 of the first actuation device, the hydraulic motor 170 is driven by the fluid and generates a torque to rotate the screw 121 of the screw actuator 120.

[0067] When the on-off valve 160 of the bypass fluid path 150 is in an open position, the hydraulic motor 170 is not allowed to generate a torque. Thus, the sliding rod 123 is allowed to readily follow a stroke motion driven by the second actuation device 200.

[0068] Third embodiment

[0069] A third embodiment of the present invention is described below with reference to figure 3.

[0070] The third embodiment differs from the first embodiment in the manner of arranging the mechanically driven actuator 120 and the hydraulically driven linear actuator 220. According to the first embodiment, the screw actuator 120 and the hydraulic cylinder 220 are arranged in parallel. That is, the screw actuator 120 and the hydraulic cylinder 220 are provided side by side with respect to the stroke motion. According to the third embodiment, the screw actuator 120 and the hydraulic cylinder 220 are arranged in series. That is, the screw actuator 120 and the hydraulic cylinder 220 are provided one after the other with respect to the direction of the stroke motion.

[0071] In particular, the screw actuator 120 and the hydraulic cylinder 220 may be arranged coaxially.

[0072] Fourth embodiment

[0073] A fourth embodiment of the present invention is described below with reference to figure 4.

[0074] The fourth embodiment differs from the second embodiment in the manner of arranging the mechanically driven actuator 120 and the hydraulically driven linear actuator 220. According to the second embodiment, the screw actuator 120 and the hydraulic cylinder 220 are arranged in parallel. That is, the screw actuator 120 and the hydraulic cylinder 220 are provided side by side with respect to the stroke motion. According to the fourth embodiment, the screw actuator 120 and the hydraulic cylinder 220 are arranged in series. That is, the screw actuator 120 and the hydraulic cylinder 220 are provided one after the other with respect to the direction of the stroke motion.

[0075] In particular, the screw actuator 120 and the hydraulic cylinder 220 may be arranged coaxially.

[0076] Further modifications of the embodiments

[0077] In the above embodiments, it has been described that the mechanically driven actuator 120 and the hydraulically driven linear actuator 220 are coupled to each other so as to move as a unit. However, the type of coupling is not particularly limited.

[0078] The mechanically driven actuator 120 and the hydraulically driven linear actuator 220 may be firmly connected one to the other. Alternatively, the mechanically driven actuator 120 and the hydraulically driven linear actuator 220 may be separably coupled to each other. That is, the mechanically driven actuator 120 and the hydraulically driven linear actuator 220 can be decoupled so that two actuators 120, 220 can be moved in a nonsynchronised manner under certain working conditions. For example, in the event of a failure of the mechanically driven actuator 120 resulting in a jammed position condition, the hydraulically driven actuator 220 could perform a final fail-safe stroke motion using the oil previously stored in a medium / high pressure accumulator.

[0079] The above description is not exhaustive, and the present invention is not limited to the above embodiments. The skilled person will recognize that various modifications and combinations of the above embodiments are possible within the scope of the invention. Accordingly, the scope of the invention should be determined from the accompanying claims.

[0080] Reference sign list

[0081] 1 drive unit

[0082] 2 moving frame

[0083] 100 first actuation device

[0084] 110 electric motor

[0085] 120 screw actuator (mechanically driven actuator)

[0086] 121 screw

[0087] 122 nut

[0088] 123 sliding rod

[0089] 140 hydraulic circuit path

[0090] 150 bypass fluid path

[0091] 160 on-off valve

[0092] 170 hydraulic motor

[0093] 200 second actuation device

[0094] 210 electric motor

[0095] 220 hydraulic cylinder (hydraulically driven linear actuator) piston piston rod fluid pump hydraulic circuit path bypass fluid path on-off valve

Claims

CLAIMS1. A drive unit (1) for driving a stroke motion of a moving frame (2) comprising a first actuation device (100) for performing a rapid stroke motion, a second actuation device (200) for performing a working stroke motion, and a control device, wherein the first actuation device (100) includes a mechanically driven actuator (120), the second actuation device (200) includes a hydraulically driven linear actuator (220), the mechanically driven actuator (120) and the hydraulically driven linear actuator (220) are coupled to each other so as to move as a unit, and the control device is configured to control the first actuation device (100) and the second actuation device (200).

2. The drive unit (1) according to claim 1, wherein, for performing the rapid stroke motion, the control device is configured to control the first actuation device (100) so as to drive the stroke motion, and the second actuation device (200) so as to follow the stroke motion driven by the first actuation device (100) while generating minimum resistance, and for performing the working stroke motion, the control device is configured to control the second actuation device (200) so as to drive the stroke motion, and the first actuation device (100) so as to follow the stroke motion driven by the second actuation device (200) while generating minimum resistance.

3. The drive unit (1) according to any one of the preceding claims, wherein the control device is configured to control the first actuation device (100) in a closed-loop position control or a closed-loop speed control, andthe second actuation device (200) in a closed-loop force control.

4. The drive unit (1) according to any one of the preceding claims, wherein the second actuation device (200) further includes a hydraulic pump (230) controlled by the control device and driving the hydraulically driven linear actuator (220).

5. The drive unit (1) according to claim 4, wherein the hydraulic pump (230) is an electrically driven hydraulic pump.

6. The drive unit (1) according to any one of the preceding claims, wherein the first actuation device (100) further includes an electric motor (110) controlled by the control device and driving the mechanically driven actuator (120).

7. The drive unit (1) according to any one of claims 1 to 5, wherein the first actuation device (100) further includes a hydraulic motor (170) controlled by the control device and driving the mechanically driven actuator (120).

8. The drive unit (1) according to claim 7, wherein the hydraulic motor (170) of the first actuation device (100) is driven by the hydraulic pump (230) of the second actuation device (200).

9. The drive unit (1) according to claim 7 or 8, the first actuation device (100) comprises a bypass fluid path (150) including an on-off valve (160) controlled by the control device, the bypass fluid path (150) connects an inlet port and an outlet port of the hydraulic motor (170) bypassing the hydraulic pump (230).

10. The drive unit (1) according to any one of the preceding claims, wherein the mechanically driven actuator (120) is an actuator comprising one of a gearbox, a roller screw, an inverted roller screw, a balls screw, rack and pinion, a crank rod, and a nonlinear mechanical lever, or any combination thereof.

11. The drive unit (1) according to any of the preceding claims, wherein the mechanically driven actuator (120) is a mechanically driven linear actuator.

12. The drive unit (1) according to any one of the preceding claims, wherein the hydraulically driven linear actuator (220) is a hydraulic cylinder.

13. The drive unit according to claim 12, wherein the second actuation device (200) comprises a bypass fluid path (250) including an on-off valve (260) controlled by the control device, the bypass fluid path (250) connects an inlet port and an outlet port of the hydraulic cylinder (220) bypassing the hydraulic pump (230).

14. A machine, in particular a pressing machine, bending machine or punch machine comprising a moving frame (2) configured to hold a tool and to perform a stroke motion, and the drive unit (1) according to any one of the preceding claims for driving a stroke motion of the moving frame (2).

15. A method for operating the drive unit (1) according to any of the preceding claims, wherein, during a rapid stroke motion of the drive unit (1), the control device controls the first actuation device (100) so as to drive the stroke motion, and controls the second actuation device (200) so as to follow the stroke motion driven by the first actuation device (100) while generating minimum resistance, and during a working stroke motion of the drive unit (1), the control device controls the second actuation device (200) so as to drive the stroke motion, and controls the first actuation device (100) so as to follow the stroke motion driven by the second actuation device (200) while generating minimum resistance.

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