GB2036377A

GB2036377A - A Control Apparatus

Info

Publication number: GB2036377A
Application number: GB7934307A
Authority: GB
Original assignee: Societe Francaise dEquipements pour la Navigation Aerienne SFENA SA
Current assignee: Societe Francaise dEquipements pour la Navigation Aerienne SFENA SA
Priority date: 1978-10-04
Filing date: 1979-10-03
Publication date: 1980-06-25
Also published as: FR2438370B1; FR2438370A1

Abstract

In an aircraft flight control apparatus controlling a motor M forming an actuator, two independent position command signals are received at E1 and E2, and the power supply means connected across the motor M to cause it to move the actuator in the direction commanded by the position command signals, if they both command the same direction of movement, until the actuator has moved to whichever of the positions commanded by the position command signals is nearer the initial position of the actuator, or for bypassing the motor and hence preventing it from operating if the two position command signals command movement in opposite directions. <IMAGE>

Description

SPECIFICATION A Control Apparatus This invention relates to a high safety control apparatus for the automatic flight control system of an aeroplane or helicopter, in which for example the flight speed is regulated by means of an electro-mechanical actuator powered by a reversible electric motor, and in which the actuator is moved in response to a position command signal from each of two independent "auto-pilot" computers.

Positional information from the actuator is fed back into the control circuitry so that the apparatus can determine how far and in which direction the actuator must be moved in order to satisfy at least one of the position command signals, provided that both signals command movement in the same direction.

In accordance with a first aspect of this invention a control apparatus for controlling power supplied to a motor or to another power element to move an actuator comprises means for receiving two independent position command signals, means for connecting a power supply across the motor to cause it to move the actuator in the direction commanded by the position command signals, if they both command the same direction of movement, until the actuator has moved to whichever of the positions commanded by the position command signals is nearer the initial position of the actuator, or for bypassing the motor and hence preventing it from operating if the two position command signals command movement in opposite directions.

In accordance with a second aspect of this invention, an aircraft flight control apparatus comprises a power supply, a motor for moving an actuator, and control circuitry for controlling the interconnection of the power supply and the motor, the electric control circuitry including means for receiving two independent position command signals, and for connecting the power supply across the motor to cause it to move the actuator in the direction commanded by the position command signals, if they both command the same direction of movement, until the actuator has moved to whichever of the positions commanded by the position command signals is nearer the initial position of the actuator, or for bypassing the motor and hence preventing it from operating if the two position command signals command movement in opposite directions.

This invention is particularly useful in the high safety flight control speed regulators in an aircraft which may be an aeroplane or a helicoptor of the type controlled by two auto-pilot computers.

Failures in the power supply, in the auto-pilots or in the control apparatus do not dangerously affect the flight controls, for the actuator motor is only powered if the auto-pilots do not contradict each other and if the control circuitry is working.

An example of a control apparatus in accordance with this invention which is used in an aircraft flight control system will now be described with reference to the accompanying drawing, which is a block diagram of part of a flight control system.

This example of control apparatus is arranged to receive two position command signals El and E2 which are derived from two independent autopilot computers and to control the operation of a reversible electric motor M of an electromechanical actuator. The control apparatus is arranged to respond to the input position command signals El and E2 by causing the actuator to move into whichever of the two positions, as represented by signals El and E2, is nearer to the original position, or, if the command signals would require the actuator to move in different directions, to ignore both command signals and not to change the position of the actuator.Thus, this apparatus performs a "voter" function by voting for or selecting whichever of the difference signals, representing the differences between the present actuator position and the two requested positions, is the smaller and moving the actuator into this position, and voting to retain the status quo and not to move the actuator if the two position control signals would require the actuator to move in contradictory directions.

The apparatus comprises a controller having two separate channels connected between a power supply and the motor M of the actuator.

The first channel of the controller consists of a differential operational amplifier Al having the position command signal El connected to one of its inputs and a signal S1 from a feedback potentiometer P 1 associated with the actuator and indicating the position of the actuator as its other input. The output E1 of the amplifier Al, representing the difference between the signals El and So, is fed to a tristable multivibrator B1.

The tristable multivibrator B1 forms a series of positive going pulses when the output from the amplifier Al is positive, has a null response when there is a null output from the amplifier Al and forms a series of negative going pulses when the output from the amplifier Al is negative. Outputs from the tristable multivibrator B1 are fed to the bases of transistors Q1 and Q3, with the arrangement being such that when positive going pulses are formed in the multivibrator B1 the transistor Ol only is turned on, when a null response occurs in the multivibrator B1 both Q1 and Q3 are turned off and when negative going pulses are formed in the multivibrator B1, transistor Q3 only is turned on.The duration of each of the positive and negative going pulses may be arranged to vary with the amplitude of the position command signal El or the frequency of the pulses may be dependent upon the amplitude of the signal El. Both of these result in the transistors Ol and Q3 being turned on for longer periods when the difference between the position command signal El and the position of the actuator as represented by the signal S1 from the feedback potentiometer P1 is greater.

