Abstract:
A locking system ( 1 ) for a safety switch includes a read head ( 2 ) and an actuator ( 3 ), each of which is provided with first or second componentry ( 10, 14 ) encompassing electrical and/or electronic components that interact with each other in an electrically contactless manner, thereby controlling the safety switch. The locking system actuator ( 3 ) can be locked to the read head ( 2 ) by a switchable electromagnet ( 7 ) which interacts with a counterelement ( 12 ). The locking action is controlled by a sensor element ( 31, 32, 33, 34 ), the output signal of which depends on the magnetic field generated by the electromagnet ( 7 ).

Description:
FIELD OF THE INVENTION 
   The present invention relates to a locking system for a safety switch having a read bead and an actuator, each with electrical components that interact without electrical contact to control the safety switch. 
   BACKGROUND OF THE INVENTION 
   Safety switches with a read head and an actuator, each having a first and/or second component set with electric and/or electronic structural elements which may be caused to interact without electric contact and as a result control the safety switch, are disclosed in DE 197 11 588 A1, for example. Such safety switches may be used to monitor movable protective devices, e.g., doors, covers, grates, and the like of machinery and equipment. As a rule, the safety switch interrupts one or more electric circuits when the relevant protective device is transferred to a safer operating state, is switched off, for example, or switching on of the device is prevented. 
   The actuator generally is introduced in a channel formed by the read head. When assembled, the actuator in the read head may be mechanically locked and as a result the protective device may be kept locked. Locking in conventional systems is accomplished as a result of extension of a rod directly through an opening in the actuator or blocking of a control gear in the read head operating in conjunction with the actuator. In order for it to be possible to apply the locking forces required, 1000 N, for example, as a function of the application the locking system, and accordingly, the safety switch, must be designed to be sufficiently rugged from the mechanical viewpoint. 
   As an alternative or in addition to the mechanical locking, the locking may be effected by electromagnetic forces, which are, of course, heavily dependent on the distance between the electromagnet and the associated counterelement. In particular, the electromagnetic forces decrease sharply with increase in distance. The fouling of the safety switch and of the locking system which occurs may impair provision of high locking forces and other aspects of operation in fouling environments, such as in the vicinity of metal-cutting machine tools. 
   DE 199 53 898 A1 discloses an access protection device having a U-shaped holding magnet. A configuration having a rotatable U-shaped permanent magnet is described. A first reed contact detects the rotary position of the permanent magnet, that is, engagement or disengagement of the magnetic locking action. A second reed contact detects the presence or absence of the counterelement, that is, whether the protective door is closed or not. 
   DE 198 40 620 C1 discloses a contact-free safety switch having a Hall sensor mounted on the read head and a permanent magnet mounted on the actuator. The Hall sensor monitors the closed position. The switching threshold of the Hall sensor is adjustable by a trimming resistor. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is an improved locking system of a safety switch, especially with reliable monitoring of locking by electromagnetic forces. 
   According to the present invention, a locking system of a safety switch has a read head and an actuator, each having a first component set and/or second component set with electric and/or electronic structural elements which may be alternately engaged and disengaged without the use of electric contacts so that the safety switch may be controlled. The actuator may be locked on the read head by a switchable electromagnet operating in conjunction with a counterelement. The locking may be controlled by a sensor element, the output signal of which depends on the magnetic field which may be generated by the electromagnet. 
   None of the state-of-the-art or conventional publications disclose a sensor element which provides an analog output signal by which the intensity of the magnetic field of an electromagnet and accordingly the locking force generated may be monitored. By using an electromagnet of the present invention, this locking force is continuously adjustable by suitable electric actuation. In contrast, only one switching state or one position is determined discretely and digitally by the known conventional sensor elements to establish whether the permanent magnet has been rotated to the locking position or whether the protective door is closed. The adjustability of the locking force also permits automatic association, in particular under program control, of different operating conditions of the machine to be monitored with different locking forces for the respective protective mechanism. 
