Patent GB-1397744-A (GB)
Title: Motor speed control device
IPC: H05K13/00
Filed: 1972-07-11
Abstract: 1397744 Photo-electric motor control system ASAHI KOGAKU KOGYO KK 11 July 1972 [15 July 1971] 32422/72 Heading G1A A motor control device comprises an optical filter arranged so that displacement by a control knob varies the amount of light from a source received by a detector, means for generating a pulse signal the frequency of which depends on the detector output and which is applied to a motor arranged so that its speed varies with the pulse frequency, the direction of the motor being controlled by means coupled to the control knob to discriminate the sense of movement commanded. A manipulating system for the alignment of objects such as masks and semi-conductor chips comprises a control knob 14 having a shaft 12 which is centred by springs 13 and on which are  mounted four optical filters 2-1, -2, -3, -4 and a magnetic screening plate 5. Each filter is illuminated by a LED 1-1, -2, -3, -4 and viewed by a light-sensitive device 3-1, -2, -3, -4 the output of which controls the frequency of a pulse generator 7-1, -2. The density of each filter varies continuously or stepwise and produces a maximum variation of 10:1 in the frequency of the output. Movement of a filter perpendicular to its direction of variation produces no change in the output. The magnetic screening plate 5 separates four permanent magnets 4-1, -2, -3, -4 from associated reed switches 6-1, -2, -3, -4 which are connected to logic circuits 8-1, -2 which determine the direction in which the knob has been moved and select the output of the appropriate pulse generators. The manipulator is provided with two pulse or stepping motors for movement in orthogonal directions, these motors being controlled by the pulse outputs in such a manner that displacement of the control knob results in movement of the manipulator in the same direction at a speed proportional to the displacement of the control knob in that direction. The control knob is also provided with two micro-switches 16, 17 one to enable the control circuit and the other to apply single pulses to the motors for fine positioning. A modified form of the system is used for rotational manipulation the filter being graduated from a point viewed when it is at rest in opposite directions along a circular track so that as the control shaft is twisted in either direction the frequency of the pulse generator is varied. The direction of rotation is discriminated by means of a D-shaped magnetic screen mounted on the shaft which passes between a permanent magnet and a reed switch which is therefore operated for only one direction of rotation of the shaft. A complete system may comprise an X-Y control and a # control arranged for operation by the two hands of an operator who views the resulting alignment operation using a TV system. Directional discrimination may also be achieved by optical systems using transmissive of reflective step filters to give an on-off signal. Since correctly graded filters for the control systems are difficult to produce they may comprise transparent supports with parallel opaque or reflective stripes the spacings between which vary along the length of the filter. When a relatively large area of such a filter is viewed by a photo-detector the output of the pulse generator varies in proportion to the displacement of the filter with suitable spacings of the stripes.