WO2024149978A1

WO2024149978A1 - A machine tool and a rotary machine drive for the machine tool

Info

Publication number: WO2024149978A1
Application number: PCT/GB2024/050030
Authority: WO
Inventors: Matthew Tucker
Original assignee: Fives Landis Limited
Priority date: 2023-01-10
Filing date: 2024-01-08
Publication date: 2024-07-18

Abstract

A rotary machine drive (322, 324) for a machine tool comprises a base portion (330, 334) and a driven portion (332, 336), and the rotary machine drive is operable to rotate the driven portion relative to the base portion about a first rotational reference axis (338, 340) to control the orientation of the driven portion relative to the base portion about the rotational reference axis. An angle adjustment assembly (342, 344) is carried by the driven portion. A support (200, 202) is carried by the angle adjustment assembly for supporting a tool or workpiece of the machine tool, the support having a support reference plane (346, 348) which extends transversely with respect to the first rotational reference axis. The angle adjustment assembly is operable to tilt the support reference plane relative to the first rotational reference axis in any direction.

Description

Title : A Machine Tool and a Rotary Machine Drive for the Machine Tool

Field of the disclosure

The present disclosure relates to a machine tool for machining a workpiece and methods of operation thereof. It also concerns a rotary machine drive for such a machine tool.

Background to the disclosure

The present applicant has developed a machine tool configuration based on two rotary machine drives arranged in fixed positions on a common machine base, with their rotational reference axes spaced apart and parallel. This configuration has axisymmetric stiffness properties in the primary motion control drives, namely the two rotary machine drives. This results in a more predictable stiffness loop and often a higher stiffness, which in turn provides higher levels of precision and repeatability. A machine tool of this form is described in WO-A-2009/093064, for example.

Figure 1 is a perspective simplified representation of a machine tool described in WO- A-2009/093064. It includes a machine base 10. First and second supports 100, 102 are mounted directly on the base for rotation about the axes of rotation of the respective rotary machine drives which are perpendicular to the plane of the machine base. Their rotational motion is indicated by arrows A and B respectively. Pointers 104 and 106 denote reference points associated with each support. Each pointer has a reference axis 108, 110 passing through it.

A mount 112 is carried by the second support 102 and is movable using a linear machine drive. Reference pointer 104 is on the first support, and reference pointer 106 is on mount 112, carried by the second support 102. Ghost representations 100', 102' and 112' of the first support, second support and mount are included in Figure 1 to show different orientations thereof following rotation using their respective rotational machine drives and movement of the mount using the linear machine drive. The two rotary machine drives and the linear drive are used to control the positions and orientations of the pointer 104 on the first support and the pointer 106 on the mount relative to the machine base.

Summary of the disclosure

The present disclosure provides a rotary machine drive for a machine tool, wherein the rotary machine drive comprises: a base portion and a driven portion, and the rotary machine drive is operable to rotate the driven portion relative to the base portion about a first rotational reference axis to control the orientation of the driven portion relative to the base portion about the rotational reference axis; an angle adjustment assembly carried by the driven portion; and a support carried by the angle adjustment assembly for supporting a tool or workpiece of the machine tool, the support having a support reference plane which extends transversely with respect to the first rotational reference axis, wherein the angle adjustment assembly is operable to tilt the support reference plane relative to the first rotational reference axis in any direction.

The inclusion of such an angle adjustment assembly in a rotary machine drive facilitates adjustment of the angle of the support carried by the assembly to counteract positioning errors. For example, when the rotary machine drive is carried by a machine base, thermal distortion of the machine base may cause the angle of the rotational reference axis of the rotary machine drive to be displaced from the intended orientation. The angle adjustment assembly may be used in such circumstances to compensate for this displacement.

The support may carry a tool or workpiece (or a drive spindle for a tool or workpiece) at a fixed, non-adjustable location on the support. Alternatively, one or more further degrees of freedom may be provided between the support and a tool or workpiece carried by the support, by means of one or more rotary and/or linear machine drives for example. In preferred examples, the rotary machine drive includes rotary bearings, preferably both journal and thrust bearings. Large thrust bearings may be mounted directly upon a machine base to provide highly stiff, damped drives with a very good bearing ratio in all directions resulting in axisymmetric stiffness characteristics.