   Electric contact-free interaction of read head and actuator may be effected with all known processes of the state of the art, in the simplest case by damping of electromagnetic waves, especially those of an electromagnetic field. As an alternative, a transponder system may be used in which identification signals are exchanged electrically, free of contact, between read head and actuator. In the state of the art, the three-dimensional area of response of the interactive system is used only to a limited extent, and a relatively precise orientation of read head and actuator toward each other in the assembled state is required. 
   The locking is not effected at all or at any rate is not effected exclusively by a bar which may be moved transversely to the direction of movement of the actuator, but rather by the action of an electromagnetic force on the counterelement. The electromagnet may be switched by the safety switch itself, and/or an associated control mechanism, and/or the machine associated with the safety switch. The level of the locking force may be adjusted, for example, as a function of the operating state of the associated machine. Preferably, the counterelement and/or the electromagnet is mounted to be pivotable relative to the base element. During locking, the electromagnet and the actuator are positioned so close to each other that sufficiently high locking forces may be achieved. In addition, the first and/or second component set preferably is integrated with the respective counterelement, so that interaction of the component sets is reliably ensured even under adverse conditions, for example, even in the event of angular displacement of the protective mechanism. 
   In one particular embodiment, the sensor element is mounted in the actuator. Preferably, the actuator has the base element, the counterelement, and the second component set. In particular, these elements form the actuator. As an alternative or in addition, the read head as well may have one or more sensor elements. It is conceivable, for example, that the damping of the magnetic field generated by the electromagnet could be measured directly in the read head. 
   Independently of the number and configuration of the one or more sensor elements, the safety switch may be controlled by direct or indirect coupling of the output signal of the sensor and by interaction of the first and second component sets. Direct coupling is effected, for example, when the first set and/or second set may be operated only if the sensor element provides a suitable output signal. Indirect coupling is effected, for example, if the output signal of the first component set and/or second component set is received by superordinate control electronics and the output signal of the sensor element is also received independently of this circumstance. Linking of the two output signals then occurs in the superordinate control electronics, which, for example, determines if an operating state of the machine to be monitored exists for which the output signal of the sensor element is relevant. 
   In one preferred embodiment of the present invention, the sensor element may assume two switching states as a function of the magnetic field which may be generated by the electromagnet. Preferably, the second component set mounted in the actuator is controlled by the switching states of the sensor element. This control yields the advantage that the actuator may be developed without external electric connections. All the electric or other connections required are preferably mounted within the actuator to be protected from disruptive influences of a mechanical or other nature from coming from the exterior. The sensor element may also be mounted directly on or in the second component set of the actuator or may be integrated into it. It is, of course, advantageous in many applications for the sensor element of the second component set to be positioned some distance away on the actuator. Preferably, at least one sensor element is mounted in an edge area of the actuator to determine not just one or in any event only one axial distance from the electromagnet, but also displacement in a direction perpendicular to the direction of movement of the relative movement between electromagnet and actuator. 
   In one preferred embodiment of the present invention, a generator coil is mounted in the actuator to provide electric energy for the second component set. This generator coil generally receives an electromagnetic signal from the first component set of the read head. This signal generates the voltage required or the current required for operation of the electric and/or electronic components. 
   In one especially simple embodiment of the present invention, the sensor element is connected electrically in series to the generator coil. This connection makes it possible to switch on the power supply for the second component set in the actuator only if the sensor element detects a sufficiently high or sufficiently low magnetic field generated by the electromagnet. 
   If several sensor elements are mounted on the actuator and/or the read head, their output signals may be interconnected as desired to monitor the locking. Three-dimensional or in any event two-dimensional distribution of the several sensor elements in keeping with the respective requirements and geometric relationships, for example, on the mounting surface of the actuator in particular, is advantageous. The relative position of the actuator in relation to the electromagnet in the locked state may also be determined in this way. 
