GB2037431A

GB2037431A - Correcting errors in measuring machines

Info

Publication number: GB2037431A
Application number: GB7939229A
Authority: GB
Original assignee: Werkzeugmaschinenkombinat Fritz Heckert VEB
Current assignee: Werkzeugmaschinenkombinat Fritz Heckert VEB
Priority date: 1978-11-14
Filing date: 1979-11-13
Publication date: 1980-07-09
Also published as: CH646086A5; DD142522B1; FR2441462A1; DD142522A1; FR2441462B1; GB2037431B; HU186730B; DE2935056A1; CS231556B1

Abstract

Geometrical errors in a translational measuring system 12 of a coordinate machine are corrected by transmitting relative movements to a measuring head 11, correction values being produced by adjusting the position of a translationally movable ruler 10 and causing the adjustments to be modified and transmitted to the head 11. The correcting apparatus comprises a base plate 1 and vertical pairs of leaf springs 4, 5, arranged respectively between the base 1 and a top plate 2, and the plates 2, 3. A lever 8 having a roller 6 is pivoted at 14 to the plate 3 and moves according to the corrections set by the ruler 10 and transmits these corrections via a further roller 7 on a pivot 9 to give a relative movement to the head 11 by deflecting the springs 4, 5 and through them the plates 2, 3 supporting the head. <IMAGE>

Description

SPECIFICATION Apparatus for correcting geometrical machine errors along one or more measuring axes Electrical apparatuses for path measuring are known for mechanical electrical transducers, such as inductive, capacitative and ohmic transducers as disclosed in German Democratic Republic Patent Specification 30315, in which the mechanical electrical transducer is attached to a stiff spring and is disposed on a base element, with the interposition of a soft spring and with provision for fine adjustment via a known adjusting device, for example, a micrometer screw, and is combined with electric or electronic devices in conjunction with an indicating or recording means.

Such apparatuses are used more particularly for measuring the accuracy of test members or compensation measurements can be effected by the fine adjustment of the transducer, in which the indicating or recording means represents the zero indicator.

When translational measuring systems are used, it is impossible to correct a total machine error by means of such apparatuses, particuiarly in the case of high precision coordinate machines.

Automatic apparatuses are also disclosed in Offenlegungsschrift 1552409 for compensating screw-threaded spindle errors relating more particularly to compensating the temperature or thermal expansions of machine tool screwthreaded or guide spindles during operation.

Such automatic apparatus enables a system to be provided for the compensation of helix and thermal expansion errors in the case of screwthreaded spindles by means of an elongate cam, changing around a pivot, but are unable to correct a total machine error when translational measuring systems are used.

In general translational measuring systems are used for various measuring operations, more particularly for machine tools.

Apparatuses are also disclosed in Offenlegungsschrift 24 50 322 which compensate the thermal expansion of a tool slide. These apparatuses are essentially so orientated that the thermal expansion occurring during the machining operation can be absorbed and defined in correction values. This does not means that geometrical machine errors can be defined along one or more random measuring axes, as in the case of the invention. Apparatuses intended more particularly for compensating for errors in rotary tables are disclosed in Offenlegungsschrift 20 59 957. These correction apparatuses merely enable faults in the rotation of rotary tables to be corrected and cannot be applied in the manner according to the invention.

However, apparatuses for correcting geometrical errors along one or more random measuring axes when such measuring systems are used cannot be derived from the prior art on which research has been based.

It is an object of the invention to provide an apparatus for correcting geometrical machine errors along one or more random measuring axes when translational measuring systems are used for high precision coordinate machines, the correction values produced being transmitted by means of a translationally moved ruler to a measuring head of the translational measuring system, so that the measuring head can be given a well-defined deflection.

The disadvantages of the known apparatuses are due to the following causes: 1. Electric path measuring appratuses for mechanical electric transducers, such as inductive capacitative and ohmic transducers are used with known adjusting devices, such as micrometer screws. However, they do not enable a total machine error to be corrected when translational measuring systems are used for coordinate machines.

