WO2001058627A1

WO2001058627A1 - Tool holder assembly

Info

Publication number: WO2001058627A1
Application number: PCT/GB2001/000455
Authority: WO
Inventors: Hannu Saarinen
Original assignee: Robotic Technology Systems Plc
Priority date: 2000-02-09
Filing date: 2001-02-05
Publication date: 2001-08-16
Also published as: GB0002960D0; GB2359035A; AU3040601A

Abstract

The present invention relates to a tool holder assembly (3) for rotating tools (13) and a method for the same. The tool holder assembly is adapted to be moved by an actuator apparatus, such as a robot, relative to an object to be processed by the rotating tool. The assembly comprises a spindle apparatus (11) for the provision of the rotational movement of the tool. A mounting structure (10) is also provided for attaching the spindle apparatus to the actuator. The mounting structure comprises a pivoting joint between the spindle apparatus and a body portion of the mounting structure in a location that is between the ends of the spindle apparatus. Biasing means are also provided for biasing the spindle apparatus towards a nominal position relative to the mounting structure.

Description

TOOL HOLDER ASSEMBLY

Field of the Invention

The present invention relates to a tool holder, and in particular, but not exclusively, to a tool holder assembly for a rotating tool .

Background of the Invention

In manufacturing operations different workpieces may be subjected to various stages of processing by rotating tools. The processing may include any operations where a rotating tool is brought into a contact with a surface or boundary of an object or workpiece to be processed. The processing may include, for example, machining operations such as milling, tooling, boring, reaming, cutting, deburring, grinding, polishing, finishing and so on.

The rotating tool is typically attached to a tool holder assembly that provides the rotational movement of the tool by appropriate drive means. The rotating part of the tool holder assembly, i.e. the part by which the rotation is transferred to the tool, is often referred to as a spindle. The spindle may be driven by an appropriate motor. The most commonly used alternatives at the present are electric, pneumatic and hydraulic motors. Although it is not necessary in all applications, the rotation of the tool around the rotational axis thereof may be provided both in clockwise and anticlockwise directions.

The tool holder assembly typically comprises means for providing a firm grip of the tool so that the drive force that is required for the rotation of the tool can be properly transmitted from the spindle to the tool. In addition, the tool has to be held firmly in order to prevent the position thereof to change relative to the tool holder. The skilled person is aware of the alternatives for the gripping means. Exemplifying gripping means include various chucks and mandrels that are adapted to receive a co-operational part of the tool and to held the tools during the machining operation and different clamping mechanisms adapted to clamp the tool to the rotating part of the tool holder assembly.

The tool holder assembly may be attached to an actuating apparatus that is adapted to move the tool holder assembly relative to the object to be processed by the tool. The actuators include industrial robots and manipulators and similar apparatus capable of moving the tool holder assembly. The movement may be provided m a three dimensional space, although some actuators may provide a movement that is limited m directions (for example, the movement may be enabled only in vertical and/or horizontal direction) .

As mentioned above, an object may be subjected to variou^s machining operations by a rotating tool that is moved by an actuator relative to the object. To be able to move the tool correctly and accurately relative to the object, the actuator, such as a robot, typically operates m accordance with a predefined set of instructions. More particularly, the actuator is typically controlled by a controller that follows a machining program. The controller instructs various components of the actuator apparatus such that the tool is moved relative to the object in an appropriate manner. The machining program may be based, for example, on a prewritten program code and/or on other information obtained e.g. through a machine vision systen. The skilled person is aware of various possibilities to control the operation of an actuator, and thus the control is not discussed here in more detail.

The actuator provides typically a stiff i.e. non-flexible support for the tool holder. That is, in order to provide accurate positioning of the tool that is required in many machining operations the actuator structure is not allowed to flex relative to the object. However, in some machining applications, such as deburring, grinding, reaming, polishing and so on, a small but controllable flex when the tool is pressed against the object could be advantageous. The flex could be utilised e.g. to allow some manufacturing tolerance for the workpieces and/or for the positioning of the workpiece and/or use of somewhat less accurate information about the object (e.g. the information of the characteristics of the object provided by means of a machine vision system) .

