A machine tool that uses two rotatable tools to machine a workpiece with robot assistance.

Abstract

Multiple steps can be performed with fewer or no tool changes. [Solution] A machine tool is disclosed that includes a holder (32), a first shaft (46) supported by the holder (32) and having an accommodating portion for a first tool (12), a second shaft (56) supported by the holder (32) and having an accommodating portion for a second tool (13), and a first drive shaft (34, 34') mechanically coupled to the first shaft (46) directly or indirectly via a first freewheel clutch (45) and mechanically coupled to the second shaft (56) directly or indirectly via a second freewheel clutch (55).

Description

【Technical Field】 【0001】 The present invention relates to a machine tool for surface machining with robot assistance. 【Background Art】 【0002】 In robot-assisted surface treatment, a machine tool (for example, a grinding machine, a drilling machine, a milling machine, a polishing machine, etc.) is guided by a manipulator, for example, an industrial robot. At that time, the so-called TCP (Tool Center Point) of the machine tool and the manipulator can be connected in various ways. The manipulator can usually adjust the position and orientation of the TCP substantially freely and move the machine tool, for example, along a trajectory parallel to the surface of the workpiece. An industrial robot is usually position-controlled, whereby the TCP is accurately moved along the target trajectory. 【0003】 In robot-assisted grinding, polishing, or other surface treatment processes, controlling the machining force (grinding force) is often necessary to achieve good results. However, conventional industrial robots often struggle to achieve sufficient precision. Because industrial robots have large, heavy arms, they have high inertial mass, and their controllers (closed-loop control) cannot quickly respond to fluctuations in machining force. To solve this problem, a smaller (and lighter) linear actuator can be placed between the manipulator's TCP and the machine tool, connecting the manipulator's TCP to the machine tool. In surface processing, the linear actuator controls only the machining force (contact force between the tool and workpiece), while the manipulator's position is controlled to move the machine tool along the desired trajectory in conjunction with the linear actuator. Force control allows the linear actuator to compensate (within a certain range) for inaccuracies in the position and shape of the workpiece being machined, as well as inaccuracies in the manipulator's trajectory. However, some robots can adjust the machining force through force / torque control even without the aforementioned linear actuator. In some devices, the relatively heavy drive unit of the machine tool (such as an electric motor or compressed air motor) is mechanically separated from the actual tool (such as a grinding plate). This means that the relatively heavy drive unit of the grinding machine is firmly connected to the manipulator, and only the relatively lighter part of the machine tool to which the (rotating) tool is attached is moved (force-controlled) by a linear actuator. For this purpose, the rotating tool can be connected to the drive unit via a telescopic shaft, as described in Patent Document 1, for example, and the entire details of this are incorporated into this description by reference. [Prior art documents] [Patent Documents] 【0004】 [Patent Document 1] U.S. Patent Application Publication No. 2019 / 0232502A1 [Overview of the Initiative] [Problems that the invention aims to solve] 【0005】 Many surface finishing processes require tool changes between different stages. Tool changes can be performed semi-automatically or fully automatically with robot assistance. For this purpose, tool change stations are known that can, for example, automatically replace worn tools or, for example, replace grinding plates with polishing plates. Although robot-assisted automatic tool changes are possible, frequent tool changes increase machining time. 【0006】 The inventors of this invention aimed to develop an improved machine tool that would require fewer tool changes, and in particular, would enable the performance of multiple processes (e.g., grinding followed by polishing) without changing tools. [Means for solving the problem] 【0007】 The above problem is solved by the apparatus described in claim 1. Different embodiments and further developments are the subject of the dependent claims. 