GB1570954A - Micromeasuring device - Google Patents

Description

(54) MICROMEASURING DEVICE (71) We, MICROLEC S.A., a Swiss Company, of 24, route de Beaumont, 1701 Fribourg, Switzerland do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a micromeasuring device for detecting deviation of the position of a surface from a desired range of positions defined between two closely adjacent limit positions. Such a device finds particular application, for example, in detecting very small changes of position of a mechanical component or in checking an actual dimension of a mechanical component against a required dimension.

According to the present invention, there is provided a micromeasuring device for detecting deviation of the position of a surface from a desired range of positions defined between two closely adjacent limit positions, which device comprises a detection head including first and second pairs of photoreceivers, illumination means for illuminating the photoreceivers, and means whereby the relative illumination of the photoreceivers of each pair varies in response to variation in the position of the said surface with respect to the head; and electronic circuitry including first and second trigger circuits connected to the first and second pairs of photoreceivers respectively and a gate connected to the trigger circuits, each trigger circuit receving a signal representing the difference in the illuminations of the photoreceivers of the associated pair, the trigger circuits delivering respective indicating signals when the position of the surface lies outside the said range on respective sides of the range, and the gate delivering an indicating signal when the surface lies within the range.

In one embodiment of the invention a window is interposed between the illumination means and the photoreceivers and a movable feeler for contacting the surface whose position is to be detected, the feeler carrying a mask interposed between the window and the illumination means for varying in opposite senses the illumination of the photoreceivers of each pair in dependence on the position of the feeler.

Another embodiment of the invention comprises first light conducting means for illuminating one photoreceiver of each pair directly from the illumination means second light conducting means for illuminating from the illumination means the surface whose position is to be detected, and third light conducting means for illuminating the other photoreceiver of each pair with light reflected from the said surface whereby to vary the illumination of the said other photoreceivers of the pairs in dependence on the position of the surface.

Preferably, differential electronic circuitry includes three signalling devices respectively connected to the two trigger circuits and the gate.

The differential electronic circuitry may include an electrical measuring instrument differentially connected to the output of the photoreceivers of one pair.

In order that the invention may be readily understood, embodiments thereof will now be described, by way of example, with reference to the accompanying drawings wherein: FIGURES 1 and 2 are cross-sectional views of a first detection head for a device embodying the invention, provided with a mechanical feeler; FIGURE 3 shows an electronic circuit which is connected to the detection head; FIGURE 4 is a cross-sectional view of a second detection head for a device embodying the invention, provided with an optical feeler; FIGURE 5 illustrates the arrangement of the optical fibres included in the detection head of Figure 4; and FIGURE 6 is an electrical diagram of a position follower device embodying the invention.

Referring to Figures 1 and 2, a detection head comprises a box 1 of general parallelepipedal shape extended by two coaxial tubular portions 2 and 3, one above and the other below the box. Four photoreceivers 11-14 disposed at the corners of a square are mounted on a back wall of the box as seen in Figures 1 and 2. A fixed diaphragm, having a window divided into two rectangular slots 4, 4' with a height slightly less than the photoreceiver diameter, is disposed in front of the photoreceivers. The top and bottom ends 4a, 4'a and 4b, 4'b of the slots 4, 4' are aligned with the centres of the photoreceivers 11, 12 and the photoreceivers 13, 14 respectively.

A control rod 5 is slidable in the tubular parts 2 and 3 and terminates in a hemispherical contact 6. A movable opaque mask 7 of rectangular shape is fixed on the rod 5 and its height is slightly less than the height of the slots of the fixed diaphragm. A guide member 8, in the form of parallelepipedal block, is connected to rod 5. With the interposition of a film of grease, it slides on an erect surface 9 of the back wall of the box. A spring 10 holds the contact 6 in contact with a component 15 under inspection. An assembly comprising four lamps 21-24, for respectively illuminating photoreceivers 11-14 through the gaps between the edges of slots 4, 4' and the edges of the mask 7, and an electronic circuit are mounted on a printed circuit board 30. Board 30 is attached to the box by means of screws (not shown) screwed into tapped holes 18 formed in the corners 19 of the box.A connector 27 at the back surface of the box enables the illuminating lamps 21-24 and the electronic circuit 30 to be supplied with current. The box is closed by a lid 16, the top of which is clasped to the box and the bottom of which is attached to the box by means of screws 17.

