GB2029646A - Improvements in or relating to electronic damping systems - Google Patents

Abstract

The invention provides a waveguide switch arrangement in which an electric motor 8 is arranged to drive the switch 1 from one position to another and means are provided for utilising the electric motor to provide a braking effect as the switch approaches the other position. The motor is driven in a chosen direction from a power supply 11 via a differential amplifier 10 governed by a bridge 10 and a bistable 18 which determines the direction of unbalance of the bridge. After a given period of acceleration determined by a relay 22 the power to the motor is interrupted and the motor is short-circuited by a switch 25 for a short period determined by pulse generator 23 followed by a period determined by pulse generator 26, in which the drive to the motor is reversed. The motor is subjected to a short circuit when in the rest position. <IMAGE>

Description

SPECIFICATION Improvements in or relating to electronic damping systems This invention relates to waveguide switches and in particular to waveguide switches wherein the changing of the switch from one position to another is effected by means of an electric motor.

Waveguide switches of the above kind are commonly employed in a communications ground station in order to effect the changeover from a main channel to a reserve channel should a fault develop in the main channel. Clearly the changeover in the event of failure should be made as quickly as possible in order to afford the minimum of interruption of traffic passing through the channel. It is desirable therefore that not only is the moving portion (usually a rotor) of the waveguide switch accelerated rapidly but also that this be brought to a stop rapidly if a satisfactorily speedy changeover is to be obtained. It is known to use dashpot dampers in order to assist in the deceleration of a waveguide switch rotor, but the mechanical shock which is experienced by the rotor as the dashpot is engaged is often undesirably high.

One object of the present invention is to provide an improved waveguide switch arrangement in which the above mentioned difficulty is reduced.

According to this invention a waveguide switch arrangement includes an electric motor arranged to drive said switch from one position to another and means for utilising said electric motor to provide a braking effect as said switch approaches said other position.

Preferably said means comprises means for imposing, at one time, a short-circuit across said motor and means for reversing, at another time, the drive applied to said motor.

Preferably said means is such that a short circuit is first applied across said motors whilst the drive thereto is interrupted and thereafter the drive applied to said motor is reversed.

Preferably said means is also such that when said rotor is in one or other of said two positions a short circuit is imposed across said motor in order to inhibit undesired movement thereof.

Preferably said motor is driven from a power supply via a differential power amplifier which is controlled by a Wheatstone bridge circuit and means are provided for unbalancing said bridge circuit when drive is required to be applied to said motor to drive said switch from one position to another.

Normally means are provided for unbalancing said bridge circuit in one direction or the other in dependence upon the direction in which said motor is required to be driven.

Where said switch is a two position switch preferably said lastmentioned means comprises a two current level bistable circuit which is connected to said bridge circuit such that when said bistable circuit is providing a high level of output said bridge circuit is unbalanced in one direction and when said bistable circuit is providing a low level of outputthe bridge circuit is unbalanced in the other direction.

Normally said bistable circuit would be triggered to change its state by a pulse generator which is itself triggered by a waveguide switch position selector which may be manual or automatic.

Preferably part of the output of said pulse generator is applied via a delay circuit of delay corresponding to the period during which initial drive is required to be applied to said motor to trigger a pulse generator operative to produce a pulse of duration corresponding to a period of short circuit required to be imposed across said motor, output from said lastmentioned pulse generator beingapplied to interrupt the power supply for said motor and to impose said short circuit thereacross.

Preferably an output from said lastmentioned pulse generator is applied to trigger with the trailing edge of the pulse produced, a further pulse generator which is operative to produce a pulse of duration corresponding to the period of time during which the drive to said motor requires to be reversed and of amplitude such that if combined with the output signal from said bistable circuit causes said bridge circuit to unbalance in an opposite direction and means for applying the output pulse of said last mentioned pulse generator in combination with the output of said bistable circuit to said bridge circuit.

Preferably means are provided responsive to the movement of the moving member of said switch for progressively restoring the balance of said bridge circuit and means are provided for monitoring the state of balance of said bridge circuit whereby to provide an output signal when said moving member reaches a position to which it is switched, means being provided for utilising said lastmentioned output signal to interrupt the power supply to said motor and to impose a short circuit thereacross.