【0008】 The following describes a machine tool that can be used for robot-assisted machining of workpieces. According to one embodiment, the machine tool includes a holder, a first shaft supported by the holder and having a housing for a first tool, and a second shaft supported by the holder and having a housing for a second tool. The machine tool further includes a first drive shaft that is mechanically coupled (directly or indirectly) to the first shaft via a first freewheel clutch and mechanically coupled to the second shaft via a second freewheel clutch. In a particular embodiment, the first and second freewheel clutches are configured such that the first shaft is driven when the drive shaft rotates in a first direction, and the second shaft is driven when the drive shaft rotates in a second direction. 【0009】 In yet another embodiment, the machine tool includes a drive unit, a first shaft having a mounting portion for mounting a first tool, and a second shaft having a mounting portion for mounting a second tool. The drive unit is directly or indirectly coupled to the first shaft via a first freewheel clutch and to the second shaft via a second freewheel clutch, and the drive unit drives the first shaft or the second shaft in accordance with the direction of rotation. Furthermore, a corresponding method for robot-assisted machining of a workpiece using a machine tool is also described. [Effects of the Invention] 【0010】 Multiple processes can be performed with minimal or no tool changes. [Brief explanation of the drawing] 【0011】 [Figure 1] This is a perspective view showing an example of a robot-assisted machine tool for surface machining, in which the machine tool can accommodate two rotary tools on two opposing sides. 【0012】 [Figure 2] This is a simplified cross-sectional view (longitudinal section) of a machine tool according to a further embodiment. 【0013】 [Figure 3] This figure shows a modified and expanded version of the embodiment shown in Figure 2, in which the tool is driven by an eccentric shaft. 【0014】 [Figure 4] This figure shows a modified example of the embodiment shown in Figure 2. 【0015】 [Figure 5] Another embodiment is shown in which a motor directly drives the shaft to which the tool is attached. [Modes for carrying out the invention] 【0016】 The various embodiments will be described in more detail below using the illustrated examples. The illustrations are not necessarily to scale, and the present invention is not limited to the illustrated embodiments. Rather, the emphasis is on explaining the underlying principles of the invention. 【0017】 For example, robots and manipulators that move machine tools along a track to automatically machine the surface of a workpiece are well known in themselves. Process forces play an important role in robot-assisted machining of workpieces, and various force control concepts have been developed. Process forces are the forces between a rotating tool and a workpiece during a machining process, such as the force between a grinding plate and the workpiece surface during grinding. 【0018】 The embodiments described herein are particularly suitable for force control using linear actuators, such as those described in Patent Document 1. In some embodiments, the rotary tool is mounted on the front of the machine tool, while the drive unit for the rotary tool (e.g., an electric motor) is mounted on the rear of the machine tool. The rear of the machine tool is also connected to a robot / manipulator. Between the front and rear is the linear actuator described above. To transmit rotational motion, a telescopic shaft is positioned between the motor on the rear of the machine tool and the tool on the front of the machine tool to compensate for changes in actuator displacement. In another embodiment, the motor is located on the front of the machine tool. In this case, the telescopic shaft is not necessary. 【0019】 It should be noted that the concepts described herein can also be used with machine tools without integrated linear actuators. If integrated linear actuators are not used, a telescopic shaft is not necessary. In this case, force control is performed directly by the robot manipulator itself (a robot with force / torque control), or the linear actuator is placed between the robot and the machine tool without being integrated into the machine tool. The exemplary embodiments described herein substantially relate to the coupling of a motor-driven shaft (telescopic shaft or conventional shaft or motor shaft) with two different rotatable tools. 