US3887252A

US3887252A - Light operated guard

Info

Publication number: US3887252A
Application number: US421719A
Authority: US
Inventors: Paul Fuller
Original assignee: RONEO VICKERS Ltd
Current assignee: VICKERS FURNITURE Ltd; RONEO VICKERS Ltd
Priority date: 1972-12-06
Filing date: 1973-12-04
Publication date: 1975-06-03
Anticipated expiration: 1992-06-03
Also published as: FR2210271A5; DE2360589A1; NL7316700A; GB1448987A

Abstract

A light operated guard for a path which may be followed by a person or part of a person with a purpose of raising an alarm, of closing the path or stopping dangerous machinery, which utilises a modulated beam of light which traverses the said path and falls upon a photocell associated with a frequency sensitive device which acts to inhibit the raising of an alarm or the closing of the path or the stopping of the dangerous machinery or the like while the beam is uninterrupted the one to maintain a constant loop gain and the other to nullify spurious signals due to vibration and other mechanical effects due to motion of the parts of the apparatus during operation of the same.

Description

United States Patent 119- Fuller 5] June 3, 1975 1 LIGHT OPERATED GUARD 3,224,825 12/1965 Sturgis a a1. 312/223 3,640,596 2 l972 K 't 312 223 [75] Inventor: Paul Fuller, Romford, England I am 2 I [73] Assignee: Roneo Vickers Limited, London, Primary Examiner lames C. Mitchell England Attorney, Agent, or FirmWigman & Cohan 2 F] d: D 4, 1973 l 2] 57 ABSTRACT [21] Appl 421719 A light operated guard for a path which may be followed by a person or part of a person with a purpose [30] F i A li ti P i it D t of raising an alarm, of closing the path or stopping 6 1972 United Kingdom llllllllllll 56370/72 dangerous machinery, which utilises a modulated 1 beam of light which traverses the said path and falls [52] Us. CL 312/223. Zl H1 upon a photocell associated with a frequency sensitive 51 lm. A451) 77/08 device which acts ihhihh the raising of an alarm 58 Field of Search 211/15 312/223 the Closing of the P the stopping 0f the dangerous machinery or the like while the beam is uninter- [56] References Cited rupted the one to maintain 'a constant loop gain and the other to nullify spurious signals due to vibration UNITED STATES PATENTS and other mechanical effects due to motion of the 21696-417 12/1954 Jouk 312/223 parts of the apparatus during operation of the same. 3,077,967 2/1963 Woodward et al. 3l2/223 X 3,181,921 5/1965 Moore et al. .1 312/223 7 Claims, 2 Drawing Flgures LIGHT OPERATED GUARD The invention relates to a light operated guard for a path which may be followed by a person or part of a person with the purpose of raising an alarm, closing the path, or stopping dangerous machinery in said path and the like, while the object of the invention is to provide such a guard which is reliable in operation, economical to manufacture and which is easily adaptable to a variety of purposes.

The invention consists in a light operated guard for a path which may be followed by a person or part of a person, with the purpose of raising an alarm, of closing the path or stopping dangerous machinery in said path and the like, comprising means for producing a beam of light, means for modulating the beam of light at a predetermined and substantially constant frequency, a system of mirrors positioned adjacent boundaries of the path which cause the beam of light to be reflectec back and forth across the path, a photo-sensitive electrical device at the end of the beam of light remote from the means for producing a beam of light, which provides an electric signal of said predetermined frequency, and an electric circuit connected to said photo-sensitive device which produces an output signal only when the light of said predetermined frequency and of a predetermined amplitude falls on the photo-sensitive device, said output signal being utilised for inhibiting the raising of an alarm, the closing of the path or stopping of dangerous machinery or the like.

The invention further consists in a light operated guard as set forth in the preceding paragraph in which the frequency of modulation of the beam of light is greater than I cycles per second.

The invention still further consists in a light operated guard as set forth above in which the electric circuit includes a relay which closes while the output signal is present, and inhibits the operation of a brake upon said dangerous machinery, and on the absence of the signal allows the brake to operate upon the dangerous ma chinery.

The invention still further consists in a light operated guard as set forth above in which the means for modu lating the beam of light is a perforated disc rotated by a synchronous electric motor operated by ac. main network current.

The invention still further consists in a light operated guard as set forth above in which the electrical circuit includes a pre-amplifier, and a two-state frequency selective electronic switching device.

The invention still further consists in an automatic file storage, retrieval and replacement system utilising a lift and incorporating a light operated guard as set forth above.

