EP2335027A1

EP2335027A1 - Optical coder

Info

Publication number: EP2335027A1
Application number: EP09783920A
Authority: EP
Inventors: Jean-Louis Bigand
Original assignee: Thales SA
Current assignee: Thales SA
Priority date: 2008-10-10
Filing date: 2009-10-09
Publication date: 2011-06-22
Also published as: WO2010040849A1; CN102209882B; CN102209882A; RU2507559C2; FR2937129A1; US20120126102A1; CA2740250A1; FR2937129B1

Abstract

The invention relates to optical coders providing binary logic signals representing the increments of relative position of two elements (10, 11) of the coder, the two elements being mobile with respect to one another. The first element (10) carries at least one mark (16) and the second element (11) carries a pair of detection cells (17, 18) for detecting the mark (16). According to the invention, the dimensions of the mark (16) are defined in such a way as to be able to be detected either by neither of the two cells (17, 18), or by just one cell (17, 18) or by both cells (17, 18). The invention is well adapted to angular coders, it makes it possible to widen the manufacturing tolerances of the marks (16) on the first element (10) and on the relative position of the two cells (17, 18).

Description

optical encoder

The invention relates to optical encoders providing binary logic signals representing relative position increments of two encoder elements, the two elements being movable relative to one another. These optical encoders, for example angular encoders, are used in the manner of potentiometers, for example for the manual control of electronic devices sensitive to an input parameter that can vary continuously or almost continuously, but they are much more reliable than the potentiometers. Typically, in an application for aeronautical equipment, an optical angular encoder may be used to indicate to an autopilot computer an altitude or speed setpoint that the pilot chooses by actuating a command button that rotates the encoder. The reliability of the encoder and the information it delivers is then an essential element of the encoder. An optical angle encoder is typically constituted by a disk bearing regular marks, this disc being actuated in rotation by a control button (for example manual). A photoelectric cell fixed in front of the disc detects the scrolling of the successive marks when the control button rotates the disc. The marks are typically openings in an opaque disc, with a light emitting diode on one side of the disc and the photocell on the other side.

Each mark passage constitutes an increment of one unit in the count of disk rotation. The angular resolution is determined by the angular pitch of the marks regularly arranged on a disk lathe. In order to detect both increments and decrements of rotation angle when reversing the direction of rotation, two photoelectric cells physically offset by an odd number of quarter-steps between them are provided. Thus, the illuminated / non-illuminated logic states of the two cells are coded on two bits which successively take the following four values: 00, 01, 1 1, 10 when the disc rotates in one direction and the following four successive values 00, 10 , 11, 01 when the disc rotates in the other, so that it is easy to determine, not only the appearance of an increment of rotation (change of state of one bits) but also the direction of rotation (by comparison between a state of the cells and the immediately previous state).

These encoders require significant precision in their construction. In particular, the relative position of the photocells must be a function of the increment step. It is the same for the disc whose dimensions and the position of each opening must be related to those of the photocells.

The invention aims at simplifying the production of an optical encoder by widening the manufacturing tolerances of certain elements of the encoder, in particular the positioning tolerances of the photocells as well as the tolerances of the dimensions and the positions of the openings of the disc.

For this purpose, the subject of the invention is an incremental optical encoder, comprising two elements that are movable relative to each other, the first element bearing at least one mark and the second element carrying a pair of detection cells. mark, characterized in that the dimensions of the mark are defined so as to be detectable by either of the two cells, or by a single cell or by both cells and in that a length of a zone of the second element including the pair of detection cells is less than one mark length, the lengths being measured in the direction of the relative displacement of the two elements.

The lengths of the zone and the mark may be a distance if the relative movement of the two elements is linear. The lengths can be angular if the relative movement is rotary.

The manufacturing tolerance of the brand is widened. Indeed, the minimum length of the mark is the length of the zone. On the other hand, the maximum length of the mark is not related to the length of the zone but depends solely on the number of increments of the encoder. Successive increments of the encoder are for example defined by the detection of the mark:

• by none of the cells,

• then by a first of the cells,

• then by the two cells simultaneously. The increments following the one defined by the detection of the mark by the two cells simultaneously are for example defined by the detection of the mark: • by the second of the cells, • then by none of the cells.

The invention will be better understood and other advantages will appear on reading the detailed description of an embodiment given by way of example, a description illustrated by the attached drawing in which: FIGS. 1 a to 1 d represent different relative positions of two elements, movable relative to each other, of an angular encoder according to the invention; FIG. 1 e shows the relative lengths of a mark of a first element with respect to a zone including detection cells of the mark; FIG. 2 represents the coding obtained by two detection cells of an encoder; Figure 3 shows in perspective an embodiment of an angular encoder. For the sake of clarity, the same elements will bear the same references in the different figures.

The following description is made with respect to an angular encoder. It is of course possible to implement the invention in a linear encoder.