2. The automatic apparatuses known from the prior art relate to the compensation of helix and thermal expansion errors in screwthreaded spindles, more particularly permitting the compensation of temperature or thermal expansions. They can be used only in that field.

To obviate these disadvantages, it is an object of the invention to provide an apparatus for correcting geometrical machine errors along one or more random measuring axes with the use of translational measuring systems, the correction values produced being transmitted by means of a translationally moved ruler to a measuring head of the measuring system, thus producing a well defined deflection of the measuring head via the agency of particular mechanical means, preferably in high accuracy coordinate machines.

Accordingly, the present invention consists in an apparatus for correcting geometrical machine errors along one or more random measuring axes in the use of translational measuring systems for high accuracy coordinate machines, characterised in that disposed on a base plate in pairs are first leaf springs bearing on their top ends a top plate which supports a part, for example, a measuring head, of the translational measuring system, and disposed in pairs on the top plate are further leaf springs having smaller stiffness than that of the first leaf springs and bearing at their bottom end a plate receiving via pin mounted in the base plate a lever, which has a roller for taking over a correction value S, from a translationally moved ruler, and a further roller guided at a pivot which further roller is operatively connected to the lever so that the correction value Sr of the translationally moved ruler is transmittable to the further roller.

The correction value S, initiated by the translationally moved ruler via the further roller results in a deflection of the resilient strips of lower stiffness disposed in pairs, such deflection acting on the pivot to produce a deflection of the resilient strips of higher stiffness disposed in pairs and producing a required relative movement between a translationally moved measuring rod and the measuring head, disposed on the top plate, of the translational measuring system, such required relative movement corresponding to a correction value S2 between the translationally moved measuring rod and the measuring head.

This means that according to the invention the required relative movement is determined by a correction value S, which is associated as path information with the translationally moved ruler and which is passed on perpendicularly to the direction of advance via the lever mounted around a pivot or in some other way, accompanied by a transformation of correction value S, to the correction value S2.

This required relative movement corresponds according to the invention, for instance, to a transmission ratio which follows the mathematical relationship: S1:S2=1 40:1 where S, embodies the position-tied correction value of the translationally moved ruler and S2 embodies the correction value, transformed by 90",for the measuring head.

According to the invention the correction path required for the correction value S1 bears a substantially linear relation to the correction path of the correction value S2 of the measuring head.

The position-tied correction values S, and S2 can be stored by means of known devices, such as a correction ruler pivoted to the direction of advance.

Also according to the invention, however, a translationally moved ruler can be made up of a number of individual pieces which can be individually pivoted to the direction of advance, so that the correction zones are subdivided, or else a translationally moved ruler of lower rigidity can be used, which is paired with a supporting ruler of high rigidity, the remaining values to be corrected being adapted to an ideal correction curve which substantially minimises the residual errors.

The apparatus according to the invention substitutes for the known method of mechanically dealing with a correction ruler perpendicularly to the direction of advance for storing the required correction values S, the more advantageous method of adjusting a correction ruler continuously over the whole adjustment path, the correction ruler being attached to the supporting ruler by means of suitable attaching elements when adjustment has been performed.

In order that the invention may be more readily understood, reference is made to the accompanying drawings which illustrate diagrammatically and by way of example an embodiment thereof, and in which: Fig. 1 is an overall view of the apparatus, Fig. 2 is a cross-section on the line B-B of Fig.

1,and Fig. 3 is a cross-section on the line A-A of Fig.

1.

Referring to Fig. 1, the apparatus comprises a base plate 1 having disposed thereon in parallel and in a pair leaf springs 4 bearing at their top side a top plate 2 which supports a part, for example, a measuring head 11 of a translational measuring system 12.

Disposed in pairs on the top plate 2 are further leaf springs 5 of low stiffness bearing at their bottom end a further plate 3 receiving via pin 14 eccentrically mounted in the base plate 1 on the one hand a lever 8, which has a roller 6 taking over a correction value S, from a translationally moved ruler 10 and on the other hand a further roller 7 guided at a pivot 9 and operatively connected to the lever 8 so that a correction value S, of a translationally moved ruler 10 is transmitted to the further roller 7.