【0020】 Figure 1 shows an example of a machine tool having an integrated linear actuator and a telescopic shaft. Only the front side of the machine tool is shown, and the linear actuator is only schematically depicted. The front side of the machine tool essentially includes a holder 32, which can be, for example, a mounting plate, a mounting frame, a housing part, etc. The holder 32 can be composed of several parts that are firmly connected to each other (for example, forming a mounting frame together). For example, in the example shown in Figure 1, the plate 32’ and the cylinder pin 32” are parts of the holder 32. On the rear side of the machine tool, a mounting plate (not shown) connected to the TCP (Tool Center Point) of, for example, a robot / manipulator can also be provided. The linear actuator 20, which is only schematically shown, couples the rear side of the machine tool, where the motor 10 is also mounted, to the holder 32 on the front side of the machine tool. The linear actuator 20 can include, for example, a double-acting pneumatic cylinder and a linear guide. 【0021】 【0022】 The telescopic shaft 33 shown in Figure 1 is mounted on the holder 32 (mounting plate) at one end of the shaft, for example, by a ball bearing. The other shaft end of the telescopic shaft is directly or indirectly coupled to the motor shaft of the motor 10. The telescopic shaft 33 drives the shafts 34, 34’ via the belts 41, 51. In the example shown, the shafts 34, 34’ are arranged substantially parallel to the telescopic shaft 33 (the shafts are parallel if their rotation axes are parallel). The shafts 34, 34’ are pivotally supported on the holder 32 (for example, on the plate 32’ and the mounting plate of the holder 32). The telescopic shaft 33 and the shafts 34, 34’ are drive shafts that can drive the tools 12, 13.Shafts 34 and 34' are coupled to and drive the first tool 12 and the second tool 13. The two tools 12 and 13 may be, for example, two different grinding plates, a grinding plate and a polishing plate, a milling cutter and a grinding plate, or another pair of tools. Since both shafts 34 and 34' are also driven by shaft 33 using a belt, shafts 34 and 34' always move synchronously, but they can also be configured to have different rotational speeds due to different transmission ratios of the belt drive. Therefore, in some embodiments, instead of shafts 34 and 34', a single shaft driven by a single belt may be provided. The coupling of shaft 34 to the rotating tools 12 and 13 is schematically shown in Figure 2 and will be described in more detail below. 【0023】 Figure 2 shows a bearing 331 (such as a ball bearing or needle bearing) on ​​which a telescopic shaft 33 (a drive shaft connected to the motor 10) is rotatably supported in a holder 32. Figure 2 also shows bearings 342 and 341 that support a shaft 34 in the holder 32 or plate 32', respectively. In this case, as described above, only one belt 41 is needed to connect shafts 33 and 34. Shafts 46 and 56 are arranged coaxially with shaft 34, and shaft 46 is connected to the first end of shaft 34 by a first freewheel clutch 45, while shaft 56 is connected to the second end of shaft 34 by a second freewheel clutch 55. Tools 12 and 13 can be attached to the outer ends of shafts 46 and 56 (i.e., opposite the freewheel clutches 45 and 55) (see also Figure 1). 【0024】 Freewheel clutches (overrunning clutches) 45, 55 can be configured, for example, as sleeve freewheels / freewheel sleeves (draw-cup roller clutches). A sleeve freewheel is a one-way clutch and typically consists of a thin-walled, non-cutting outer cup with a clamp ramp, plastic cage, pressure spring, and needle rollers. Sleeve freewheels transmit torque in only one direction, saving radial space. Freewheels are available with or without bearings. Sleeve freewheels typically have a relatively low idling friction moment (overrunning friction torque). Sleeve freewheels and other freewheel clutches are known in themselves and are commercially available from various manufacturers (e.g., Schaeffler). Therefore, they will not be described further here. 【0025】 The freewheel clutches 45 and 55 are installed such that when shafts 33 and 34 rotate to the left, shaft 46 (the first tool shaft) is driven via the freewheel clutch 45, while the freewheel clutch 55 rotates freely and does not transmit a large torque to shaft 56 (the second tool shaft). When shafts 33 and 34 rotate to the right, the situation is reversed. That is, shaft 56 is driven via the freewheel clutch 55, while the freewheel clutch 45 is idle and does not transmit a large torque to shaft 46. At idle, the freewheel clutches 45 and 55 can only transmit torque up to the friction torque. 【0026】 In robot-assisted machining of a workpiece, the workpiece can first be machined using a first grinding plate (e.g., tool 12) mounted on shaft 46. Motor 10 (see Figure 1), and therefore shafts 33 and 34, also rotate counterclockwise. To change the tool and machine the workpiece using a second grinding plate (e.g., tool 13) mounted on shaft 56, the robot only needs to rotate the machine tool (180° around an axis of rotation in a plane perpendicular to the axis of rotation of shaft 33) and reverse the direction of rotation of motor 10. While machining the workpiece with the second grinding plate, motor 10 rotates clockwise. In other embodiments, all directions of rotation may be reversed. As described above, shaft 34 can be split into two. In this case, two belts are required (as in the example in Figure 1). In this case, the transmission ratios of the two belt drives may be different. 