FIGS. 1a to 1d show four positions of an angular encoder comprising two elements 10 and 11 that are movable relative to one another. The first element is a disk 10 movable in rotation around an axis 12. The second element 11 forms a housing of the encoder. The axis 12 is for example connected to a rotary knob that a user can maneuver to enter a binary data by means of the encoder. The encoder makes it possible to determine the angular position of the disk 10 with respect to the housing 1 1 during the rotation of the disk 10 around the axis 12, in a step of increment.

Advantageously, the encoder comprises means for mechanically defining stable positions of the two elements 10 and 11, one by report to the other. In the case of an angular encoder, these means comprise for example a notched internal wheel 13 integral with the housing.

1 and a ball 14 connected to the disk 10. The ball 14 is free in translation relative to the disk 10 in a radial direction of the disk 10. The ball 14 can move from one notch to the other of the wheel 13 The ball 14 may be urged by a spring, not shown, to hold it at the bottom of each notch. The stable positions of the disc 10 relative to the housing 1 1 are defined by the positions of the ball 14 at the bottom of each notch of the wheel 13.

The disk 10 comprises a succession of openings 1 6 between which the disk 10 is full. Each opening 16 forms a mark on the disc 10 and the full space between each opening forms an absence of mark. In other words, the disc 10 comprises an alternating succession of marks 1 6 and absence of marks. The marks are arranged radially about the axis 12. It is also possible to make the disc 10 in a solid material without openings by radially alternating transparent areas forming the marks and opaque areas. Subsequently, the transparent areas will be assimilated to the openings 1 6. It is understood that the invention can be implemented from a single mark made on the disk 10. The box 1 1 comprises a pair of cells 17 and 18 of detection of the mark 16. In the example considered, the encoder further comprises an optical transmitter capable of being detected by the two detection cells 17 and 18 separately. As a variant, the encoder may comprise two optical emitters each capable of being detected by one of the detection cells 17 or 18. The disc 10 can move between the emitter (s) on the one hand and the cells 17 and 18 on the other hand. The emitter or emitters are for example light emitting diodes and the cells 17 and 18 of photodiodes sensitive to radiation emitted by the diode or diodes. In the variant where the encoder comprises two light-emitting diodes it is important that each cell 17 or 18 is sensitive to only one diode.

The need for separate detection by each of the cells 17 and

18 makes it possible to define a minimum distance separating the cells 17 and 18 on the one hand and possibly the diodes on the other hand. This distance must allow a mark 1 6 to be detected either by none or by one or by the two cells 17 and 18. In other words, an edge of one mark 16 can stop between the two cells 17 and 18 during the rotation of the disc 10. In the presence of an alternating succession of marks 16 and absence of mark 16, the pair of cells 17 and 18 is able to detect each mark 16 regardless of the next. The detection of the mark 16 is on one edge thereof. The length of the mark 16 therefore has no influence on the detection of the mark 16. It is therefore possible to widen the manufacturing tolerances of the mark 16. The maximum limit of the length of the mark 16 is solely a function of the number of marks. encoder increments. FIG. 1e is an enlarged view of FIG. 1c on which is shown the angular length α of the mark 16 which must be greater than an angular length β of a zone 19 including the pair of detection cells 17 and 18 In other words, the area 19 is the minimum area occupied by the two detection cells 17 and 18, including the space between the cells 17 and 18. On the other hand, the implementation of the invention does not lead to no maximum limit for the distance between cells 17 and 18. A maximum limit exists only to set the number of sufficient increments on disk 10.

In addition, the relative position of the two cells 17 and 18 is not a function of the number of increments. It is therefore possible to standardize a support of cells 17 and 18 for different coders that do not have the same number of increments.

During the movement of the disk 10 about its axis 12, each cell 17 and 18 receives or does not receive the radiation emitted by the associated diode as a function of the presence or absence of an opening 16 between the cell 17 or 18 and its diode associated.

In FIG. 1a, the two cells 17 and 18 are masked by the disc 10. In FIG. 1b, the cell 17 is illuminated and the cell 18 is masked. In Figure 1c, the two cells 17 and 18 are illuminated. In FIG. 1 d, the cell 17 is masked and the cell 18 is illuminated.

The four figures 1 to 1 d represent in the order of four successive stable positions in the rotation of the disc 10 about the axis 12 in the clockwise direction. In the position that follows that shown in Figure 1 d, the disk masks the two cells 17 and 18. This position is equivalent to that of Figure 1a. It is of course possible to make turn the disc counter clockwise. We would then obtain an inverse succession in the order of illumination and masking of the cells 17 and 18.

FIG. 2 shows the coding obtained by the two detection cells 17 and 18 as a function of the stable positions of the disk 10 relative to the housing 1 1. Eight stable positions, numbered from 1 to 8, are represented in the upper part of FIG. A broken line 20, sawtooth, represents the notches of the wheel 13. A curve 27 represents the coding obtained by means of the cell 17 and a curve 28 represents the coding obtained by means of the cell 18. The coding from cells 17 and 18 are binary and can take two values denoted 0 and 1. The coding from cell 17 takes the value 0 for positions 1, 2, 5 and 6 and the value 1 for positions 3, 4, 7 and 8. The coding from cell 18 assumes the value 0 for positions 1, 4, 5 and 8 and the value 1 for positions 2, 3, 6 and 7.