The invention still further consists in an automated filing system incorporating a lift for bringing the file to a window in the system for presentation to an operator and returning them to their allotted positions when required, in which the window is provided with a light op erated guard as set forth above, in which the beam is reflected from side to side of the window, and in consequence transversely of the direction of motion of the lift, so that should an operator pass a part of his person through the window into the path traversed by the light, said part of the person is sure to be moved by the motion of the lift into the path of said beam to interrupt the beam, if the beam has not been interrupted previously by the part of the person.

The accompanying drawings show, by way of example only, one embodiment of the invention when applied to an automatic file storage andd retrieval and replacement system in which,

FIG. I is a perspective view of the automatic file storage retrieval and replacement system, showing the incorporation of the light operated guard, while FIG. 2 shows a circuit diagram of the light operated guard when particularly adapted for use in a system as shown in FIG. 1.

The automated file storage system shown in FIG. I comprises a framework 1, which supports shelves or runners 2, for files 3, and covered with a sheet metal covering 4. The central space is provided with a lift platform 5, which can be raised and lowered by the op erating chains 6, driven by the electric motor 7. When the controls, (not shown), are operated, the platform 5 is raised or lowered as the case may be to the level of the tile required, thereupon the file 3 is pulled onto the platform 5 by the magnetic means 8, which is movable automatically into contact with the required file 3 and the file is then pulled on to the lift platform 5. The magnet of the magnetic means is energised automatically as and when required.

The front of the storage system is provided with a window 9 by way of which the file may be withdrawn from the platform 5. In FIG. 1 the platform 5 is shown halfway down the window, and the file of course cannot be withdrawn until it has reached the bottom of said window, where it automatically stops. It will be apparent that it is extremely dangerous to pass an arm through the window, while the lift patform is in motion, seeing that it is possible for the arm to be trapped either against the upper or lower extremities of the window, either by a file or by the empty lift. In consequence, the storage system is provided with a light operated guard to immediately stop the lift if this should happen, and for this purpose, there is provided a long box like structure 10, 11, on each side of the window 9.

The box 11 has five apertures therein, behind the top one 12 of which is provided an electric lamp, with suitable optical system for providing a narrow beam of light, and a synchronous electric motor driving a perforated disc which modulates the beam emerging from the aperture 12. The box 10 has four corresponding apertures behind each of which is positioned a mirror which reflects the beam across the opening. The apertures 13, 14 and 15 in box 11 also have mirrors positioned behind them. The mirrors are adjustable as to the angle they present to the beam, so that it is finally projected upon the photo-sensitive electrical device behind the bottom aperture in box 11.

Although paths of the beam back and forth across the window 9 are closely spaced, should a hand or an object be inserted between the beams it will be pushed by the motion of the moving platform 5 into the path of a beam. The beam will then be interrupted and the lift motor 7 immediately de-energised and a brake, (not shown), applied to stop the platform 5. If the hand or object is then removed, the lift platform 5 is inhibited from further motion until the apparatus is switched off and the controls are re-set.

FIG. 2 shows a circuit diagram of the essential parts of the electrical circuit operating the guard, in which the principal components are housed for protection in a casing represented by the dashed line 16 which is housed in the box 11. This is provided with a plug and socket connector 17 with terminals A K, which is connected by leads to the three units, 18, 19 and 20, housed in the filing system itself. Seeing that the circuit in the casing 16 is an inhibiting unit, the lift platform will not move if the plug and socket connector 17 is separated. Only while the circuit in the casing 16 is operating in the required manner, will the lift work.

The three units l8, l9 and 20 comprise a power supply unit operated from the main current supply network and providing current for motor M and the transformer T at main supply voltage and the remainder of the apparatus at 26v do The unit 19 is a control logic for inhibiting the operation of the lift motor in the absence of the current from the electronic circuit by way of the terminal E. The unit 20 is an emergency brake logic operated when the contacts 26 and 27 of the relay RL open. by way of the terminals H and K.

As may been seen from FIG. 2, the lamp L is operated by the transformer T and may be a 6 volt watt quartz iodide lamp, the primary of the transformer T being connected in parallel with the motor M and supplied with current at the main network supply voltage by way of terminals A and B.

The electronic circuit is supplied with 26 volts d.c. between the terminal C and the earth terminal D, when it is divided to supply the relay RL and transistor TR2 direct and by way of the resistor R1 to supply the transistor TRl and the unit FX301. The resistor R1 acts as a current limiting resistor for the zener diode Z. The fixed resistor R2 in series with the variable resistors R3 and R5 provide an adjustable bias for the transistor amplifier TR] and hence the switching threshold of transistor amplifier TRl. R4 is a current limiting resistor, and R6 is the collector load resistor for the transistor amplifier TRl.