The present disclosure also provides a machine tool comprising a machine base, and a first rotary machine drive as described herein, with the base portion of the rotary machine drive mounted on the machine base in a non-adjustable location relative to the machine base.

The machine tool may include a second rotary machine drive which comprises a second base portion and a second driven portion, with the second rotary machine drive being operable to rotate the second driven portion relative to the second base portion about a second rotational reference axis to control the orientation of the second driven portion relative to the second base portion about the second rotational reference axis, and the second base portion mounted on the machine base in a non- adjustable location relative to the machine base, with the second rotational reference axis arranged to be parallel to and spaced laterally from the first rotational reference axis. The angle adjustment assembly of the first rotary machine drive may be controlled to compensate for effects which may cause the first and second rotational reference axes to become non-parallel.

In some implementations, the second rotary machine drive may include a second angle adjustment assembly carried by the second driven portion, and a second support carried by the second angle adjustment assembly for supporting a tool or workpiece of the machine tool, the second support having a second support reference plane which extends transversely with respect to the second rotational reference axis, wherein the second angle adjustment assembly is operable to tilt the second support reference plane relative to the second rotational reference axis in any direction. Preferably, in a machine tool including two rotary machine axes mounted at fixed, non-adjustable locations on a common machine base, both rotary machine axes include respective angle adjustment assemblies, enabling the angular orientations of both the first and second supports to be independently adjusted.

A control arrangement of the machine tool may be operable to control the orientations of the respective driven portions of the rotary machine drives about their rotational reference axes, so as to govern the locations of a workpiece (or tool) mounted on one of the drives and one or more tools mounted on another drive relative to each other.

It will be appreciated that references herein to a tool carried by a rotary machine drive encompass a wide range of tools, such as grinding wheels, dressing tools, probes, gauges, sensors, peripherals and the like.

For some applications, it may be desirable to have three or more rotary machine drives mounted in non-adjustable locations on a common base with their rotational reference axes arranged to be parallel and laterally spaced apart. Examples of machine tools having this configuration are described in the applicant’s co-pending UK patent application no. 2217119.3. The present disclosure is equally applicable to such configurations.

The or each angle adjustment assembly may comprise at least three actuators operable to vary the distance between the support and the driven portion at respective locations which are distributed circumferentially spaced apart around the respective rotational reference axis. The actuators may be circumferentially spaced apart around the respective rotational reference axis. The three actuators may then be controlled individually so as to adjust the orientation of the associated support in the desired direction.

For example, the actuators may be linear actuators.

Preferably, the actuators are piezoelectric actuators. It is desirable for the actuators to have high stiffness properties and to be able to provide high precision adjustment of the distance between a support and a driven portion of a rotary machine drive. To this end, piezoelectric actuators may be suitable in many cases and may be sufficiently compact for this purpose. Piezoelectric actuators may include bolt holes to enable them to be bolted onto a supporting substrate. Some piezoelectric actuators include a thread on an outer diameter of their housing to enable them to be fastened to a support.

A range of short stroke, stiff and high accuracy actuators may be used. For example, a vertical motion stage, such as a M-VP-5ZA vertical stage marketed by Newport Corporation, could be utilised together with some form of feedback control.

For some applications, an angle adjustment assembly may be implemented using a set of pistons. For example, the pistons may be configured in a “hexapod” or “Stewart platform” configuration.

In other implementations, each actuator of the angle adjustment assembly may be in the form of a metallic block (formed from aluminium for example) which includes a series of channels for receiving a temperature-controlled fluid. In this way, thermal expansion of the block may be controlled by varying the temperature of a fluid flowing through the channels to provide the required linear displacement. Each block may include holes for receiving bolts to fasten them to an underlying support.

The angle of the support carried by the angle adjustment assembly may need to be controlled with a high degree of accuracy. For example, this angle may be adjusted with arcsecond levels of precision. The actuators are preferably controllable at a level of precision of around one micron.