   The position of one or more of the sensor elements may be adjusted by individual or collective adjustment means. The adjustment may generally be made in all three spatial directions and/or in rotary directions. In many applications, however, the possibility of adjustment in the direction of the relative movement of actuator and electromagnet or at an angle of 90° to such movement is a consideration of importance. 
   In one particular embodiment, the sensor element has a reed contact and/or a Hall element. In particular, the sensor element may be in the form of a reed contact or a Hall element. A Hall element presents the advantage over a reed contact, not only that one or more switching points may be assigned but also that an analog output signal relating to the intensity of the magnetic field generated by the electromagnet may be produced. 
   Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring to the drawings which form a part of this disclosure: 
       FIG. 1  is a perspective view of a read head of a safety switch having a locking system according to a first embodiment of the present invention; 
       FIG. 2  is a perspective view of an accompanying actuator according to a first embodiment of the present invention; 
       FIG. 3   a  is a diagrammatic, perspective view of the second component of the actuator of  FIG. 2  in which a generator coil and a transponder are mounted, according to a first embodiment of the present invention; 
       FIG. 3   b  is a diagrammatic perspective view of the second component of the actuator of  FIG. 2  in which the transponder is connected directly to the generator coil, according to a second embodiment of the present invention; 
       FIG. 4  is a side elevational view in a section of the read head of  FIG. 1  and the actuator of  FIG. 2  of the locking system in the assembled state; 
       FIG. 5  is a side elevational view in a section of the locking system of  FIG. 4  in a modified state; 
       FIG. 6  is a diagram of the measured locking force of the locking system of the present invention; and 
       FIG. 7  is a diagram of a protective mechanism and a machine incorporating the locking system of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  presents a perspective view of the read head  2  of a safety switch have a locking system  1  according to the present invention ( FIG. 4 ). The read head  2  is at least a part of the safety switch (not shown). The electric switching function may be performed inside the head housing  4  or in a switching component of the safety switch mounted remote from the head housing  4 . Electric contact of the read head  2  is effected by one or more plug-and-socket connectors  5 . The head housing  4  is more or less square in shape, with an essentially rectangular and preferably planar front surface  6 . Below its center, the head housing  4  has a cylindrical boring with a longitudinal axis forming a right angle with the front surface  6  and receiving electromagnet  7 . In one preferred exemplary embodiment, the read head  2  is secured by the head housing  4  on a frame of the protective device (not shown) or on the machine itself. 
   The electromagnet  7  has a more or less cylindrical housing forming on its side facing the actuator  3  a more or less round and preferably planar mounting surface  8 . The housing of the electromagnet  7  is within a radially outwardly spaced annular, and preferably planar, edge  9  separated from the first mounting surface  8  by an annular groove  28 . The first mounting surface  8 , the annular edge  9 , and the front surface  6  preferably are positioned in one plane. 
   The first component set  10  is mounted to be stationary above and relative to the electromagnet  7  in the head housing  4 . In particular, set  10  is detachably or non-detachably secured by a threaded connection to the head housing  4 . The wiring between the first component set  10 , the electromagnet  7 , and the connections for the plug-and-socket connectors  5  preferably are mounted inside the head housing  4 . A cable clip  11  for securing the connecting lines for the plug-and-socket connector  5  is mounted on a side surface on the head housing  4 . The preferably planar front surface or third mounting surface  23  ( FIG. 4 ) of the first component set  10  is aligned with the first mounting surface  8  or is offset slightly to the rear of this surface. 