The second channel consists of a differential operational amplifierA2 having the position command signal E2 as one input and a signal S2 from a second feedback potentiometer P2 associated with the actuator and indicating the position of the actuator as the other input. The output E2 of the amplifier A2, representing the difference between signals E2 and S2, is fed to a tristable flip-flop B2. The tristable flip-flop B2 provides outputs to transistors Q2 and Q4, arranged such that when the difference signal E2 is positive, only the transistor 02 is turned on, when the signal E2 is negative, only transistor Q4 is turned on and when the signal E2 is null, both transistors Q2 and Q4 are turned off.

The transistors Q1, Q2, Q3 and Q4 are connected in a bridge configuration in series with the power supply for the actuator and the earth, with the motor M connected across the bridge.

Circuit breakers D1 and D2 which reset automatically as soon as the overload is removed are also connected in series with the actuator power supply and the bridge.

Typically, the signal S1 from the feedback potentiometer P1 and the signal S2 from the feedback potentiometer P2 are approximately the same. When the control apparatus is in equilibrium, with the position control signal El equal to the position control signal E2, and both equal to the signals S1 and S2, so that the actuator is in the position called for by both of the position command signals, the output of the differential operational amplifiers Al and A2 is zero and hence the outputs of the tristable multivibrator B1 and the tristable flip-flop B2 are also zero. Thus, all four transistors 01, Q2, Q3 and Q4 are turned off so that the motor is isolated from its power supply and the actuator is not moved.

If both position control signals El and E2 are changed by an equal amount so that they are no longer equal to the signals S1 and S2 representing the position of the actuator then, assuming that they are now greater in magnitude than the signals S1 and S2, there will be a positive output from both of the differential operational amplifiers Al and A2. This leads to a series of positive going pulses being generated in the multivibrator B1 and to the flip-flop B2 assuming its positive state. Thus transistor 02 is turned on and transistor Q1 is turned on during each positive going pulse in the multivibrator B1.

When both Ol and Q2 are turned on, the motor M is connected between the power supply and earth. The motor rotates in a direction in which it moves the actuator in the required direction and, as the motor rotates, the wipers on the potentiometers P1 and P2 move to increase the magnitude of signals S1 and S2. Since the duration or the frequency of the pulses generated in the multivibrator Bl is proportional to the difference in magnitude between the signals S1 and El, the greater the difference, the greater the period of time for which the transistor Ol and hence the motor is energised.Thus, the actuator is made to move more quickly the greater the difference between the two signals P1 and Si. As the magnitude of the signals S1 and S2 increases, the difference between them and the signals El and E2 decreases. As soon as they become equal, indicating that the actuator has moved to its required position, the output from both amplifiers Al and A2 falls to zero leading to the outputs from both multivibrator B1 and flip-flop B2 falling to zero and transistors Q1 and Q2 being turned off. This isolates the motor M from its power supply and so stops the movement of the actuator.

If the initial change in the position command signals El and E2 is to reduce their magnitude, with respect to the signals S1 and S2, the outputs E1 and E2 from the amplifiers Al and A2 are negative resulting in negative going pulses being generated in the multivibrator B1 and a negative output from the flip-flop B2. This turns on transistors Q3 and 04 and so results in the connection of the motor M in between its power supply and earth in the opposite direction so that the motor rotates in the opposite direction.

When the difference signals E1 and E2 agree in sign but differ in magnitude, the actuator is moved to a new position corresponding to either El or E2, whichever position is nearer to the original position of the actuator. Assume first that both control signals El and E2 are greater than the actuator position signals S1 and S2, but that signal El is greater than signal E2, i.e. assume signals E1 and E2 to be positive, with E1 the larger. The negative going pulses from the multivibrator B1 cause the transistor Q1 to turn on during the pulses, and the positive potential from the flip-flop B2 turns transistor 02 on.Thus the motor M is energised during the pulses from the multivibrator B1 and this continues until the actuator has moved into a position where signals S2 and E2 are equal. When the actuator has reached this new position, which is that corresponding to control signal E2, the output E2 is zero and transistor Q2 is turned off. This isolates the power supply from the motor M. As the actuator approaches this position, the difference signal E1 diminishes and so the periods for which the transistor Owl is turned on and the motor is powered become either less frequent or shorter, thus slowing the movement of the actuator.

Now assume instead that both signals El and E2 are greater than S1 and S2, but that signal E2 is the greater of the two, i.e. E2 is greater than E1.

The flip-flop B2 turns the transistor Q2 on, and the multivibrator B1 turns the transistor Q1 on periodically, and thus the power circuit to the motor M is completed intermittently, until the actuator is moved into the position corresponding to the control signal El. As the actuator approaches this position, the difference signal E1 diminishes and so the periods for which the transistor Owl is turned on and the motor is powered become either less frequent or shorter, thus slowing the movement of the actuator.

