Abstract:
The present invention relates to a safety switching apparatus having a first and a second input switch, whose respective switch settings define an input-side manipulated variable redundantly with respect to one another. The safety switching apparatus furthermore has at least one output switching element which is arranged in an output circuit. In addition, an evaluation and control unit is provided, which drives the at least one output switching element as a function of the defined manipulated variable. Switching contacts of the first and of the second input switch are coupled with one another, in terms of their switch positions, via a common actuating member. According to one aspect of the invention, the switching contacts of the first and of the second input switch are spatially arranged in one plane.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of copending international patent application PCT/EP01/01728 filed on Feb. 16, 2001 and designating the U.S., which claims priority from German patent application DE 100 09 707.3, filed on Feb. 29, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a safety switching apparatus and a method of manufacturing the same. The invention particularly relates to a safety switching apparatus having a first and a second input switch, whose respective switch settings define an input-sided manipulated variable redundantly with respect to one another, further having at least one output switching element which is arranged in an output circuit of the safety switching apparatus, and having an evaluation and control unit which drives or controls the at least one output switching element as a function of the defined manipulated variable, wherein the switching contacts of the first and of the second input switch are coupled to one another, in terms of their switch positions, via a common actuating member. 
     A safety switching apparatus of this type is distributed by the applicant of the present invention under the type designation PNOZ XV2. 
     The safety switching apparatuses in the meaning of the present invention comprise both autonomous safety switching devices and complex safety controllers and control systems, for example based on a fail-safe PLC controller. Apparatuses such as these are used primarily in the industrial field, in order to carry out switching processes safely. In this context, “safe” means that the apparatus complies with at least Category 3 of European Standard EN 954-1. By way of example, apparatuses such as these are used in order to stop, or in some other way to change to a safe state, a machine system from which a hazard has originated, as a reaction to the operation of an emergency-off button or the opening of a protective guard door. Since failure of the apparatus in a situation such as this results in a direct hazard to people or else to material values, the fail-safety of safety switching apparatuses is subject to very stringent requirements. This leads to a high level of complexity associated with high costs for the development and manufacture of safety switching apparatuses. 
     In the known safety switching apparatus, the input-side manipulated variable is a time constant, which governs a delay time for switching off. A delay time such as this is required, for example, in order to make it possible to move moving drives in a controlled manner to a safe rest position when switching off a machine system. In the case of the known safety switching apparatus, the time constant is set by means of two mutually redundant rotary switches, which are arranged one above the other or one behind the other on a common shaft. This configuration is explained in more detail further below, with reference to FIG.  2 . 
     In general, however, the manipulated variable that is to be set may be any input parameter which is relevant for a safety switching apparatus. 
     The known safety switching apparatus satisfies the safety requirements of Standard EN 954-1 in particular because the two input switches each define the desired time constant separately from one another. The resultant redundancy means that a fault in one of the switches can be identified reliably by the evaluation and control unit. However, this has the disadvantage that a large amount of mechanical complexity is required in the manufacture of the known safety switching apparatus, and this is associated with correspondingly high costs. Furthermore, the configuration of the known safety switching apparatus occupies a comparatively large amount of space, which prevents miniaturization of apparatuses of this generic type, or at least makes it more difficult. 
     SUMMARY OF THE INVENTION 
     It is one object of the present invention to specify a safety switching apparatus of the type mentioned initially, which is configured in more simple and more space-saving manner while still satisfying the same stringent safety requirements. 
     According to one aspect of the invention, this object is achieved in that the switching contacts of the first and of the second input switches are spatially arranged in one plane. 
     In contrast to this, the switching contacts of the two input switches in the known safety switching apparatus are located in two planes which are offset parallel to one another. This means that the two input switches must be mounted in the enclosure of the safety switching apparatus in two separate process steps. In contrast to this, the two input switches in the safety switching apparatus according to the invention can be mounted in a single process step. This simplifies the manufacture, and the safety switching apparatus according to the invention can be produced more cost-effectively. 