Summary of the Invention

It is an aim of the embodiments of the present invention to address one or several of the problems that relate to provision of a tool holder assembly such that the rotating tool is allowed to flex relative to the actuator apparatus.

According to one aspect of the present invention, there is provided a tool holder assembly for a rotating tool, the tool holder assembly being adapted to be moved by an actuator apparatus relative to an object to be processed by the rotating tool, comprising: a spindle apparatus for providing the rotational movement of the tool, the spindle apparatus having a first end and a second end; mounting structure for attaching the spindle apparatus to the actuator, the mounting structure comprising a pivoting joint between the spindle apparatus and a body portion of the mounting structure in a location that is between the first end and the second end of the spindle apparatus, whereby the spindle apparatus and the tool attached to the spindle apparatus are allowed to pivot from a nominal position relative to the mounting structure; and biasing means for biasing the spindle apparatus towards the nominal position relative to the mounting structure.

According to another aspect of the present invention there is provided a mounting structure for a tool holder assembly, the tool holder assembly being arranged to rotatably held a tool and movably supported by an actuator apparatus, the mounting structure comprising: a body portion; fixing means for attaching the body portion to the actuator apparatus; a pivoting joint between a spindle apparatus of the tool holder assembly and the body portion in a location that is between the first end and the second end of the spindle apparatus, whereby the spindle apparatus and the tool attached to the spindle apparatus are allowed to pivot from a nominal position relative to the body portion; and biasing means for biasing the spindle apparatus towards the nominal position relative to the mounting structure.

According to another aspect of the present invention there is provided a method m a tool holder assembly, the tool holder assembly including a spindle apparatus and a mounting structure for providing a mount between the spindle apparatus and the actuator apparatus, said actuator apparatus being adapted to move the tool holder assembly relative to an object to be processed by a rotating tool attached to the spindle apparatus, comprising: biasing the spindle apparatus about a pivoting joint between the spindle apparatus and a body portion of the mounting structure towards a nominal position thereof, the pivoting joint being located between the first end and second end of the spindle apparatus; and bearing the tool against the object to be processed, wherein the rotating tool is allowed to pivot about the pivoting joint from the nominal position thereof.

In more specific embodiments the pivoting point may be relatively close to the rotational axis of the rotating tool. The pivoting joint may comprise a ball joint or at least one bearing. The position of the spindle apparatus relative to the mounting structure may be adjustable. The pivoting joint may also be positioned, in the direction from the first end to the second end of the spindle apparatus, at or close to a mass weight centre of the tool holder assembly. The assembly of the mounting structure around the surface of the spindle apparatus may be releasable. The position of the mounting structure relative to the spindle apparatus may be adjustable.

The tool holder assembly may also be provided with an automatic tool change function. The automatic tool change function may be provided by an automatic tool holder of the spindle apparatus, by an arrangement enabling an automatic change of the entire tool holder assembly or by a clamping and release unit of the mounting structure enabling the mounting structure to automatically clamp and release the spindle apparatus . The embodiments of the invention provide several advantages. A rotating tool that bears against an object may flex in a predefined manner so that a predefined amount of variances in the contour and/or dimensions and/or position of the object are allowed. The information required for the control of the machining operation does not necessarily need to be that accurate than what is required for the non- flexible arrangements. Some of the embodiments provide a balanced tool holder assembly. In addition, some of the embodiments allow an adjustment of the stiffness of the flexibility.

Brief Description of Drawings

For better understanding of the present invention, reference will now be made by way of example to the accompanying drawings in which:

Figure 1 shows a robot deburring system employing an embodiment of the present invention;

Figure 2 is a side view of a tool holder assembly in accordance with the present invention;

Figure 3 is an end view of the tool holder assembly of Figure 2 ;

Figure 4 is a sectional view of a tool holder assembly in accordance with an embodiment; Figures 5 and 6 show more detailed sectioned views of the components of the Figure 4 assembly; and

Figure 7 is a flowchart illustrating the operation of one embodiment of the present invention.

Description of Preferred Embodiments of the Invention

Reference is made to Figure 1 which shows a machining system including a tool holder assembly 3 in accordance with an embodiment of the present invention. The machining system includes an industrial robot 1 for movably supporting the tool holder assembly 3. The structure and operation of an industrial robot is well known by the skilled person, and will thus not be described in detail herein. It is sufficient to note that a robot typically comprises a frame portion and one or several swivelling and/or rotational arms so that it is capable of providing different movements in a three dimensional working space thereof. The various possibilities for a rotational and pivotal movement of the robot 1 are indicated by the two headed arrows in Figure 1.

