FR2534836A1 - Optoelectronic positioning method and device - Google Patents

Abstract

The invention is a positioning system using the difference in reflectivity between a matt surface in the form of a line and two bright zones. The line is scanned by the image of a slot 2 illuminated by a bulb 1, focused by the lens 6 onto the surface 7 and driven by the mirror 4 mounted on the synchronous vibrator 5 with an oscillation at 50 Hz, the reflected beam is deflected by the semi-reflecting mirror 3 onto a cell 8. This optical assembly allows the production of an electronic calculator adapted to a repetitive configuration of lines, comprising a phase discriminator referenced on the current of the vibrator and an electronic occultation based on the storage in memory of the distance separating two previously scanned lines. The applications concern, in particular, machines for slotting the commutators of DC motors.

Description

 The already known methods and devices use the light contrast between two surfaces. The image is projected onto one or more photoelectric cells by a conventional optical assembly which can be associated with fiberglass optics in cases where the space requirement is limited at the reading level.

 These methods and the corresponding devices using the variation in amplitude of the light flux are relatively imprecise due to the sensitivity to ambient lighting, variations in the surface state and the shape of the sensitive surface produced by the cells. is often geometrically ill-suited to the object to be detected.

 The invention aims to remedy these drawbacks by using phase modulation device, the main optical member of which is a synchronous vibrator to which an oscillating mirror is fixed.

 This vibrator can be included in various optical assemblies.

By way of example, the following description relates to a device produced for controlling a machine for grooving the collectors of DC motors.

 For this particular application, it is a question of precisely positioning a milling cutter which machines the insulation between two collector blades. This insulator is in the form of a more or less wide matt line between two reflecting areas. For the sake of clarity in the description which follows, the denomination of "line" will represent the insulator from the optical point of view.

 The assembly used for this particular application is shown in Figure 1.

 An electric bulb 1 illuminates a rectangular window 2 from which a light beam passes through a semi-transparent mirror 50% 50% tilted at 45 represented at 3 then is reflected at 9fil0 by the oscillating mirror 4 and is focused by the converging lens 6 which gives an image of the slit being on the surface of the collector 7.

 The largest dimension of the rectangular window thus projected is in the direction of the line, the detection of which is favored in relation to any spots of any contour.

 The oscillation of the fixed mirror 4 on the synchronous vibrator 5 gives the image of the window an alternating transverse movement carrying out a permanent exploration of the edges of the line.

 On the return, the light reflected by the surface of the collector follows the same path to the semi-transparent mirror 3 which derives it from 90 to form a second image of the window on the cell 8 placed at a symmetrical point of the window lit with respect to the mirror 3.

 The light beam being deflected back and forth by the oscillating mirror, the image of the window on the cell is stationary but its brightness varies according to the reflecting power of the surface of the collector encountered during the exploration carried out by the oscillating mirror.

 Furthermore, the immobility of this second image is very important in order to avoid parasitic modulation due to variations in sensitivity of the surface of the cell.

 The synchronous vibrator is described in Figure 2.

 It consists of a magnetic circuit comprising a fixed part and a mobile part.

 The fixed part comprises a piece of soft iron 9 and two permanent magnets IO and II, the polarity of which is indicated in the drawing.

 The movable part I2 also made of soft iron, carries the mirror I3 and is separated from the fixed part by an air gap 14; it is suspended by a spring 15.

 The coil I6 is placed in the fixed part according to the drawing. This coil being traversed by an alternating current, due to the polarization of the magnetic field by the permanent magnets, the movable part and its mirror vibrate at the frequency of this current.

 By choosing the stiffness of the spring to obtain a natural frequency of the mobile part sufficiently high compared to the frequency of the control current, the displacement of the mobile part is in phase with the current, moreover the amplitude of the displacement is proportional to this same current.

 These two properties are crucial for the operation of the electronic signal processing assembly which aims to position the cutter in the middle of the line, that is to say in the middle of the insulating part to be machined.

 This electronic assembly, the operation of which is shown diagrammatically in FIG. 3, can be finished as a discriminator which precisely detects a phase inversion at the moment when the exploration system passes through the middle of the line.

 The drawings AI, A0 and A2 represent the exploration of a line by the image of the light window; in A1, it is offset towards the top of the figure, in A2, it is offset towards the bottom and in A0, the line is in the center of the explored area.

 The sinusorde IC represents the intensity in the coil of the vibrator, agreeing with the position of the window during its movement.

The frequency of 50 Hz was chosen for the application described here.

 Drawings 81, 80 and, 82 show the electrical signals generated by the light flux received by the cell.

 The lines marked 0 indicate the instant when the control current is zero and or simultaneously the window passes through its central position.

 Examination of drawings A and 8 as a whole, and in particular of the relationship between the surfaces of the window which are in a matt zone or in a reflecting zone, shows that when the line is in the center of the zone explored , the cell emits a signal of 100 Hz.

 -On the other hand, when the line deviates from the center, a 50 Hz signal appears, the phase of which reverses in the direction of the deviation from the phase of the control current IC.

This result is only acquired for an amplitude of exploration adapted to the width of the line; in fact, when the exploration is too small, the window remains inside the matt area and the cell does not receive a signal; on the other hand, when the exploration is too large, the slit goes entirely outside the limits of the line, which introduces uncertainty in the measurement of the median position.

 It is therefore very important to be able to easily modify the exploration amplitude by varying the intensity of the vibrator control current.

 The signal processing device is a phase discriminator using the control current of the vibrator as a reference.

 Still referring to FIG. 3, IC is delayed by 900 by the phase shifting circuit I7 then amplified at 18 to give a rectangular signal whose flanks derived in circuit I9 constitute pulses coming out on two channels and whose position relative to the zero is indicated in the figure in each case of slot position. These pulses control the logic input of two samplers 20 and 21 and thus serve as a reference for the phase discriminator.