     FIG. 2  presents a perspective view of an associated actuator  3  which has a counterelement  12 , such as one of steel, by which the actuator  3  may be secured on the read head  2  by the electromagnet  7  and by which the protective mechanism may be locked. The counterelement  12  may be in one piece of steel or only partly so, for example, for the purpose of forming a frame of aluminum for seating an insert operating in conjunction with the electromagnet. The counterelement  12  is rigidly connected to an associated base element  13 , such as one of aluminum, but is pivotable relative to this element, as is explained in the following description in connection with  FIG. 4 . The second component set  14 , which may be made to interact with the first component set  10  of the read head  2  in the absence of electric contact, is rigidly connected to the counterelement  12 . Preferably, it is detachably attached to counterelement  12  by fastening screws. 
   The counterelement  12  forms a preferably planar second mounting surface  15  which may be brought into surface-to surface contact with the first mounting surface  8  of the read head  2  during the locking process. The preferably planar front surface or fourth mounting surface  24  ( FIG. 4 ) of the second component set  14  is aligned with the second mounting surface  15  or is slightly offset relative to this mounting surface. It is essential in the process for the configuration of the first and second component sets  10 ,  14  to ensure establishment of contact between the first and second mounting surfaces  8 ,  15  of the electromagnet  7  and respectively of the counterelement  12 , since especially great locking forces may be thereby achieved. 
   The actuator  3  is secured, for example, on a protective mechanism by the base element  13  for a machine switchable by the safety switch. The counterelement  12  together with the second component set  14  may be pivoted relative to this protective device about the three spatial directions or axes x, y, z shown in  FIG. 2 . Each axis encloses a right angle relative to each other. The direction of spacing between the counterelement  12  and the base element  13  is represented in this instance by the spatial direction z. In the main, the counterelement  12  may not be displaced relative to the base element  13  in this direction of spacing z. Both the counterelement  12  and the base element  13  have a more or less rectangular basic shape with rounded edges. The grooved recesses  16  in the counterelement  12  serve the purpose of accessibility of the fastening means, screws in particular, which may be introduced into the fastening openings  17  in the base element  13  and may be used to secure the actuator  3  on the movable part of the protective mechanism. 
   In the embodiment illustrated, the second component set  14  has no connecting lines, so that establishment of electric contact with the actuator  3  is not necessary. Preferably, energy is conducted to the second component set  14  in the actuator  3  by the first component set  10  mounted in the read head  2  for the purpose of reading identification data stored in the second component set  14  and transmitting such data back to the first component set  10 . In a simplified embodiment, the second component set  14  may only damp, as desired, an alternating electromagnetic field generated by the first component set  10 , and, as a result, announce to the first component set  10  and the read head  2  respectively the presence of the of the second component set  14  and accordingly the closed position of the protective mechanism. 
   In the exemplary embodiment illustrated, a total of four sensor elements  31 ,  32 ,  33 ,  34  are mounted more or less centrally relative to the second mounting surface  15  and at the corners of an assumed isosceles triangle. Each sensor element is embedded in or secured on a suitable disk, circular in the exemplary embodiment, of plastic or the like. This plastic disk has, as adjusting means  30 , an adjustment slot by which the position of the associated sensor element  31  may be adjusted in the direction of the z axis. The second sensor element  32  mounted in the center may be used to determine if a relevant magnetic field is at all present in the field surrounding the actuator  3 . The first, third, and fourth sensor elements  31 ,  33 ,  34  located at the corners of the assumed isosceles triangle in addition make it possible to determine the position of the actuator  3 , in particular, the position of the counterelement  12  relative to the magnetic field which may be present. The output signals of the sensor elements  31 ,  32 ,  33 ,  34  preferably are connected by use of the electric and/or electronic components in the second component set  14 . 
     FIG. 3   a  illustrates a first exemplary embodiment of the second component set  14 , in which embodiment a generator coil  35  and a transponder  36  are mounted. A reed contact  37  mounted outside the second component set  14  in the embodiment illustrated is connected electrically in series to the generator coil  35 . In the event of approach of the reed contact  37  to the vicinity of the magnetic field generated by the electromagnet  7 , the contact stud  42  of the reed contact  37  is deflected in the direction of actuation  43 . As a result of the deflection, the transponder  36  is connected electrically to the generator coil  35 . In place of a make contact, use may also be made of a break contact which short-circuits when the generator coil  35  is not actuated, thereby preventing exchange of signals between the first and second component sets  10 ,  14 . 