The robot of Figure 1 is provided with a first arm 5 that is pivotally attached to a frame portion 6 and a second or outer arm 4 that is attached pivotally to the first arm 5. A further pivoting point 7 is arranged at the end of the outer arm 4. A short mounting arm or fixture 8 projects from the pivoting point 7 and provides an attachment point for the tool holder assembly, and more particularly, for a counterpart 14 that projects from the tool holder assembly. The mounting arm of a robot is sometimes referred to as a wrist. The mounting arm 8 typically revolves around the axis thereof, as is illustrated by the two headed arrow. The rotational and/or swivelling movements of the various components of the robot may be provided by suitable actuators, such as by servomotors and/or pneumatic or hydraulic cylinders.

Figure 1 discloses further a workpiece 19 that is disposed on a workbench 18. It is noted that the workbench 18 is only an example of a supporting structure that may be used for supporting tha workpiece. The workpiece 19 could be supported by any appropriate supporting means, such as by an appropriate conveying apparatus. It is also possible to arrange the workpiece to be supported by another actuator device so that the workpiece 19 may be moved in a controlled manner by said other actuator device while it is processed by the rotating tool 13.

A control unit 2 of the robot 1 is also shown. The control unit is arranged to process information concerning the object 19 to be processed by means of the robot 1. A part of the information may be retrieved/received from an external database or from an imaging apparatus of a machine vision system (not shown) via an appropriate communication media. The controller 2 typically includes required data processing and storage capability, such as an appropriate central processing unit (CPU) . The central processing unit may be based on microprocessor technology. As a more practical example, the controller unit may be based on a Pentium™ processor, even thoug a less or more powerfull processor may also be employed depending on the requirements of the system and the objects to be handled. Depending on the application, the controller 2 may be provided with appropriate memory devices, drives, display means, a keyboard, a mouse or other pointing device and any adapters and interfaces that may be required by the application. In addition, if the processing of the object 19 is based on information received from e.g. a camera of a machine vision system (not shown) , an appropriate imaging software is typically required. The controller may also be provided with a network card for installations where the imaging system is connected to a data network, such as to a network based on TCP/IP (Transport Control Protocol/Internet Protocol) . A connection is provided between the controller 2 and the robot "1 for transmission of data therebetween. As is shown by arrow 17 in Figure 1, the tool 13 is attached flexibly relative to the mounting arm 8. In other words, the tool is allowed to pivot about a pivoting point PP relative to the point where the tool holder assembly 3 is attached to the robot 1. An embodiment of the flexible tool holder assembly will now be described in more detail with reference to Figures 2 to 6.

The tool holder assembly 3 comprises a spindle member 11 that is attached to the robot through a mounting structure 10. The skilled person is familiar with the operation and structure of a typical spindle arrangement, and thus the internal parts within the spindle housing 11 are not shown or explained in more detail . It is sufficient to note that a spindle apparatus may comprise a spindle portion within the housing 11 and a motor 12 arranged to provide the drive force for the rotating tool 13 at the other end of the spindle housing 11. The rotating tool 13 may be attached to the spindle 11 by means of a chuck, a mandrel or other appropriate clamping device (not shown) . The machining tool 13 is arranged to rotate around a tool centre line TCL.

The drive motor 12 is preferably provided at the other end of the spindle housing 11, although other type of positioning may also be used. The drive motor 12 may be of any appropriate type capable of providing the required rotation power for the tool 13 through the spindle, such as an electric, pneumatic or hydraulic motor.

Figure 3 discloses an end view of the tool holder assembly 3 of Figure 2 (seen from the tool end of the holder assembly) . The spindle housing 11 is shown to have a circular i.e. tubular cross section. However, it is noted that the cross sectional shape of the housing may differ from the shape shown by Figure 3, and may be, for example square, rectangular, hexagonal, oval and so on. A mounting structure 10 in accordance with an embodiment of the present invention surrounds the spindle housing 11. The mounting structure 10 is attached to the robot 1 by means of a flange 15 that is connected to the mounting structure by a fixture 14. More particularly, the flange 15 is attached by bolts 16 to a counterpart flange 9 of the mounting arm 8. It is noted that Figure 2 is only an example of possible attachment means, and that the tool holder assembly may be attached to the robot 1 in various alternative manners as well .

