EP3969224B1 - Orbital grinding machine having a braking device - Google Patents

Description

TECHNICAL AREA

The present description relates to the field of machine tools, in particular an orbital grinding machine for automated, robot-assisted grinding.

BACKGROUND

In robot-supported surface processing, a machine tool such as a grinding or polishing machine (eg an electrically operated grinding machine with a rotating grinding wheel as the grinding tool) is guided by a manipulator, for example an industrial robot. The machine tool can be coupled in different ways to the so-called TCP ( Tool Center Point ) of the manipulator; the manipulator can usually adjust the position and orientation of the machine practically at will and move the machine tool, for example, on a trajectory parallel to the surface of the workpiece. Industrial robots are usually position-controlled, which allows precise movement of the TCP along the desired trajectory. With a separate actuator, the process force between the machine tool and the workpiece surface can be set and controlled independently of the manipulator.

In many cases, eccentric sanders ( orbital sanding machines ) are used, in which a sanding disk is attached to a mounting plate ( backing pad ), with the sanding plate rotating around an eccentrically arranged first axis of rotation, which itself rotates around a central second axis of rotation. Orbital grinding machines are known per se (see e.g US6257970B1 ) and their functional principle is therefore not further discussed here. Devices are also known that enable the grinding wheels to be changed automatically (see, for example, US8517799B2 ). The problem with orbital grinding machines is that the mounting plate comes to a standstill in an undefined position, whereas for the automated changing of the grinding wheels it can be desirable for the mounting plate to be in a defined position at the start of the automated changing process. Further it can happen that the assembly plate continues to turn for a comparatively long time after the motor has been switched off, which delays the changing process.

The inventor's goal is to improve existing orbital grinding machines so that an automated process for changing grinding wheels becomes faster and more reliable.

SUMMARY

The above object is achieved by the device according to claim 1. Different embodiments and further developments are the subject matter of the dependent claims.

A device with a machine tool and a braking device is described below, the machine tool having an eccentrically mounted, rotatable assembly plate for receiving a tool. The braking device has a frame that is fixed to the machine tool, a leaf spring that is fixed at a first end to the frame, and a lever that is connected to a second end of the spring. The braking device also has an actuator which is designed to move the lever, with movement of the lever tensioning the spring and pressing part of the lever against the mounting plate of the machine tool.

BRIEF DESCRIPTION OF THE DRAWINGS

• Figur 1 illustriert ein Beispiel eines Orbitalschleifers mit einer Bremsvorrichtung gemäß einem Ausführungsbeispiel.
• Figur 2 zeigt das Beispiel aus Fig. 1 mit aktivierter Bremsvorrichtung.
• Figur 3 illustriert ein Beispiel der Bremsvorrichtung (ohne Schleifmaschine) detaillierter.

The invention is explained in more detail below using the examples shown in the figures. The illustrations are not necessarily to scale, and the invention is not limited to only the aspects illustrated. Instead, value is placed on presenting the principles on which the invention is based. In the pictures shows:

• figure 1 12 illustrates an example of an orbital grinder with a braking device according to an embodiment.
• figure 2 shows the example 1 with activated braking device.
• figure 3 illustrates an example of the braking device (without grinding machine) in more detail.

DETAILED DESCRIPTION

Before various exemplary embodiments of the present invention are explained in detail, an example of a robot-assisted grinding device will first be described. It goes without saying that the concepts described here can also be transferred to other types of surface treatment (in particular polishing) and are not limited to grinding.

figure 1 illustrates an example of an orbital grinder with a braking device. The grinding machine 1 essentially comprises a motor 11 for driving an eccentrically mounted (in a housing) mounting plate 12 ( backing pad ) on which a grinding wheel 13 can be fastened. The eccentric mounting of the mounting plate 12 causes it to rotate about an eccentric axis of rotation D′ during operation, which in turn rotates about a central axis of rotation D. The grinding wheel 13 thereby performs a small elliptical movement as it rotates (the elliptical path also rotates). The construction of an orbital grinder is known per se and is therefore not explained in more detail here. Relevant for the further discussion, however, is the fact that the rest position of the mounting plate 12 is not defined by the eccentricity e of the axis of rotation D` (distance between the axes of rotation D and D'). When the motor 11 is switched off, the mounting plate 12 continues to run for a while and can stop in any angular position.