   Both the second component set  14  and the reed contact  37  are mounted on or in the actuator so that movement of the reed contact  37  and accordingly of the actuator  3  is accompanied by approach of the second component set  14  to the first component set  10  mounted in the read head  2 . A suitable transmitting coil in the first component set  10  sends an electromagnetic signal which is received in the generator coil  35  and is converted at least to some extent back to electric energy. By this electric energy, a data signal stored in the transponder  36  is read out and transmitted back to the first component set  10  of the read head by the generator coil  35 . However, this data signal may be read out only if the contact stud  42  has been deflected, such being the case only if the magnetic field generated by the electromagnet  7  is of an assigned strength such that, for example, locking to a sufficient extent is ensured. 
     FIG. 3   b  illustrates a second exemplary embodiment of the second component set  114  in which the transponder  136  is connected directly to the generator coil  135 . Spaced a certain distance from the second component set  114 , a sensor element in the form of a Hall element  38  is mounted, and is fed over the feed lines  44  from the transponder  136 . The output lines  45  of the Hall element are extended back to the transponder  136  for evaluation. 
     FIG. 4  shows a section in the y/z plane through the read head  2  and the actuator  3  of the locking system  1  when assembled. The shape of the elastically deformable element or socket  18  is designed to be symmetrical in rotation relative to the direction of spacing or axis z. The washer  20  is designed to be more or less cupshaped and forms a stop especially during locking and the accompanying transfer of force from the counterelement  12  by the connecting element  19  to the base element  13 , and accordingly from the read head  2  to the actuator  3  and respectively the protective device, and/or during screwing in of the connecting element  19  and/or swiveling of the counterelement  12  relative to the base element  13 . The socket  18  is in contact with both the base element  13  and the connecting element  12 . When vibrations or impacts occur, socket  18  damps the tendency of the counterelement  12  to oscillate, thereby preventing generation of noise or rattling such as is caused, for example, by impact of the counterelement  12  on the base element  13 . 
   The first sensor element  31  may be screwed into a threaded opening  41  in the counterelement, against the action of an energy storing element  40 , in the exemplary embodiment a helical spring. Insertion is effected preferably by engagement of a tool into the adjusting slot  30 , or optionally by use of a suitable coin. Establishment of electric contact with the electric sensor element  31  is for the sake of clarity of illustration not shown in  FIG. 4 . It may be effected, for example, by sufficiently long connecting leads which subsequently are connected to component set  14 . The threshold value when reached by the first sensor element  31  can cause element  31  to generate an assigned output signal. The output signal may be adjusted by rotation of the first sensor element  31  forward or backward. The first sensor element  31  is adjusted in the z direction only in the exemplary embodiment illustrated, but may also be adjusted in the x and y direction by suitable adjusting devices. 
   As a variation of the exemplary embodiment shown in  FIG. 4 , it may be advantageous to mount at least one sensor element  31 ,  32 ,  33 ,  34  near or on the surface of the counterelement  12  facing the base element  13 , but in any event offset backward from the first mounting surface  8  of the counterelement  12 . The sensor element  31 ,  32 ,  33 ,  34  and/or the associated adjusting means  30  in particular may be accessible from this rear side. As a result, a first mounting surface  8  of the counterelement  12  with at least some of its area closed may be provided, and the sensor element  31 ,  32 ,  33 ,  34  and/or the associated adjusting means  30  are mounted so as to be protected. 
   The adjusting means  30  may be actuated, above all in the direction of the z axis, by openings in the base element  13  and/or in the connecting element  19 . The longitudinal axis of a reed contact  37  and/or the direction of switching of the latter may extend more or less in parallel with the z axis or enclose an angle more or less of 90° with this axis. 
