GB2272484A - Method and apparatus of operating powered devices, for example, automatic doors - Google Patents

Abstract

Safety apparatus for powered devices, such as automatic doors for railway trains, ensures that the door will only be opened when both a power operating circuit therefor is enabled and a pushbutton assembly 10 is subject to pressure in a manner within predetermined criteria representative of a normal action by a person. Thus, the door is not opened in response to pressure applied by wind or other freak or transient conditions. The pushbutton assembly 10 has an illuminable surround 34 and indicator means 30 which are illuminated when the powered operating circuit for the door is enabled, for example, by the train driver. A sensing and determining circuit utilises a piezo electric device (40, Fig 2) to detect the forces applied to the pressel plate 22 of the pushbutton and to generate a door opening demand signal if the pressure is detected to be within a predetermined range. The voltage developed across the piezo electric device is applied to comparators which determine if the voltage is within the preset range. The circuit may also determine whether the time the pressure is applied is within an acceptable range for door operation. <IMAGE>

Description

METHOD AND APPARATUS OF OPERATING POWERED DEVICES, FOR EXAMPLE, AUTOMATIC DOORS The present invention relates to a method and apparatus of operating a powered device, for example, an automatic door, and to a pushbutton apparatus therefor.

Increasingly powered devices are used in a different environments, particularly in the home and in public places. This means that it is becoming much more important to consider the safety of the public when using powered devices. Safety can be enhanced by ensuring that the devices are switched off if their performance is likely to become unacceptable or even dangerous, and/or to ensure that the powered devices are not operated in situations which may be hazardous. For example, it is important to ensure that powered automatic doors of railway trains can only be opened when it is safe to do so, for example, only when the train is stationary or slowing to a halt at a station. With a machine tool, for example, it may be required to switch off the tool if it is vibrating in a manner which suggests that the vibrations may get out of control.

It is an object of the present invention to provide a method and apparatus of operating a powered device which improves the inherent safety thereof.

According to a first aspect of the present invention there is provided a method of operating a powered device by way of a powered operating circuit, the method comprising the steps of sensing stresses applied to and/or generated by said powered device, determining if said sensed stresses meet predetermined criteria, and enabling said powered operating circuit if said stresses are within said predetermined criteria, and/or disabling said powered operating circuit if said stresses are outside such predetermined criteria.

Preferably, the predetermined criteria of said stresses are within a predetermined range.

Thus, with a method of the invention the stresses applied to and/or generated by the powered device are compared with a "window" of acceptable values so that the operating circuit can be disabled or not enabled if the stresses are not within that window.

Preferably, the predetermined criteria are that said stresses prevail for longer or shorter than a preset duration, that is that the duration of the stresses is compared with a "window" of acceptable values.

In this respect, it is generally required that the powered device not be shut down, or prevented from operating, due to transients, for example. In some circumstances, the stresses may be internal forces or vibrations generated by the device in response to the application of power thereto. For example, where the device is a powered machine tool it will be required to switch off the tool if unacceptable vibrations are generated.

Additionally, and/or alternatively, the stresses may be external forces or pressures applied to said powered device. For example, where said powered device is an automatic door, the method may further comprise the steps of enabling said powered operating circuit, and, whilst said powered operating circuit is enabled, causing operation of said door if forces or pressures applied to a manual door control are within the predetermined criteria.

Where the manual door control is a pushbutton, the predetermined criteria may be that the pressure applied to the pushbutton is within a predetermined range, and that the pressure is applied for longer than a preset duration at a preselected rate.

The present invention also extends to a method of operating an automatic door by way of a powered operating circuit, the method comprising the steps of enabling said powered operating circuit, and, whilst said powered operating circuit is enabled, causing operation of the door thereby if a manual door control is operated in a manner within predetermined criteria representative of a normal action by a person.

With doors of a railway train, for example, it is generally provided that a powered operating circuit there for is only enabled when the train is stationary or travelling slowly towards a station. On some trains the enabling of the circuit is by way of the driver or guard, or alternatively the circuit may be enabled automatically.

However the operating circuit is enabled there is always a possibility that a situation will arise in which the train is moving rapidly when the operating circuit is enabled.

If, in such a situation the door control is operated, for example, by an environmental pressure, a potentially dangerous situation arises in that the door or doors may be opened thereby. The present invention minimises the risk of the door operating in such circumstances and therefore enhances the safety of automatic doors.

