GB1601058A - Angle resolvers - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO ANGLE RESOLVERS (71) We, E M I LIMITED, a British company of Blyth Road, Hayes, Middlesex, 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: The present invention relates to angle resolvers, and it relates especially, though not exclusively, to such resolvers as may be used to continuously and accurately monitor the angular position of a rotatable member. In one particular example, the member constitutes the rotating head of a multi probe ultrasonic transducer used in a medical scanner.

It is an object of this invention to provide an angle resolver which is accurate and continuous in operation and which, in addition, is of the contactless form - i.e. requires no electrical connections to be made to the rotatabie member itself.

According to the invention there is provided an angle resolver for monitoring the rotation of a rotatable member, the resolver comprising poiarised material arranged to rotate with the member, first and second light paths traversing respective portions of said material and respective further polarised material placed in each of said paths and fixed relative to said paths, the directions of polarisation of said firstmentioned polarised material and of said other polarised material being such that the intensities of light traversing said first and second light path vary in phase quadrature with one another when said member rotates.

In order that the invention may be clearly understood and readily carried into effect, one embodiment thereof will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a schematic view of a resolver in accordance with one example of the invention, and Figure 2 shows, in side view, a practical embodiment of a resolver in accordance with the invention.

Referring now to Figure 1, a disc 1 of polarised material is constrained to rotate with a member (not shown) the rotation of which is to be monitored, and the disc 1 is geared to rotate at one half of the speed of the member. The material of the disc 1 is polarised in the direction indicated by the parallel dashed lines, such as 2, drawn thereon.

Two smaller, fixed discs 3 and 4,.also of polarised material, are juxtaposed with the larger disc 1 and the directions of polarisation of the two smaller discs are offset from each other by 45 , as indicated by the chain-dotted lines such as 5 and 6 respectively. Light paths, as indicated by the circles 7 and 8 are caused to traverse the discs 1, 3 and 1, 4 respectively; the light being detected in each case by a respective photocell (not shown). It will be appreciated that, as the disc 1 rotates, its direction of polarisation will change relative to those of the fixed discs 3 and 4, and that these changes of relative polarisation directions will influence the intensity of the light transmitted to the photocells via paths 7 and 8.

If it is assumed that the rotation starts with disc 1 in the position shown in the drawing, i.e. with its direction of polarisation aligned with that of the disc 3, then at the starting point the photocell associated with light path 7 (the one via discs 1 and 3) will receive light of maximum intensity whereas the photocell associated with light path 8 will receive light the intensity of which is intermediate between maximum and minimum values, because there is a 45" misalignment between the polarisation directions of the discs 1 and 4. Clockwise rotation of the disc 1 causes its direction of polarisation to align to a greater extent with that of disc 4 and to a lesser extent with that of disc 3. Correspondingly the intensity of the light transmitted to the photocell associated with the path 8 increases while that transmitted to the photocell for path 7 decreases.

This state of affairs persists until the disc 1 has rotated through 45" when its direction of polarisation is exactly aligned with that of disc 4. Further rotation beyond 45" tends to reduce the intensity of light transmitted along both paths 7 and 8 until the disc 1 has rotated through 90 , when the intensity of light transmitted along path 7 reaches a minimum value.

Further rotation of disc 1 causes the light detected by the two photocells to continue to fluctuate in phase quadrature with one another; a full cycle of the fluctuations, which are of sine and cosine nature respectively, occurring during one half of a revolution of the disc 1.

The electrical output signals produced by the photocells during continuous rotation of the disc 1 can be used in known manner to identify unambiguously, at any time, the angular position of the member, bearing in mind the 2 : 1 gearing that exists between the member and the disc 1.

