WO1996001200A1

WO1996001200A1 - Stop motion device

Info

Publication number: WO1996001200A1
Application number: PCT/GB1995/001570
Authority: WO
Inventors: Colin Minkley; Brian Fisher; Norman Harold George Palmer
Original assignee: Automotive Control Equipment Limited
Priority date: 1994-07-05
Filing date: 1995-07-04
Publication date: 1996-01-18
Also published as: GB2291151A; GB9413504D0; GB9513566D0; AU2803795A

Abstract

A stop motion device for use in preventing or arresting movement, more especially as a safety device for a vehicle when reversing comprises detection means (26 or 51, 53, 50) moveable between an inoperative or retracted position on the rear of a vehicle to a rearwardly extending activated or operative position. On detection of an obstacle by the detection means immediate automatic application of the vehicle brakes is caused to take place and also simultaneous retraction of the detector means back to the rear of the vehicle. Thus, for a reasonably cautious reversing speed for which the device is intended, braking distance of the vehicle is accommodated before it strikes the obstacle. Therefore, only light initial contact of the detection means (26) with the obstacle occurs. Where the detection means (51, 53) provides a transverse infrared detection beam (50), there is no actual physical contact with the obstacle.

Description

Title - Stop Motion Device

The present invention relates to a stop motion device and particularly, but not exclusively, to such a device for a vehicle for preventing or arresting reversing movement of the vehicle when an object such as a person or other obstruction is present in the vehicle's path.

Various reversing vehicle safety systems have been developed in order to reduce accidents during this potentially hazardous manoeuvre. These systems vary from simple audible alarms such as reversing bleepers and speech synthesisers to more sophisticated systems which automatically apply a vehicles brakes when an obstacle is detected in the path of the reversing vehicle.

Typical examples of the latter system are the systems described in Swedish patent no. 7605613 and also that known as the Hope Underrun bar. An under-run bar is fitted at the rear of a vehicle to prevent a smaller vehicle, such as a car, from passing under the vehicle to which the bar is fitted.

The Hope Underrun bar is pivoted at its top to the vehicle chassis and when the bar strikes an object whilst the vehicle is reversing, the complete under-run bar pivots forward and this motion initiates application of the brakes. The under-run bar is prevented from swinging on its pivot during normal use of the vehicle by a substantial spring which pushes the under-run bar rearwards until it reaches a stop. The spring must be strong enough to prevent the under¬ run bar from swinging during normal use but this results in a considerable force being required to move the bar forward when it strikes an object whilst reversing. Thus, considerable damage can still occur should the vehicle strike a fragile object such as a person or a child's pram.

An alternative to the Hope Underrun bar is a hollow rubber sensor fitted across the entire width of the vehicle at the rear. When this sensor strikes an object whilst the vehicle is reversing, the brakes are automatically applied. This system is reasonably satisfactory if the obstacle is moveable such as a person, vehicle or loose drums etc, but if the vehicle is reversing against a wall or loading dock for example, the braking distance of the vehicle may exceed the compression distance of the rubber sensor. This is especially likely to happen if the vehicle reversing speed is high. Under these circumstances damage may occur to the rubber sensor, the vehicle and/or the obstacle.

According to the present invention there is provided a stop motion device for use in preventing movement, or arresting existing movement, of a vehicle or other support on which the device is mounted in use, said device comprising detection means movable between a first or inoperative position and a second or activated position whereby the detection means is moved in advance of the selected direction of movement of a said vehicle or other support carrying the device, and means for positively moving the detection means between the first and second positions upon activation and between the second and first positions upon detection of the presence of an object in the path, or projected path, of the detection means and whereby automatic operation of motion stopping means of a said vehicle or other support is effected upon said detection of such object.

The invention will now be described further by way of example with reference to the accompanying drawings in which:-

Figure 1 A is a diagrammatic side elevation of under-run bar detection means according to one embodiment of the invention showing the bar and detection means in a first or inoperative position;

Figure IB corresponds to Figure 1 A but showing the under-run bar and detection means in a second or activated position;

Figure 2 illustrates diagrammatically part of one control system for displacing the under-run bar and detection means of Figures 1A and IB between the two positions; Figure 3 A is a diagrammatic plan view of the rear of a vehicle showing a further embodiment in which the detection means is in the first or inoperative position;

Figure 3B corresponds to Figure 3 A but with the detection means in the second or activated position;

Figures 4A and 4B are respectively a plan view and side elevation showing support and actuation of part of the detection means of Figures 3A and 3B, and

Figure 5 is a circuit diagram of an electronic control unit.