In order to compensate for thermal distortion, it may be desirable to be able to alter the angle of the support over a range of up to around 100 arcseconds. A range of motion of each actuator may be up to around 20 microns. If an angle adjustment assembly is also intended to compensate for predicted positioning errors, a greater range of motion may be required.

The present disclosure further provides a method of operating a rotary machine drive as described herein, comprising sending control signals to the angle adjustment assembly of the rotary machine drive to tilt the reference plane of its support relative to the rotational reference axis of the rotary machine drive.

In addition, the present disclosure provides a method of operating a machine tool as described herein, comprising the steps of: receiving distortion signals in a controller of the machine tool which are responsive to distortion of the machine base; and determining with the controller control signals to send to the angle adjustment assembly in order to compensate for the distortion of the machine base.

The control signals sent to the angle adjustment assembly will be determined with reference to the orientation of the driven portion of the respective rotary machine drive about its rotational reference axis and with reference to changes in that orientation in order to provide the desired tilt adjustment in relation to the machine base as the driven portion rotates.

The method of operating a machine tool may include a step of: determining, with the controller of the machine tool, drive control signals to send to drives of the machine tool which are adjusted in order to compensate, in combination with the control signals to send to the angle adjustment assembly, for the distortion of the machine base.

In this way, the positional error compensation afforded by the angle adjustment assembly may be used together with adjustment of control signals sent to drives of the machine tool in order to counteract positioning errors. This facilitates more versatile error compensation.

The present disclosure also provides a method of operating a machine tool as described herein comprising the step of determining, with the controller of the machine tool, control signals to send to the angle adjustment assembly of a rotary machine drive in order to compensate for predicted positioning errors occurring in the machine tool. For example, positioning errors occurring over the range of travel of a supporting guideway or shaft may be predictable and result in angular positioning errors which may be compensated for using an angle adjustment assembly of the form described herein.

The angle adjustment assembly may provide the compensation for predicted positioning errors in combination with compensation for errors from other sources. These other errors, such as thermal distortion for example, may change over time and be compensated for accordingly.

Brief description of the drawings

Known machine tool configurations and examples of the present disclosure are described herein with reference to the accompanying schematic drawings, wherein:

Figure 1 is a perspective view of a simplified representation of a known machine tool configuration;

Figure 2 is a side view of a machine tool having the configuration shown in Figure 1 which has been modified in accordance with the present disclosure;

Figure 3 is a perspective view of a rotary machine drive according to example of the present disclosure;

Figure 4 is a perspective view of part of the rotary machine drive of Figure 3; and Figures 5 and 6 are perspective views of a turret including a drive spindle mounted on a retractable shaft in retracted and extended configurations, respectively.

Detailed description

Figure 2 shows a side view of a machine tool having the configuration shown schematically in Figure 1. The machine tool has been modified in accordance with the present disclosure to include angle adjustment assemblies in each of its rotary machine drives. The machine tool of Figure 2 includes two rotary machine drives 322 and 324 which are carried by a machine base 198. A plate-shaped support 202 is rotated by the rotary machine drive 322 and a plate-shaped support 200 is rotated by the rotary machine drive 324. A linear machine drive 318 is mounted on the support 202. A drive spindle 222 is provided on the linear machine drive 318 for carrying a tool (not shown) to be brought into engagement with a workpiece (not shown) held in a workpiece mount 224 on support 200 during a machining operation. In the arrangement of Figure 2, each of two rotary machine drives 322 and 324 is mounted onto a respective side of a central support 320 of the machine base 198. Each rotary machine drive is coupled to the adjacent side of the central support by a mounting 326, 328, which extends horizontally between the respective machine drive and the support. The central support or slab thus carries the weight of each machine drive on either side. As a result, forces generated during operation of the machine tool act via the machine drives in opposite directions on the central support 320. Thus, the central support resists these forces in a state of tension or compression, rather than in bending, as would be the case with a machine drives mounted on top of a horizontal machine bed slab. This results in a substantially constant (and potentially stiffer) stiffness loop in the machine tool irrespective of the orientations of the supports 200, 202. This serves to further reduce positioning errors during operation of the machine.