With a method of the invention, an automatic door can be operated only if, whilst the powered operating circuit is enabled, the manual door control is operated, and that operation meets the predetermined criteria. Where the automatic door is provided on a railway train or other transport means, an embodiment of the invention can be employed to prevent the door from being opened, for example, whilst the train is moving at speed, in response to pressure applied by wind or other weather conditions, for example, and/or to a change in air pressure caused by a passing train, freezing climatic conditions, and/or other conditions, and/or to pressure occurring as a train enters or leaves a tunnel, and/or in response to the occurrence of freak or transient conditions.Furthermore, whilst preventing door operation in response to such external conditions and occurrences, an embodiment of the present invention will continue to provide door operation in response to the demand of passengers even in conditions of extreme cold, or in hot and/or wet and/or otherwise harsh environmental conditions.

To prevent operation of the doors in response to any pressure condition and/or the occurrence of a freak event, the method of the invention comprises causing operation of the door if the door control is operated within predetermined criteria representative of a normal action by a person. Where the door control, for example, is a latch or operating handle, the predetermined criteria may comprise the amount of force or pressure applied to the latch or handle and/or the amount of rotation or twist applied thereto.

Particularly with railway trains and other means of transport, it is generally the case that the manual door control is a pushbutton. In this circumstance, the predetermined criteria may comprise the amount of pressure applied and/or the period or duration for which the pressure is applied.

In a particularly preferred embodiment, where the manual door control is a pushbutton, the predetermined criteria are that the pressure applied to the pushbutton is within a predetermined range, and that the pressure is applied for longer than a preset duration at a preselected rate.

It is preferred that the applied pressure be within a preset range so that door opening cannot be achieved by the application of excessive forces, for example, as would result from an attack by a hammer. It is preferred that the pressure be applied for longer than a preset duration to avoid opening of the door when the applied pressure is transient.

According to a further aspect of the invention, there is provided apparatus for operating an automatic door by way of the methods as defined above.

According to a further aspect of the present invention there is provided apparatus for operating a powered device comprising a powered operating circuit for operating said device, sensing means coupled to said device for monitoring stresses applied to and/or generated by said powered device, and determining means for determining if said sensed stresses meet predetermined criteria, and for enabling said powered operating circuit if said stresses are within said predetermined criteria and/or disabling said powered operating circuit if said stresses are outside said predetermined criteria.

Preferably, the predetermined criteria are that said stresses are within a predetermined range. This provides a "window" through which the determined stresses can be filtered.

In an embodiment, for example, to prevent the apparatus being responsive to transients, the predetermined criteria may be that said stresses prevail for longer than a preset duration.

Where the powered device is a powered tool, for example, said sensing means may be arranged to sense internal forces or vibrations generated by operation of said device.

Additionally, and/or alternatively, said sensing means may be arranged to sense forces or pressures applied externally to said powered device. For example, the sensing means may be responsive to the operation of a manual control by a person.

In a preferred embodiment, said powered device is an automatic door and has a manual door control coupled to said powered operating circuit and arranged upon actuation to demand operation of the door. Preferably, said sensing means is arranged to sense the forces or pressures applied to said manual door control, and wherein said determining means is arranged, whilst said powered operating circuit is enabled, and if said forces or pressures are within said predetermined criteria, to enable said powered operating circuit to operate the door.

The present invention also extends to apparatus for operating an automatic door comprising a powered operating circuit for operating the door, a manual door control coupled to said powered operating circuit and arranged upon operation to demand operation of the door, and identification means coupled to said door control and arranged to identify if said manual door control is operated in a manner within predetermined criteria, wherein said powered operating circuit is enabled to operate the door only if, whilst said powered operating circuit is enabled, said manual door control is operated to demand operation in a manner identified by said identification means as within said predetermined criteria.

The identification means prevents operation of the door in response to, for example, any rapid variation in air pressure, and/or the occurrence of a freak event, by identifying if the manual door control is operated within predetermined criteria representative of a normal action by a person. The door control may be, for example, a latch or operating handle, and in this case the predetermined criteria may comprise the amount of force or pressure applied to the latch or handle and/or the amount of rotation or twist applied thereto.