In Figures 1A and IB the chassis frame of a vehicle is designated 10 to which an under-run bar 12 is pivotally mounted at 14 by depending arms 13. The bar 12 is displaceable between the first position shown in Figure 1A and the second position shown in Figure IB.

The means for displacing the under-run bar 12 between the two positions comprises an actuator 16 in the form of a pneumatic or hydraulic piston and cylinder assembly. The cylinder 17 is pivoted at 18 to a bracket or lug 20 which is firmly secured, for example by welding, to the chassis frame 10. The piston rod 22 carries a clevis 24 which is pivotally connected to the under-run bar 12 at a position intermediate its ends.

A detector 26 is mounted on the operative face of the under-run bar 12 and is connected to the actuator 16 via an electronic control unit (see Figure 5) and valve arrangement such as that shown at 34 in Figure 2.

In general terms, when a driver engages reverse gear the electronic control unit issues a signal to the control valve arrangement 34 to cause the piston and cylinder assembly 16 to move the under-run bar 12 from its first to its second position. At the same time the vehicle braking system is primed for operation. Should the detector 26 contact an obstacle which would be in the path of the vehicle, then a signal is sent to the electronic control unit which causes the vehicles brakes to be applied and this prevents the vehicle from reversing. However, should no obstacle be detected, then the vehicle is able to commence reversing movement until such time, if any, as an obstacle is detected whereupon the vehicle brakes are applied. Simultaneously, the actuator 16 positively and rapidly retracts the under-run bar 12 from its second to its first position (Figure 1A). Thus the vehicle is promptly brought to rest. No further reversing movement is then possible even if the driver were to disengage and then re¬ engage reverse gear.

A fixed stop 28 may be fitted to back-up the movable under-run bar 12 for use when the vehicle is travelling in a forward direction. The mechanical stop 28 is mounted in front of the under-run bar in order to provide a definite limit of travel. The arrangement also provides for a shock absorbing action of the under-run bar. The stop 28 may be a statutory requirement in some countries, such as the United Kingdom.

Further operational details are as follows :-

If the vehicle is not in reverse gear, the actuator 16 will, if necessary, move the under-run bar 12 forwards into its normal or first position. The double acting pneumatic actuator (Figure 2) used to control the under-run bar is of a special design with one port 30 at the piston rod end of the cylinder whilst the other port 32 is positioned part way along the cylinder 17, i.e. not at the other end as with a conventional cylinder.

The actuator 16 is controlled by a double acting solenoid valve 34 which may be either a double solenoid type or one with a single solenoid and an internal return spring. The arrangement of double acting actuator and double actmg, double solenoid valve is shown in Figure 2 and operates as follows:-

When the retract solenoid 36 is energised, high pressure air will enter the piston rod end of the cylinder 17 at the port 30 and force the piston 33 back in the cylinder which will retract the under-run bar 12. The air on the other side of the piston will be forced out of the cylinder via the double acting control valve 34 to atmosphere. When the piston covers the port 32 it will continue to move back in the cylinder 17 and compress the air in the closed end 38 of the cylinder until the air pressure on both sides of the piston 33 is equal.

When the vehicle is put into reverse gear, the extend solenoid 40 will be energised. The control valve will then allow the air at the piston rod end of the cylinder to exhaust to atmosphere through the port 30. The compressed air in the closed end 38 of the cylinder will force the piston rod 22 out of the cylinder. When the piston 33 uncovers the port 32, high pressure air will be supplied from the control valve to complete the extension of the piston rod 22 and under-run bar 12. The under-run bar 12 is therefore held in the activated position by full air pressure.

The detector 26 may consist of an electrical contact strip, a hinged plate operating a micro switch, a hollow flexible air or gas filled sensor operating in conjunction with a pressure switch or any other means which will detect contact between it and an obstacle.

When the detector 26 makes contact with an obstacle a signal will be sent to the electronic control unit which will cause the vehicle brakes to be applied and the under-run bar 12 to be retracted simultaneously.