The photo-sensitive device P.V.C. is a large area, red sensitive photovoltaic cell. It is preferable to provide a red filter in the path of the beam emerging from the top aperture of the box 11 to avoid unpleasant effects upon the operator as would be the case if a white light is used. and that is why a red sensitive photovoltaic cell is preferred.

The unit marked FX301 is a commercially available unit from Consumer Microcircuits Limited, and comprises a high performance microcircuit which functions as a frequency operated switch providing two states, the one when the input signal corresponds in frequency to that to which the unit is adjusted, and the other state when the signal is interrupted or varies in frequency from that to which the unit is adjusted. Resistor R7 is a current limiting resistor for the unit FX301, while resistor R8 is a current limiting resistor for transistor TR2. The zener diode provides a stable volts supply for the unit FX301.

The transistor TR1 amplifies the signal from the photo-cell P.\".C. to the level required for introduction to the unit FX301, and is fed by way of the capacitor C1 and resistor R7 to the terminal 1 thereof. The diode D1 is provided as a requirement of the manufacturers of the unit FX301. Capacitor 02 connected to terminal 2 of the unit FX301 controls the operating time of the circuit which is approximately 10 milliseconds. excluding the relay RL. The

terminals

3, 6 and 9 are connected to the 15 volt d.c. line, while the terminal 4 is the output from the unit and is connected to the transistor TR2 by way of the current limiting resistor R8. Terminal 7 is earthed.

Resistors R9, R10, R11 and R12 are chosen of such values as to provide suitable switching threshold of the unit FX301. The switching point with the values of these resistors and the capacitors C3 and C4 may be adjusted by means of the variable resistors R11 and R12 between 800 c/s and 1.2 Kc/s. From these figures it can be realised that in this form of construction it is preferred to arrange for the modulation frequency to be in the neighbourhood of 1000 c/s. The relay RL is a volt do. two pole changeover relay which acts as one of the final control elements, and the contacts of which are used depends upon the purpose to which the guard is being put. The diode D2 is provided to suppress high voltage spikes due to the presence of the relay coil damaging the transistors and the unit FX301.

The modulator is interposed between the lamp and lens system, and is preferably in the form of a perforated aluminium disc with holes equally spaced around its periphery. The disc rotates at approximately 2,800 r.p.m. and is driven by a low power shaded pole motor. The light beam is modulated at a frequency of approximately 1 Kc/s. As the system is only responsive to light modulated at the predetermined frequency, it is not affected by sunlight or other unmodulated light or modulated light of any frequency other than the chosen fre quency falling on the photocell.

It will be seen from FIG. 1 that the top and bottom paths of the light beam are at right angles to the boxes 10 and 11, as this prevents apertures being available for access without operation of the device.

The use of a light guard as opposed to a mechanical shutter offers the advantage of at least a 20 percent decrease in the total operating time.

Besides providing a signal for inhibiting the motion of dangerous machinery, the system may be used to ring an alarm if the beam is caused to cross back and forth across an opening through which a person can walk, thus preventing a burglar entering a prohibited area, or it can be used to close a shutter or other obstruction to the entry of a prohibited area. In the latter case the contacts 26 and 27 may be closed as the device operates to ring the alarm or close the shutter. Also, the path followed by the beam may be different from that shown in FIG. 1, and the light source may be at the bottom and photocell at the top, or alternatively the beam may be reflected from top to bottom and back or at an angle and so on.

One purpose of the modulation of the beam is to prevent the apparatus from being rendered inoperative by the introduction of an external source of light not hav ing the precise frequency of modulation of the beam of the apparatus. Also, the modulation of the beam allows one to use an a.c. amplifier and thus produce considerable amplification without difficulty, and without loss of stability, thereby avoiding inherent disadvantages such as drift of do. amplifiers. The higher the frequency at which the light is modulated the greater is the discrimination possible by the electronic means, and differentiation in respect of a light of constant amplitude falling on the photocell.

Other means of modulating the light may be used but the method preferred is the most economical and reliable method found. It is preferred to use a shaded pole motor as the speed of rotation is substantially constant with frequency, and therefore may be said to be synchronous with the main supply frequency.

A quartz iodide lamp is preferred as it gives high luminosity and long life.

Although the circuit illustrated is preferred as it simplifies the method of construction and therefore reduces the cost of manufacture, other circuits having the same characteristics may be used and may include an amplifier of a conventional type which includes frequency sensitive selecting means to inhibit the amplifier if the modulation frequency should vary from the desired frequency or should be reduced to such an extent as to prevent proper operation of the amplifier.