     Furthermore, as will be shown in the following text on the basis of preferred refinements of the invention, the physical space required for the two input switches can be reduced considerably, so that the safety switching apparatus according to the invention can be implemented in a spatially smaller way overall. Nevertheless, despite all this, it is still possible to use input switches which are separate from one another, and are thus redundant with respect to one another. The required fail-safety thus remains completely preserved. 
     In a preferred refinement of the invention, the actuating member comprises a common mounting element, on which the switching contacts of the first and of the second input switch are arranged such that they are spatially offset with respect to one another. 
     This measure has the advantage that the switching contacts of the two input switches are constructionally coupled in a very simple, and hence cost-effective, manner. It is thus possible to dispense with couplings, drives and other measures for transmitting a switching movement from the first input switch to the second, without this resulting in any risk of a different operator setting. 
     In a further refinement of the measure mentioned above, the common mounting element can be rotated for adjustment. 
     As an alternative to this, it is also feasible to design the common mounting element such that it can be translated for adjustment. In contrast to this, the preferred refinement is particularly advantageous when the two input switches are multiposition switches, since the switching contacts in this case can thus be arranged in a more space-saving manner with respect to one another, and thus in a spatially smaller manner. 
     In a further refinement of the measures mentioned above, the common mounting element is a mounting disk, on which the switching contacts of the first and of the second input switch are arranged radially offset with respect to one another. 
     This measure allows the two input switches, which are separate from one another, to be integrated in a particularly spatially small and space-saving manner in a common mechanical structure. Furthermore, this also simplifies the process of installing the input switches in the enclosure of the safety switching apparatus according to the invention. 
     In a further refinement of the invention, the first and the second input switch as well as the common actuating member are enclosed by a common switch enclosure. 
     This measure has the advantage that the input switches, which are separate from one another, form a common, intrinsically redundant component, which can be mounted in a very simple and hence cost-effective manner in the safety switching apparatus according to the invention. Furthermore, the fail-safety is improved even further, since the risk of damage to the redundant switch arrangement during the installation process or during any subsequent intervention in the safety switching apparatus is reduced. Furthermore, the safety-relevant switch arrangement is in this way protected particularly well against external environmental influences, such as dirt. This also contributes to improving the fail-safety. 
     In a further refinement of the invention, the switching contacts of the first and of the second input switch are sliding contacts, which can be moved over stationary contact surfaces by means of the actuating member. 
     This measure allows a particularly simple mechanical configuration, especially when the switching contacts are arranged on a common mounting element as the actuating member. 
     In a further refinement of the measure mentioned above, the contact surfaces are conductive track structures which are applied to a printed circuit board. 
     This measure allows the two input switches to be produced even in very large quantities in a fail-safe manner, thus minimizing the costs for the two input switches. At the same time, it is in this case possible, by means of a suitable design of the conductive track structures, to provide switching paths which include internal circuit logic. As a consequence of this, even complicated circuit schemes can be implemented in a simple and reproducible manner. Furthermore, this measure further improves the fail-safety, since conductive track structures are not subject to any wear, or at most are subject to extremely low wear, during operation of the apparatus, thus largely precluding any faults occurring only subsequently during operation of the apparatus. The risk of subsequently occurring cross-connections or short-circuits is likewise reduced. 
     In a further refinement of the invention, the first and the second input switches are each multiposition switches. 
     This measure can be implemented particularly easily in conjunction with the refinements of the invention mentioned above. This has the advantage that the safety switching apparatus according to the invention has a large number of setting options, thus improving its range of use and its adaptability. This means that larger quantities can be produced, and this leads to a cost reduction. 
     In a further refinement of the invention, the first and the second input switch have input-sided and output-sided connecting contacts or terminal contacts, which are arranged in a matrix structure with respect to one another. 
     This measure has the advantage that the number of connecting contacts required for the two input switches can be reduced, which likewise allows the physical space required to be reduced. Furthermore, this also simplifies the manufacture process. 
     In a further refinement of the measure mentioned above, the input-side connecting contacts of the first and of the second input switch are connected to one another. 
