Patent GB-1462879-A (GB)
Title: Hydraulic actuator controls
IPC: F15B11/04
Filed: 1973-10-10
Abstract: 1462879 Fluid-pressure servomotor systems SPERRY RAND Ltd 9 Oct 1974 [10 Oct 1973] 47213/73 Heading G3P The rate of fluid-flow to an actuator 10 causes a sensor 53 to produce an electrical signal 52, 62 which is fed into a comparator 74 together with a flow control signal 50, the output from the comparator serving to control the actuator through pilot and main valves 27, 14. Pressure transducers 35, 36 on the pilot valve are connected to an electronic reversing switch 61 so that the signal 62 from the sensor always opposes the flow input signal, even though this may have been reversed by a direction control switch 77. Further pressure transducers 55, 56 are connected through a potentiometer 59, set to compensate for the difference in area of the opposite sides of the piston 11, and a rectifier 65, producing a positive output 66 for either polarity of input, to a comparator 66 where the force on the actuator is compared with a negative force control signal 51. If the force on the transducers exceeds the value determined by the signal 51, a rectifier 69 allows a signal 68 to override the flow control and relieve the load on the actuator. During overrun of the actuator, the force control signal is rendered inoperative by a clamp 90. In a second embodiment, the flow sensor 53 is inserted in the return line from the main valve and the polarity of the signal from it is reversed by an invertor/follower (123) controlled by a shuttle operated switch (126), Fig. 3 (not shown), the shuttle being connected to the chambers (39, 40) at opposite ends of the main valve. The output of the inverter is connected to the comparator 74 which has its second input connected through a clamp (117) to a potentiometer (119) for setting both the rate of flow and direction of movement of the actuator. The signal from the transducers 55, 56 and the potentiometer 59 is applied to a discriminator (113) which receives a force control signal from a potentiometer (114). The discriminator replaces the rectifier 65, comparator 67 and rectifier 69 to produce an output signal when the transducers 55/56 provide a signal greater than that from the potentiometer (114). When the load drives the actuator, the signal from the discriminator and the potentiometer (119) have the same polarity and the clamp (117) blocks the signal from the discriminator to prevent instability. A stationary load causes the signal from the discriminator to pass through one of a pair of oppositely-poled rectifiers (143, 144) and open a solenoid valve (131) so that fluid continues to flow through the main valve to enable the position of the actuator to be maintained. If a fault occurs causing the signal to the pilot valve to build up, an integrator (146) applies a signal through an OR gate (147) to a clamp (130) which removes the signal from the pilot valve to allow it to close. The OR gate is also connected through an amplifier (153) to the centre point of a potential divider in parallel with the flow and force signal potentiometers (114, 119) to operate the clamp if the voltage source fails. The sliders of the potentiometers may be operated by pressure-responsive diaphragms.