Patent GB-1433340-A (GB)
Title: X-ray apparatus
IPC: G03B42/02
Filed: 1973-07-10
Abstract: 1433340 Automatic control of position PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 10 July 1973 [13 July 1972]  32795/73 Heading G3N [Also in Division G1] A drive system for the displacement of the image section of an x-ray apparatus for medical purposes comprises an electro-mechanical transducer which converts a force exerted by an operator on a control member into an electric voltage controlling a drive motor so that its speed, and hence the displacement of the image section, is dependent on the force exerted by the operator on the control member, the transducer output voltage being substantially proportional to the operator force and being connected to the input of an integrator whose output determines the speed of the motor in proportion thereto. In Fig. 1 the vertical movement of an image section 100 is produced by the vertical force exerted on a hand grip 2 which, as shown in Fig. 2, varies the force exerted on a Piezo-electric crystal 8 clamped between a rod 13 secured to the section 100 and a rod 10 connected by a pin 9 with the grip 2 and by a pin 12 with the prod 13, members 8, 10, 12, 13 being secured by a screw 11. Fig. 3 shows the circuit for converting the output voltage of the crystal 8 to a voltage V which controls a unit 30, Fig. 1, for driving a motor 3 coupled to the section 100 via members 5, 6. The members 3, 30 may comprise the motor and control system described in Specification 1322974 and the voltage V may replace the desired value generator 31 of that Specification. The crystal 8 is connected via resistor 14 to the high-ohmic input of an operational amplifier 16 provided by field effect transistors, the interaction of members 8, 14, 16 and a parallel capacitor 15 producing an output voltage from amplifier 16 proportional to the force on the grip 2. This output voltage is integrated by operational amplifier 17, capacitor 18 and resistor 19 to produce the voltage V, the resistor 19 being adjustable to vary the ratio between operator force and motor speed or being replaced by a variable potentiometer connected across the output of amplifier 17 to achieve the same effect. Polarity change of the latter output voltage produces reversal of the rotation of motor 3. Drifting of the zero point of amplifier 16 is prevented by a switch 20 which automatically closes when grip 2, which may be rotatable, is released by the operator and returns to a rest position. Capacitor 18 may be connected in parallel with a similar switch or a resistor (not shown) to reduce the motor speed to zero, if grip 2 is released by the operator before the section 100 has come to a standstill. Downward movement of the latter (due to the absence of a counterweight) is prevented by a self-braking transmission in the motor drive. The image section 100 may be displaced in three mutuallyperpendicular directions by respective drive systems each comprising the members shown in Figs. 1 and 3, with all three transducers 8 being controlled by a common handgrip 2 and the circuits of Fig. 3 having the same proportionality factor between the exerted force and voltage V, so that a given force on the grip 2 produces substantially the same speed for all of the motors.