 Furthermore, the cell signal is amplified and shaped by the amplifier 22 and clipped to a fixed value, thus making the system insensitive to variations in the level of contrast due to the surface state.

In Figure 3, Cl; CO and C2 represent in the different positions of the line this clipped signal connected to the analog input of samplers 20 and 21. D1, DO and
D2 represent the output of the two samplers, which is the voltage C1, CO and C2 stored in memory at the time of each pulse always for each case of slot position.

 The samplers are connected to the input of the operational amplifier 23 mounted as a subtractor and whose output voltage resulting from this operation is represented in El, EO and E2.

 We see that this tension is zero for the middle position and is negative or positive depending on the direction of the deviation from the middle of the exploration.

 All the whole being synchronized on 50Hz, the response time is IOms; it should also be noted that whatever the phase of a signal at IOOHz, the output voltage is zero, csQui achieves interference rejection which may be due to ambient lighting.

 In the application described here; that is to say the machine for grooving the armature collectors of direct current motors, hock of the rotation of the collector is controlled by the phase inversion at the middle position of the line with respect to the exploration-system; the gain is very high to get this. position with maximum precision, but there are often spots and irregularities on the surface of the collector capable of triggering an unexpected stop and milling in the copper, which requires a new rectification of the collector.

 To avoid this serious drawback and in accordance with the invention, a process has been added which achieves the essential security.

 From the start of the armature rotation, stopping is prohibited until the opening of an electronic door just before the presumed stop, which closes after a very short time.

 This time range is positioned by memorizing the time of rotation of the armature corresponding to the distance between two slots, this time being readjusted at each stop, which makes it possible to accept the slight differences in spacing of these last, as well as a slow variation in the speed of rotation of the armature.

 This electronic security device is produced in the following manner: FIG. 4 representing the evolution of the different voltages and FIG. 5 the constituent elements.

 Time is measured by the capacitor 24 charged by the constant current generator 25 so that its voltage U varies linearly as a function of time.

 The reset system 26 which discharges the capacitor is controlled by the start of the rotation referenced by O in FIG. 4; a sampler 27 measures at the time of stopping At the variable voltage U and stores it in the form of a fixed voltage.

 A voltage Um-e is obtained by means of potentiometer 28; a computer composed of an operational amplifier 29 connected as a subtractor supplies a voltage Um + e; e represents the opening advance and the closing delay with respect to Um which corresponds to the presumed instant of the stop calculated as a function of the duration of the preceding journey.

The door opening time set by the potentiometer 28 is obtained by two comparators 30 and 31, the output of which changes state when the voltage U successively reaches the level Um-e and Um + e, these changes of state being combined in the subtractor 32 to control the opening of the door, which is done when the line is already in the exploration zone, just before the phase reversal which causes the stop.

 The storage of the travel time is done by a manual control maneuver, without the possibility of milling and with a reduced braid to avoid possible stops; normal gain is restored when switching to automatic control.

 The assembly having a high selectivity focused on the detection of the optical configuration of the insulating part and immunity to external influences, allows a sufficient distance between the optics and the collector for the passage of the milling mechanism without air. use of a retraction system.

 In addition, the electronic ban prevents accidental milling of a blade, which would require a serious new rectification of consequence for a traction motor whose life would be thus shortened.

Claims (8)

 REUENDICATIONS I. Opto-electronic positioning method with a view in particular to the control of a machine for grooving DC motor collectors, in which the contrast between two collector blades and the insulator which separates them is explored by the image of a lighted window whose shape is adapted to the optical configuration of the insulating zone. 2. Method according to claim 7, characterized in that the alternating movement at 50 Hz of the window image has a variable amplitude to adapt to the different widths of the insulator. 3. Method according to claims 1 and 2, characterized by the processing of the signal from the photoelectric cell which receives the light reflected by the collector, from the image of the window, by a phase discriminator whose reference is the current. for controlling the synchronous vibrator which causes the exploration movement, this assembly being arranged for the rejection of the I00 Hz coming from the ambient lighting. 4. Method according to claims 1, 2 and 3 characterized by an electronic blanking whose door opens only when the insulation is in the area explored, which avoiding untimely stops, allows to increase the gain enough to that the positioning is carried out with precision on a phase inversion, independently of any amplitude modulation sensitive to variations in the surface state and in ambient light. 5 .. -Device according to claims 1 and 2 characterized by a rectangular window lit by a bulb supplied with direct current, adjustable in its two dimensions and whose image projected on the collector is animated by a sinusoidal movement produced by a mirror mounted on synchronous vibrator, amplitude-adjustable movement by varying the control current of this vibrator, the reflected light being focused on a photoelectric cell. 6. Device according to claims 1, 2 and 3 characterized by a phase discriminator whose reference is provided by two pulse trains, offset by 180 ders, synchronized by the current at 50 Hz controlling the vibrator, which constitute the input logic of two samplers, the analog input being the amplified cell signal, shaped and clipped to a fixed value, the combination in a computer of the outputs of these samplers providing a voltage which is reversed with the phase inversion while eliminating the double quenca signals, ie the residual at 10 Hz of the ambient lighting. 7. Device according to one of claims 1 to 4 characterized by an electronic gate based on the measurement of the duration of the rotation of the collector during the passage from an insulating zone to the next, duration materialized by the storage in the moment of stopping, of the tensio of a capacitor charging at constant current and the setting of which was done at the time of departure, voltage which treated by a computer, opens a door a little before planned stop and closes it a little later, this sequence is readjusted with each milling operation.  8. Machine control to groove the collectors of DC motors or any other machine using one of claims 5 to 7.