The internal components of the mounting structure 10 will now be described in more detail with reference to Figures 4 to 6.

A reference is first made to the sectioned view of Figure 4 of an embodiment of the mounting structure 10. It is to be appreciated that the structure is cut along the tool centre line TLC and thus only a half of the mounting structure is shown. The other half would be a mirror image of the disclosed upper half, and is not illustrated for clarity reasons.

The mounting structure 10 comprises a body part 20 surrounding the internal components of the structure. A ball joint 24 comprising a convex portion 25 and a concave portion 26 is shown to be mounted within the body portion 20 such that the ball joint ring surrounds the spindle housing 11. The ball joint ring 24 is mounted between a bearing retainer 22 and a bearing ring 21. The ball joint 24 is fixed around the retainer 22. The retainer 22 is provided with threaded bores 30 by means of which the retainer 22 can be clamped around the circumference of the spindle housing 11 (for the bores, see Figure 5) .

The screws in the bores 30 may be opened, and thus it is possible, when desired, to adjust the axial position of the mounting structure on the circumference of the spindle apparatus 11. In addition, it is possible to replace the spindle apparatus with another spindle apparatus, e.g. with a stronger or faster spindle apparatus, in accordance with the task to be accomplished by the machining system.

The outer circumference 26 of the ball joint 24 is fixed by means of the retainer ring 21 and a clamp screw 31 to the body portion 20 of the mounting structure 10.

By means of this structure the spindle housing 11 is pivotally attached to the mounting structure 10 and may pivot relative to the robot arm 8. The pivoting point PP is located in a point where the tool centre line TLC and the bearing centre line BLC of the ball joint 24 intersect.

The assembly 10 comprises a ring 27 provided with cylinder bores 35 (see Fig. 6) . A pneumatically operated piston 28 is placed within each bore 35 in the ring 27. The retainer 22 is provided with a flange 23 that is co-operational with the ends of the pistons 28. The piston ends are arranged to press against the flange 23 of the bearing retainer 22 so as to provide a biasing force for pressing the spindle housing 11 towards a desired nominal pivotal position thereof. A typical nominal position may be a position in which the tool centre line TCL is parallel with the imaginary centre line of the mounting structure 10, although other positions may also be used in here. More particularly, the arrangement is such that an appropriate number, for example 12 cylinder bores 35 and pistons 28 within the bores are provided into the ring 27, thereby causing an even biasing force against the flange 23 of the retainer 22. A possibility for the distribution of the cylinder bores is disclosed by Figure 6. A bore 29 in the body portion 20 is for supplying pressurised air (or other suitable fluid) into the bore 35 and for actuating the piston 28 within the bore 35. The biasing force that bears against the flange 23 of the retainer 22 may thus be adjusted through the bores 29 by adjusting the pressure of the fluid. The pressure may be the same in all bores, but it is also possible to adjust the biasing force such that the pressure, and thus the biasing force, is higher in one side of the flange than in the other by supplying different pressures to different bores 29 of the ring 27.

Figure 4 shows the spindle apparatus in the nominal (i.e. non- pivoted) position. The dashed line Hi illustrates an inclined position of the spindle apparatus. To enable the spindle apparatus to tilt relative to the body portion 20, the structure is provided with a play 32 between the body portion 20 and the outer circumference of the spindle housing 11. The required maximum pivoting angle and play between the spidle and the body depends on the application.

The mounting structure 10 is mounted around the spindle housing 11 at a location between the first and second ends of the spindle apparatus. The pivoting joint 24 is preferably located close -to the mass centre point of the tool holder assembly 3 in the longitudinal direction of the spindle apparatus . By means of this it is possible to achieve a tool holder assembly that is balanced such that the position of the tool holder assembly does not affect the operation of the holder assembly. In other words, if a balanced tool holder assembly is provided, the mass of the assembly does not cause substantially different forces when the tool holder assembly is in different positions. In embodiments where the pivoting point is distant from the mass centre, the mass of the tool holder assembly may in some applications affect the biasing and/or pivoting of the tool . Different forces may, for example, appear between a relatively horizontal position and a relatively vertical position of a non-balanced tool holder assembly.