     This measure once again reduces the number of connections required for the two input switches. For example, this measure makes it possible to provide 16 mutually redundant switch positions, that is to say a total of 32 switch positions, with a total of only 12 connecting contacts. As a consequence of this, the physical space for the arrangement according to the invention can be further reduced, and the manufacture process simplified. 
     In a further refinement of the invention, the evaluation and control unit has two channels, with a first channel being connected to the first input switch, and a second channel being connected to the second input switch. 
     This measure has the advantage that the safety switching apparatus has a generally redundant design, thus making it possible to achieve a particularly high level of fail-safety. 
     It goes without saying that the features which have been mentioned above as well as those which are still to be explained in the following text can be used not only in the respectively stated combination but also in other combinations or on their own, without departing from the scope of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the invention are illustrated in the drawing and will be explained in more detail in the following description. In the drawing: 
     FIG. 1 shows the circuit configuration of a safety switching apparatus according to the invention, in the form of a safety switching device; 
     FIG. 2 shows a cross section of a prior art safety switching device; 
     FIG. 3 shows a cross section of the safety switching device according to the invention as shown in FIG. 1; 
     FIG. 4 shows an input switch unit for the safety switching device as shown in FIG. 3, along the line IV—IV; 
     FIG. 5 shows the input switch unit for the safety switching device shown in FIG. 3, along the line V—V; and 
     FIG. 6 shows a preferred matrix structure, in which the input-side and output-side switching contacts of two mutually redundant input switches are arranged. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In FIG. 1, a safety switching apparatus according to the invention, in the form of a safety switching device, is denoted by reference number  10 . 
     The safety switching device  10  has two mutually redundant input switches  12  and  14  which are coupled to one another, with regard to their switch positions, via a common actuating member  16 , which is illustrated only schematically here. The input switches  12 ,  14  are included in an identical manner in a respective voltage divider, which is in each case formed from a respective resistor  18   a ,  18   b  and a respective resistor group  20   a ,  20   b . The resistor groups  20   a ,  20   b  in the present exemplary embodiment include three resistors, which are arranged in parallel with one another and have different resistance values. An operating voltage, which in the present exemplary embodiment is 24 V, is applied across the two voltage dividers. Depending on the respective switch positions of the input switches  12 ,  14 , the two voltage dividers produce an output signal which is supplied via a respective further resistor  22   a ,  22   b  to a timer  24   a ,  24   b . The timers  24   a ,  24   b  define, redundantly with respect to one another and as a function of the respectively received voltage, a time constant which is supplied to an evaluation and control unit  26 . The received voltage in this case depends on the respective switch position of the two input switches  12 ,  14 . 
     The evaluation and control unit  26  in the present exemplary embodiment has two channels, and has a microcontroller  28   a ,  28   b  in each channel. The microcontrollers  28   a ,  28   b  additionally evaluate further input signals, which are not illustrated here, and which are generated, by way of example, by an emergency-off button or a protective guard. The microcontrollers  28   a ,  28   b  drive the respective output switching contacts  30   a ,  30   b  as a function of these input signals and of the time constants, which are defined redundantly with respect to one another. The output switching contacts  30   a ,  30   b  are arranged in series with one another in a power supply path to a machine system  32 . 
     The invention is not restricted to safety switching apparatuses having outputs with contacts. Instead of the relay contacts  30   a ,  30   b  used here, it is also possible to use semiconductor elements as output switching elements. 
     The overall safety switching device  10  is accommodated in a device enclosure  34  which, in a manner known per se, has connecting terminals  36  for connection of the power supply and of the machine system  32 . 
     In the description of the other figures in the following text, identical reference numbers denote the same elements as in FIG.  1 . 
     In FIG. 2, a safety switching device of this generic type, as is distributed by the applicant for the present invention, is denoted in its totality by reference number  40 . 
