GB2203863A - Phase control for master-slave system - Google Patents

Abstract

An automatic dynamic control system comprises two similar sub-systems such as servo actuators A,B each having at least one output variable which is a physical characteristic of a moving mass incorporated in the system, e.g. servo values A1, B1. The phase difference between the output of one of the sub-systems A, a master sub-system, and the output of the other sub-system B is measured by processing the output variables such as position and velocity of the two sub-systems, and the measured phase difference is used by a phase locked loop C to bring about and maintain a fixed phase relationship between the output of the other sub-system and the output of the master sub-system. The system may control an electro-hydraulic shaker for resonance testing. <IMAGE>

Description

DESCRIPTION AUTOMATIC DYNAMIC CONTROL SYSTEMS This invention relates to automatic dynamic control systems which comprise at least two similar subsystems1 each having an output variable which is a physical characteristic of a moving mass incorporated in the system (such as displacement, velocity or acceleration of the moving mass), the output variable either being detected dynamically, being used in the system as a control variable to control operation of the control system or being used as a basis from which such a control variable is derived. Such control systems may incorporate mechanical, electrical, electronic or fluid power actuating loops and may be incorporated in or associated with fluid power machinery, hydraulic transmission systems, aerospace and military systems or equipment, vibration and shaking machines, process systems and biotechnological systems.

An object of this invention is to improve the ability of an automatic dynamic control system to control and minimise phase angle error between various control loops, channels, tranducers, actuators etc incorporated in the system. Processes which are intended for resolving this problem are known variously as alignment, synchronisation or matching processes.

Broadly this object is achieved by the use of phase locking techniques in a way in which they have not been used before, viz. by applying them to fields of technology in which they have not been used before and by processing information of dynamically detected variables of the system or of actual control variables of the system.

According to this invention, in an automatic dynamic control system comprising at least two similar subsystems each having an output variable which is a physical characteristic of a moving mass incorporated in the system, the output variable either being detected dynamically or being used in the system as a control variable to control operation of the control system or as a basis from which such a control variable is derived, phase difference between the output of one of the sub-systems, a master sub-system, and the output of another of the sub-systems is measured by processing said output variables of the two sub-systems, and the measured phase difference is used to bring about and maintain a fixed phase relationship between the output of the other subsystem and the output of the master sub-system.

Preferably an electronic phase locked loop is used for measuring phase difference and bringing about and maintaining a fixed phase relationship between the output of said other sub-system and the output of the master sub-system.

An actuating system in which this invention is embodied is described now by way of example with reference to the accompanying drawings, of which: Figure 1 is a diagram illustrating part of an actuating system of an electro-hydraulic shaker for resonance testing of vehicle shells and various structures, the actuating system comprising four linear electro-hydraulic servo-actuators, of which only two are shown for the sake of simplicity; Figure 2 is a diagram of electronic phase locking circuitry which is an example of the kind of circuitry that may be used as the phase locking network of the control system shown in figure 1; and Figures 3 to 5 are graphical illustrations of good phase locking characteristics obtained by operation of the control system shown in figure 1 and incorporating phase locking circuitry of the kind shown in figure 2.

Figure 1 shows two electro-hydraulic actuators A and B. Each actuator A, B incorporates an electrohydraulic servo-valve Al, B1 which is controlled by a signal transmitted to it via a respective feedback amplifier A2, B2. A reference input signal is fed to one terminal of each amplifier A2, B2 which has two other terminals connected to respective inputs of a phase locking network C. The output of the phase locking network C is fed to a fourth input terminal of the amplifier B2.

The actuator rod A3, B3 of each actuator A, B is associated with a potentiometer A4, B4 and a velocity transducer A5, B5. The output of each velocity transducer A5, B5 is connected between one of the terminals of the respective feedback amplifier A2, B2 and the phase locking network C and the output of each potentiometer A4, B4 is connected between another of the terminals of the respective feedback amplifier A2, B2 and the phase locking network C. Hence displacement of each actuator rod A3, B3 is measured by the respective potentiometer A4, B4 whilst the velocity of that actuator rod A4, B4 is measured by the respective velocity transducer A5, B5.

The displacement of each actuator rod A3, B3 may be measured by a variable differential transducer in the position feedback loop, instead of by the respective potentiometer A4, B4. The velocity of each actuator rod A3, B3 may be measured by a tachometer instead of by the respective velocity transducer.

The phase locking system incorporated in the phase locking network C is based on the following mathematical analysis, the actuator A being regarded as a master. For any sinusoidal input, V = sinwt, the steady state sinusoidal displacement and velocity outputs from the actuators A and B are given by: For the master actuator A: x1 = X1 sin (wt + eel) . .. (1) #1 = X1 cos (#t + #1) ... (2) and for the follower, or target actuator B: x2 = X2 sin (#t + #2) ... (3) #2 = X2 cos (#t + #2) ... (4) Combining equations (1) to (4) results in the following relationship for phase difference 81 - #2: sin (# - #) = 2 (# x - x #) ... (5) 1 2 # #X1 X2 1 2 1 2 This is a sinusoidal function of the phase errors in terms of the system output variables, displacement and velocity.For small values of the phase angle error (#1 - 82) equation (5) can be written as: #1 - #2 = (#1 x2 - x1 #2) ... (6) Equation (6) is the basis on which the phase detector module of the phase locking system operates.