Preferably said means for imposing a short circuit across said motor comprises a crow-bar switch.

The invention is illustrated in and further described with reference to the accompanying drawings in which Figure 1 is a block schematic diagram illustrating one embodiment of waveguide switch arrangement in accordance with the present invention and Figure 2 is an explanatory graph.

Referring to Figure 1, the waveguide switch as such is represented at 1. This consists of a stationary housing 2 having an input port 3 and two output ports 4 and 5. A rotor 6 having a transfer port 7 is moveable by means of a motor 8 (as represented by the dashed line 9) from the position shown in which it connects input port 3 to output port 4 to an alternative position in which it connects input port 3 to output port 5. Whilst not sown, output port 4 may be assumed to be connected to a main communica tions channel in a ground station whilst port 5 is connected to a standby channel provided to replace the main channel should this latter become faulty.

The motor 8 is driven via a differential power amplifier 10 from a switchable power supply source: 11 which is such as to be capable of being switched off by a signal applied to either of its input control leads 12 and 13. Differential power amplifier 10 derives input control signals from an opto-isolator Wheatstone bridge circuit 14 such that the motor8 is driven in one direction or the other in dependence upon the direction of unbalance in the Wheatstone bridge circuit 14. Whiist not shown in detail the Wheatstone bridge circuit 14 comprises two arms containing opto-isolators and the remaining two arms formed by a motor driven potentiometer which is controlled by means of a control input 15 which is connected to a potentiometer represented at 16 driven with the rotor 6 of the waveguide switch 1 so that as the rotor switch approaches a position into which it is being switched the signal applied to the Wheatstone bridge circuit 14 from the potentiometer 16 tends to restore the balance of this. The current drive for the reference opto-isolator is represented by the lead 17.

Atwo level bistable circuit 18 is provided to control the state of balance of the bridge circuit 14.

The current output levels provided by bistable circuit 18 are relatively precise and constant. When bistable circuit 18 provides a high level of output signal the Wheatstone bridge circuit 14 is unbalanced in one direction whilst when the bistable circuit 18 provides a low level of output signal the Wheatstone bridge is unbalanced in the other direction. Thus if bistable circuit 18 provides a high level of output signal the motor 8 drives in one direction and the rotor 6 is driven in one direction whilst if bistable circuit 18 provides a low level of output the motor 8 drives in the other direction and the rotor 6 is driven in the other direction.

Bistable circuit 18 is triggered to change from high level to low level output or vice versa by a trigger pulse from a pulse generator 19 which itself is triggered by the waveguide switch position selector 20. Whilst not illustrated in detail in this example the waveguide switch position selector 20 is a manual instrument which incorporates an indicator showing the position of the switch rotor 6. When rotor 6 is required to be changed from one position to the other the selector 20 is operated which causes pulse generator 19 to emit a trigger pulse which in turn causes the output of bistable circuit 18 to change and the bridge circuit 14 becomes unbalanced in the appropriate direction.

The trigger pulse from pulse generator 19 is sampled as represented at 21 and applied to a 40 ms delay network 22. The output of delay network 22 is applied to a 5ms duration pulse generator 23 which applies a pulse of 5ms duration to control lead 12 to switch off power supply 11 and via lead 24 to a crow-bar switch 25 which applies a short circuit of 5ms duration across the motor 8. At the end of the 5ms pulse generated by pulse generator 23 crow-bar swith 25 releases to remove the short circuit across the motor 8 and power supply circuit 11 is switched on.At the same time and by means of the trailing edge of the pulse generated by pulse generator 23 a furtherpulse generator 26 is triggered which pro vides one of two alternating output pulses which are applied via lead 27 to combine with the output of bistable circuit 18 so as to cause bridge circuit 14 to unbalance in the opposite direction for a period of 5ms. This has the effect of reversing the direction of drive applied to the motor 8 and so provides a relatively large braking effect.

As will be appreciated the next time the pulse generator 26 is operated the other of its two outputs will be provided since bistable circuit 18 will be providing its other output the operation being synchronised to ensure that the bridge circuit 14 is driven into unbalance in the opposite direction to provide the required braking effect.