A needle ammeter 20 with a centre zero and three signalling lamps 25, 25' and 26 are mounted on the lid.

The electronic circuit of board 30 is shown in Figure 3. It comprises first and second trigger circuits for respectively comparing the illuminations of the pairs of the photoreceivers 11, 14 and 12, 13, and a NAND gate 350.

In the first trigger circuit, the photoreceivers 11 and 14 are connected in series with one another and with two resistors 303, 304 of the same value between the leads 301 and 302 of the power supply line. The potential of the common point 300 of the two photoreceivers can be controlled by means of the potentiometer 305. The common point 300 is connected to the inverting input of an operational amplifier 307 via a resistor 308 and the non-inverting input of this amplifier is connected to the slider of a potentiometer 306 connected between leads 301, 302. The gain of amplifier 307 is controlled by means of a variable resistor 309. The output of the operational amplifier 307 is connected in one position of a switch 310, to a bistable circuit 311, such as a Schmitt trigger.The Q output 311, of this trigger is connected via a resistor 312 to an amplifier transistor 313 in the collector circuit of which the signalling lamp 25 is connected.

In a second position, the switch 310 connects the output of amplifier 307 via a resistor 314. to the centre-zero micro-ammeter which is connected between leads 301, 302.

Two diodes 316 and 317 are connected in opposite directions between the inputs of amplifier 307 to limit the input voltage in the two directions, positive and negative.

The Q output 3112 of the trigger circuit 311 is connected to one input of the NAND gate 350, the output of which is connected via a resistor 351 to the base of an amplifier transistor 352 in the emitter circuit of which is disposed the signalling lamp 26.

Potentiometers 305 and 306 permit setting of the value and the direction of the voltage difference between both inputs of amplifier 307 for a predetermined relative value of illumination reaching photoreceivers 11 and 14, i.e. for a reference position of mask 7 (Figures 1-2) and consequently for a reference position of rod 5. Potentiometer 315 enables the ammeter 20 to be set to zero for said reference position.

The second trigger circuit includes substantially the same components as the first trigger circuit hereinbefore described and its components are denoted by the same reference numerals as the corresponding components of the first circuit, followed by the prime sign. Nevertheless, in said second trigger circuit: - there is no switch such as 310 and the output of amplifier 307' is directly connected to the input of trigger 311 l; - there is no ammeter such as 20; - the Q output 31111 of trigger 3111 is connected to the base of transistor 313' via the resistor 312' while the other Q output 31121 is connected to the other input of NAND gate 350.

By means of potentiometers 305, 306, 305' and 306', it is consequently possible to obtain the following states of signalling lamps 25, 25' and 26 in dependence on the position of rod 5 relative to the reference position: - when the rod 5 is set in a position over an upper limit that corresponds to a predetermined indication of ammeter 20, both triggers 311 and 311' are in state 1, lamp 25 is "on", lamp 25' is "off"; - when the rod 5 is set in a position under a lower limit that corresponds to another predetermined indication of ammeter 20, both triggers 311 and 311' are in state 0, lamp 25 is "off", lamp 25' is "on" and lamp 26 is "off";; - when the rod 5 is set between said limits, trigger 311 is in state 0, trigger 311' is in state 1, both lamps 25 and 25' are "off" and lamp 26 is "on be "on". that the symmetrical It should mounting of the pairs of photoreceivers associated with the same trigger circuit with respect to the centre of the square formed by the four photoreceivers makes the device insensitive to mechanical play of the rod 5 in the transverse direction, which does not affect the illumination differences of the photoreceivers of a pair, and any play due to flexure of the rod 5 resulting in an oblique position of the mask 7.Such oblique position would in fact cause variations of the illumination of the photoreceivers 11 and 14 on the one hand, and 12 and 13 on the other hand, in the same sense, but these variations cancel one another out since it is their difference which forms the input signal of each trigger circuit.

Figure 4 shows a dimensional inspection apparatus with an optical head without a slidable control rod.