【0027】 Figure 3 is a modified / extended version of the example in Figure 2. This modification / extension is similarly relevant to shafts 46 and 56. For simplicity, Figure 3 shows only the portion of the machine tool that has shaft 56. In this embodiment, shaft 56 has its outer end coupled to an eccentric shaft 57, as is common in, for example, eccentric grinders and track grinders. Grinding machines with eccentric shafts are well known and will not be described further here. 【0028】 Furthermore, in the example of Figure 3, a flag, tab, or other member 61 protruding asymmetrically from the shaft 56 is connected to the shaft 56. In particular, the member 61 can be positioned on a ring 62 or sleeve extending around the shaft 56. The ring 62 can be clamped to the shaft 56 at any angular position to allow adjustment of the angular position of the member 61. A magnet 58, in particular a permanent magnet, can be positioned near the member 61 (flag). If the member 61 is made of a ferromagnetic material (e.g., ferritic tool steel), the magnet 58 will attract the member 61 and thus attract the shaft 56 to a specified angular position. This angular position can also be considered a reference position (see Figure 3(a), where the flag 61 and magnet 58 are directly opposite each other). The arrangement of the magnet 58 and member 61 can be sized such that the friction torque of the freewheel clutch 55 at idle is insufficient to rotate the shaft from this specified position. This ensures that when the motor 10 rotates to the left, the shaft 56 remains stationary and does not rotate due to the friction torque of the freewheel clutch 55 at idle. If the shaft 56 were to rotate unintentionally while the motor 10 is rotating counterclockwise, materials attached to the tool 13 (e.g., dust particles, abrasives, etc.) could be scattered from the tool 13. This is prevented by the magnet 58. The same applies to the shaft 46 and tool 12 when the motor is rotating clockwise. The arrangement of the magnet 58 and component 61 is also useful for machines without eccentric shafts. 【0029】 In addition to, or as a substitute for, the permanent magnet 58, the machine tool may have a sensor 60 positioned to detect a specific angular position of the shaft 56. The sensor 60 may be, for example, an optical sensor (e.g., a reflective light barrier) or other proximity sensor that essentially detects that the member 61 or the shaft 56 is in a reference position. When the shaft 56 is in the reference position, the eccentric shaft 57 is also in a reference position, which may be advantageous when automatically changing the tool 13. 【0030】 Shaft 46 (not shown in Figure 3) may also have a ring with an asymmetrically protruding member. This member is attracted by a magnet to pull the shaft to a reference position and prevent the shaft 46 from rotating due to the friction torque at idle when the freewheel clutch 45 is idling. A sensor for detecting the reference position may also be provided. To avoid unnecessary repetition, refer to the above description in Figure 3. In other exemplary embodiments, instead of the magnet 58, a friction lining or one or more latch rollers may be provided to prevent each shaft 46, 56 from rotating due to the friction torque at idle of their respective freewheel clutches. 【0031】 Figure 4 shows a modified example of the example in Figure 2. In this example, two belts 41, 51 are used, as in Figure 1, but the freewheel sleeves 45, 55 are positioned on the opposite side of the belt drive compared to the example in Figure 1. However, the function of the mechanism is essentially the same as in the example described above. The freewheel clutches 45, 55 are attached to the shaft 33 (e.g., a telescopic shaft or a normal drive shaft or motor shaft). When the shaft 33 rotates counterclockwise, the freewheel sleeves 45 can transmit torque, resulting in the shaft 46 (the first tool shaft) being driven via the belt 41, while the freewheel sleeves 55 remain idle. When the shaft 33 rotates clockwise, the situation is reversed. In this case, only the freewheel sleeves 55 can transmit torque, the shaft 56 is driven via the belt 41, while the freewheel sleeves 45 remain idle. Belt pulleys can be positioned outside the freewheel sleeves 45, 55. Depending on the direction of rotation of the shaft 33, one or the other belt pulley is rotated by the shaft 33. In the example in Figure 4, it is understood that shafts 33, 46, and 56 are not only supported at one end (see Figure 4, bearings 331, 341, and 342), but may also be supported at other locations, although these are not explicitly shown in Figure 4 for simplicity. 