As mentioned at the outset, it can be advantageous for an automatic, robot-supported changing of the grinding wheel 13 if the mounting plate 12 is in a defined angular position. According to the exemplary embodiments described here, the grinding machine 1 has a braking device 2 which is designed to brake the mounting plate 12 (when the motor 11 is switched off) and to press it into a defined angular position. 2 shows the same embodiment as 1 with activated brake.

According to the Figures 1 and 2 illustrated embodiment, the braking device 2 includes a spring 21, in particular a leaf spring made of spring steel. One end of the spring 21 is clamped to a frame 25 of the braking device 2, for example by means a clamping element 24. As in 1 shown, the spring 21 is clamped between a part of the frame 25 and the clamping element, which can be fastened to the frame 25 by means of screws. At the other end of the spring 21, a lever 22 is mounted (e.g. also by means of screws) which has the shape of an elongate bar ( bar ) which is bent by approximately 90° at its free end. Spring 21 and lever 22 are positioned such that the free end of lever 22 can be moved toward mounting plate 12 until the free end of lever 22 contacts a circumferential surface of mounting plate 12 . During this movement of the lever 22, the spring is flexed. The movement is brought about by a linear actuator 23 . The linear actuator can be a pneumatic actuator, which can be implemented, for example, as a bellows cylinder. Alternatively, a magnetic actuator can be used, which can be designed, for example, as a lifting magnet ( solenoid actuator ). Regardless of the specific implementation, the actuator 23 acts between the frame 25 and the lever 22.

In particular, the combination of the lever 22, which is mounted on the frame 25 via a leaf spring, with a direct drive (without gears and other mechanisms) such as a bellows cylinder, makes it possible for the braking mechanism (lever 22, spring 21) to do without swivel joints. This means that no mechanism is required that contains parts that can move in relation to one another. As a result, the braking device 2 becomes more robust and less prone to errors. The bellows cylinder also does not contain any parts that can move in relation to one another; the bellows is merely inflated by means of compressed air, as a result of which the end of the bellows cylinder presses against the lever 22 .

When the brake is activated, the actuator 23 presses against the lever 22 and thus also the free, angled end of the lever 22 against the mounting plate 12, with the spring 21 being bent and pretensioned. This situation is in 2 shown. Because the free, angled end of the lever 22 presses against the mounting plate 12, the latter is moved into a defined angular position. The eccentric axis of rotation D' is pushed away from the braking device 2 as far as possible. In the example shown, the braking device is arranged on the right side of the grinding machine 1 and the eccentric axis of rotation is shifted as far as possible to the left by the activated braking device. At the same time, any rotary movement of the mounting plate 12 is braked until it comes to a standstill.

3 illustrates an exemplary implementation of the braking device 2 in a perspective view. The frame 25 consists of several parts and is designed to be mounted on a grinding machine (see Fig Figures 1 and 2 ). The frame 25 comprises a base plate 25a (support), the outer surface of which can be adapted to the (eg cylindrical) surface of the grinding machine. The spring 21 is fastened to the base plate 25a by means of the clamping element 24 and screws 24a. This means that the spring 21 embodied as a leaf spring is clamped between a surface of the base plate 25a and a corresponding surface of the clamping element 24 . The screws 24a ensure the necessary contact pressure. The lever 22 is screwed to the spring 21, as shown in 1 has already been presented. The lever 22 can be seen as an "extension" of the leaf spring 21, so to speak, the lever 22 being rigid in comparison to the spring 21.

To fasten the actuator 23, the frame 25 includes a bracket 25b ( bracket ) which is mounted on the base plate 25a (eg by means of screws 25c) and which at least partially surrounds the lever 22. The actuator 23 is mounted on the bracket 25b so that it can push the lever 22 towards the base plate 25a (and thus towards the grinding machine in use). In the example shown, the actuator 23 is attached to the bracket 25b by means of the screws 25d in such a way that it can push the lever 22 towards the base plate 25a (and thus also towards the grinding machine).

It is understood that the frame 25 can be constructed in a variety of ways. In the 3 The construction shown can be modified in many ways without changing the function of the braking device 2 described here. A frame is therefore understood to mean any structural component or any assembly of structural components that is suitable and designed to fulfill the function described here, namely in particular to enable one end of the spring 21 to be fixed in place and also the actuator 23 to be mounted in such a way that it can move the lever 22 attached to the spring 21. The frame as such is designed to be mounted on the grinding machine.

A number of important aspects of the exemplary embodiments described here are summarized below, which is not an exhaustive but rather a purely exemplary list of important aspects and technical features.

