Abstract:
A safety switch for monitoring movable protection devices comprises a switching member with at least one reading head, and an actuating element which can be moved in relation the reading head. The actuating element engages in contactless interaction with the reading head. The actuating element has an inductive reactance for interaction with the reading head.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a safety switch for monitoring movable protection devices having a switching member with a reading head and having an actuating element movable relative to the reading head and co-operating with the reading head in a contactless manner. 
     BACKGROUND OF THE INVENTION 
     Movable protection devices in the configuration of doors and coverings on machines and processing plants are monitored with safety switches. The protection devices separate persons and machines form one another for the protection of both. For this purpose, during opening of doors or coverings, the safety switch must safely interrupt one or more current circuits and hold them disconnected until the protection device is closed again. 
     Electrical/mechanical safety switches for this purpose have a switching member connected with the stationary part of the protection device, into which can be introduced a separate operation control arrangement connected with the movable protection device. The separate operation control arrangement in the introduced state closes the switch contacts. When the protection device is opened, in other words without the operation control arrangement being introduced, the switch contacts are forcibly opened by a form-locking arrangement transferring the energy. 
     In those cases of use in which electrical/mechanical safety switches cannot be used because the environment is of extraordinary hygienic or other environmental conditions (foodstuffs processing, purification plants), operation control s with several permanent magnets are used. The magnets interact with reading heads without contact. Coils are provided in the reading heads. For safety reasons, at least three magnets must be provided. As opposed to electrical/mechanical safety switches, magnetic safety switches are considerably more sensitive in the case of vibrations. Additionally, when a breakdown occurs the preferred reaction is that the switch not be opened. 
     SUMMARY OF THE INVENTION 
     Objects of the present invention are to provide an improved safety switch for movable protection devices. These objects are attained according to the present invention by a safety switch for monitoring movable protection devices, comprising a switching member having at least one reading head, and an operation actuating element movable relative to the reading head and interacting with the reading head without contacting the reading head. The actuating element has an inductive reactance for interacting with the reading head and an electronic code in a first storage specifically identifying the actuating element. An evaluation device is connected at an output of the reading head, includes an electronic code in at least two second storages specifically identifying one of the reading head and the switching member, and includes at least two sets of components for analyzing and evaluating signals from the reading head. 
     Since the actuating element for interaction with the reading head has an inductive reactance, permanent magnets of any sort are no longer required in the operation control mechanism. The safety switch is thus insensitive to vibrations. At the same time, the problem of the magnets having an extended operation range, creating a disruptive effect when the mechanism is moved to either side, is also overcome. Upon breakdown of the inductive reactance of the reading head, no existence of an actuating element can be established. Thus, the safety switch then switches over into the safe state, in other words into opened state. When that occurs an inductive reactance offers greater safety than the device using three permanent magnets. As a result of the relatively extensive mechanical tolerances between actuating element and reading head, use of the safety switch according to the present invention is possible even in the case of heavy protection doors. 
     The reading head likewise advantageously has an inductive reactance which interacts over a magnetic alternating field with the inductive reactance of the actuating element. The two inductive reactances then form a transformer. This transformer can be operated under the safety technology principle of dynamic signal transmission. This allows for operation even with very high safety requirements using a structure having one single channel. The production of the reading head is greatly simplified and is of considerably lower cost. 
     It is especially advantageous when the actuating element picks up or absorbs its energy for operation from this magnetic alternating field. No separate voltage supply is required for the actuating element. Thus, the probability of a technical breakdown of the inductive reactance (with the resultant switching of the safety switch setting into the opened state) is greatly decreased. Also, the corresponding maintenance costs of the operation control are greatly decreased. 
     It is advantageous when the actuating element includes an electronic coding in a storage area, which specifically identifies the actuating element. Each actuating element is then a unique element. Any manipulations of the safety switch with the aid of another actuating element are precluded. At the same time, digital analysis/evaluation is possible instead of analog analysis/evaluation over a frequency shift. Similar actuating elements are used for identification systems in which movable ramming or tamping tools or ramming or tamping tool pallets carry such actuating element, which is detected by graphics- or registration-reading heads, and thereafter, is suitably programmed in order to supply instructions and/or feedback to a machine for the movement or transport of these parts. 
     When an analysis and evaluation device is series-connected at the outlet side on the reading head, which reading head includes an electronic coding in at least one further storage, specifically identifying the reading head or the switching member, each safety switch is also a unique element. In combination with a specifically identifiable actuating element, each individual safety switch reacts only to the signal from one single actuating element. For this purpose it is preferred that a comparison device be provided within the analysis/evaluation device. The comparison device compares the coding coming out of the actuating element with the stored coding of the same. Preferably, the coding coming form the actuating element for inducement of the operation of the reading head is read and picked up by the latter. Similar systems which are called transponders can also be used for the electronic automatic travel stop devices of automobiles, for example, in connection with ignition keys. 