By the time 5ms pulse provided by pulse generator 26 is finished rotor 6 will be very close to its other position and travelling relatively slowly before engagement with a mechanical stop. Potentiometer 16 will have so adjusted bridge circuit 14 that it is nearly in a state of balance and when balance occurs as the rotor 6 attains its other position this is detected by a balance detector 28 which via control lead 29 again operates the crow-bar switch 25 to apply a short circuit across the motor 8 and a signal to control lead 13 of power supply 11 to switch this off. The short circuit thus applied across motor 8 is held until the next operation or change of switch position as a form of stationary brake.

The effect achieved is illustrated in Figure 2 which is a graph of switch rotor velocity V against time t.

The period a represents the period during which the rotor is being accelerated which in the example described is 40ms. The period b represents the period during which the 5ms short circuit is imposed across the motor 8 underthe control of pulse generator 23 and period c represents the period during which reverse drive is applied to the motor8 due to the action of pulse generator 26.

Claims (12)

1. Awaveguideswitch arrangement including an electric motor arranged to drive said switch from one position to another and means for utilising said electric motor to provide a braking effect as said switch approaches said other position.

2. An arrangement as claimed in claim 1 and wherein said means comprises means for imposing, at one time, a short circuit across said motor and means for reversing, at another time, the drive applied to said motor.

3. An arrangement as claimed in claim 2 and wherein said means is such that a short circuit is first applied across said motor whilst the drive thereto is interrupted and thereafter the drive applied to said motor is reversed.

4. An arrangement as claimed in claim 2 or 3 and wherein said means is also such that when said rotor is in one or other of said two positions a short circuit is imposed across said motor in order to inhibit undesired movement thereof.

5. An arrangement as claimed in any of the above claims and wherein said motor is driven from a power supply via a differential power amplifier which is controlled by a Wheatstone bridge circuit and means are provided for unbalancing said bridge circuit when drive is required to be applied to said motor to drive said switch from one position to another.

6. An arrangement as claimed in claim 5 and wherein means are provided for unbalancing said bridge circuit in one direction or the other in dependence upon the direction in which said motor is required to be driven.

7. An arrangement as claimed in claim 6 wherein said switch is a two position switch and wherein said lastmentioned means comprises a two current level bistable circuit which is connected to said bridge circuit such that when said bistable circuit is providing a high level of output said bridge circuit is unbalanced in one direction and when said bistable circuit is providing a low level of output the bridge circuit is unbalanced in the other direction.

8. An arrangement as claimed in claim 7 and wherein said bistable circuit is arranged to be triggered to change its state by a pulse generator which is itself triggered by a waveguide switch position selector which may be manual or automatic.

9. An arrangement as claimed in claim 8 and wherein part of the output of said pulse generator is applied via a delay circuit of delay corresponding to the period during which initial drive is required to be applied to said motor to trigger a pulse generator operative to produce a pulse of duration corresponding to a period of short circuit required to be imposed across said motor, output from said lastmentioned pulse generator being applied to interrupt the power supply for said motor and to impose said short circuit thereacross.

10. An arrangement as claimed in claim 9 and wherein an output from said last mentiond pulse generator is applied to trigger, with the trailing edge of the pulse produced, a further pulse generator which is operative to produce a pulse of duration corresponding to the period of time during which the drive to said motor requires to be reversed and of amplitude such that if combined with the output signal from said bistable circuit causes said bridge circuit to unbalance in an opposite direction and means for applying the output pulse of said lastmentioned pulse generator in combination with the output of said bistable circuit to said bridge circuit.

11. An arrangement as claimed in claim 2 or in any of the above claims 2 to 10 as dependent upon claim 2 and wherein means are provided responsive to the movement of the moving member of said switch for progressively restoring the balance of said bridge circuit and means are provided for monitoring the state of balance of said bridge circuit whereby to provide an output signal when said moving member reaches a position to which it is switched, means being provided for utilising said lastmentioned output signal to interrupt the power supply to said motor and to impose a short circuit thereacross.

12. An arrangement as claimed in claim 2 or in any of the above claims 2 to 11 as dependent upon claim 2 and wherein said means for imposing a short circuit across said motor comprises a crow-bar switch.

13 A waveguide switch arrangementsubstantially as herein described with reference to the accompanying drawings.