Providing the vehicle reversing speed does not exceed that for which the system has been designed, the under-run bar retracting distance will exceed the vehicle braking distance and the under-run bar retracting speed will exceed the vehicle reversing speed. Thus, the maximum force exerted between the under-run bar and obstacle will be limited to that required to operate the detector which can be made very small.

If the vehicle reversing speed exceeds the speed for which the system has been designed, the difference between the vehicle reversing speed and the under-run bar retracting speed will determine the speed of the piston 33 entering the cylinder 17 of the actuator 16 attached to the under-run bar 12. If the obstacle is immovable such as a loading dock, the increasing pressure in the cylinder will assist in the slowing down of the vehicle. If the obstacle is movable it will affect the force exerted between the under-run bar and obstacle.

The vehicle brakes will remain applied until the vehicle is taken out of reverse gear whilst the under-run bar will remain retracted until the vehicle is put into reverse gear again.

An essential requirement of this invention is that the detector 26, in its operative position, projects in advance or upstream of the path or projected path of the vehicle. In the above description the necessary projection has been provided by mounting the detector on a pivoted under-run bar. It will be apparent that the mounting could be on a telescopic or lazy tong arrangement for example which is itself carried by a fixed vehicle part such as the vehicle chassis frame 10.

Referring now to a further embodiment of the invention shown in Figures 3 A and 3B, the chassis frame or body 10 of the vehicle has detector support members or arms 42A, 42B pivotally mounted on it at the rear of the vehicle and adjacent each side at 44 A, 44B.

When the support arms 42A, 42B are operated so as to fully extend rearwardly from the vehicle, detection means carried by them are then in spaced apart and opposed relationship substantially corresponding to the width of the vehicle. Thus the arm 42A carries a transmitter 51 which faces a receiver or sensor 53 on the arm 42B for transmitting a transverse infra red detecting beam 50 to the receiver 53.

When the beam 50 is interrupted by an obstacle, the presence of a signal from the receiver 53 to the electronic control unit (Figure 5) is terminated which causes immediate automatic operation of the vehicle brakes and simultaneous retraction of the arms 42 A, 42B.

If desired the arm 42 A may carry a light source for transmitting a light beam to a receiver in the form of a photo electric cell on the arm 42B.

An arrangement for operating the arms 42 A, 42B between the retracted position (Figure 3 A) and the operative position (Figure 3B) or vice versa by respective actuators 46 is shown in Figures 4A and 4B in which in the case of the left hand or near side of the vehicle (and similarly for the right hand or off side), a mounting member 43B fixed to the rear of the vehicle pivotally carries at 44B the arm 42B. The actuator 46 in the form of a pneumatic or hydraulic piston and cylinder assembly has its cylinder 47 pivoted at 48 to the mounting member 43B and its piston rod 45 pivotally connected at 49 to the arm 42B whereby contraction of the actuator 46 pulls the arm 42B to the rearwardly extending position and extension of the actuator retracts the arm 42B into the mounting member 43B.

The arm 42B and member 43B are of channel or other suitable cross section so as to interfit and protectively accommodate the actuator 46 and detection means.

The actuators 46 are controlled by a single standard solenoid valve operated in conjunction with or by the electronic control unit.

Touch sensitive switches 52A and 52B are also mounted at the ends of the arms 42 A and 42B and are operated by sensitive feeler probes 54A and 54B respectively which protrude away from the vehicle when the arms fully extend rearwardly.

As before and in general terms when a driver engages reverse gear the electronic control unit issues a signal to the control valve arrangement to cause the piston and cylinder actuators 46 to move the arms 42A and 42B from their first to their second position. At the same time the vehicle braking system is primed for operation. Should the detector beam 50 detect an obstacle which would be in the path of the vehicle, then a signal is sent to the electronic control unit which cause the vehicles brakes to be applied and this prevents the vehicle from reversing. However, should no obstacle be detected, then the vehicle is able to commence reversing movement until such time, if any, an obstacle is detected whereupon the vehicle brakes are applied. Simultaneously, the respective actuators 46 positively and rapidly retract the arms 42A and 42B from their second to their first positions (Figure 3 A). Thus the vehicle is promptly brought to rest. No further reversing movement is then possible even if the driver were to disengage and then re-engage reverse gear.