     Because of the high safety level of the actuating element-reading head-system, it suffices for this arrangement to be configured with only one channel. On account of high sensitivity of the analysis/evaluation electronics, it is advantageous for the information flow to occur in two channels in the analysis/evaluation device. This is attained when at least twice as many parts of the analyzing/evaluating device, which are competent and authorized for the customary analysis/evaluation of the signal picked up from the reading head, are present. 
     Using a reliable technique, the safety switch has a key-like operation control which can be introduced into the housing of the switching member. One arrangement for use of the present invention is when the actuating element is provided mounted on the operation control, while correspondingly the reading head is provided within the housing of the switching member. An interchangeable arrangement however would also be conceivable. With use of known technology, the operation control is interlocked by use of a ramming or tamping rod. Another use of the present invention is with the actuating element mounted on the ramming or tamping rod, and with the reading head arranged within the housing of the switching member. Also, the arrangements could be suitably interchanged. 
     Because of the cost of material, it can be advantageous that the operating control be configured of plastic rather than metal. One advantageous protection against fault or error function as a result of a break of the operation control is obtained when one winding of the inductive reactance of the actuating element extends over almost the entire length of the operation control. 
     Other objects, advantages and salient features of the present invention will become apparent form the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring to the drawings which form a part of this disclosure: 
     FIG. 1 is a side elevational view in section of a safety switch according to an embodiment of the present invention; 
     FIG. 2 is a schematic or wiring diagram of the operation control reading head and analysis/evaluation device of the safety switch of FIG. 1; and 
     FIG. 3 is a diagram of the operation control. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A safety switch according to the present invention comprises a switching member  1  with a housing  3 , which can be connected with the stationary part of a protection device. An operation control channel  5  passes all the way through the frontal area of housing  3 . The channel is open at both ends. A key-like operation control member or actuator  7  can be introduced into operation control channel  5 , and can be fastened to the mobile or movable part of a protection device, for example to a door or hood member. Operation control member  7  carries an actuating element  9  encased in plastic. Actuating element  9  is located within operation control channel  5  when operation control member  7  is introduced completely into operation control channel  5 . Switching member  1  has a reading head  11  on the border or periphery of operation control  5 . When operation control member  7  is completely introduced, actuating element  9  and reading head  11  are arranged opposite one another and can interact alternately with one another. 
     Reading head  11  is connected to an analysis and evaluation device  13 . Analysis/evaluation device  13  has connections  15  fed an apparatus supply voltage of 24 V. The inputs of a control  17  are connected with these connections  15 . The output of control  17  discharges an internal supply voltage of 5 V to the collector of an npn transistor  19  connected thereto. The output of transistor  19  is connected to a pnp transistor  21 , as well as to a first microprocessor  23  and, for safety reasons, a second microprocessor  25 . First microprocessor  23  is monitored over an additional control line from control  17 . An output from first microprocessor  23  is connected over an amplifier to the bases of transistors  19  and  21 . While the collector of the pnp transistor  21  is grounded, a conductor extends from and connects the two emitters of transistors  19  and  21  with one another, and extends into reading head  11  where it is connected to a coil or inductor  27 . This coil  27  is arranged within reading head  11  on the side facing operation control channel  5 , and extends with its longitudinal axis parallel thereto. A capacitor  29  is connected at the output of coil  27 , which capacitor in turn is grounded over two resistances  31 , and, on the other hand, is connected over a receiver amplifier  33  with band-pass filters to one input of each of the two microprocessors  23  and  25 . For reasons of safety, parallel to each of the two resistances  31 , one transmission level monitor  35  is connected in turn. One transmission level monitor is connected to an input of first microprocessor  23 , while the other transmission level monitor is connected to an input of second microprocessor  25 . 
     First microprocessor  23  generates from the computer circuit a frequency of 125 kHz, with which it controls both transistors  19  and  21 , which switch alternately from locked or blocked into saturated state. By means of this circuit, the oscillation circuit of coil  27  and capacitor  29 , of which the resonance frequency is likewise 125 kHz, is induced to oscillate. Coil  27  thus radiates a magnetic alternating field. Resistances  31  limit the current in the oscillation circuit, and thus, the amplitude of the magnetic alternating field. At the same time, the distance between operation actuation element  9  and reading head  11  is also established, at such a distance that the two members can continue to interact. Since twice as many resistances  31 , as their customary number, are present, the transmission level monitors  35  by comparison can recognize a drift of one of the resistances  31 . 