【0032】 Figure 5 shows a modified embodiment of the example in Figure 2. In this embodiment, the drive shaft 33 and belt drive are replaced by a motor 10 that directly (without gears) drives the tool shafts 46 and 56. In this case, the shaft 34 is a motor shaft that protrudes from both sides of the motor housing. Both ends of the motor shaft are coupled to the tool shafts 46 and 56 to which the tools are attached by freewheel clutches 45 and 55. In this embodiment, the freewheel clutches 45 and 55 operate in the same manner as in the embodiment of Figure 2, and refer to the above description. 【0033】 As can be seen from Figure 5, a telescopic shaft is not required in this example. The motor 10 is mounted and supported on the front side of the machine tool. Nevertheless, the linear actuator 20 can be positioned between the front side of the machine tool (holder 32) and the rear side of the machine tool (not explicitly shown). The rear side of the machine tool can then be attached to the TCP of the robot. 【0034】 The following is a summary of some aspects of the embodiments described herein, which is not an exhaustive list but merely an illustrative summary. One embodiment relates to a machine tool that can be used for robot-assisted machining of a workpiece. The machine tool has a holder, a first shaft (see Figure 2, shaft 46) supported by the holder and having a housing for a first tool (e.g., grinding plate 12), and a second shaft (see Figure 2, shaft 56) supported by the holder and having a housing for a second tool (e.g., polishing plate 13). The machine tool further has (at least) one drive shaft (see Figure 2, telescopic shaft 33 and shaft 34, or Figure 1, partial shaft 34 and 34') which is mechanically coupled (directly or indirectly) to the first shaft via a first freewheel clutch and mechanically coupled to the second shaft via a second freewheel clutch (see Figure 2, sleeve freewheels 45 and 55). 【0035】 The drive shaft can be coupled to the first and second (tool) shafts by first and second belt drives (see, for example, Figure 4, belts 41 and 51). The freewheel clutch can be located on the input side (see Figure 4) or output side (see Figure 2) of the belt drive. 【0036】 The first and second freewheel clutches are coupled to the drive shaft in opposite directions. This means that one of the freewheel clutches is always idle. Thus, the two freewheel clutches are arranged such that the first shaft is driven when the drive shaft rotates in the first direction, and the second shaft is driven when the drive shaft rotates in the second direction. In one embodiment, the machine tool has a motor (see motor 10 in Figure 1) that is directly or indirectly coupled to the first drive shaft and drives the first drive shaft. In Figures 1 and 2, the telescopic shaft 33 is considered the drive shaft. The telescopic shaft 33 may be mechanically connected coaxially with the motor shaft, for example. Since the motor 10 is also indirectly coupled to the shaft 34 (or partial shafts 34 and 34') via a belt (or any other means of transmission), the shaft 34 can be considered part of the drive and, consequently, can be considered the drive shaft. 【0037】 In one embodiment, the motor is mechanically connected directly to a drive shaft (see Figure 1, where the drive shaft 33 is coaxial with the motor shaft), and this drive shaft is connected to at least one further drive shaft via a gearbox, particularly a belt drive (see Figure 2, shaft 34, or see Figure 1, sub-shafts 34 and 34'). This further drive shaft has two sub-shafts (see Figure 1, sub-shafts 34 and 34'), both of which are driven by the motor. The motor drives both tools 12 and 13. The drivetrain can be separated at different locations in various embodiments. In other embodiments, shaft 34 may be the shaft of a motor (e.g., an electric motor or a compressed air motor, see Figure 5). 【0038】 In one embodiment, a linear actuator is connected to a holder of a machine tool. In this case, one of the drive shafts can be configured as a telescopic shaft (see Figure 1). The actuator is used, in particular, to adjust the machining force. If the motor is mounted on the front side of the machine tool where the tool shaft is supported and mounted, a telescopic shaft is not necessary (see, for example, Figure 5). 