Particularly with railway trains and other means of transport, it is generally the case that the manual door control is a pushbutton. In this circumstance, the predetermined criteria may comprise the amount of pressure applied to the pushbutton and/or the rate and/or duration for which the pressure is applied thereto.

In a particularly preferred embodiment, where the manual door control is a pushbutton, the predetermined criteria are that the pressure applied to the pushbutton is within a predetermined range, and that the pressure is applied for longer than a preset duration.

The powered operating circuit of apparatus of the invention may be powered in any appropriate manner. For example, the powered device may be arranged to be operated by pneumatic, hydraulic, or electrical power. Furthermore, the powered operating circuit may be controlled by control means powered by one source, and arranged to cause operation of the powered device by an alternative source of power. For example, pneumatic door operating means may be controlled by electrical control means. The nature and control of the powered operating circuit may be selected as is required.

In order to operate the device,for example, the door by the powered operating circuit it is necessary to enable the powered operating circuit. For safety, enabling means may be provided which are arranged to selectively enable said operating circuit. The nature and control of said enabling means may be selected as required. By way of example only, where the automatic door is provided on a railway train or pther means of transport, it is generally.

required that the enabling means enable the powered operating circuit only when the train is stationary or travelling slowly. The enabling means may be switched on manually by a driver or guard, or alternatively can be responsive to speed detection means, and/or to the application of train brakes, for example.

In a preferred embodiment, the manual door control is a pushbutton, and the identification means comprises sensor means arranged to respond to the application of pressure to the pushbutton, and monitoring means arranged to generate a door operation demand signal if the pressure applied to the pushbutton is within the predetermined criteria.

In a particularly preferred embodiment, the apparatus for operating an automatic door comprises pushbutton apparatus as defined herein below.

According to a still further aspect of the present invention there is provided pushbutton apparatus for generating a demand signal for operating an automatic door, said pushbutton apparatus comprising a pressel, sensor means arranged to respond to the application of force to the pressel and to generate an output representative of the applied force, and determining means coupled to receive, and respond to, said sensor means output and arranged to generate a door operation demand signal if the force applied to the pressel accords with predetermined criteria.

Preferably, the predetermined criteria comprise the amount of force applied and/or the rate and/or the period and/or the duration for which the force is applied to the pressel.

In a particularly preferred embodiment, the predetermined criteria are that the force applied to the pressel is within a predetermined range, and that the force is applied for longer than a preset duration. It is preferred that the force be dynamic, for example, either a push or release.

It is preferred that the force be within a range so that door opening cannot be achieved by the application of excessive forces, for example, as would result from an attack by a hammer. It is preferred that the force be applied for longer than a preset duration to avoid opening of the door when the force applied is transient.

The sensor means may, of course, comprise any suitable pressure and/or vibration sensing means. In one embodiment the sensor means comprises a piezo electric device or other sensor arranged to generate an output voltage which is determined by, and generally is representative of, the force applied to said pressel. Said determining means is preferably arranged to determine if the voltage output of said sensor is within a range determined by low level and high level reference voltages. Where the output voltage of the sensor-is within said range said determining means may generate, or may cause to be generated, a door operation demand signal. In a preferred embodiment, said pushbutton apparatus may comprise an output stage coupled to said monitoring means and arranged to generate said door operation demand signal.

In a preferred embodiment, said determining means comprises a timing circuit coupled to said output stage and arranged to enable the output stage to generate the demand signal.

The sensor means preferably comprises first comparing means having a first input to which the output voltage of said sensor is applied and a second input to which a low level reference voltage is applied, said first comparing means being arranged to produce an output signal when the applied output voltage is above the low level reference voltage.

In an embodiment, the sensor means also comprises low level reference voltage determining means arranged to provide said low level reference voltage. Preferably, said low level reference voltage determining means comprises one or more temperature dependent devices, whereby the low level reference voltage is variable with temperature to compensate for any temperature dependent effect of the piezo electric device. In an embodiment, the low level reference voltage determining means comprises a voltage divider incorporating one or more thermistors.

Preferably, said first comparing means comprises a first comparator.

The sensor means preferably comprises second comparing means having a first input to which the output voltage of said sensor is applied, and a second input to which a high level reference voltage is applied, said second comparing means being arranged to produce an output signal when the applied output voltage is above the high level reference voltage.

