The present invention relates to apparatus for actively protecting people and machines from the effect of equipment which is hazardous from the aspect of per¬ sonal safety, and also to a method of using the appara¬ tus. The apparatus comprises an optical transmitter, an optical receiver and an electronic monitoring unit and is characterized in that the serviceability or opera- tional reliability of the apparatus is tested by a sig¬ nal-synchronized and duplicated active monitoring procedure; in that resetting is duplicated and inter¬ ruptions and short-circuits are monitored; and in that by-passing of the monitoring unit is duplicated and monitored. In separate embodiments, several optical receivers and transmitters are connected in series and/or parallel, so as to enable the apparatus to be used over a wider field.

Background of the Invention

In the case of known safety guard beam light switches, the necessary oscillator is placed in an optical trans¬ mitter and the duplicating functions are inserted in a relay unit. A safety guard beam light switch which operates according to known techniques is illustrated schematically in Figure 1.

Figure 1 is a block schematic in which:

100 is an optical transmitter in which components 107-110 are incorporated 107 is an osciilator

110 is an apparatus for converting an electric pulse train to an optical pulse train having the same

signal pattern as the electrical pulse train 200 is an optical receiver in which components 205-230 are incorporated

205 is an apparatus for converting an optical pulse train to an electrical pulse train which has the same signal pattern as the optical pulse train 210 is a logic pulse-counting unit 215 is a passive monitoring device

- 220 is a dynamic testing device - 225 is a relay

230 is a relay

- 300 is a logic relay unit

- 400 is a resetting device

- Output 1 is an output to monitored equipment - Output 2 is an output to monitored equipment

The broken line frames embrace devices having built-in components. The full-line circles denote coupling terminals. The full lines denote signal connections. The arrows denote the directional sense of respective connections. The line-crossings which include a point denote a signal connection in the direction of the arrows between the crossing lines. The line-crossings which have no point denote that these lines have no signal connection. The above also applies to Figure 2 referred to below.

Apparatus incorporating an active monitoring facility as described in this document is an apparatus in which all of the apparatus components that are capable of occupying different states (e.g. high and low, one and zero, conductive and non-conductive) at short time intervals are constantly switched between these states and in which when switching is completed, the outputs of the apparatus send to the monitored equipment

signals which instruct said equipment to carry out in¬ tended working cycles, and in which when said switching is unsatisfactory, no signals are sent to the monitored equipment instructing said equipment to carry out its working cycles. Thus, an apparatus of this kind con¬ stantly monitors the serviceability or operational reliability of its components. The serviceability of the components of apparatus provided with a passive monitoring facility is not tested constantly.

An embodiment of a safety guard beam light switch according to known techniques illustrated in Figure l has the following modus operandi.

The transmitter 100 transmits an optical pulse train

105, which normally has a continuously repeated signal pattern. The pulse train 105 is received by the re¬ ceiver 200, the converter 205 of which converts the pulse train 105 to an electric pulse train 207 which has the same signal pattern as the optical pulse train 105. The pulse train 207 is transmitted to the logic unit 210, which counts the number of pulses in the pulse train, and also to the passive monitoring device 215, which monitors the frequency of the pulse train and the number of pulses contained therein. The passive monitoring device 215 sends a signal 217 to the logic unit 210. If the passive monitoring device 215 fails to detect an error or a fault, the signal 217 sent to the logic unit 210 is a clear signal, whereas if an error or a fault is detected, the signal 217 to the logic unit 210 is an error signal. Provided that the logic unit 210 does not receive an error signal from the passive monitoring device 215, the logic unit will send to a dynamic test device 220 a signal 212 which essen- tially has the form of a squarewave of the same

frequency as the pulse train 207. Provided that the dynamic test device 220 receives such a squarewave, the device will send to the relays 225 and 230 signals whose energy content is such as hold the relays closed and therewith send to the logic relay unit 300 signals 227 and 237 such that said logic unit will produce on its outputs Utg. 1 and Utg. 2 clear signals which are transmitted to the monitored equipment. No clear sig¬ nals are sent from the outputs Utg. l and Utg. 2 in the absence of said squarewave.

This safety guard has a single-channel signal- connection from the transmitter 100 to the dynamic test device, whereafter the signal connection is a two- channel connection.

Safety guard beam light switches of the aforesaid kind have only passive monitoring devices. Consequently, among other things, there is a risk that clear signals will be transmitted despite the fact that components may be malfunctioning. For instance, clear signals can be sent despite the act that an integrated circuit in the final stage of the logic relay unit 210 is in auto- oscillation or that a stoppage or break-down has occurred in the connection between the converter 205 and the passive monitoring device 215.

Neither does a safety guard beam light switch of the aforesaid kind _. monitor the synchronization between the signals from the transmitter and the signals from the receiver. This means that signals transmitted from an optical transmitter different to that belonging to the safety guard switch can be understood by the receiver as being transmitted from the optical transmitter of said safety guard switch when the optical transmitter

of said safety guard switch is not in operation.

