STEADY REST

Abstract

In a steady rest (1) for centring a rotationally symmetrical workpiece (2) in relation to a longitudinal axis of a processing machine, consisting of, two housing shells (4, 5) arranged at a distance from one another and firmly connected together, an actuating piston (7) mounted in an axially moving arrangement in the housing shells (4, 5) for generating a clamping force (3) which acts on the workpiece (2), with three steady rest arms (8, 9, 10) in a driving connection with the actuating piston (7) mounted in the two housing shells (4, 5), by means of which the workpiece (2) is clamped at three positions spaced apart, in which case the two outer steady rest arms (8, 9) are held in a swiveling arrangement on the housing shells (4, 5) about a bearing pin (11),
the clamping forces actually occurring on the steady rest arms (8, 9, 10) should be registered reliably.

This is achieved in that a force measuring device (21) is provided on at least one of the two outer steady rest arms (8, 9), by means of which the clamping force (3) of the particular outer steady rest arm (8, 9) is registered during the clamped condition and passed onto an evaluation device (22).

Claims

1. A steady rest for centring a rotationally symmetrical workpiece in relation to a longitudinal axis of a processing machine, consisting of: two housing shells arranged at a distance from one another and firmly connected together, an actuating piston mounted in an axially moving arrangement in the housing shells for generating a clamping force which acts on the workpiece, with three steady rest arms in a driving connection with the actuating piston mounted in the two housing shells, by means of which the workpiece is clamped at three positions spaced apart, in which case the two outer steady rest arms are held in a swiveling arrangement on the housing shells about a bearing pin, characterised in that, a force measuring device is provided on at least one of the two outer steady rest arms, by means of which the clamping force of the particular outer steady rest arm is registered during the clamped condition and passed onto an evaluation device.

2. The steady rest in accordance with claim 1, characterised in that, the force measuring device consists of one of the bearing pins that is configured as a force measuring shaft about which the particular outer steady rest arm is swiveled within a predefined angle range and of at least one strain gauge assigned to the force measuring shaft.

3. The steady rest in accordance with claim 2, characterised in that, the force measuring axis has at least one circumferential groove in which at least one of the strain gauges is arranged, and that the corresponding strain gauge is linked electrically by means of cables to the evaluation device.

4. The steady rest in accordance with claim 3, characterised in that, one or more blind holes is/are worked into the circumferential groove and that the strain gauges are arranged on the side wall and/or the base of the blind hole.

5. The steady rest in accordance with claim 1, characterised in that, a roller is provided on one or both of the free ends of the outer steady rest arms where it is mounted in a rotating arrangement, and that the bearing shaft of the roller is configured as a force measuring device is.

6. The steady rest in accordance with claim 5, characterised in that, the bearing shaft is configured as a force measuring shaft with at least one circumferential groove worked into it, and that at least one strain gauge is arranged in the groove and is connected to the evaluation device by means of electrical cables.

7. The steady rest in accordance with claim 6, characterised in that, at least one blind hole is worked into the corresponding groove and that the particular strain gauge(s) is or are arranged on the wall and/or base of the blind hole.

8. The steady rest in accordance with claim 1, characterised in that, at least one strain gauge is arranged on one of the two outer steady rest arms and is connected to the evaluation device by means of electrical cables and that the strain gauge(s) is or are arranged on the outside of the particular steady rest arm.

9. The steady rest in accordance with claim 8, characterised in that, a groove is worked into one of the outer steady rest arms and that the corresponding strain gauge is arranged on the wall and/or the base of the groove.

10. The steady rest in accordance with claim 2, characterised in that, the corresponding strain gauge is located in the area of the force profile and is aligned in parallel with it.

11. The steady rest in accordance with claim 2, characterised in that, the axial advance force of the actuating piston is registered by means of one or more sensors and that the evaluation device establishes a mathematical or physical relationship between the axial clamping force and the force measuring values registered by the particular strain gauges.

12. The steady rest in accordance with claim 2, characterised in that, the electrical cables of the corresponding strain gauge are coupled to a socket by means of a plug in a releasable arrangement and that the socket is connected to the evaluation device by means of additional electrical cables.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawing shows three sample embodiments of a steady rest configured in accordance with the present invention, the details of which are explained below. In the drawing,

[0020] FIG. 1 shows a steady rest with a housing comprising two housing shells on which three steady rest arms are mounted in a swiveling or axially moving arrangement and in which an actuating piston is located in a driving arrangement with the three steady rest arms, and a bearing pin is provided on one of the two outer steady rest arms which is configured as a force measuring shaft,

[0021] FIG. 2 shows the steady rest in accordance with FIG. 1 with a schematically shown force profile between the clamping position of a workpiece and the force transmission between the outer steady rest arm and the actuating piston,

[0022] FIG. 3 shows a section in accordance with FIG. 1 along the section line III-III through the measuring shaft device as well as an electric coupling,

[0023] FIG. 4 shows the steady rest in accordance with FIG. 1 with a roller shaft attached to one of the free ends of the outer steady rest arms which serves as a force measuring shaft,

[0024] FIG. 5 shows a section along the section line V-V in accordance with

[0025] FIG. 4,

[0026] FIG. 6 shows a steady rest in accordance with FIG. 1 with a force measuring device attached to one of the outer steady rest arms, in a perspective view and