Further operation details are as follows:-

If the vehicle is not in reverse gear, the arms 42A and 42B will be held in their first or inoperative positions by return springs if single acting actuators are used or by fluid pressure if double acting actuators 46 are used.

When the vehicle is put into reverse gear, a solenoid valve controlling the actuators 46 will cause the arms 42A, 42B to move from their first or inoperative position to their second or activated position.

Instead of an infra-red beam 50, the detector means may consist of an electrical contact strip, a touch sensitive microswitch, a hollow flexible air or gas filled sensor operating in conjunction with a pressure switch, or any other means either singly or in combination which will detect an obstacle.

When no obstacle is present, a signal will be sent to eh electronic control unit which will inhibit automatic operation of the brakes.

On detection of an obstacle, this signal will be interrupted and the electronic control unit will cause the vehicle brakes to be automatically applied and the arms 42A, 42B to be retracted simultaneously.

Again as before and providing the vehicle reversing speed does not exceed that for which the system was designed, the movable member retracting distance will exceed the vehicle braking distance and the moveable member retracting speed will exceed the vehicle reversing speed. Thus, the maximum force exerted on the device will be limited to that required to operate the detection means which in the case of touch sensitive switches 52A, 52B can be made very small and in the case of an infra-red beam 50 will be zero.,

If the vehicle reversing speed exceeds the speed for which the system has been designed, the vehicle will strike the obstacle but with much less force that it would if the device was not fitted.

The vehicle brakes will remain applied until the vehicle is taken out of reverse gear whilst the movable arms 42A, 42B will remain retracted until the vehicle is put into reverse gear again.

An important characteristic of this invention is its fail-safe features. The vehicle brakes will be applied automatically when the vehicle is in reverse gear if there is no signal from the infra¬ red or other detector. Normally, this will be due to the presence of an obstacle but it could be due to a fault in the system such as failure of the arms 42 A, 42B to extend fully, faulty or very dirty detectors or broken connections etc. Such a fault will cause the vehicle brakes to be applied when reverse is selected and hence the fault must be repaired before the vehicle can be driven in reverse.

In order to prevent the vehicle brakes from being automatically operated by the infra-red or other detector whilst the arms 42A, 42B are moving to their operational position, a timer provides a signal of approximately 2 seconds which prevents the lack of a signal form the infra-red receiver 53 or other detector during this interval form operating the brakes. If the infra-red beam 50 or the like is operational within the 2 second period the timer pulse will be teπninated as soon as the signal from the receiver 53 occurs.

Signals from the touch sensitive switches 52A, 52B are not affected by the 2 second timer and hence the vehicle brakes will be applied immediately if a feeler probe 54 A, 54B makes contact with an obstacle. An essential requirement of this invention is that the detection means in its operative position, projects in advance or upstream of the path or projected path of the vehicle. In the above described infra-red arrangement the necessary projection has been provided by mounting the detection means on moveable members 42 A, 42B.

Whereas in the above description the invention has been applied to a safety device for reversing vehicle, it will be appreciated that the device may also be used in other situations where a stop motion device is desirable, such for example in the loading of aircraft where the motion controlled may be a forward or lateral movement of a loading vehicle or platform. The control unit may incorporate a safety feature which prevents further engagement of reverse gear without driver investigation to the rear of vehicle should an obstacle have been detected more than twice.

SAFETY FEATURES

The complete system is inherently fail-safe. As mentioned before, the system is armed as soon as reverse hear is selected and at this instant the detector arms should extend. If they should fail to extend for any reason, be it mechanical, pneumatic or electrical then the infra-red beam will not shine on the detector and the brakes will be applied after 2 seconds.

If the lenses on the infra-red transmitter and/or receiver become very dirty or are covered up, this will also cause the brakes to come on.

The infra-red receiver sends a continuous signal to the electronic unit (Figure 5) when there is no obstacle. The brakes only come on when this signal is interrupted. Hence, the brakes will come on if the connection between the infra-red received and the electronic control unit is broken.

If either the infra-red transmitter or receiver is faulty there will be no beam detected and hence the brakes will be applied.