A suitable phase locking network based on the circuitry shown in Figure 2 can be developed using equation (6) and assuming first order transfer functions for the two actuator A and B and their servo systems. The phase detector, which is the core of the phase locked loop, receives its inputs from two multipliers which use the output of the master loop of the actuator A, and the derivative of the output of the target loop of the actuator B. By this arrangement the velocity output of one of the actuators is multiplied by the displacement of the other actuator and compared with the multiple of the velocity output of the other actuator and the displacement of the first mentioned actuator to identify the phase difference. The circuitry shown in Figure 2 is suitable where the velocity outputs are used. The target loop is simply one of the loops of the system whose phase angle is to be locked to that of the master loop (similar systems to that shown linking the actuator B and the master actuator A may be used for linking each of the other two actuators of the system that are not shown, to the master actuator A). In general two multipliers are needed to generate the input to the summer that produces the phase detection signal.

The phase locking systems also comprises a proportional gain filter and a voltage controlled oscillator which is a simple integrator. There is also a ss - potentiometer, the setting of which is crucial to achieving the desired phase locking function, as is seen from the simulation results shown in figures 3 to 5.

The output of the phase locking system is fed to the respective amplifier B2 that controls operation of the electro-hydraulic servo-valve B1 of the target actuator B. A stable phase locking of the sinusoidal wave forms of the master loop and follower, or target loop can be achieved in less than 5 cycles of the system output response (x2).

Large errors in phase angle detection can lead to a non-linear output of the phase detector. This could be overcome by adding a linearizing signal conditioning unit after the phase detector.

The phase locking technique carried out by operation of this invention can be applied to all types of dynamic control systems where the output variable and any one of its derivatives can be dynamically detected, or is actually being used within the system itself leg. position control systems with velocity and/or pressure or acceleration feedback.

The application of this invention to aerospace and aircraft systems, military systems (eg. positioning gun turrets), shaking and vibration testing, process control (synchronizing the phase angle of process variable subpressure, flow rate etc) are but a few examples of the technological fields in which such a phase locking system can be used.

Claims (9)

1. An automatic dynamic control system comprising at least two similar sub-systems each having an output variable which is a physical characteristic of a moving mass incorporated in the system, the output variable either being detected dynamically or being used in the system as a control variable to control operation of the control system or as a basis from which such a control variable is derived, wherein phase difference between the output of one of the sub-systems, a master sub-system, and the output of another of the sub-systems is measured by processing said output variables of the two sub-systems, and the measured phase difference is used to bring about and maintain a fixed phase relationship between the output of the other sub-system and the output of the master sub-system.

2. An automatic dynamic control system according to claim 1, wherein an electronic phase locked loop is used for measuring phase difference and bringing about and maintaining a fixed phase relationship between the output of said other sub-system and the output of the master sub-system.

3. An actuating system substantially as described hereinbefore with reference to the accompanying drawings, and as illustrated in Figures 1 and 2 thereof.

Amendments to the claims have been filed as follows CLAIHS 1. An automatic dynamic control system comprising a plurality of dynamically-similar sub-systems each having an output variable which is either being detected dynamically or is being used in the system as a control variable to control operation of the control system or as a basis from which such a control variable is derived. in which phase difference between the output variables of the two sub-systems of the or each of one or more pairings of the sub-systems of the control system is measured for each such pairing and is used to bring about and maintain a fixed phase relationship between the two output variables of the respective pairing of sub-systems wherein. for each pairing, said phase difference is identified by multiplying the output variable of a first of the sub-systems of that pairing with a derivative of the output variable of the second sub-system of that pairing and comparing the resultant multiple with the multiple of the output variable of said second sub-system with a derivative of the output variable of said first sub-system.

2. An automatic dynamic control system according to Claim 1, wherein the sub-systems include mechanical, electrical. electronic or fluid power actuating loops.

3. An automatic dynamic control system according to Claim 1 or Claim 2, incorporated in or associated with fluid power machinery, an hydraulic transmission system, an aerospace system, a military system or equipment, a vibration machine, a shaking machine. a process system, or a biotechnological system.

4. An automatic dynamic control system according to any one of Claims 1 to 3, wherein the output variable of at least one of the dynamically-similar sub-systems is a physical characteristic of a moving mass incorporated in the system, such as displacement, velocity or acceleration of the moving mass.

5. An automatic dynamic control system according to Claim 4. wherein the output variable of at least one of the dynamically-similar sub-systems is displacement of an actuating element and its derivative is the velocity of that actuating element.

6. An automatic dynamic control system according to any one of claims 1 to 3, wherein the output variable of at least one of the dynamically-similar sub-systems is a pressure or flowrate signal.

7. An automatic dynamic control system according to any one of Claims 1 to 6, wherein. for each pairing an electronic phase locked loop is used for measuring phase difference and bringing about and maintaining a fixed phase relationship between the outputs of said first and second sub-systems.

8. An automatic dynamic control system according to claim 7, wherein a linearising circuit conditioning unit is connected into the electronic phase locked loop after a phase detector of that loop.

9. An actuating system substantially as described hereinbefore with reference to the accompanying drawings, and as illustrated in Figures 1 and 2 thereof.