A thermal/stiffness loop 310 is marked on Figure 2. As the supports 200 and 202 are rotated to present different parts of a workpiece on workpiece mount 224 to a machine tool carried by spindle 222, the thermal loop 310 is substantially unchanged, thereby avoiding inaccuracies resulting from a variable thermal loop.

The rotary machine drive 322 comprises a base portion 330 and a driven portion 332, whilst the rotary machine drive 324 comprises a base portion 334 and a driven portion 336. Each driven portion includes an electric motor for rotating the corresponding driven portion about its rotational reference axis 338, 340, respectively.

An angle adjustment assembly 342 is carried by the driven portion 332 and an angle adjustment assembly 344 is carried by the driven portion 336. Each support 202 and 200 is mounted on the corresponding angle adjustment assembly and extends in a respective reference plane 346, 348. Each angle adjustment assembly is able to tilt the associated support relative to the corresponding rotational reference axis 338, 340.

Each angle adjustment assembly comprises a set of three linear actuators. Each actuator is located between the driven portion of the associated rotary machine drive and the corresponding support. Each actuator is operable to change the spacing between two surfaces thereof which are in contact with the associated driven portion and support, respectively, thereby adjusting the height of the support above the driven portion at the location of the actuator. Accordingly, by coordinated adjustment of the heights of each actuator in a set of actuators, the angular orientation of the associated support relative its rotational reference axis can be altered in a desired direction.

Each actuator may be a stiff, short stroke linear actuator. A piezoelectric actuator may be used for example.

Distortion of the machine base may result from uneven or localised heating of the machine base. This may cause a change in the orientation of a rotary machine drive mounted on the machine base. This change may have a rotational component about a reference axis which extends perpendicular to a plane containing the rotational reference axes 338 and 340 (in their intended positions), causing a tilting effect. It may also have a rotational component about a reference axis which is perpendicular to, and intersects with, both of the rotational reference axes 338 and 340 (in their intended positions), resulting in a twisting effect. These displacements may be compensated for using an angle adjustment assembly as described herein.

At least one linear distortion sensor may be mounted on the machine base. Alternatively, the location of reference points on the machine base may be detected using at least one sensor mounted elsewhere on the machine tool or using at least one separate device which may be remote from the machine tool. Signals generated by such sensors may be used to measure distortion of the machine base. A controller of the machine tool may then utilise these measurements to generate control signals to be sent to an angle adjustment assembly in order to compensate for measured distortion of the machine base. A machine tool including a distortion sensor and methods for measuring distortion of the base of a machine tool are disclosed in a co-pending application filed by the present applicant, namely UK patent application no. 2212420.0.

Figures 3 and 4 show another example of a rotary machine drive according to the present disclosure. This drive has a base portion 400 and a driven portion 402 mounted thereon. The base portion includes a motor for rotating the driven portion relative to the base portion about a rotational reference axis 404 to control precisely the orientation of the driven portion relative to base portion about that axis.

An angle adjustment assembly is mounted on the driven portion 402. This assembly comprises three linear actuators 406, 408 and 410. A circular plate forms a support 412 which is carried on the angle adjustment assembly. In the example shown in Figures 3 and 4, a drive spindle 414 is attached to the support by a mount 416. Figure 4 is a view of the underside of the angle adjustment assembly and the support 412 to show the configuration of the three linear actuators. The linear actuators are disposed at locations which are equally circumferentially spaced apart around the rotational reference axis 404, close to the radially outermost edge of the support 412.

An example of a predictable positioning error which may be compensated for with a rotary machine drive as described herein will now be described with reference to Figures 5 and 6. Figures 5 and 6 show a turret 500 suitable for mounting on a rotary machine drive. The turret includes a drive spindle 502 which is mounted within a shaft 504. The shaft is mounted in the turret for linear motion between a retracted position shown in Figure 5 and an extended position shown in Figure 6. The location of the shaft is controlled using a linear machine drive within the turret which is not visible in the Figures.

