GB2098759A

GB2098759A - Apparatus for correcting misalignment

Info

Publication number: GB2098759A
Application number: GB8213003A
Authority: GB
Original assignee: LK TOOL CO Ltd
Current assignee: LK TOOL CO Ltd
Priority date: 1981-05-14
Filing date: 1982-05-05
Publication date: 1982-11-24

Abstract

A high accuracy dimensional measuring and checking machine comprises a bridge structure not shown carrying a measuring or checking device and movably arranged on parallel guideways (10, 12). In one embodiment level sensors (16, 18) are respectively operatively associated with the guideways (10, 12) and are operatively interconnected whereby one of the sensors (18) can produce a differential output signal indicative of any relative misalignment. The signal is applied to a servojack at A associated with the same guideway (12) whereby to reposition the guideway (12) to correct the misalignment. In alternative embodiments each guideway may be individually levelled by comparing each sensor with an external reference, or one may be so levelled which then becomes a reference for the other, or a sensor may be mounted on the bridge to control the guideways or to level the bridge directly. The alignment is automatically checked and corrected at intervals. <IMAGE>

Description

SPECIFICATION Apparatus for correcting misalignment The invention relates to apparatus for correcting misalignment of component parts and is particularly concerned with high accuracy measuring machines ofthetype having a bridge movable along parallel guideways.

In high accuracy machines for measuring and checking the dimensions of workpieces of the type where a bridge is movable along parallel guideways, it is essential that the guideways are aligned as accurately with one another as possible, and often the foundations on which the machine is supported are not sufficiently stable to maintain the required degree of accuracy of parallelism.

According to the present invention there is provided alignment correction apparatus comprising first and second component parts which are subject to forces capable of creating movement from a desired alignment, means for sensing the misalignment of the component parts, and means operable by the sensing means to correct the misalignment or make a compensating adjustment in relation to a third component part of the apparatus, which is affected by the misalignment of the first and second component parts.

Preferably the sensing means comprises a sensor associated with each of the first and second component parts, the sensors being operatively interconnected to produce differential signals for operating the correcting means. The latter may comprise a servo-jack controlling one of the first and second component parts.

Alternatively, the sensing means may comprise a sensor associated with each of the first and second parts, each sensor producing a signal indicative of misalignment with an external datum for operating the correcting means. In a modification, one of the sensors may produce a signal indicative of misalignment with the external datum and the other sensor may produce a signal indicative of misalignment with the component part having said one sensor.

The sensing means may further comprise a sensor associated with the third componenet part for producing a signal corresponding to misalignment between the the first and second component parts for controlling the compensating adjustment for the third componenet part.

Embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic view of part of a dimensional measuring apparatus according to one embodiment of the invention; Figure2 is a section through a feature of the apparatus of Figure 1; Figure 3 is a diagrammatic view of part of a measuring apparatus according to a second embodiment.

Figure 4 is a diagrammatic view similar to Figure 3 showing a third embodiment; Figure 5 is a diagrammatic view of a modificaton applicable to any of the embodiments; Figure 6 is a diagrammatic view of a measuring apparatus according to a fourth embodiment; and Figure 7 is a view similar to Figure 6 according to a fifth embodiment.

Referring to the drawings, Figure 1 shows parallel guideways 10, of a high accuracy dimensional measuring and checking machine. An electronic level sensor 16 is operatively connected with the guideway 10 and a furter electronic level sensor 18 is operatively associated with the guideway 12. The sensors 16, 18 are interconnected electrically and the sensor 18 is adapted to receive a signal from the sensor 16 and produce a differential output signal which is indicative of any relative misalignment.

Each of the guideways 10, 12 is supported at three points A, B, and C and the guideways 12 is supported at point A through a servo-jack (Figure 2). The differential output signal from the sensor 18 is applied to the servo-jack through an electrical interface and operation of the servo-jack can reposition the guideway 12 so asto correct the misalignment.

The servo-jack may be electro-mechanical or electro-hydraulic. In an electro-mechanical system as shown in Figure 2, the servo-jack comprises an electrical servo-motor 20 driving a recirculating ball screw 22 in a recirculating ball nut 24 through a worm gear box 25, the ball nut 24 being mounted on a lower face of the guideway 12. The servo-jack is suppoted on a foundation plate 26 through a ball thrust bearing 28. In an alternative electro-hydraulic system, the jack comprises an electrical servo-motor and metering pump with a changeover valve to reverse the jack direction, or a reversible pump may be provided. Alternatively, two pumps may be used one to lift and one to lower.

In the embodiment of Figure 3, the sensor 16 associated with the guideway 10 is in the form of an external datum sensor which can sense the deviation of the guideway 10 relative to an external dataum. The sensor 18 associated with the guideway 12 is also an external datum sensor and a deviation signal from each sensor is applied to a servo-jack associated with the respective guideway through an electrical interface to control the position of each guideway.