An illuminating lamp 55, a mirror 56 inclined ar 45Q to the beam emitted by the lamp, and four photoreceivers 51-54 are disposed in a box 50. The mouthpieces of a number of bunches of optical fibres 62, 64 and 70 are disposed at the location of the image of the lamp in relation to the mirror, the bunches 62, 64 constituting first light conducting means for illuminating photoreceivers 52 and 54 directly from lamp 55.

By way of example, the bunches of fibres 62 and 64 each comprise two fibres and the bunch 70 comprises eight fibres. The bunches of fibres 62 and 64 are bent and their ends are fixed to a bar 58 and are situated opposite and near the photoreceivers 52 and 54. The bunch of fibres 70 constitutes second light conducting means for illuminating the surface of component 15 from lamp 55. The bunch of fibres 70 passes through the hollow rod 57 and terminates in the end section plane 59 thereof. Two bunches 61 and 63 each of two optical fibres lead from this end section plane 59 and terminate opposite and near the photoreceivers 51 and 53, their ends being held by the bar 58. The bunches 61, 63 constitute third light conducting means for illuminating photoreceivers 51,53 with light reflected from component 15.

The two photoreceivers 52 and 54 are mounted on an assembly 60, the position of which can be adjusted by means of the screw 65 so that the spacing between the ends of the bunches of fibres 62 and 64 and the photoreceivers 52 and 54 can be adjusted. A diaphragm 66 formed with apertures can be inserted into the assembly 60 in order suitably to adjust the beams of light falling on the photoreceivers 52 and 54 in dependence on the coefficient of reflection of the component 15 under inspection.

A connector 67 situated on the back surface of the box enables the lamp 55 and the electronic circuit 30 to be supplied with power.

Figure 5 shows the end plane 59 of the optical feeler. It will be seen that the ends of the fibres of bunch 70 for illuminating the component 15 form a circle surrounding the ends of the fibres of the bunches 61 and 63 which are arranged at the corners of a square.

The light picked up by the fibres 61 and 63 and, hence, the illumination of the cells 51 and 53, depend on the distance d between the end of the rod of the optical feeler and the surface of the component 15.

The optical detection head described above is used with the electronic circuit of Figure 3. It suffices merely to substitute the photoreceivers 51, 53, 52 and 54 respectivelyforphotoreceivers 11,12,13 and 14in said circuit. When the distance d increases, the light reaching photoreceivers 52 and 54 does not vary but the light reaching photoreceivers 51 and 53 decreases.

Figure 6 illustrates apparatus for very accurately positioning a component, e.g. a cutting tool. Tool 80 is positioned in respect of translatory movements by a motor 81, which will be assumed to be a diphase motor, and is driven in rotation by means of a motor 82. Motor 81 drives a micrometer screw 83 which displaces the tool 80 and motor 82 in a given direction, e.g. vertically. The position of the head of the tool 80 is to follow the position of the mechanical contact 6 or the position of the optical contact 59. The electronic circuit is the same as in Figure 3 except that the lamps 25, 25' and 26 can be omitted and that windings of relays 85,85' and 86 are provided respectively in the collector circuits of the transistors 313 and 313' and in the emitter circuit of transistor 352.Motor 81 is powered by an a.c. supply 84 via a switch 860 controlled by relay 86 and either of the two switches 850 or 850' respectively controlled by relay 85 or 85'. A capacitor 87 is connected between the two windings of the diphase motor 81 as is conventional. Motor 81 drives the micrometer screw 83 which drives a platform 88 which is prevented from rotating and on which the motor 82 and a reduction gear 89 are mounted, reduction gear 89 bearing the tool 80.

It will be apparent that depending upon whether lamp 25 or lamp 25' is illuminated motor 81 will rotate in one or other direction and is stopped when the lamp 26 is illuminated as a result of the switch 860 opening.

The photoreceivers used in the circuit according to Figure 3 are preferably phototransistors or photodiodes and the illumination lamps are preferably electroluminescent diodes.