     An operation control coil or inductor  37  is provided in actuating element  9  as the inductive reactance. The coil is arranged on the side of actuating element  9  facing reading head  11  in longitudinal alignment along operation control member  7 . Operation control coil  37  together with an operation control capacitor  39  forms an oscillation circuit. An IC building block  41  lies parallel to control capacitor  39 . When operation control member  7  is completely introduced, actuating element  9  and reading head  11  are arranged opposite one another, and coil  27  and operation control coil  37  together form a transformer. In other words, a transmitter and transducer arrangement is formed. Since a gap is found between the two coils  27  and  37 , the transformer has only a small degree of coupling (typically between 0.01 and 0.1). The magnetic alternating field being radiated from coil  27  induces a voltage in operation control coil  37 , and with that excites oscillations in oscillation circuit  37  and  39 . The IC building block  41  includes a converter, whereupon it can absorb or pick up energy from oscillation circuit  37  and  39 . Furthermore, IC building block  41  has an EEPROM, which supplies a 32-bit lengthwise code, with which actuating element  9  is specifically identifiable. The IC building block  41  with this code modulates the amplitude in oscillating circuit  37  and  39  with a rate of 1 bit per msec. Operation control coil  37 , determining a new course, joins back onto coil  27  in reading head  11 , whereupon its oscillation circuit  37  and  39  is likewise modulated. This modulated signal is fed through receiver-amplifier  33  to microprocessors  23  and  25 . 
     Each of the two microprocessors  23  and  25  has an EEPROM  43 , in which is supplied a 32-bit lengthwise code with which reading head  11  is specifically identifiable. The two microprocessors  23  and  25  independent of one another determine whether a code is transmitted form actuating element  9  at all, and whether this code adapts to that code out of the EEPROM  43 , in other words whether the pair made up of actuating element  9  and reading head  11  associated with one another is arranged with the elements of the pair facing one another. Only when the pair is in alignment does microprocessor  23  or  25  discharge the signal over an amplifier to a relay  45 , for the closing of a switch  47 . For greater safety then, opening contacts and line are provided for the closing of the switch  47 , with which each microprocessor  23  and  25  can determine the switching state of the relevant other relay  45 . The two switches  47  form the outputs of the safety switch, and for example, can be arranged connected in series thereto, to control the voltage feed into the machine provided with the protection device. If the distance between actuating element  9  and reading head  11  is too great, in other words for example when operation control member  7  is not introduced into operation control channel  5  (in other words when the protection device is open), microprocessors  23  or  25  can determine no fitting code, so that microprocessors  23  and  25  give the signal for the opening of switch  47 , and thus, for disconnection of the voltage feed to the machine. 
     To increase safety, switching member  1  has a ramming or tamping tool  51  slidable longitudinally in housing  3 , and configured preferably as an armature of a lifting magnet. Ramming or tamping tool  51  can pass crosswise through operation control channel  5 , extending perpendicular to the tool direction of movement, and engage on the opposite side in a cutout in housing  3 . Operation control member  7  includes an opening  53  through which ramming or tamping tool or slide  51  can engage when operation control member  7  is introduced completely into operation control channel  5 . Ramming or tamping tool  51  is spring-biased counter to the lift direction of the magnet. The arrangement and control of the lift magnet is thus determined so that with operation control member  7  arranged inserted completely in operation control channel  5 , ramming or tamping tool  51 , passing through opening  53 , engages in the cutout in the head of housing  3  and locks down operation control member  7 . Thus ramming or tamping tool  51  frees operation control member  7  only following disconnection of the machine, when the machine has come to a standstill, so that the protection device cannot be opened while the machine is still running. To monitor the position of ramming or tamping tool  51 , this arrangement also includes another actuating element  55 , configured identical to actuating element  9 . Furthermore, switching member  1  in housing  3  has another reading head  57 , which is configured identical to reading head  11 . The additional actuating element  55  and the additional reading head  57  are thus arranged so that they lie opposite one another when ramming or tamping tool  51  locks down actuating element  7 . The other analysis/evaluation device connected at the output of the other reading head  57  has two switches, preferably laid out in series with switch  47  of analysis/evaluation device  13 . 
     Operation control member  7  is plastic. At the ends most distant from opening  53  are provided fastening apertures, with which operation control member  7  is fastened to the movable part of the protection device. A copper wire winding of operation control coil  37  extends outward form actuating element  9  to operation control member  7 , around the fastening apertures  59  and back to actuating element  9 . The winding can also be laid again around opening  53 . when there is an interruption of operation control member  7 , this winding and with it operation control coil  37  are disconnected, so that actuating element  9  can no longer operate on the magnetic alternating field of reading head  11 . In this case it is signaled to the switching member  1  that the protection device is open, so that the safety switch switches over into safety state, in other words the voltage supply to the machine is disconnected. 
     While an embodiment has been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.