As shown by the flowchart of Figure 7, during the operation of a tool holder assembly, a spindle apparatus is biased about a pivoting point, such as a pivoting point provided by means of a ball joint, towards a predefined nominal position thereof. As explained, the pivoting joint is located intermediate the first and second ends of the spindle apparatus. When a tool is pressed against the object to be processed, the tool is allowed to flex a predefined amount about the pivoting point from the nominal position thereof since the biasing means, such as pneumatically actuated pistons, will provide a flexible support for the spindle apparatus.

It is to be appreciated that instead of a ball joint the pivoting joint between the mounting structure and the spindle apparatus may also be implemented by other means providing a pivotal movement between said elements. For example, an appropriate spherical bearing or any other bearing arrangement enabling an inclination in about its axis may be employed herein. In addition, instead of the above described pistons for the biasing, alternative biasing structures, such as biasing springs or inflatable bellows, may be used.

According to a further embodiment the tool holder assembly is provided with automatic tool change function. The automatic tool change function may be provided by a tool holder of the spindle apparatus that has been adapted to enable the automatic tool change operation. Such spindle arrangement are per se known and are not described in more detail . It is sufficient to note that the automatic tool holders are adapted to automatically clamp and/or release a rotating tool.

According to an alternative arrangement the automatic tool change function is provided by an arrangement enabling an automatic change of the entire tool holder assembly. This may be provided by means of any appropriate releasable gripping or locking means. In this type of operation a number of tool holder assemblies may be utilised such that the tool is changed by changing the holder assembly.

The automatic tool change function may also be provided by a clamping and release unit that is provided in the mounting structure. The unit is adapted to enable the mounting structure to automatically clamp and release the spindle apparatus, thereby enabling change of the spindle apparatus and the tool attached thereto.

The embodiments provide a flexible tool holder assembly that may be used in various applications, such as in machining of an edge contour of an object. The amount of the flexibility of the tool may be adjusted in accordance with specific requirements of the machining work to be accomplished. In some of the embodiments it is also possible to replace a spindle with another and/or us-; different types of spindle apparatus with the mounting structure.

The disclosed attachment construction enables also of a high speed spindle apparatus. The high speed spindle apparatus enable rotational speeds of the tool that are in the order of 50000 1/min or higher.

It should be appreciated that whilst embodiments of the present invention have been described in relation to an industrial robot, the embodiments of the present invention are applicable to any other suitable type of actuator apparatus capable of moving the tool holder assembly.

It is also noted herein that while the above describes exemplifying embodiments of the invention, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the present invention as defined in the appended claims.

Claims

1. A tool holder assembly for a rotating tool, the tool holder assembly being adapted to be moved by an actuator apparatus relative to an object to be processed by the rotating tool, comprising: a spindle apparatus for providing the rotational movement of the tool, the spindle apparatus having a first end and a second end; mounting structure for attaching the spindle apparatus to the actuator, the mounting structure comprising a pivoting joint between the spindle apparatus and a body portion of the mounting structure in a location that is between the first end and the second end of the spindle apparatus, whereby the spindle apparatus and the tool attached to the spindle apparatus are allowed to pivot from a nominal position relative to the mounting structure; and biasing means for biasing the spindle apparatus towards the nominal position relative to the mounting structure.

2. A tool holder assembly as claimed in claim 1, wherein the pivoting point provided by the pivoting joint is relatively close to the rotational axis of the rotating tool.

3. A tool holder assembly as claimed in claim 1 or 2 , wherein the pivoting joint comprises a ball joint.

4. A tool holder assembly as claimed in claim 3 , wherein the ball joint is mounted around the circumference of the spindle apparatus .

5. A tool holder assembly as claimed in claim 1 or 2 , wherein the pivoting joint comprises at least one bearing.

6. A tool holder assembly as claimed in any preceding claim, wherein the spindle apparatus comprises a motor for rotating the tool attached to a spindle portion of the spindle apparatus .