If instead the signals El and E2 were both less than S1 and S2, and unequal, then the actuator would be moved in the opposite direction until the output from either tristable, B1 or B2, become null, indicating that the actuator had reached the nearer of the two requested positions.

Assume now that either signal El is greater than S1 and E2 less than S2, or El is less than S1 and E2 is greater than S2, making E1 and E2 of opposite sign, i.e. assume the auto-pilots to be contradicting one another and requesting movement in opposite directions. Either transistors Q1 and Q4, or Q3 and Q2, are turned on, connecting the power supply to earth and bypassing the motor M. This causes at least one of the circuit breakers D1 and D2 to act and to isolate the power supply until Q1 and Q4, or Q3 and Q2, no longer conduct. The circuit breakers are then automatically reset. Thus, in this case, as the motor is isolated from its power supply, the actuator is not moved.

Claims

1. A control apparatus for controlling power supplied to a motor or to another power element, hereinafter referred to as a motor, to move an actuator; comprising means for receiving two independent position command signals, means for connecting a power supply across the motor to cause it to move the actuator in the direction commanded by the position command signals, if they both command the same direction of movement, until the actuator has moved to whichever of the positions commanded by the position command signals is nearer the initial position of the actuator, or for bypassing the motor and hence preventing it from operating if the two position command signals command movement in opposite directions.

2. An aircraft flight control apparatus comprising a power supply, a motor for moving an actuator, and control circuitry for controlling the interconnection of the power supply and the motor, the control circuitry including means for receiving two independent position command signals, and for connecting the power supply across the motor to cause it to move the actuator in the direction commanded by the position command signals, if they both command the same direction of movement, until the actuator has moved to whichever of the positions commanded by the position command signals is nearer the initial position of the actuator, or for bypassing the motor and hence preventing it from operating if the two position command signals command movement in opposite directions.

3. An aircraft flight control apparatus according to Claim 2, in which there is at least one circuit breaker in series with the power supply, which cuts off the power supply when the motor is bypassed and the power supply short circuited, and which automatically resets itself when the power supply is no longer short circuited.

4. An aircraft flight control apparatus according to Claims 2 or 3, where the control circuitry comprises two channels, one for each of the position command signals, each channel having a comparator to compare the position command signal with a position signal fed back from the actuator indicative of the position of the actuator, and a tristable device for generating an output which has three distinct states corresponding to the positive zero or negative difference between the position command signal and the position signal.

5. An aircraft flight control apparatus according to Claim 4, in which one of the tristable devices incorporates a multivibrator, to generate a series of pulses, the duration of each pulse depending upon the magnitude of the difference between its position command signal and its position signal.

6. An aircraft flight control apparatus according to any one of Claims 2 to 5, in which the control circuitry includes four power transistors connected in a bridge configuration with the motor connected between the two opposite nodes of the bridge, and the power supply connected between the other two opposite nodes, the control circuitry being arranged to control the state of the power transistors so that the motor is connected in one sense or the other sense across the power supply, or is bypassed.

7. A control apparatus according to Claim 1, or an aircraft flight control apparatus according to Claim 2, constructed substantially as described with reference to the accompanying drawings.

8. High safety power electronic amplifier for the automatic flight control system of an helicopter or an aircraft, featuring a power amplifier which is an electrical circuit assuming the "Voter" function without using a conventional "Voter" set-up, controlling a flight control drive unit which consists of an electrical motor operating an actuator or analogue, this circuit operating in combination with a self-protected power supply circuit.

9. Power amplifier according to Claim 1 in which the abovementioned voter function results from a circuit which consists upstream the power supply circuit of two channels which constitutes two separate channels up to the motor power supply level; a channel C1 which consists of a summing amplifier Al connected to a tristable flip-flop B1 and a channel C2 which consists of a summing-amplifier A2 connected to a tristable flip-flop B2; the first channel receiving signal El at the instant to sending at the output of Al a deviation signal E1 and sending a constant amplitude signal at B1 output, but of sign, duration and frequency variable as a function of the sign and amplitude of the deviation signal E1; a second channel receiving at the instant to, i.e.

simultaneously, (in synchronisation) a signal E2 sending a deviation signal E2 at the output of A2; a bridge-connected switching static device; two fast operating electronic circuit-breakers seriesconnected in the motor power supply circuit; this circuit as shown in the only figure operates as a voter due to the fact that the motor control signal is always an "AND" function: on the one hand of the two signs, and on the other hand, of amplitudes of the deviation signals E1 and E2 delivered by the two summers Al and A2.

10. Voter power amplifier according to Claim 2 in which the abovementioned switching static device consists of four power transistors operating as static breakers, and the abovementioned motor connected to one of the transverse branches of the bridge thus ensuring protection against all cases of active failures of the flight control unit.