In an embodiment, the sensor means also comprises high level reference voltage determining means arranged to provide said high level reference voltage. Preferably, said high level reference voltage determining means comprises one or more temperature dependent devices, whereby the high level reference voltage is variable with temperature to compensate for any temperature dependent effect of the sensor. In an embodiment, the high level reference voltage determining means comprises a voltage divider incorporating one or more thermistors.

Preferably, said second comparing means comprises a second comparator.

In an embodiment, the output signal from said first comparing means is arranged to trigger said timing circuit which enables the output stage to generate the demand output signal if the output voltage of the piezo electric device is still above said low level reference voltage at the end of the period determined by said timing circuit.

For example, the timing circuit may be a clocked monostable, but any suitable timing device may be used. In an embodiment, the period determined by said timing circuit is set to eliminate transient effects.

To ensure that the demand signal can be used effectively by a powered operating circuit, the output stage preferably comprises an active output circuit which is switched on by said demand signal for at least a preset period. The output circuit is arranged to enable switching of the power operated circuit, for example, by providing a low impedance path to ground.

In a preferred embodiment, the determining means is provided with reset means arranged to prevent the generation of a demand signal until power up of the sensor means and of the monitoring means has been completed.

An embodiment of the present invention will hereinafter be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows an elevation through a pushbutton assembly of the present invention, and Figure 2 shows a circuit diagram of an identification circuit which is incorporated in the pushbutton assembly of Figure 1.

In the following description the invention is particularly described with reference to a pushbutton assembly used for opening the doors on a railway train.

However, it will be appreciated that the invention is not limited to this specific example, which is described for convenience. Thus, for example, the pushbutton may be replaced by any appropriate door control or mechanism. The invention may also be utilised in respect of devices other than automatic doors. For example, the invention may be used to monitor the operation of any powered device and to enable or disable a powered operating circuit therefor if the stresses generated by operation of the device and/or stresses applied thereto are outside an acceptable window.

The specific embodiment described and illustrated is a pushbutton assembly for opening the doors on a railway train. It will be appreciated that this specific implementation may be used for automatic doors in other locations. For example, the invention may be used to ensure that automatic doors of public buildings opened by way of pressure on a floor platform are not opened by freak events and/or by misuse such as by children leaping on and off the floor platform. In addition, whilst the invention is described with particular reference to the opening of doors, it can also be used for closing doors.

Figure 1 shows an elevation through one embodiment of a pushbutton assembly of the present invention. In the embodiment shown in Figure 1 the pushbutton assembly 10 is mounted with respect to a door skin 14. This door skin 14 is secured by appropriate means (not shown) to the door to be operated. The pushbutton assembly 10 has a body 16 which is a generally rectangular, hollow member, for example, made of a polycarbonate moulding, and is held onto the door skin 14 by screws or other fixings as indicated at 18. At its front surface, the body 16 has an upstanding surround 34 which extends around and defines a generally rectangular recess in which a pressel plate 22 is seated.

The pressel plate 22 is fixed to the body 16 by appropriate fixings 32.

The pressel plate 22 is sufficiently thin to be resilient, and carries a polycarbonate moulding 30 comprising indicator means for the pushbutton assembly.

For example, the moulding 30 may be provided with a window in the shape of an arrow, and house means, such as an LED, to provide illumination to that window as required. In known manner, the arrow of the window may be illuminated to indicate an opening direction available when a circuit controlled by the pushbutton assembly is activated.

It will be appreciated that the surround 34, which in the completed assembly surrounds the pressel plate 22, defines the periphery of the pressel plate 22 to facilitate use of the pushbutton assembly. If required, the surround 34 may be illuminable, to enable it to indicate to a user that the circuit controlled by the pushbutton assembly is enabled.

In the embodiment of the pushbutton assembly illustrated, the fixings 18 supporting the body 16 on the door skin 14 enable some movement of the housing 16 relative to the door skin 14. This movement of the body 16 is to allow for some distortion of the door skin 14. The flexure of the pressel plate 22, when pressed, can be used to initiate door opening.

In a manner which is known, when the train is stopped or stopping, the driver enables a powered operating circuit for the door. This causes illumination of the surround 34 and/or of the indicator means 30 of the pushbutton assembly and thereby encourages a user to open the door by pushing the pressel plate 22. In known manner the pressure on the pressel plate 22 makes an appropriate switch (not shown) and the door is thereby caused to open.