The Object of the Invention and the Most Important Characteristic Features Thereof

The aforesaid drawbacks are avoided by the present invention, in that the inventive safety guard is more reliable in operation than hitherto known safety guards, since the inventive safety guard is provided, inter alia, with a facility for active and duplicated monitoring of both signals and components. The inven¬ tive safety guard is also operative to reset the guard to an operating state subsequent to an interruption in operation, caused in some way or another, and to set the guard in operation through a continuously monitor¬ ing and duplicating facility in which the service¬ ability of all the components included in the safety guard is tested. Furthermore, the inventive safety guard is constructed from commerically available com- ponents and therefore can be manufactured at a low price.

The invention will now be described in more detail with reference to a number of exemplifying embodiments thereof and also with reference to the accompanying drawings.

Description of the Figures of the Drawings and of Exemplifying Embodiments

Figure 2 is a block schematic illustrative of the inventive safety guard beam light switch, in which:

10 is a resetting device - 15 is a logic blocking device

- 20 is a by-pass strap 25 is an oscillator

- 30 is a resetting device

- 35 is a logic by-pass coupling unit - 40 is an optical transmitter

45 is a logical test unit 50 is a dynamic test unit 53 is a positively controlled relay

- 55 is a logic relay unit - 60 is an optical receiver

- 65 is a logictest unit

- 70 is a dynamic test unit

- 73 is a positively controlled relay 75 is a logic by-pass unit - 80 is a by-pass strap

Utg. 1 is an output to monitored equipment Utg. 2 is an output to monitored equipment

Utg. 1 and Utg. 2 together form a two-channel output. The above components, enclosed in a broken line frame, are incorporated in a monitoring unit (1) .

The oscillator 25 is operative to transmit an electric pulse train 26, preferably having a frequency of 50-500 Hz, which is received by the blocking device 15, the by-pass unit 35 and the by-pass unit 75. The block¬ ing device 15 sends the electric pulse train 27 to the optical transmitter 40, the test unit 45 and the test unit 65. When the resetting device 10 is not activated, the pulse train 27 will be identical with the pulse train 26. On the other hand, when the resetting device 10 is activated, the pulse train 27 will be equal to zero. The optical transmitter 40 is operative to ^• transmit in a direction towards the optical receiver 60 an optical pulse train 46 which has the same signal

pattern as the electrical pulse train 27. The optical pulse train 46 is received by the optical receiver 60, which converts said optical pulse train 46 to an elec¬ trical pulse train 61 having the same signal pattern as the optical pulse train 46. The pulse train 61 is sent to the test units 45 and 65, and the pulse train 61 is compared in both units with the electrical pulse train 27. By the expression "have coincidence with" or any like expression in which "coincidence" is inferred in the following is meant "to have the same frequency and an inverted and/or phase-reversed signal pattern with or without phase displacement". The reason why the term "coincide" has been defined in the above manner is because if signals in this invention do not have such coincidence, it is impossible to obtain a residual apparatus function when a short circuit occurs between the said signals. As a result, the highest possible safety level is achieved.

The following Cases 1 or 2 and 3 or 4 occur when comparing the pulse trains 27 and 61:

Case 1. The pulse trains in the test unit 45 coincide, wherewith this unit sends to the dynamic test unit 50 a pulse train 47 of such frequency and pulse-shape as to enable the dynamic test unit 50 to transfer to the relay 53 sufficient energy to hold the relay closed.

Case 2. The pulse trains in the test unit 45 do not coincide, wherewith the pulse train 47 sent by the unit to the dynamic test unit 50 will not have a frequency and/or pulse-shape which will enable the unit to transmit sufficient energy to the relay 53 to hold the unit closed.

Case 3. The pulse trains in the test unit 65 coincide, wherewith the unit sends to the dynamic test unit 70 a pulse train of such frequency and pulse-shape as to enable the dynamic control unit 70 to send to the relay 73 sufficient energy to hold the relay closed.

Case 4. The pulse trains in the test unit 65 do not coincide, wherewith the unit sends to the dynamic test unit 70 a pulse train 67 which does not have a fre¬ quency and/or pulse-shape such as to enable the dynamic test unit 70 to transfer to the relay 73 sufficient energy to hold the relay closed.

The relay 53 and the relay 73 are open except in Cases 3 and 4 above, even in those instances when the dynamic test units 50 or 70 detects a static state of duration longer than 10 ms.

When signal transmission between the optical trans¬ mitter 40 and the optical receiver 60 is fault-free and no optical obstacle is present between these two opti¬ cal units, both the relay 53 and the relay 73 are closed, or activated.