It has been found that the path followed by a component displaced using an extendable driveshaft or quill of the form shown in Figures 5 and 6 may deviate from a straight line. The weight of the shaft and the component carried by it may cause the distal end of the shaft to droop slightly in an extended configuration. This means in turn that a central rotational axis of a component mounted on the drive spindle will lie at an angle to the desired orientation. According to the present disclosure, this positioning error may be measured over the throw of the drive shaft to generate calibration data, which can then be used to generate control signals to send to an angle adjustment assembly of the form described herein in order to compensate for the positioning error. These control signals may also take into account other adjustments, such as compensation for thermal distortion of the machine bed.

In examples of machine tools described herein, in cooperation with an angle adjustment assembly, positioning errors may also be counteracted by adjusting control signals sent to position controlling machine drives of the machine tool. Positioning errors between two components carried by respective rotary machine drives may be compensated for in real time by the machine tool’s control system.

It will be appreciated that references herein to perpendicular or parallel relative orientations and the like are to be interpreted as defining perpendicular or parallel relationships between components within practical tolerances.

Claims

1. A rotary machine drive for a machine tool, wherein the rotary machine drive comprises: a base portion and a driven portion, and the rotary machine drive is operable to rotate the driven portion relative to the base portion about a first rotational reference axis to control the orientation of the driven portion relative to the base portion about the rotational reference axis; an angle adjustment assembly carried by the driven portion; and a support carried by the angle adjustment assembly for supporting a tool or workpiece of the machine tool, the support having a support reference plane which extends transversely with respect to the first rotational reference axis, wherein the angle adjustment assembly is operable to tilt the support reference plane relative to the first rotational reference axis in any direction.

2. A machine tool comprising: a machine base; and a rotary machine drive of claim 1 with its base portion mounted on the machine base in a non-adjustable location relative to the machine base.

3. A machine tool of claim 2 including a second rotary machine drive which comprises a second base portion and a second driven portion, with the second rotary machine drive being operable to rotate the second driven portion relative to the second base portion about a second rotational reference axis to control the orientation of the second driven portion relative to the second base portion about the second rotational reference axis, and the second base portion mounted on the machine base in a non- adjustable location relative to the machine base, with the second rotational reference axis arranged to be parallel to and spaced laterally from the first rotational reference axis.

4. A machine tool of claim 3, wherein the second rotary machine drive includes a second angle adjustment assembly carried by the second driven portion, and a second support carried by the second angle adjustment assembly for supporting a tool or workpiece of the machine tool, the second support having a second support reference plane which extends transversely with respect to the second rotational reference axis, wherein the second angle adjustment assembly is operable to tilt the second support reference plane relative to the second rotational reference axis in any direction.

5. A machine drive of claim 1 or a machine tool of any of claims 2 to 4, wherein the or each angle adjustment assembly comprises at least three actuators operable to vary the distance between the support and the driven portion at respective locations which are circumferentially distributed around the respective rotational reference axis.

6. A machine drive or a machine tool of claim 5, wherein the actuators are linear actuators.

7. A machine drive or a machine tool of claim 5 or claim 6, wherein the actuators are piezoelectric actuators.

8. A method of operating a rotary machine drive of any of claims 1 and 5 to 7 comprising sending control signals to the angle adjustment assembly to tilt the support reference plane relative to the first rotational reference axis of the rotary machine drive.

9. A method of operating a machine tool of any of claims 2 to 7 comprising the steps of: receiving distortion signals in a controller of the machine tool which are responsive to distortion of the machine base; and determining with the controller control signals to send to the angle adjustment assembly in order to compensate for the distortion of the machine base.

10. A method of claim 9 including the step of: determining with the controller drive control signals to send to drives of the machine tool which are adjusted in order to compensate, in combination with the control signals to send to the angle adjustment assembly, for the distortion of the machine base.

11. A method of operating a machine tool of any of claims 2 to 7 comprising the step of: determining with a controller of the machine tool control signals to send to the angle adjustment assembly in order to compensate for predicted positioning errors occurring in the machine tool.

12. A method of claim 9 or claim 10 wherein the control signals sent to the angle adjustment assembly are also adjusted to compensate for predicted positioning errors occurring in the machine tool.