As illustrated, a generally annular gasket 36 which is rectangular in shape is provided in the pushbutton assembly between the body 16 and the door skin 14 to absorb any vibration and to prevent moisture ingress into the pushbutton assembly.

With an embodiment of the present invention, pressure on the pressel plate 22, with the power operated circuit enabled, is not necessarily sufficient to cause the door to open. In this respect, the electrical circuit mounted in the area 28 comprises an identification circuit which acts to ensure that the pressure applied to the pressel plate 22 is representative of a normal opening action by a person, before a door opening action is caused.

The identification circuit which is housed in an area 28 of the pushbutton assembly is illustrated in Figure 2.

This circuit is arranged to distinguish an intentional push on the pressel plate 22 by a person seeking to open the door from transient forces, external pressure, and hammer blows. Thus, the circuit seeks to identify and respond to operation of the pushbutton assembly in a normal manner by a person seeking to open the door.

The circuit shown in Figure 2 utilises a piezo electric crystal 40 to detect the forces applied to the pressel plate 22. In this respect, the piezo electric crystal 40 is arranged to produce a voltage which is dependent upon and corresponds to the force applied thereto, and hence to the pressel plate 22. Thus, the larger the force applied to the piezo electric crystal 40, the larger the output voltage produced thereby. The circuit of Figure 2 is arranged to detect the level of the output voltage from the piezo electric signal 40 to determine if the door is to be opened.

The voltage developed across the piezo electric crystal 40 is applied to comparators 42 and 44 which determine if the voltage is within a predetermined range.

Thus, the comparator 42 is a high level voltage comparator arranged to establish if the piezo output voltage exceeds a predetermined high level reference voltage VH, whilst the comparator 44 is a low level voltage comparator arranged to detect if the piezo output voltage is above a predetermined low level reference voltage VL. For the door to be opened, an intentional push on the pressel plate 22 is required, and an intentional push is defined as one producing a voltage above the low level reference voltage VL but below the high level reference voltage VH.

As can be seen, the piezo output voltage is applied to the inverting input of each of the two comparators 42 and 44 by way of a unity gain amplifier 46 which acts as a buffering device. The piezo output voltage is applied to the non-inverting input of the unity gain amplifier 46, and a pull down resistor R1 is also connected to this input to provide a discharge path for the piezo output voltage. The output of the unity gain amplifier 46 is connected to the comparators 42 and 44 by way of a capacitor C1, which acts to block any DC signal present at the piezo voltage output which may be due to the unity gain amplifier 46, and by way of a further pull down resistor R2 which provides a discharge path for the capacitor C1.

Each of the comparators 42 and 44 has a respective reference voltage applied to its non-inverting input by way of a respective voltage divider. In this respect, a regulated DC supply is applied to each voltage divider, and the values of the resistors in the voltage dividers are chosen to set the high and low voltage reference levels as required. If required, the or each voltage divider may incorporate variable resistors to enable the reference voltages to be adjusted.

The low level reference voltage VL applied to the low level comparator 44 is determined by two resistors R3 and R4. The output of the comparator 44 will not be switched to low level unless the piezo output voltage is higher than the low level reference voltage VL, and the value of the resistors R3 and R4 is chosen such that the low level reference voltage corresponds to the piezo output voltage which occurs if the pressel plate 22 has been subjected to a firm intentional push. As will become apparent, the appearance of a low level signal on the output of the low level comparator 44 is a prerequisite for an output signal from the circuit of Figure 2.

Similarly, the high level comparator 42 will produce a low level signal on its output if the piezo output voltage is above a high level reference voltage, determined in this instance by resistors R5 and R6 of the voltage divider connected to the non-inverting input of the high level comparator 42. The identification circuit is arranged so that, as will become apparent, the existence of a low level signal at the output of the high level comparator 42 will disable the circuit so that an output signal is not provided.

Most piezo electric devices are temperature dependent, and as the temperature drops, the voltage output by the piezo electric crystal 40, for the same applied force, increases. To compensate for this, it is arranged that the reference voltages applied to the high and low level voltage comparators 42 and 44 similarly change with temperature, and in fact that the reference voltages VH and VL increase as the temperature decreases. In this respect, one of the resistors, for example R4 and R6, in each voltage divider may be provided by a thermistor, for example, an NTC thermistor.

