GB2198229A

GB2198229A - Opto-electric device for switching on power-consuming equipment

Info

Publication number: GB2198229A
Application number: GB08726319A
Authority: GB
Inventors: Nicholas Waterton
Original assignee: Smiths Group PLC
Current assignee: Smiths Group PLC
Priority date: 1986-12-05
Filing date: 1987-11-10
Publication date: 1988-06-08
Also published as: GB8726319D0; GB8629209D0

Abstract

A surgical mirror demisting unit, warm air hand dryer or the like has two resistive light detectors 6 and 7 mounted at the bottom of respective sighting tubes 8 and 9 close the outlet 3 of a hot air blower 2. The detectors are series connected between voltage rails and their common junction is a.c. coupled to an amplifier (11 Figure 2) and comparator (13 Figure 2). The blower is turned on when an object e.g. surgical mirror 30 shadows from ambient light a part of the unit such that the output of one detector changes relative to the other. This causes an output to the amplifier and starts a timer (15 Figure 2) which turns on the blower 2 for a preset time. <IMAGE>

Description

CONTROL NEANS This invention relates to control means.

The invention is more particularly concerned with control means for use in switching on a heater or the like, such as a heater in an air blower for demisting optical surfaces used in surgery.

In surgery of the larynx, mouth and teeth the surgeon often has need to use a hand-held mirror for observation of regions not directly visible.

Because of the humid environment of the mouth and the fact that the mirror is generally below body temperature, condensation soon forms on its surface. It is necessary therefore to remove the condensation frequently in order to render the mirror usable.

One way of demisting such mirrors is to use a hot-air blower placed in the vicinity of the surgeon. It is preferable for such a demister to be turned on and off as required, in order to avoid generating unwanted heat.

Although this can be done by some form of conventional touch-operated switch, this is undesirable in some applications because physical contact with the switch can lead to cross-infection and require sterilisation procedures, also, operation of such a switch can be awkward in some circumstances.

It is an object of the present invention to provide control means for use in operating equipment which does not require physical contact.

According to one aspect of the present invention there is provided control means for controlling switching of a power supply to associated equipment including first and second light detectors responsive to ambient light at different locations, means responsive to differential change in the outputs of the first and second light detectors to provide an output switching signal when the output of one of the detectors changes relative to the output of the other of the detectors, and switching means responsive to the switching signal to effect switching of the power supply to the associated equipment in accordance therewith, such that the equipment can be controlled by varying the ambient light incident on one or other of the detectors.

The detectors are preferably located in sighting tubes so that they are responsive to ambient light axially of the sighting tubes. The detectors preferably vary their resistance with change in incident light level and may be connected in series across a voltage rail, an output being taken from their common junction which may be a.c. coupled in the control means by capacitor means. The control means may include comparator means arranged to compare the output from the detectors with a reference signal and to produce an output in accordance therewith. The control means may include timer means arranged to maintain switching of the power supply to the associated equipment for a prede,ermined time following switching by said switching signal.The control means may include a sensitivity control arranged to control the sensitivity of the unit to change in light levels. The associated equipment may include a warm air blower, the detectors preferably being located close to an outlet of the blower.

According to another aspect of the present invention there is provided a surgical mirror demisting unit including a warm air blower and control means according to the above one aspect of the present invention arranged to control operation of the blower.

According to a further aspect of the present invention there is provided a warm air hand drying unit including a warm air blower and control means according to the above one aspect of the present invention arranged to control operation of the blower.

A surgical mirror demisting unit, in accordance with the present invention will now be described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a side elevation view of the demisting unit; and Figure 2 is a schematic diagram of an electrical circuit in the unit.

The surgical mirror demisting unit has a casing 1 containing a warm air blower 2 with an outlet 3. The casing 1 also includes a control unit 5 which switches the blower 2 on and off in response to shadowing of one of two light detectors 6 and 7 mounted close to the blower outlet 3.

The detectors 6 and 7 are identical electrical devices which respond to the levels of light incident on them by varying their resistance. The detectors 6 and 7 are each located at the bottom of respective parallel sighting tubes 8 and 9 so that they respond to ambient light falling axially on the forward end of the tubes. The detectors 6 and 7 are connected together in series between voltage rails and their common junction is a.c. coupled, via a capacitor 10, to a variable gain amplifier 11. The amplifier 11 will therefore produce a large output signal whenever there is a change in light leve' detected b one of the detectors 6 or 7, but not by the other detector.