Positions 1 and 5 correspond to those shown in Figure 1a. Positions 2 and 6 correspond to those shown in Figure 1d. Positions 3 and 7 correspond to those shown in Figure 1c. Positions 4 and 8 correspond to those shown in Figure 1b. The order of succession of the positions 1 to 8 corresponds to a rotation of the disk 10 in the trigonometric direction as defined by means of FIGS. 1a to 1d.

FIG. 3 represents in perspective an exemplary embodiment of an angular encoder comprising two emitters and two cells 17 and 18 integral with a U-shaped support 30. The support 30 comprises two branches 31 and 32 facing each other. The emitters are located on one of the branches 31 of the U and the cells 17 and 18 are located on the other branch 32 of the U. The disc 10 moves between the branches of the U. When the disc 10 rotates about its axis 12, the openings 16 pass between the branches of the support 30 so as to be detected by the cells 17 and 18. A shaft 33 extending along the axis 12 is integral with the disc 10. The shaft 33 is connected to the housing 1 1 by means of bearing allowing a degree of freedom in rotation about the axis 12 to remain. The shaft 33 allows an operator to maneuver the disk 10 in rotation. Advantageously, the support 30 is integral with a printed circuit board 34 making it possible to provide the connections necessary for the operation of the emitters and the cells 17 and 18. It is also possible to have on the card 34 electronic components related to the processing of the coding coming from the cells 17 and 18. The card 34 is for example located in a plane parallel to the axis 12.

Advantageously, to ensure the redundancy of the coding, the support 30 can be doubled. The second support 30 also carries two emitters and two cells 17 and 18. The second support 30 can also be arranged on a printed circuit board 34. compactness of the encoder, the two cards 34 can be parallel. More generally, the encoder comprises two second movable elements with respect to a single first element bearing at least two marks, each of the second two elements carrying a pair of detection cells of one of the two marks so as to ensure redundancy. the detection of marks. Indeed, the cards 34 have a level of reliability lower than that of the disc 10. To improve the reliability of the encoder simply double the cards 34 around a single disc 10. This doubling can also be used to detect a failure of components of the card 34 when the coding issued by each of the pairs of cells 17 and 18 becomes different.

Claims

An incremental optical encoder comprising two movable elements relative to each other, the first element (10) bearing at least one mark (16) and the second element (1 1) carrying a pair of detection cells ( 17, 18) of the mark (16), characterized in that the dimensions of the mark (16) are defined so that they can be detected by either of the two cells (17, 18) or by a single cell (17). , 18) either by the two cells (17, 18) and in that a length of an area of the second element (11) including the pair of detection cells (17, 18) is less than one length of the mark (16), the lengths being measured in the direction of the relative displacement of the two elements (10, 11).

Encoder according to Claim 1, characterized in that the maximum length of the mark depends solely on the number of increments of the encoder.

Encoder according to one of the preceding claims, characterized in that successive increments of the encoder are defined by the detection of the mark (1 6):

• by any of the cells, • then by a first (17) cell,

• then by the two cells (17, 18) simultaneously.

4. Encoder according to claim 3, characterized in that the increments succeeding that defined by the detection of the mark (1 6) by the two cells (17, 18) simultaneously are defined by the detection of the mark (16):

• by the second (18) of the cells,

• then by none of the cells.

5. Encoder according to one of the preceding claims, characterized in that the first element (10) comprises an alternating succession of marks (16) and absence of mark.

6. Encoder according to one of the preceding claims, characterized in that the encoder is an angular encoder, in that the first element is a disk (10) movable in rotation relative to the second element (1 1).

7. Encoder according to one of the preceding claims, characterized in that the mark (16) is an opening in the first element (10), in that the second element comprises one or two optical emitters each capable of being detected by a detection cells (17, 18) and in that the first element (10) can move between the emitter (s) on the one hand and the cells (17, 18) on the other hand.

8. Encoder according to claim 7, characterized in that the transmitter or the cells (17, 18) are integral with a support (30) U-shaped, the support (30) comprising two branches (31, 32). ) facing each other, in that the transmitter or emitters are located on one (31) of the branches of the U and the cells (17, 18) are located on the other branch (32) of the U and in that the first element (10) moves between the branches (31, 32) of the U.

9. Encoder according to claim 8, characterized in that the support (30) is integral with a printed circuit board (34).

10. Encoder according to one of the preceding claims, characterized in that it comprises two second elements (30, 34) movable relative to a single first element (10) carrying at least two marks (16), each of the two second elements (30, 34) carrying a pair of detection cells (17, 18) of one of the two marks (16) to provide redundancy of the mark detection (16).

1 1. Encoder according to one of the preceding claims, characterized in that it comprises means (13, 14) for mechanically defining stable positions of the two elements (10, 1 1) relative to each other and in that in a first stable position neither of the two cells (17, 18) detects the mark (16), in a second stable position, a single cell (17, 18) detects the mark (16) and in a third stable position, the two cells (17, 18) detect the mark (16).