It is preferred to operate the modulation at a frequency greater than 100 cycles per second so as to avoid interference by the artificial illumination of a room in which the apparatus is housed. It is also preferable not to use a multiple of the frequency of the main supply frequency as thereby it would be possible to prevent the apparatus from working by shining a light into the photocell operated from the main supply at a frequency by which is a multiple of the main supply frequency. By varying the number of apertures in the modulating disc it is possible to operate the devices at different frequencies so that guards in different establishments may operate at different frequencies and therefore make it more difficult for the operation of the apparatus to be interfered with.

The electric circuit is so arranged that if any of the circuits are interrupted or any of the apparatus interfered with by breaking a circuit or temporarily interrupting the main supply the operation of the lift is interfered with and the apparatus cannot be reinstated into the operative state until all the circuits are completed and the main supply connection finally made.

The 26 volts d.c. supply is derived from the power supply unit via inhibit control logic 19 with the object of incorporating a delay, to allow the modulator motor to attain full speed and the lamp to attain full brightness. A further inhibit facility is carried out by the inhibit control logic 19 to enable the operator to remove items from the prohibited area without operating the brake, and thus rendering the machine immobile. This is provided through terminals D and E.

It is to be understood that the above description is by way of example only, and that details for carrying the invention into effect may be varied without departing from the scope of the invention.

I claim:

1. A light operated guard for a path which may be traversed by a person or part of a person, for the purpose of raising an alarm, closing the path or stopping dangerous machinery or the like in said path, comprising means for producing a beam of light, means for modulating the beam of light at a predetermined and substantially constant frequency, a system of mirrors positioned adjacent boundaries of the path for reflecting the beam of light back and forth across the path, a photo-sensitive electrical device at the end of the beam of light remote from the means for producing a beam of light for generating an electric signal of said prede termined frequency, and an electric circuit connected to said photo-sensitive device for producing an output signal responsive to said electric signal only when the light of said predetermined frequency and of a predetermined amplitude falls on said photo-sensitive device, said electric circuit including means activated by said output signal for inhibiting the raising of an alarm. the closing of the path or stopping of dangerous machinery or the like, whereby interruption of said beam of light will prevent production of said output signal therebyprecluding activation of said inhibiting means.

2. A light operated guard as claimed in claim 1, including means for modulating the beam of light at a frequency greater than lOO cycles per second.

3. A light operated guard as claimed in claim 1 in which the electric circuit includes a relay adapted to close during production of said output signal thereby inhibiting the operation of a brake upon said dangerous machinery, and adapted to open on the absence of said output signal thereby allowing the brake to operate upon the dangerous machinery.

4. A light operated guard as claimed in claim 1 in which the means for modulating the beam of light is a perforated disc rotated by a synchronous electric motor operated by ac main supply network current.

5. A light operated guard as claimed in claim 1 in which the electric circuit includes a pre-amplifier, and a two-state frequency selective electronic switching de vice.

6. An automatic file storage, retrieval and replacement system utilising a lift and incorporating a light operated guard as claimed in claim 1.

7. An automated filing system incorporating a lift movable along a path for bringing a file to a window in the system for presentation to an operator and returning the file to its allotted position when required, wherein the window is provided with a light operated guard as claimed in claim 1 in which the beam is reflected from side to side of the window transversely of the direction of motion of the lift along said path, whereby in the event an operator should pass a part of his person through the window into the path traversed by the beam, said part of the person will be moved by the lift into the path of said beam by the motion of the lift, to interrupt the beam, if the beam has not been interrupted previously by the part of the person.

Claims

1. A light operated guard for a path which may be traversed by a person or part of a person, for the purpose of raising an alarm, closing the path or stopping dangerous machinery or the like in said path, comprising means for producing a beam of light, means for modulating the beam of light at a predetermined and substantially constant frequency, a system of mirrors positioned adjacent boundaries of the path for reflecting the beam of light back and forth across the path, a photo-sensitive electrical device at the end of the beam of light remote from the means for producing a beam of light for generating an electric signal of said predetermined frequency, and an electric circuit connected to said photo-sensitive device for producing an output signal responsive to said electric signal only when the light of said predetermined frequency and of a predetermined amplitude falls on said photo-sensitive device, said electric circuit including means activated by said output signal for inhibiting the raising of an alarm, the closing of the path or stopping of dangerous machinery or the like, whereby interruption of said beam of light will prevent production of said output signal thereby precluding activation of said inhibiting means.

2. A light operated guard as claimed in claim 1, including means for modulating the beam of light at a frequency greater than 100 cycles per second.

4. A light operated guard as claimed in claim 1 in which the means for modulating the beam of light is a perforated disc rotated by a synchronous electric motor operated by a.c. main supply network current.

5. A light operated guard as claimed in claim 1 in which the electric circuit includes a pre-amplifier, and a two-state frequency selective electronic switching device.