7. A tool holder assembly as claimed in claim 6, wherein the motor comprises an electric motor.

8. A tool holder assembly as claimed in claim 6, wherein the motor comprises a pneumatic motor.

9. A tool holder assembly as claimed in any preceding claim, wherein the spindle apparatus consists of a high speed spindle.

10. A tool holder assembly as claimed in any preceding claim, wherein the position of the spindle apparatus relative to the mounting structure is adjustable.

11. A tool holder assembly as claimed in any preceding claim, wherein the biasing means comprise at least one pneumatically actuated piston.

12. A tool holder assembly as claimed in claim 11, wherein said at least one piston is arranged to bear against an element that is attached to the spindle apparatus.

13. A tool holder assembly as claimed in claim 12, wherein the element comprises a flange provided by a fixing member for attaching the -pivoting joint to the spindle apparatus.

14. A tool holder assembly as claimed in any of claims 11 to

13, wherein the biasing force by said at least one piston is adjustable .

15. A tool holder assembly as claimed in any of claims 11 to

14, wherein at least two pistons are provided and the biasing forces provided by said pistons can be adjusted separately.

16. A tool holder assembly as claimed in any preceding claim, wherein the actuator apparatus comprises a robot.

17. A tool holder assembly as claimed in any preceding claim, wherein the pivoting joint is positioned, in the direction from the first end to the second end of the spindle apparatus, at or close to a mass weight centre of the tool holder assembly.

18. A tool holder assembly as claimed in any preceding claim, wherein the assembly of the mounting structure around the surface of the spindle apparatus is releasable.

19. A tool holder assembly as claimed in any preceding claim, wherein the position of the mounting structure relative to the spindle apparatus is adjustable.

20. A tool holder assembly as claimed in any preceding claim, wherein the tool holder assembly is provided with automatic tool change function.

21. A tool holder assembly as claimed in claim 20, wherein the automatic -tool change function is provided by an automatic tool holder of the spindle apparatus, said automatic tool holder being adapted to automatically clamp and/or release a rotating tool.

22. A tool holder assembly as claimed in claim 20, wherein the automatic tool change function is provided by an arrangement enabling an automatic change of the tool holder assembly.

23. A tool holder assembly as claimed in claim 20, wherein the automatic tool change function is provided by a clamping and release unit of the mounting structure enabling the mounting structure to automatically clamp and release the spindle apparatus.

24. A tool holder assembly as claimed in any preceding claim, wherein the rotating tool comprises a machine tool for machining the object.

25. A tool holder assembly as claimed in claim 24, wherein the machining of the object comprises at least one of the following operations: deburring; grinding; milling; tooling; reaming; boring; polishing; finishing.

26. A mounting structure for a tool holder assembly, the tool holder assembly being arranged to rotatably held a tool and movably supported by an actuator apparatus, the mounting structure comprising: a body portion; fixing means for attaching the body portion to the actuator apparatus; a pivoting joint between a spindle apparatus of the tool holder assembly and the body portion in a location that is between the first end and the second end of the spindle apparatus, whereby the spindle apparatus and the tool attached to the spindle apparatus are allowed to pivot from a nominal position relative to the body portion; and biasing means for biasing the spindle apparatus towards the nominal position relative to the mounting structure.

27. A mounting structure as claimed in claim 26, wherein the pivoting joint provides a pivoting point that is relatively close to the rotational axis of the rotating tool.

28. A mounting structure as claimed in claim 26 or 27, wherein the pivoting joint comprises a ball joint.

29. A method in a tool holder assembly, the tool holder assembly including a spindle apparatus and a mounting structure for providing a mount between the spindle apparatus and the actuator apparatus, said actuator apparatus being adapted to move the tool holder assembly relative to an object to be processed by a rotating tool attached to the spindle apparatus, comprising: biasing the spindle apparatus about a pivoting joint between the spindle apparatus and a body portion of the mounting structure towards a nominal position thereof, the pivoting joint being located between the first end and second end of the spindle apparatus; and bearing the tool against the object to be processed, wherein the rotating tool is allowed to pivot about the pivoting joint from the nominal position thereof.

30. A method as claimed in claim 29, wherein the pivoting point is relatively close to the rotational axis of the rotating tool .