An audible warning device in the cab pulses as soon as reverse is selected to confirm that the system has been armed. If the connection between the electronic control unit and the brake solenoid should be broken then the cab audible alarm will pulse at a higher frequency. This audible alarm will switch to a continuous note when an obstacle is detected. This will inform the driver to apply the brakes if for any reason the brake solenoid valve should fail to operate.

DESCRIPTION OF ELECTRONIC CIRCUIT (^"Figure 5.

When the ignition is ON and the vehicle is put into reverse gear to close the reverse switch the following operations will occur:-

STABΓLISED POWER SUPPLY

Current will flow through the reverse polarity diode Dl, the series resistor Rl and zener diode ZD1 to provide a stabilised 12v power supply.

CAB WARNING BUZZER

The cab warning buzzer will emit a pulsing sound as soon as reverse gear is selected. The buzzer circuit is controlled by an astable oscillator based on a 555 timer. The circuit is protected against short circuits at the buzzer or interconnecting wiring and operates as follows:-

As soon as the stabilised power supply is established the output for the 555 timer, pin 3, will go high and capacitor Cl will commence to charge via R2 and R3 on a 506 m sec time constant. When the voltage across Cl reaches 2/3 rds of the stabilised supply voltage i.e. 8 volts, the output of the 555 timer will drop to zero and capacitor Cl will start to discharge into pin 7 of the 555 timer on a 484 m sec time constant. As soon as the voltage across Cl reaches 1/3 of the supply voltage, the output of the 555 will go high again and the cycle will repeat. The output of the 555 timer will therefore be seen to consist of a series of pulses approximately 500 m sec wide with a pulse repetition frequency of 60 pulses per minute. As soon as the output of the 555 timer goes high capacitor C3 will start to charge via resistor R4 on a 0.1 m sec time constant. This charging current will cause transistor TR1 to conduct which in turn enable base current to flow out of the Darlington transistor TR2 which will conduct and energise the cab warning buzzer. The voltage across the buzzer -will rise and reverse bias diode D3 and enable current to flow from ICI pin 3 through resistor R 5 and diode D2 into the base of transistor TR1 to augment the charging current of capacitor Cl which drops to a very low value after 0.5 m sees. The buzzer will continue operating until the end of the pulse from the 555 timer whereupon it will fall silent until the next pulse. If an obstacle is detected, transistor TR8 will conduct and enable base current to flow continuously out of Darlington TR2 via resistor R7 and diode Dl 1.

The buzzer will therefore change from pulsing to a continuous note as soon as an obstacle is detected.

If a short circuit should occur across the buzzer or associated wiring, the voltage at the cathode of D3 will be held at zero volts with its anode consequently limited to 0.6 volts which is insufficient to maintain TR1 in conduction. TR1 will therefore switch and prevent transistor TR2 from conducting approximately 0.5. m sec after the beginning of each pulse. Transistor TR2 will therefore provide pulses of current 0.5 m sees wide into the short circuit and is quite capable of doing this on a repetitive basis. Transistor TR2 has a current rating of 4 amps and is quite capable of pulsing a 21 W bulb as well as a buzzer.

EXTENDING ARMS

As soon as reverse is selected, the detector arms 42A, 42B move rearwards under the influence of a single acting pneumatic cylinder which is controlled by an electro-pneumatic solenoid valve and operates as follows:-

As soon as the stabilised supply is established, transistor TR3 will receive base current via R9 and will conduct. This will enable base current to flow out of TR4 via resistors R10 and Rl 1 which will cause TR4 to conduct and energise the Extend valve solenoid.

The circuit is protected against short-circuits across the solenoid valve in the following manneπ-

When the circuit is operating normally there will be approximately 1 volt across the emitter- collector junction of transistor TR4 and 0.6 volts across diode D4. There will therefore be 1.6 volts across resistors R13 and R14 of which 0.51 volts will occur across resistor R4 and this is insufficient to cause transistor TR5 to conduct. However, if the current through TR4 should become excessive due to overload or short circuit, then the emitter-collector voltage of TR4 will rise to a level which will increase the voltage across R14 to a level where transistor TR5 will be able to start conducting. This will reduce the base current out of TR4 which will further increase the emitter-collector voltage of TR4. It will be seen that positive feedback occurs and TR4 will switch off very rapidly and decisively. Capacitor C4 ensures that transistor TR5 does not conduct during the turn-on time of TR4.