The correction value S, obtained via roller 6 from the translationally moved ruler 10 results in a deflection of the leaf springs 5 disposed in a pair, such deflection acting on the pivot 9 to produce a deflection of the leaf springs 4 of higher stiffness disposed in pairs and bringing about a required relative movement between a translationally moved measuring rod 13 and the measuring head disposed on the top late 2 of the translational measuring system 12. The translationally moved ruler 10 shown in Fig. 3 is on the one hand formed of a number of individual pieces, which can be pivoted to the direction of advance, being on the other hand a translationally moved ruler 10 of low rigidity, which is paired with a supporting ruler 15 of high rigidity or is constructed in some other manner.The position-tied correction values are taken over from the translationally moved ruler 10 by means of roller 6 and lever 8. In correspondence with an associated transmission ratio the lever 8 is connected to the pin 14, mounted fixed eccentrically in the base plate 1.

The roller 7 guided on the plate 3 at the pivot 9 transmits the correction value existing from the lever 8 via the pin 14, the roller 7 with the plate 2 being displaced at the same time in the direction of advance, the result being a translation of the correction value in the direction of advance, such displacement results in a deflection of the leaf springs 5 of lower stiffness which causes a deflection of the springs 4 of higher stiffness.

This puts into effect the principle, associated with the special arrangement, of the correction as between measuring rod and measuring head in accordance with the transmission ratio made possible by the invention and the resulting transmission of the correction values.

Claims

1. An apparatus for correcting geometrical machine errors along one or more random measuring axes in the use of translational measuring systems for high accuracy coordinate machines, characterised in that disposed on a base plate in pairs are first leaf springs bearing on their top ends a top plate which supports a part, for example, a measuring head of the translational measuring system, and disposed in pairs on the top plate are further leaf springs having smaller stiffness than that of the first leaf springs and bearing at their bottom end a plate receiving via a pin mounted in the base plate a lever, which has a roller for taking over a correction value S, from a translationally moved ruler, and a further roller guided at a pivot which further roller is operatively connected to the lever so that the correction value Sl of the translationally moved ruler is transmittable to the further roller.

2. An apparatus according to claim 1, wherein the correction value S1 transmitted from the translationally moved ruler via the roller to the further roller deflects the leaf springs of smaller stiffness arranged in pairs, such deflection causing a deflection of the first leaf springs of greater stiffness and a required relative movement is produced between a translationally moved measuring rod and the measuring head, disposed, for example, on the top plate of the translational measuring system, the required relative movement corresponding to a correction value S2 between translationally moved measuring rod and the measuring head.

3. An apparatus according to claim 1 or2, wherein the required relative movement is determined by a correction value S, which is associated as path information with the translationally moved ruler and which is passed on perpendicularly to the direction of advance via the lever or in some other way, the correction value S being simultaneously transformed to the correction value S2.

4. An apparatus according to any of the preceding claims, wherein the required relative movement between the translationally moved measuring rod and the measuring head, disposed on the top plate of the movable measuring system corresponds, for example, to a transmission ratio S:S=l 40:1 where S1 embodies the position-tied value of the translationally moved ruler and S2 embodies the correction value, transformed by 900, for the measuring head.

5. An apparatus according to claim 3, wherein the translationally moved ruler can store the position-tied correction values S1 in various ways, and on the one hand in addition to the known type of ruler pivoted to the direction of advance, the ruler can be made up of a number of coherent individual pieces which can be pivoted in the direction of advance, the correction range being thus subdivided, while on the other hand the correction ruler of low rigidity is used paired with a supporting ruler and very accurately approximated to the correction curve by means of suitable adjusting and clamping elements.

6. An apparatus for correcting geometrical machine errors along one or more random measuring axes, substantially as herein described with reference to and as shown in the accompanying drawings.