     FIG. 5  shows the locking system  1  in a state in which the actuator  3  is separated from the read head  2  by a distance d. The electromagnet  7  mounted in the read head  2  is represented by broken lines and has several turns 25. A magnetic field is induced in the coil core  26  when current is applied to the turns 25. Another or second Hall element  39  mounted in the coil core  26  determines the field intensity which occurs. This field intensity depends, among other things, on the distance d of the counterelement  12  of the actuator  3  short-circuiting the magnetic flux. In particular, the field intensity determined by the other Hall element  39 , and accordingly, the associated hall voltage U Hall  increase with decrease in distance d. 
   As an alternative or in addition, the first sensor element  31  in the actuator  3  may be in the form of a Hall element and measure the magnetic intensity present in the actuator  3  and respectively the associated magnetic induction. The associated magnetic induction also is a function of the distance d of the actuator  3  from the read head  2 , and respectively, from the electromagnet  7 . 
   The magnetic field intensity measured by the other Hall element  39  and/or by the first sensor element  31  is a gauge of the locking force F acting between the read head  2  and the actuator  3 , in the case of a rigidly mounted read head  2  acting in particular on the actuator  3  and in the direction of the read head  2 . There may accordingly be assigned for the other Hall element  39  and/or the first sensor element  31  threshold values which when reached may signal the control mechanism of a machine not only that the protective mechanism is closed, but also that there is present a locking force high enough to keep the protective mechanism reliably in the closed state. If the first sensor element  31  in the actuator  3  is used for this purpose, reaching of the assignable threshold value for the locking force F may be used to determine if an exchange of signals between the first and second component sets  10 ,  14  between actuator  3  and read head  2  is possible. 
     FIG. 6  presents a diagram of a locking force F measured as a function of the distance d between actuator  3  and read head  2  in the case of a locking system  1  as illustrated in  FIG. 4 . The distance d was varied from 0.1 mm to 1.1 mm. The Hall voltages U Hall  measured with the other Hall element  39  may be correspondingly associated with an empirically determined locking force F characteristic. Correlation of measured Hall voltage U Hall  with locking force F depends in particular on the configuration of the other Hall element  39  relative to the electromagnet  7 , on the geometry of the electromagnet  7 , and on the geometry and material of the counterelement  12  on the actuator  3 . 
   The value pair U Hall /F generally determined with a prototype may be stored by electronic data storage in a reference table, or it may be found from the empirically determined values for the respective locking system  1 . The measured values shown are based on a rated volume of the electromagnet  7 . For this purpose, a Hall voltage of approximately 2.87 volts was measured at a distance d=0.1 mm, this corresponding to a locking force of more than 900 N. At a distance d=1.1 mm a Hall voltage of approximately 2.50 volts was measured, this corresponding to a locking force of approximately 60 N. 
     FIG. 7  presents a diagram of a protective mechanism  47 , for example, one with a protective grill  48  by which the operating area of a machine tool  50  may be closed off, in particular to protect operating personnel and to prevent access to the machine tool during operation. The protective grill  48  may be moved in the direction of the double arrow  49 . The actuator  3  secured on the protective grill  48  operates when the grill is in the closed state in conjunction with the read head  2 . In particular, signals are exchanged between the two component sets  10 ,  14 . The closed state of the protective grill  48  may be determined by the electromagnet  7 . The read head  2  is connected by the connecting line  51  to the evaluation unit  46 , unless this unit is integrated with the read head. The evaluation unit  46  transmits signals to the control mechanism of the machine tool over the control line  52 , in particular to signal the closed state of the protective grill  48 , and thereby to indicate freeing of the machine tool for operation. Accordingly, the evaluation unit receives signals from the control mechanism, in particular for activation of the electromagnet  7  to determine the closed state of the protective grill  48  during operation of the machine tool. 
   While various embodiments have 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.