When the signal transmission between the optical trans¬ mitter 40 and the optical receiver 60 and/or if optical obstacles are present between these two optical units, the relay 53 and/or the relay 73 is, or are, open. In order to enable the relay unit 55 to impart duplicated switch-closing functions to the monitored equipment, it must first be reset. Resetting of the relay unit is effected as follows:

The resetting device 10 is activated, wherewith the blocking device 15 will transmit the pulse train 27, which is now zero, causing the relays 53 and 73 to open. The re-setting device 30 is closed while the relays 53 and 73 are still open. The resetting devices 10 and 30 are opened. If the relays 53 and 73 are then activated within a limited time period, preferably a time period shorter than 0.5 s, subsequent to opening of the resetting devices 10 and 30, safety relays in the relay unit 55 will switch-in, whereupon the outputs Utg. 1 and Utg. 2 impart duplicated switch-closing functions to the monitored equipment. The essence of this paragraph is that the resetting function is dupli¬ cated and that the safety guard is monitored for possible malfunction and short circuiting.

The monitoring unit l can only be by-passed when re¬ setting is effected in accordance with the aforegoing and when the aforesaid safety relays in the relay unit 55 have been activated or cut-in. By-passing of the monitoring unit is effected in the following manner:

The by-pass stirrup or strap 20 is closed and therewith couples the pulse train 26 to the dynamic test unit 50, via a logic by-pass unit 35, at the same time as the by-pass stirrup or strap 80 is closed and therewith couples the pulse train 26 to the dynamic test unit 70, via a logic by-pass unit 75. In this respect, either one of the by-pass stirrups 20 and 80 may already be closed when the other by-pass stirrup is closed. When the two by-pass stirrups 20 and 80 are closed simul¬ taneously, the relay 53, 73 will not open and neither will the safety relays in the relay unit 55, even though an optical obstacle is introduced or a

malfunction occurs between the optical transmitter 40 and the optical receiver 60. When one or both of the by-pass straps 20 and 80 is/are closed, the relay 53 and/or the relay 73 is unable to open when an attempt is made to reset the device, which instigates an auto¬ matic test to ascertain whether or not said straps have been closed.

Figure 3 illustrates another embodiment of the inven- tion, in which Figure:

- 41 identifies one or more receiver/transmitter units, each consisting of an optical receiver 41A which is connected directly to an optical transmit- ter 41B,

- Other components and operational functions of the embodiment coincide with the embodiment illustrated in Figure 2 and have been identified with the same reference signs as those used in Figure 2.

The receiver/transmitter units 41 are so arranged so that the pulse train 46 is received by the optical receiver 41A of the first receiver/transmitter unit 41, this receiver transferring the pulse train to its optical transmitter 4IB which in turn transmits the pulse train to the optical receiver 41A of the next receiver/transmitter unit, and so on in an analogous manner until the pulse train has been transmitted from the optical transmitter of the last receiver/trans- mitter unit in line to the optical receiver 60. In order to improve safety, the pulse train 46 is inverted and/or phase-reversed again, once or several times in any desired manner and at any desired location between the optical transmitter 40 and the optical receiver 60, so that the pulse trains 27 and 61

and the signals between mutually sequential optical transmitters 41A and optical receivers 4IB obtain an inverted and/or phase-reversed signal pattern, with or without phase displacement. By phase-reversed is meant here and in the following reversal of the signal pattern about a given axis.

The object of this embodiment is to enable several safety guard beam light switches to be monitored simul- taneously with the aid of solely one monitoring unit 1, while maintaining a high degree of safety. As soon as one or more of the light beams between the optical transmitter 40 and the optical receiver 60 is/are interrupted, the relay unit 55 will no longer provide a switch/closing function.

Figure 4 illustrates a further embodiment of the inven¬ tion, in which:

- The optical transmitter 40 consists of one or more parallel-connected optical transmitter 40A, - The optical receiver 60 consists of one or more parallel-connected optical receiver 60A, The number of optical transmitters 40A is equal to the number of optical receivers 60A.

The transmitters 40A and the receivers 60A are arranged so that each receiver 60A can receive a light signal from a transmitter 40A. In the case of the Figure 4 embodiment, the relay unit provides a switch-closing function provided that there is no interruption of at least one of the light-signal transfers between the transmitters 40A and the receivers 60A. This enables, for instance, a distinction to be made between the passage of people or objects past the light beams. When

the distance between pairs of transmitters 40A and re¬ ceivers 60A is made narrower than the breadth of a human being, people are unable to pass the light beam guard. A narrower object, on the other hand, is able to pass the guard. An approximate distance between said pairs which will permit the passage of a human being is 100 mm at waist height and 40 mm at ankle height. This embodiment can be used for object identification pur¬ poses and for distinguishing between objects of mutual- ly different shape, by positioning the transmitters 40A and the receivers 60A differently.

Although the invention has been described in conjunc¬ tion with a safety guard beam light switch, it will be understood that the invention can also be used in other equipment for personal protection, e.g. and protective gates.