The output of the high level comparator 42 is arranged to prevent the generation of an output signal if too high a force is applied to the pressel plate 22. Such a force may occur, for example, if the pushbutton assembly is being misused, for example, and is subjected to blows from a hammer or other tool. In this respect, the output from the high level comparator 42 is connected to the input of a resettable latch 48. If the piezo output voltage exceeds the high level reference voltage VH, the output of the high level comparator 42 will go low, and this sets the latch 48, which is preferably a flip-flop as illustrated. The latch 48 puts a latch signal on one input of an output monostable 50. Whilst the latch signal is applied to the input of the monostable 50, the monostable is prevented from triggering.

The latch 48 can be reset, for example, to enable triggering of the output monostable 50, but this can only occur if the output of the low level comparator 44 goes high, indicating that a low, or no, pressure is applied to the pushbutton assembly, and if a timer circuit 52 has "timed out" so that its output is low. In these circumstances there is a high signal on the Q output of the timer 52 which is applied to one input of a NAND gate 54 which also receives the high output of the comparator 44.

The NAND gate 54 thereby puts a low, reset pulse on the reset terminal of the latch 48 which is reset.

The timer 52 is triggered by the appearance of a low level signal on the output of the low level comparator 44 which represents the application of pressure to the pressel plate 22 which is above the low level. In this respect, clock pulses are applied to a clock input CLK of the timer 52 from an appropriate source. The low output from the comparator 44 is applied to an input of a NAND gate 56 whose output is connected to the input of the timer 52 and the high signal thereby applied triggers operation of the timer 52.

The timer is arranged to run, when triggered, for a period to eliminate transient effects. On the application of a trigger input to the timer 52 the Q output goes high and applies this signal to one input of a NAND gate 55 and to one input of a NAND gate 58 by way of a RC delay circuit RC. The output of the NAND gate 58 is applied to a diode D2. In this respect, it will be appreciated that the low level signal at the output of the low level comparator 44 is applied to a diode D1, and that the diodes D1 and D2 are connected to the second input of the output monostable 50.

In fact, the two diodes D1 and D2 act as an OR gate. If the inputs thereto are a low signal from the output of the comparator 44 and a low signal from the output of NAND gate 58 with the 9 output of the timer 52 going low, it will cause the reset pin of the monostable 50 to go high which triggers the monostable 50. Thus, it will be appreciated that triggering of the monostable 50 therefore requires that a time after the timer 52 has been triggered the comparator 44 still has a low output, and that at this time, the output monostable 50 is not latched off. This time period is that determined by the timer 52. If these conditions apply the output monostable 50 is triggered.

The other input to the NAND gate 55 is connected to the Q output of the monostable 50. This disables the reset input of the monostable 50 from going low and hence resetting the output of the monostable 50 before it has timed out.

The outputs of the output monostable 50 are connected to the gates of two FET devices indicated at 60. These FET devices 60 are arranged to be rendered active while there is an output on the output monostable 50. In this respect, the two FET devices are preferably a normally open device and a normally closed device. The monostable 50 has a clock input CLK and is generally arranged to hold the two FETs 60 active, once triggered, for a minimum of 500 milliseconds. If the output monostable 50 has not been retriggered at the end of this period the FETs are switched back to their quiescent state. Retriggering will generally occur if the pressel plate 22 is being pumped in the sense that it is being subject to a plurality of individual pressure applications.

As has been described, where the latch 48 has been set the output monostable 50 is disabled from triggering.

Thus, it is ensured that, for the FET devices 60 to be rendered active, the force applied to the pushbutton assembly has to produce a piezo output voltage which is within the limits set by the reference voltages applied to the two comparators 42 and 44. Of course, the timer 52 can be retriggered whilst the output monostable 50 is disabled from triggering. If the input is "ringing" in the sense that pressure is periodically applied, the timer 52 will be retriggered and this can start the timer period. This will prevent the timer 52 resetting the latch 48 whilst the input is still ringing.