【0039】 According to one embodiment, the machine tool comprises a first element (e.g., a ferromagnetic flag) projecting asymmetrically from a second shaft (see shaft 56 in Figure 3) and a second member (e.g., a magnet) stationary relative to a holder. The second member is suitable for holding the first member and, consequently, the second shaft, in a reference position when the second shaft is not actively driven (i.e., when the associated freewheel clutch is idle). Alternatively, the first member (connected to the shaft and rotating with the shaft) may be a magnet, and the second member (stationary relative to the holder) may be a ferromagnetic material. In some embodiments, the second member has a friction lining or a latch roller. 【0040】 Another embodiment relates to a robot-assisted machining method for a workpiece using a machine tool, in which a motor can drive either a first tool or a second tool by two freewheel clutches depending on the direction of rotation. This method includes the steps of machining the workpiece with a first rotary tool mounted on a first shaft of the machine tool, rotating the machine tool to change the direction of rotation of the drive shaft of the machine tool, and machining the workpiece with a second rotary tool mounted on a second shaft of the machine tool. [Explanation of symbols] 【0041】 10…motor 12…The first tool 13…Second tool 20…Actuator 32... Holder 34, 34'... Drive shaft 46, 56... shaft 45, 55... Freewheel clutch 58…Magnet 62... Ring

Claims

[Claim 1] Holder (32) and The first shaft (46) is supported by the holder (32) and has a housing for the first tool (12), A second shaft (56) is supported by the holder (32) and has a housing for the second tool (13), A first drive shaft (34, 34') is mechanically coupled directly or indirectly to the first shaft (46) via a first freewheel clutch (45) and to the second shaft (56) via a second freewheel clutch (55), It has, The first freewheel clutch (45) and the second freewheel clutch (55) are configured such that the first shaft (46) is driven when the first drive shaft (34, 34') rotates in a first direction, and the second shaft (56) is driven when the first drive shaft (34, 34') rotates in a second direction. A first member (62) protrudes from the second shaft (56) asymmetrically with respect to the axis of the second shaft (56), A second member (58) is fixed relative to the holder (32) and is adapted to hold the first member (62) and consequently the second shaft (56) in a reference position when the second shaft (56) is not actively driven, A machine tool that further possesses the following. [Claim 2] The machine tool according to claim 1, further comprising a motor (10) directly or indirectly connected to the first drive shafts (34, 34') and capable of driving the first drive shafts (34, 34'). [Claim 3] The machine tool according to claim 2, wherein the first drive shaft (34) is a motor shaft coupled to the first shaft (46) by the first freewheel clutch (45) and coupled to the second shaft (56) by the second freewheel clutch (55). [Claim 4] The first drive shaft is coupled to the first and second shafts (46, 56) by the first and second belt drive devices, The machine tool according to claim 1 or claim 2, wherein the first freewheel clutch (45) and the second freewheel clutch (55) are arranged on the input side or output side of the belt drive device. [Claim 5] A motor (10) connected to the second drive shaft (33), At least one belt (41, 51) connecting the second drive shaft (33) and the first drive shaft (34, 34'), The machine tool according to claim 1, further comprising the following: [Claim 6] The machine tool according to claim 5, wherein the second drive shaft (33) is an extendable shaft. [Claim 7] The machine tool according to any one of claims 1 to 6, wherein the first drive shaft comprises two sub-shafts (34, 34') that are respectively driven by belts (41, 51). [Claim 8] The machine tool according to any one of claims 1 to 7, further comprising an actuator (20) coupled to the holder (32) and configured to exert force on the holder (32) so that force control is performed between the first tool (12) and the workpiece or between the second tool (13) and the workpiece. [Claim 9] A machine tool according to any one of claims 1 to 8, wherein the first member (62) is a ferromagnetic material and the second member (58) is a magnet, or the first member (62) is a magnet and the second member (58) is a ferromagnetic material. [Claim 10] The machine tool according to any one of claims 1 to 8, wherein the second member is a friction lining or a latch roller. [Claim 11] A method for processing a workpiece using a machine tool described in any one of claims 1 to 10 with robot assistance, The steps include: machining the workpiece using a first rotating tool (12) mounted on a first shaft (46); The steps include rotating the machine tool and The steps include changing the rotation direction of the first drive shaft (34, 34'), The steps include: machining the workpiece using a second rotary tool (13) mounted on the second shaft (46); A method of having.

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