The output of the amplifier 11 is supplied via a peak detector 12 to a comparator unit 13 which compares the peak detector output with a reference voltage and provides a step waveform output when there is a differential change in the outputs of the two detectors 6 and 7. The output of the comparator unit 13 is supplied as a switching signal to initiate operation of a timer 15.

The timer 15 is connected to a relay 20 between the mains supply 21 and the blower 2 which is of conventional construction, including an electrical heating filament 22 mounted in front of a fan 23 to heat the airflow from the fan.

In operation, the user moves a mirror 30, which is to be demisted, over the region of the blower outlet 3. The two detectors 6 and 7 are spaced from one another close to the outlet 3 so that the edge of the shadow produced by the mirror 30 will fall first on one or other of the detectors causing a differential change in their outputs. A differential change in the outputs of the detectors would also be produced by the edge of a light beam falling first on one of the detectors, such as might be produced by reflection from the surface of the mirror 30. This causes a signal to be supplied to start the timer 15 and close the relay 20, thereby causing energisation of the hot-air blower. The stream of heated air at the blower outlet 3 is used to demist the surface of the mirror. After a time interval pre-set in the timer 15 the relay 20 will be opened and the blower 2 turned off.If demisting is still required, movement of the mirror 30 in the region of the blower outlet 3 will again bring the blower back into operation.

The unit may have a manually-adjustable sensitivity control for use in controlling the sensitivity of the unit to change in light levels.

Alternatively, the sensitivity control may be effected automatically.

It will be appreciated that change in the overall ambient light level will not cause switching of the blower since this will affect both detectors equally. Because the unit is responsive only to a relatively rapid change in light level at one or other of the detectors it will not be affected by any gradual change in performance of one detector or by, for example, the gradual accumulation of opaque material on one of the detectors. Also, if the direction of ambient light is such that the detectors 6 and 7 are initially illuminated to different levels, this will not cause operation of the blower 2.

The control means of the present invention may be used for switching power supply to a warm air blower in other units such as, for example, warm air hand drying units. The control means may also be used for switching power supply to equipment other than warm air blowers.

Claims

1. Control means for controlling switching of a power supply to associated equipment including first and second light detectors responsive to ambient light at different locations, means responsive to differential change in the outputs of the first and second light detectors to provide an output switching signal when the output of one of said detectors changes relative to the output of the other of said detectors, and switching means responsive to the switching signal to effect switching of the power supply to the associated equipment in accordance therewith, such that said equipment can be controlled by varying the ambient light incident on one or other of the detectors.

2. Control means according to Claim 1, wherein the detectors are located in sighting tubes so that they are responsive to ambient light axially of the sighting tubes.

3. Control means according to Claim 1 or 2, wherein the said detectors vary their resistance with change in incident light level.

4. Control means according to Claim 3, wherein the said detectors are connected in series across a voltage rail and wherein an output is taken from their common junction.

5. Control means according to Claim 4, wherein their common junction is a.c. coupled in the control means by capacitor means.

6. Control means according to any one of the preceding claims, including comparator means arranged to compare the output from the detectors with a reference signal and to produce an output in accordance therewith.

7. Control means according to any one of the preceding claims, including timer means, wherein said timer means is arranged to maintain switching of the power supply to the associated equipment for a predetermined time following switching by said switching signal.

8. Control means according to any one of the preceding claims, including a sensitivity control arranged to control the sensitivity of the unit to change in light levels.

9. Control means according to any one of the preceding claims, wherein the said associated equipment includes a warm air blower.

10. Control means according to Claim 9, wherein the said detectors are located close to an outlet of the blower.

11. Control means substantially as hereinbefore described with reference to the accompanying drawing.

12. A surgical mirror demisting unit including a warm air blower and control means according to any one of the preceding claims arranged to control operation of said blower.

13. A surgical mirror demisting unit substantially as hereinbefore described with reference to the accompanying drawing.

14. A warm air hand drying unit including a warm air blower and control means according to any one of Claims 1 to 11 arranged to control operation of said blower.

15. Any novel feature or combination of features as hereinbefore described.