In the embodiment of Figure 4the guideway 10 is considered to define a master surface and the sensor 16 is an external datum sensor as in the Figure 3 embodiment. The sensor 18 is however electrically interconnected with the sensor 16 and produces a differential output signal dependent on misalignment with the master surface once this has been correctly aligned with the external datum. Each of the sensors operates a respective servo-jack to control the position of the respective guideway.

To prevent the sensors being influenced by elastic deflections of the guideways caused, for example, by a moving mass on the guideways, the sensors may be mounted on beams 30 which are mounted on the guideways through flexible mountings (Figure 5). Each mounting comprises a flexible anchor 31 and spring strips 32 which are in tension to support the beam.

Referring to the embodiment shown in Figure 6, where a bridge structure 34 is shown to be movably mounted on the guideways 10, 12, the guideways are provided with sensors as in the previous embodiments. In addition, a further independent electronic sensor 36 is provided in the bridge structure 34, preferably as a permanent feature of the machine, and this sensor 36 can set the initial setting of the other sensors and check that the system is operating correctly.

The machine according to the Figure 7 embodiment provides an electronic level sensor 38 in the bridge structure 34 as an alternative to the sensors associated with the guideways. This sensor 38 senses the deviations from alignment of the guideways 10,12 but, instead of correcting the deviations themselves, provides an output signal for operating a servo-jack 40 connected at the lower side of a leg 42 of the bridge structure 34. Vibrations can however affect the operation of the sensor 38 and therefore it is preferable to sense the misalignment at two or more points along the path of movement of the bridge structure 34 and then store the sensed information in a computer or micro-processor44 provided on the bridge structure 34. Linear interpolation can be used to determine the corrections to be applied at any other point in the path of movement.

All the calculations and signals are handled by the computer or microprocessor 44 which is provided with continuous information regarding the position of the bridge structure 34 on the guideways 10, 12 from a suitable transducer. The latter may form a permanent component of the machine. The information given to the computer or microprocessor 44 must be continuously updated at suitable intervals, say once per day or once per week.

The sensors may be subjected to external influences which may cuase the sensors to give false information, for example electronic level sensors are also sensitive to dynamic forces such as vibrations due to the operation of the apparatus itself, from adjacent machines, or from traffic, aircraft etc. To overcome this problem a timeswitch may be incorporated in the electrical circuit to enable the system to operate only at specific times when external influences are at a minimum.

Various modifications may be made without departing from the invention. For example, although the invention has been described in relation to a measuring machine it should be appreciated that it can be applied to many other types of machine where alignment between component parts is necessary.

Whilst endeavouring in the foregoing Specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to whether or not particular emphasis has been placed thereon.

Claims

1. Apparatus for correcting misalignment of component parts, said apparatus comprising first and second component parts which are subject to forces capable of creating movement from a desired alignment, means for sensing the misalignment of the component parts, and means operable by the sensing means to correct the misalignment or make a compensating adjustment in relation to a third component part of the apparatus, which is affected by the alignment of the first and second component parts.

2. Apparatus according to claim 1, wherein the sensing means comprises a sensor associated with each of the first and second component parts, the sensors being operatively interconnected to produce differential signals for operating the correcting means.

3. Apparatus according to claim 2, wherein the correcting means comprises a servo-jack controlling one of the first and second componenet parts.

4. Apparatus according to claim 1, wherein the sensing means comprises a sensor associated with each of the first and second parts, each sensor producing a signal indicative of misalignment with an external datum for operating the correcting means.

5. Apparatus according to claim 1, wherein the sensing means comprises a sensor associated with each of the first and second parts, one of the sensors producing a signal indicative of misalignment with an external datum and the other sensor producing a signal indicative of misalignment with the component part having said one sensor.

6. Apparatus according to claim 4 or 5, wherein the correcting means comprises a servo-jack controlling each of the first and second component parts.

7. Apparatus according to any of the preceding claims, wherein a sensor is associated with the third component part and is operatively connected with the other sensors for setting thereof.

8. Apparatus according to claim 1, wherein the sensing means comprises a sensor associated with the third componenet part to produce a signal indicative of misalignment of the first and second componenet parts for operating the compensating means

9. Apparatus according to claim 8, wherein the compensating means comprises a servo-jack controlling the adjustment of one of a pair of legs of the third component part by means of which the latter is supported on the first and second component parts.

10. Apparatus according to claim 8 or 9, wherein means is provided to prevent the operation of the sensor associated with the third component part being affected by vibrations of the apparatus.

11. Apparatus according to any of the preceding claims, wherein the first and second component parts comprise parallel guideways and the third component part comprises a bridge structure which is movably arranged on the guideways and carries a device for measuring or checking a workpiece.

12. Apparatus for correcting misalignment of componenet parts substantially as hereinbefore described with reference to the accompanying drawings.