WHAT WE CLAIM IS: 1. A micromeasuring device for detecting deviation of the position of a surface from a desired range of positions defined between two closely adjacent limit positions, which device comprises a detection head including first and second pairs of photoreceivers, illumination means for illuminating the photoreceivers, and means whereby the relative illumination of the photoreceivers of each pair varies in response to variation in the position of the said surface with respect to the head; and electronic circuitry including first and second trigger circuits connected to the first and second pairs of photoreceivers respectively and a gate connected to the trigger circuits, each trigger circuit receiving a signal representing the difference in the illuminations of the photoreceivers of the associated pair, the trigger circuits delivering respective indicating signals when the position of the surface lies outside the said range on respective sides of the range, and the gate delivering an indicating signal when the surface lies within the range.

2. A device according to claim 1, comprising a window interposed between the illumination means and the photoreceivers and a movable feeler for contacting the surface whose position is to be detected, the feeler carrying a mask interposed between the window and the illumination means for varying the illumination of the photoreceivers of each pair in dependence on the position of the feeler.

3. A device according to claim 2, wherein the window is divided into two slots and the photoreceivers forming a pair are disposed at opposite ends of different slots.

4. A device according to claim 1, comprising first light conducting means for illuminating one photoreceiver of each pair directly from the illuminating means, second light conducting means for illuminating from the illumination means the surface whose position is to be detected, and third light conducting means for illuminating the other photoreceiver of each pair with light reflected from the said surface whereby to vary the illumination of the said other photoreceivers of the pairs in dependence on the position of the surface.

5. A device according to any preceding claim, wherein the electronic circuitry includes three signalling devices respectively connected to the two trigger circuits and the gate. A 6. A device according to any preceding claim, wherein the electronic circuitry includes an electrical measuring instrument differentially connected to the output of the photoreceivers of one pair.

7. A micromeasuring device substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.

8. A micromeasuring device substantially as hereinbefore described with reference to Figures 3 to 5 of the accompanying drawings.

9. Apparatus for positioning a component, including a micromeasuring device according to claim 7 or 8 and substantially as hereinbefore described with reference to Figure 6 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. The photoreceivers used in the circuit according to Figure 3 are preferably phototransistors or photodiodes and the illumination lamps are preferably electroluminescent diodes. WHAT WE CLAIM IS:

1. A micromeasuring device for detecting deviation of the position of a surface from a desired range of positions defined between two closely adjacent limit positions, which device comprises a detection head including first and second pairs of photoreceivers, illumination means for illuminating the photoreceivers, and means whereby the relative illumination of the photoreceivers of each pair varies in response to variation in the position of the said surface with respect to the head; and electronic circuitry including first and second trigger circuits connected to the first and second pairs of photoreceivers respectively and a gate connected to the trigger circuits, each trigger circuit receiving a signal representing the difference in the illuminations of the photoreceivers of the associated pair, the trigger circuits delivering respective indicating signals when the position of the surface lies outside the said range on respective sides of the range, and the gate delivering an indicating signal when the surface lies within the range.

2. A device according to claim 1, comprising a window interposed between the illumination means and the photoreceivers and a movable feeler for contacting the surface whose position is to be detected, the feeler carrying a mask interposed between the window and the illumination means for varying the illumination of the photoreceivers of each pair in dependence on the position of the feeler.

3. A device according to claim 2, wherein the window is divided into two slots and the photoreceivers forming a pair are disposed at opposite ends of different slots.

4. A device according to claim 1, comprising first light conducting means for illuminating one photoreceiver of each pair directly from the illuminating means, second light conducting means for illuminating from the illumination means the surface whose position is to be detected, and third light conducting means for illuminating the other photoreceiver of each pair with light reflected from the said surface whereby to vary the illumination of the said other photoreceivers of the pairs in dependence on the position of the surface.

5. A device according to any preceding claim, wherein the electronic circuitry includes three signalling devices respectively connected to the two trigger circuits and the gate. A

6. A device according to any preceding claim, wherein the electronic circuitry includes an electrical measuring instrument differentially connected to the output of the photoreceivers of one pair.

7. A micromeasuring device substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.

8. A micromeasuring device substantially as hereinbefore described with reference to Figures 3 to 5 of the accompanying drawings.

9. Apparatus for positioning a component, including a micromeasuring device according to claim 7 or 8 and substantially as hereinbefore described with reference to Figure 6 of the accompanying drawings.