Transistor TR6 is connected across the base-emitter junction of TR3 whilst its base is connected to the junction between the collector of TR4 and the brake solenoid valve via resistor R15. As soon as an obstacle is detected and the brake solenoid is energised, transistor TR6 will conduct and clamp the base of TR3 which will turn off and cause TR4 to cease conducting thus de-energising the extend solenoid valve. The arms 42A 42B will therefore retract away form the obstacle as soon as it is detected.

TIME DELAY

The infra-red transmitter 51 and receiver 53 are operational as soon as reverse gear is selected but the infra-red beam 50 can only be detected by the receiver when the arms are fully extended. In order to prevent false operation, it is necessary to inhibit the infra-red detection system for a short time to give the arms 42A, 42B time to extend fully and this is achieved as follows:- An operational amplifier IC2a has its non-inverting input connected to the junction of a voltage divider consisting of resistors R17 and R18 connected across the stabilised supply whilst its inverting input is connected to the junction of a resistor R19 and capacitor C5 which are also connected across the stabilised supply.

When reverse gear is first selected, there will not be any voltage across capacitor C5 but the voltage at the junction of resistors R17 and R18 will immediately rise to 8 volts. Thus the voltage at the non-inverting input of the Op-amp will be higher than that at its inverting input and hence its output will be high. This output voltage will be connected to the potential divider comprising resistors R20 and R21 via diode D6. The voltage across R21 is connected direcdy to transistor TR7 and is sufficiently high to cause TR7 to conduct and clamp the base- emitter voltage of TR8 via resistor R24 thus preventing it from conducting and hence inhibits the operation of the brake solenoid. After a period of approximately 2 seconds, capacitor C5 will have charged about 8 volts and thus will cause Op-amp 2a output voltage to go low and remove the base current to TR7 which flowed through diode D6. If the infra-red beam 50 from the transmitter 51 does not reach the receiver 53 by this time due either to an obstacle or fault in the system, then the brake solenoid will be energised. When the reverse gear is de¬ selected, it is necessary for capacitor C5 to discharge quickly in order to ensure that the timer will inhibit the operation of the infra-red system for a full 2 seconds if reverse gear is selected again within a short period. Rapid discharge of C5 is achieved by connecting diode D8 across resistor R19 and by making the potential divider change R17, R19 low resistance. The discharge time of C5 is further reduced by diode D7 whose primary function is to provide positive feedback to the Op-amp.

INFRA-RED DETECTOR SYSTEM

The infra-red transmitter 51 and receiver 53 are energised via diode Dl as soon as reverse gear is selected. The emitter of the PNP output transistor of the receiver is connected directly to the positive supply of the remainder of the receiver circuit.

14

SUBSTITUTE SHEET (RUL€ 26) The receiver 53 is arranged to provide an output signal when it receives a beam from the transmitter. This output is fed via resistor 22 to the base of the clamping transistor TR7 which therefore inhibits operation of the brake valve solenoid.

At the same time the output of the infra-red receiver 53 is fed to the junction of resistor R19 and capacitor C5 via diode D13 and resistor R36. This resets the timer circuit and makes the infra-red detector system operational as soon as the beam 50 shines on the receiver 53.

The faα that no signal is available from the infra-red detector until the infra-red transmitter 51 and receiver 53 are lined up does not cause a problem as an alterative signal is provided for the duration of the normal time required for the infra-=red beam to line up.

BRAKE SOLENOID VALVE DRIVE CIRCUIT

As soon as transistor TR8 conducts, base current will flow out of Darlington transistor TR9 via resistors R27 and R28 and hence TR9 will conduct and energise the brake valve solenoid. The short circuit protection for the brake solenoid is identical to that used for the extend solenoid with diode D9 preventing transistor TRIO from conducting unless an overload or short circuit condition occurs at the brake solenoid valve.

PROTECTION

REVERSE VOLTAGE

The entire system is protected against reverse supply voltage by diode Dl.

SHORT CIRCUIT

Each of the output transistors TR2, TR4 and TR9 is protected against short circuits as described in the foregoing circuit description. HIGH VOLTAGE TRANSIENTS

The only components exposed to high voltage transients are the output transistors TR2, TR4 and TR90. These are protected by capacitors C7, C9 and C8 respectively which cause the output transistors to conduct whenever a high voltage transient occurs.