The circuit of Figure 2 is for use with a powered operating circuit for a door which is only to be actuated in certain circumstances. This requires that electrical power is only supplied when opening of the door is to be enabled Because of this the circuit of Figure 2 is provided with a reset circuit generally indicated at 62 to ensure that the output monostable 50 cannot be triggered until a power up has been completed. In this respect, it is required to ensure that the comparators 42 and 44 have a chance to stabilise after power up. The reset circuit 62 comprises a comparator 64 whose output is applied to the reset input of the timer 52. A low level output on the comparator 64, as will appear on power up, holds the timer 52 which in its turn holds the output monostable 50 in reset. Once power up is complete, the output of the comparator 64 is arranged to go high.

The circuit shown in Figure 2 is, of course, only one implementation of a circuit able to perform the necessary functions. Alternative components may be used to those illustrated in order to perform the particular functions.

In this respect, it is necessary to provide an output stage which is active for a predetermined period if the force applied to the pushbutton assembly is above a predetermined level for a predetermined time, but does not exceed an excess level. Retriggering of the output stage to keep it active is preferably enabled, particularly if the pushbutton assembly is subjected to additional applications of pressure forces which meet those requirements.

It will be appreciated that further amendments and modifications may be made to the embodiment of the invention as described and illustrated within the scope of this application.

Claims (37)

1. A method of operating a powered device by way of a powered operating circuit, the method comprising the steps of sensing stresses applied to and/or generated by said powered device, determining if said sensed stresses meet predetermined criteria, and enabling said powered operating circuit if said stresses are within said predetermined criteria, and/or disabling said powered operating circuit if said stresses are outside said predetermined criteria.

2. A method as claimed in Claim 1, wherein the predetermined criteria are that said stresses are within a predetermined range.

3. A method as claimed in Claim 1 or Claim 2, wherein the predetermined criteria are that the duration of said stresses is within a predetermined range.

4. A method as claimed in any preceding claim, wherein said stresses are internal forces or vibrations generated by the device in response to the application of power thereto.

5. A method as claimed in any preceding claim, wherein said stresses are external forces or pressures applied to said powered device.

6. A method as claimed in Claim 5, where said powered device is an automatic door, and further comprising the steps of enabling said powered operating circuit, and, whilst said powered operating circuit is enabled, causing operation of said door if forces or pressures applied to a manual door control are within the predetermined criteria.

7. A method as claimed in Claim 6, where the manual door control is a pushbutton, the predetermined criteria are that the pressure applied to the pushbutton is within a predetermined range, and that the pressure is applied for longer than a preset duration at a preselected rate.

8. A method of operating an automatic door by way of a powered operating circuit, the method comprising the steps of enabling said powered operating circuit, and whilst said powered operating circuit is enabled, causing operation of the door thereby if a manual door control is operated in a manner within predetermined criteria representative of a normal action by a person.

9. Apparatus for operating a powered device by way of a method as claimed in any of the preceding claims.

10. Apparatus for operating a powered device comprising a powered operating circuit for operating said device, sensing means coupled to said device for monitoring stresses applied to and/or generated by said powered device, and determining means for determining if said sensed stresses meet predetermined criteria, and for enabling said powered operating circuit if said stresses are within said predetermined criteria and/or disabling said powered operating circuit if said stresses are outside said predetermined criteria.

Il. Apparatus as claimed in Claim 10, wherein the predetermined criteria are that said stresses are within a predetermined range.

12. Apparatus as claimed in Claim 10 or 11, wherein the predetermined criteria are that the duration of said stresses is within a predetermined range.

13. Apparatus as claimed in any of Claims 10 to 12, wherein said sensing means is arranged to sense internal forces or vibrations generated by operation of said device.

14. Apparatus as claimed in any of Claims 10 to 13, wherein said sensing means is arranged to sense forces or pressures applied externally to said powered device.

15. Apparatus as claimed in Claim 14, where said powered device is an automatic door, and comprising a manual door control coupled to said powered operating circuit and arranged upon actuation to demand operation of the door, wherein said sensing means is arranged to sense the forces or pressures applied to said manual door control, and wherein said determining means is arranged, whilst said powered operating circuit is enabled, and if said forces or pressures are within said predetermined criteria, to enable said powered operating circuit to operate the door.

16. Apparatus as claimed in Claim 15, wherein the manual door control is a pushbutton, and wherein the predetermined criteria comprise the amount of pressure applied to the pushbutton and/or the rate and/or duration for which the pressure is applied thereto.

17. Apparatus as claimed in Claim 16, wherein the predetermined criteria are that the pressure applied to the pushbutton is within a predetermined range, and that the pressure is applied for longer than a preset duration.