Figure 2 shows, schematically and in side view, one embodiment of a resolver in accordance with the invention. A rotatable member is shown in part at 9 and it carries a plurality (typically four) of ultrasonic transducer heads (not shown). The member 9 is rotated in conventional manner by means which are not shown. The member 9 is formed with a protruding shaft 10 which carries a gear 11 arranged to mesh with a gear 12 carried upon a shaft 13 secured to the central hub of the disc member 1 (c.f. Fig. 1). The shafts 10 and 13 rotate in suitable bearings 14, 15 and 16, 17 respectively formed in a fixed frame member 18. Frame member 18 also supports two light sources 19 and 20 and two co-operating photocells, 21 and 22 respectively. The sources 19 and 20 and the photocells 21 and 22 define the light paths 7 and 8 described in relation to Figure 1. In this example, the fixed discs 3 and 4 of polarised material are disposed directly upon the front surfaces of the photocells 21 and 22, this being particularly advantageous as, provided the photocells are approximately mounted in the frame member 18, initial adjustments of relative orientation can be effected by merely rotating the photocells in their holders. For this purpose the rear ends of the photocell housings can advantageously be formed with curfs as at 23 and 24, to enable the rotation to be effected with the aid of a screwdriver.

WHAT WE CLAIM IS:- 1. An angle resolver for monitoring the rotation of a rotatable member, the resolver comprising polarised material arranged to rotate with the member, first and second light paths transversing respective portions of said material and respective further polarised material placed in each of said paths and fixed relative to said paths, the directions of polarisation of said first-mentioned polarised material and of said other polarised material being such that the intensities of light traversing said first and second light path vary in phase quadrature with one another when said member rotates.

2. A resolver according to Claim 1 wherein the directions of polarisation of the further polarised material in said first and second light paths are inclined at 43 to one another.

3. A resolver according to either of Claims 1 or 2 including a reduction gearing of 2:1 in the rotary drive coupling said first-mentioned polarised material to said rotatable member.

4. A resolver according to any one of Claims 1-3 wherein the further polarised material in said first and second paths comprise material deposited on or secured to respective photodetecting means, said photo-detecting means being mounted for relative rotation.

5. An angle resolver substantially as herein described with reference to the accompanying drawings.

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

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. detected by the two photocells to continue to fluctuate in phase quadrature with one another; a full cycle of the fluctuations, which are of sine and cosine nature respectively, occurring during one half of a revolution of the disc 1. The electrical output signals produced by the photocells during continuous rotation of the disc 1 can be used in known manner to identify unambiguously, at any time, the angular position of the member, bearing in mind the 2 : 1 gearing that exists between the member and the disc 1. Figure 2 shows, schematically and in side view, one embodiment of a resolver in accordance with the invention. A rotatable member is shown in part at 9 and it carries a plurality (typically four) of ultrasonic transducer heads (not shown). The member 9 is rotated in conventional manner by means which are not shown. The member 9 is formed with a protruding shaft 10 which carries a gear 11 arranged to mesh with a gear 12 carried upon a shaft 13 secured to the central hub of the disc member 1 (c.f. Fig. 1). The shafts 10 and 13 rotate in suitable bearings 14, 15 and 16, 17 respectively formed in a fixed frame member 18. Frame member 18 also supports two light sources 19 and 20 and two co-operating photocells, 21 and 22 respectively. The sources 19 and 20 and the photocells 21 and 22 define the light paths 7 and 8 described in relation to Figure 1. In this example, the fixed discs 3 and 4 of polarised material are disposed directly upon the front surfaces of the photocells 21 and 22, this being particularly advantageous as, provided the photocells are approximately mounted in the frame member 18, initial adjustments of relative orientation can be effected by merely rotating the photocells in their holders. For this purpose the rear ends of the photocell housings can advantageously be formed with curfs as at 23 and 24, to enable the rotation to be effected with the aid of a screwdriver. WHAT WE CLAIM IS:-

1. An angle resolver for monitoring the rotation of a rotatable member, the resolver comprising polarised material arranged to rotate with the member, first and second light paths transversing respective portions of said material and respective further polarised material placed in each of said paths and fixed relative to said paths, the directions of polarisation of said first-mentioned polarised material and of said other polarised material being such that the intensities of light traversing said first and second light path vary in phase quadrature with one another when said member rotates.

2. A resolver according to Claim 1 wherein the directions of polarisation of the further polarised material in said first and second light paths are inclined at 43 to one another.

3. A resolver according to either of Claims 1 or 2 including a reduction gearing of 2:1 in the rotary drive coupling said first-mentioned polarised material to said rotatable member.

4. A resolver according to any one of Claims 1-3 wherein the further polarised material in said first and second paths comprise material deposited on or secured to respective photodetecting means, said photo-detecting means being mounted for relative rotation.

5. An angle resolver substantially as herein described with reference to the accompanying drawings.