FAIL-SAFE FEATURES

The system is designed to automatically supply the brakes when reverse gear is selected and an obstacle is detected in the path of the vehicle.

The brakes will also be applied automatically if any of the following occur: -

1 One or both of the detector arms fails to extend fully. This may be due to mechanical damage or obstruction, seized pivots, lack of pneumatic pressure or any other reason.

2 Faulty infra-red transmitter or receiver.

3 Very dirty infra-red transmitter or receiver lenses.

4 Timer circuit fails to produce a 2 second pulse.

Obviously the brakes will not be able to be applied automatically if the brake solenoid is not connected to the electronic control unit. However, the driver can be warned of this condition in the following manneπ-

A resistor is connected across the Darlington transistor TR9 and has a valve which will cause a small voltage to occur across the brake valve solenoid. It is imperative that this voltage is not high enough to hold in the brake valve solenoid when it is de-energised after having been operated. This voltage is applied to the inverting input of a second Op-amp IC2b. The non inverting input of this Op-amp is connected to the junction of a potential divider consisting of resistors R33 and R34 where the voltage is higher than that at the inverting input when the brake valve solenoid is connected. Under this condition the output of IC2b will be high and have no effect on the system.

However, if the brake solenoid should become disconnected or open circuit, the voltage at the inverting input of IC2b will rise to vehicle positive voltage and this will cause the output of IC2b to go low. Current will then flow via resistor R35 and diode D 12 from the CONTROL pin 5 of the 555 timer and this will increase the frequency of the cab warning buzzer.

Claims

1 A stop motion device for use in preventing movement, or arresting existing movement, of a vehicle or other support on which the device is mounted in use, said device comprising detection means (26 or 51, 53 50) movable between a first or inoperative position and a second or activated position whereby the detection means is moved in advance of the selected direction of movement of a said vehicle or other support carrying the device, and means (16, 46) for positively moving the detection means (26 or 51, 53, 50) between the first and second positions upon activation and between the second and first positions upon detection of the presence of an object in the path, or projected path, of the detection means (26 or 51, 53 50) and whereby automatic operation of motion stopping means of a said vehicle (10) or other support is effected upon said detection of such object.

2 A stop motion device according to claim 1 wherein retraction of the movable detection means (26 or 51, 53, 50) from the second or activated advanced position and automatic operation of the motion stopping means is inhibited by the presence of a signal from the detection means, i.e. while the latter is not in detecting reach of an object.

3 A stop motion device according to claim 2 wherein retraction of the moveable detection means (26 or 51, 53, 50) from the second or activated advanced position and automatic operation of the motion stopping means is initiated by the termination of a signal from the detection means i.e. on detection by the latter of an object or by operational failure of the detection means.

4 A stop motion device according to claim 1 wherein any lack of a signal from the detection means (26 or 51, 53, 50) while the latter is moving to its second or activated advance position which would otherwise cause undesired automatic operation of the motion stopping means is overcome by the provision of a timer signal for a period substantially equal to the time taken for the movable detection means to reach said activated advanced position.

A stop motion device according to claim 1 wherein retraction of the movable detection means (26 or 51, 53, 50) from the second or activated advanced position and automatic operation of the motion stopping means is caused to take place as soon as a switch sensor or sensors (52A, 52B) of or associated with the detection means contacts an object.

A stop motion device according to claim 1 wherein the movable detection means (26 or 51, 53, 50) remains in its first or retracted inoperative position until motion in the selected direction is reselected.

A stop motion device according to any of the preceding claims wherein the detection means (26) is carried by a transverse member or bar (12) which is operable (16) for movement between the first or inoperative position and the second or activated position.

A stop motion device according to any of claims 1 to 6 wherein the detection means (51, 53, 50) is of spaced apart two part form in which the parts (42 A and 42B) are operable (46) for movement to the second or activated position so as to be opposed to one another, one part (42 A) carrying a transmitter (51) for transmitting a transverse light beam (50) to a receiver or sensor (53) on the other part (42B), a signal from said receiver or sensor (53) being terminated on the beam (50) being interrupted by an object.

A stop motion device according to claim 8 wherein, in use the transmitter^ 1) transmits a transverse infra-red light beam (50) to the receiver or sensor (53).