18. Apparatus as claimed in Claim 16 or 17, wherein said sensing means is arranged to respond to the application of pressure to the pushbutton, and said determining means is arranged to generate a door operation demand signal if the pressure applied to the pushbutton is within the predetermined criteria.

19. Apparatus as claimed in any of Claims 10 to 18, wherein the powered operating circuit is powered by pneumatic, hydraulic, or electrical power.

20. Apparatus for operating an automatic door comprising a powered operating circuit for operating the door, a manual door control coupled to said powered operating circuit and arranged upon operation to demand operation of the door, and identification means coupled to said door control and arranged to identify if said manual door control is operated in a manner within predetermined criteria, wherein said powered operating circuit is enabled to operate the door only if, whilst said powered operating circuit is enabled, said manual door control is operated to demand operation in a manner identified by said identification means as within said predetermined criteria.

21. Pushbutton apparatus for generating a demand signal for operating an automatic door, said pushbutton apparatus comprising a pressel, sensor means arranged to respond to the application of force to the pressel and to generate an output representative of the applied force, and determining means coupled to receive, and respond to, said sensor means output and arranged to generate a door operation demand signal if the force applied to the pressel accords with predetermined criteria.

22. Pushbutton apparatus as claimed in Claim 21, wherein said predetermined criteria comprise the amount of force applied and/or the rate and/or the period and/or the duration for which the force is applied to the pressel.

23. Pushbutton apparatus as claimed in Claim 22, wherein said predetermined criteria are that the force applied to the pressel is within a predetermined range, and that the force is applied for longer than a preset duration.

24. Pushbutton apparatus as claimed in any of Claims 21 to 23, wherein said sensor means comprises a sensor arranged to generate an output voltage which is determined by, and generally is representative of, the force applied to said pressel, and wherein said determining means is arranged to determine if the voltage output is within a range determined by low level and high level reference voltages.

25. Pushbutton apparatus as claimed in Claim 24, wherein where the output voltage of the sensor is within said range, said determining means is arranged to cause a door operation demand signal to be generated.

26. Pushbutton apparatus as claimed in Claim 24 or Claim 25, wherein said sensor means comprises first comparing means having a first input to which the output voltage of said sensor is applied and a second input to which a low level reference voltage is applied, said first comparing means being arranged to produce an output signal when the applied output voltage is above the low level reference voltage.

27. Pushbutton apparatus as claimed in Claim 26, wherein said sensor means comprises low level reference voltage determining means arranged to provide said low level reference voltage.

28. Pushbutton apparatus as claimed in Claim 26 or Claim 27, wherein said sensor means comprises second comparing means having a first input to which the output voltage of said sensor is applied, and a second input to which a high level reference voltage is applied, said second comparing means being arranged to produce an output signal when the applied output voltage is above the high level reference voltage.

29. Pushbutton apparatus as claimed in Claim 28, wherein said sensor means comprises high level reference voltage determining means arranged to provide said high level reference voltage.

30. Pushbutton apparatus as claimed in any of Claims 26 to 29, wherein said determining means comprises a timing circuit coupled to an output stage of said pushbutton apparatus, and wherein the output signal from said first comparing means is arranged to trigger said timing circuit to enable the output stage to generate the door operation demand output signal if the output voltage of the sensor is still above said low level reference voltage at the end of the period determined by said timing circuit.

31. Pushbutton apparatus as claimed in Claim 30, wherein the output stage comprises an active output circuit which is switched on by said demand signal for at least a preset period, and is arranged to enable switching of the power operated circuit.

32. Pushbutton apparatus as claimed in any of Claims 21 to 31, wherein said determining means is provided with reset means arranged to prevent the generation of a door operation demand signal until power up of the sensor means and of the determining means has been completed.

33. A method of operating a powered device substantially as hereinbefore described with reference to the accompanying drawings.

34. A method of operating an automatic door substantially as hereinbefore described with reference to the accompanying drawings.

35. Apparatus for operating a powered device substantially as hereinbefore described with reference to the accompanying drawings.

36. Apparatus for operating an automatic door substantially as hereinbefore described with reference to the accompanying drawings.

37. Pushbutton apparatus substantially as hereinbefore described with reference to the accompanying drawings.