The exemplary embodiments described here relate to a device with a machine tool (in particular an orbital grinding machine) and a braking device, the machine tool having an eccentrically mounted, rotatable mounting plate for receiving a tool. The braking device has a frame (see e.g 3 , frame with base plate 25a and mounting bracket 25b) attached to the machine tool, a spring (see e.g Figures 1 and 2 , leaf spring 21) which is fixed at a first end to the frame, and a lever (see e.g Figures 1 to 3 , lever 22) connected to a second end of the spring. The braking device also has an actuator (see e.g Figures 1 to 3 , pneumatic linear actuator 23) which is designed to move the lever, with movement of the lever tensioning the spring and part of the lever being pressed against the mounting plate of the machine tool. As mentioned, the spring in the examples described here is a leaf spring, which can be made of spring steel, for example, and the lever is connected to the frame (eg to the base plate of the frame) exclusively via the leaf spring.

The actuator can be a pneumatic or electric direct drive and in particular does not include a gear or other rotating parts. An example of a pneumatic direct drive is a bellows cylinder.

In some embodiments, the frame includes a base plate to which the first end of the spring is clamped by a clamp member. The frame may have a bracket attached to the base plate, in this example the actuator being mounted on the bracket (see Fig 3 , Actuator 23 is mounted on bracket 25b by means of screws 25d). The bracket at least partially encloses the lever. In this example, the lever is arranged between the actuator mounted on the bracket and the base plate in the assembled state.

One end of the lever can be angled, with the angled end of the lever being pressed against a peripheral surface of the mounting plate of the machine tool when the lever is moved by the actuator. Due to a movement of the lever, it is pressed against the assembly plate of the machine tool (grinding machine), whereby the assembly plate is braked and pushed into a defined position.

Another aspect concerns the natural frequency of the lever (see Figures 1 to 3 , Lever 22) which, depending on its geometric shape and the rigidity of the material from which it is made, has certain natural frequencies and associated vibration modes, with one (namely the lowest) natural frequency dominating as a rule. According to one exemplary embodiment, the lever is constructed in such a way that its dominant natural frequency is not excited during operation of the grinding machine. That is, the natural frequency of the lever is higher than a specified maximum rotational frequency (in revolutions per second) of the grinding machine's mounting plate.

Claims (11)

1. A device, having:

   a machine tool (1) with an eccentrically mounted rotatable mounting plate (12) for receiving a tool (13); and

   a braking device (2), having

   a frame (25) fixed to the machine tool (1);

   a leaf spring (21), a first end thereof being fixed to the frame (25) ;

   a lever (22) connected to a second end of the spring,

   an actuator (23) designed to move the lever (25), wherein movement of the lever (22) tensions the spring (21) and part of the lever (22) is pressed against the mounting plate (12) of the machine tool (1).
2. The device according to claim 1,
   wherein the lever (22) is connected to the frame (25) exclusively via the spring (21), in particular without a swivel joint.
3. The device according to claim 1 or 2,
   wherein the actuator (23) is a pneumatic or an electromechanical direct drive.
4. The device according to claim 1 or 2,
   wherein the actuator (23) is a bellows cylinder.
5. The device according to any one of claims 1 to 4,
   wherein the frame (25) has a base plate to which the first end of the spring (21) is clamped by means of a clamping member (24) .
6. The device according to claim 5,

   wherein the frame (25) further has a bracket fixed to the base plate, and

   wherein the actuator (23) is mounted on the bracket.
7. The device according to claim 6,
   wherein the bracket encloses the lever (22) at least partially.
8. The device according to any one of claims 1 to 7,

   wherein one end of the lever (22) is angled, and

   wherein the angled end of the lever (22) is pressed against a peripheral surface of the mounting plate (12) of the machine tool when the lever (22) is moved by the actuator (23).
9. The device according to any one of claims 1 to 8,
   wherein, when the lever (22) is pressed against the mounting plate (12) of the machine tool (1) due to a movement thereof, the mounting plate (12) is braked and pushed into a defined position.
10. The device according to any one of claims 1 to 9,
    wherein the lever (22) has a dominant natural frequency which is higher than the rotational frequency of the machine tool during operation.
11. The device according to any one of claims 1 to 10,
    wherein the machine tool (1) is an orbital grinding machine in which the mounting plate (12) is mounted eccentrically rotatable about an axis of rotation.

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