[0027] FIG. 7 shows a magnified view of the force measuring device in accordance with FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] FIG. 1 shows a steady rest 1 by means of which a rotationally symmetrical workpiece 2 is to be held centrally in the space by means of a clamping force. Steady rests 1 of this kind are intended to hold the workpieces 2 as coaxially as possible with a longitudinal axis of a machine tool that is not illustrated. Often, such workpieces 2 are shafts with a long length which are provided for an electric motor, for example, and are machined by the machine tool. During the machining process, significant processing forces are applied to the particular workpiece 2, with the effect that it is pressed out of the required position not only under its own weight but also by means of the machining forces. Furthermore, the workpieces 2 are rotated for the purpose of machining them, meaning that additional centrifugal forces apply which are also to be supported by the steady rest 1

[0029] The steady rest 1 consists of two housing shells 4, 5 in which a guide slide 6 firmly attached to an actuating piston 7 is mounted in an axially moving arrangement. The direction of movement of the actuating piston 7 is at right angles to the longitudinal axis of the workpiece 2. The guide slide 6 largely has a triangular contour in the cross-section and both outer legs of the guide slide 6 are configured as a control cam 6′. The actuating piston 7 can be moved axially by mechanical or electrical driving means, and generates an axial clamping force 7′.

[0030] Furthermore, two outer steady rest arms 8, 9 and a middle steady rest arm 10 are allocated to the steady rest 1, by means of which the workpiece 2 is clamped. The middle steady rest arm 10 carries out an axial advance movement, because it is directly attached to the actuating piston 7.

[0031] The two outer steady rest arms 8, 9 are mounted in a swiveling arrangement by means of a bearing pin 11 on the housing shells 4, 5 of the steady rest, and thus carry out a swiveling movement on the workpiece 2 when this is to be clamped, or move away from it when the machining procedure for the workpiece 2 has been completed and it should be removed from the machine tool, because the free ends of the steady rest arms 8, 9 running within the housing shells 4, 5 make contact with the control cam 6′ and are thus in a permanent, active connection with it.

[0032] In accordance with FIG. 2, one of the bearing pins 11 of the second steady rest arm 9 is configured as a force measuring shaft 12. The force measuring shaft 12 as well as strain gauges 23 attached to it form a force measuring device 21 that is connected to an evaluation device 22 by means of one or more electrical cables 50.

[0033] FIG. 3 shows the detailed design of the force measuring shaft 12 in which two circumferential grooves 13 are worked that are to be regarded as weak points in the force measuring shaft 12. The clamping forces transmitted by the force measuring shaft 12 give rise to the effect in the area of the particular groove 13 that the force measuring shaft 12 is compressed or stretched. Moreover, one or more blind holes 14 can be worked into the corresponding groove 13, by means of which additional weak points or bending profiles are created in the force measuring shaft 12. The strain gauges 23 in this case can be attached either in the groove 13 or in the blind hole 14 and normally run parallel to the force profile in the force measuring shaft 12. The strain gauges 23 are connected by electrical cables 15 to a plug 16 which can be connected to a socket 17 outside the steady rest arm 9, in which case the socket 17 is connected to the evaluation device 22 by means of the electrical cables 15. As a result, the electrical signals generated by the strain gauges 23 can be registered directly and permanently, and evaluated accordingly, so that the corresponding operating status of the steady rest 1 can be digitalised and the clamping forces 3 actually occurring are registered and can be displayed. As a result of this, the corresponding machining processes can be measured precisely for each operating status and at any time, because they are registered directly by the force measuring shaft 12 and transferred to the strain gauges 23.

[0034] Normally, in accordance with FIG. 4, the free ends of both outer steady rest arms 8, 9 are equipped with a roller 18 which makes direct contact with the surface of the workpiece 2 to be clamped and which are connected to the corresponding steady rest arm 8 or 9 in a rotating arrangement by means of a roller shaft 19. The speed of rotation of the workpiece 2 is thus registered by the particular roller 18 which is in direct contact with the workpiece 2, with the effect that the clamping forces 3 actually prevailing act directly on the roller 18 or its roller shaft 19. One of the roller shafts 19 is replaced by the force measuring shaft 12 as shown in FIG. 5. A bearing 20 is provided between the steady rest arm 9 and the force measuring shaft 12. The force measuring shaft 12 once again has two circumferential grooves 13 each of which has one or more blind holes 14 into which one or more of the strain gauges 23 is/are attached at the wall or the base of the blind hole 14. The strain gauges 23 are connected via electrical cables 19 to a plug which can be connected to a socket 17 provided outside the roller.

[0035] FIGS. 6 and 7 show a further possibility for providing the strain gauges 23 between the force application at the workpiece 2 and the bearing shaft 11 of one of the two outer steady rest arms 8 or 9. In this case, the strain gauge 23 is attached to the outside of the steady rest arm 9. In the area of the strain gauge 23, it is possible to work a weak point into the steady rest arm 9 in the form of a groove or the like so as to increase the flexure of the steady rest arm 9 in this area of the strain gauge 23 and thus improve the measuring accuracy.