     The enclosure  34  of the safety switching device  40  has, as can be seen, a front face  42  as well as two side walls  44 ,  46  in the present cross-section illustration. Component mounts in the form of so-called printed circuit boards  48 ,  50  are arranged along each of the two side walls  44 ,  46  in the interior of the enclosure  34 . By way of example, individual components with reference numbers  52  and  54  are shown on the circuit board  48 . Likewise by way of example, the comparatively large casing of a relay  56 , which contains the output switching contacts  30   a ,  30   b , is shown on the circuit board  50 . 
     The reference numbers  58  and  60  denote two further circuit boards, which are mounted between the circuit boards  48  and  50 , parallel to the front face  42  and parallel to one another. The input switches  12  and  14  are also located on these two circuit boards, in addition to the further components  52 ,  54 . The switches are rotary switches, which are mounted one above the other or one behind the other on a common shaft  62 . The shaft  62  emerges to the exterior on the front face  42  of the enclosure  34 , where it is connected to a rotary knob  64 . The shaft  62  thus forms a common actuating member for the two input switches  12  and  14 . In this case, the switching contacts of the two input switches  12  and  14  are arranged in different planes  66 ,  68 , which are offset parallel to one another, as can be seen in the illustration in FIG.  2 . 
     As can be seen in FIG. 3, the safety switching device  10  according to the invention differs from the known safety switching device  40  in that, inter alia, there is no need for the two circuit boards  58 ,  60  which are arranged parallel to the front face  42 . Instead of this, the two input switches  12  and  14  in this exemplary embodiment are located in a common input switch unit  70 , whose configuration will be explained in more detail in the following text with reference to FIGS. 4 and 5. The input switch unit  70  is connected to the circuit board  48  via contact pins  72 . However, this arrangement reflects only one possible exemplary embodiment. 
     In alternative exemplary embodiments, the input switch unit  70  may also be made contact with via a circuit board  58  which is arranged parallel to the front face  42 . In contrast to the known safety switching device  40 , it is, however, not essential to have a circuit board  58  such as this or a second circuit board  60 , arranged parallel to it. 
     According to FIGS. 4 and 5, the input switch unit  70  has a switch enclosure  74 , in which the mechanical operating parts are accommodated. The switch enclosure  74  is arranged on a printed circuit board  76 . On its side facing the switch enclosure  74 , the circuit board  76  has a number of conductive tracks  78 ,  80 ,  82 ,  84 , which run along circular paths. Each of the conductive tracks  78  to  84  is connected to a respective contact pin  72 , with the connections for the conductive tracks  82  and  84  being located on the rear face of the board  76  in the present exemplary embodiment, as is represented by the dotted line. 
     A circular mounting disk  86 , which can be rotated in the direction of the arrow  88 , is arranged in the switch enclosure  74  of the input switch unit  70 . The mounting disk  86  is operated selectively by means of one of two buttons  90 ,  92 , which are each arranged tangentially and parallel to one another along two side walls of the switch enclosure  74 . On the side facing away from the circuit board  76 , the mounting disk  86  has a star-shaped structure  94 , in which studs  96 ,  98  on the two buttons  90 ,  92  can engage. At their end at the bottom in FIG. 4, the buttons  90 ,  92  are supported by springs  100 ,  102  against the rear wall of the switch enclosure  74 . The operation of one of the two buttons  90 ,  92  thus results in the mounting disk  86  being rotated in the direction of the arrow  88  by in each case one tooth pitch of the star-shaped structure  94 . 
     The mechanical configuration of such switches is known per se. By way of example, one mechanically comparable switch is distributed under the designation “two-button coding switch” by the company Fritz Hartmann Gerätebau GmbH &amp; Co. KG at 91083 Baiersdorf, Germany. 
     In contrast to these known two-button coding switches, there are, however, two mutually separate sliding contact pairs  104  and  106 , which are arranged radially offset with respect to one another, on that side of the mounting disk  86  which faces the circuit board  76 , in the present exemplary embodiment. The pair of sliding contacts  104  in this case interact with the conductive tracks  78  and  80 , while the pair of sliding contacts  106  interact with the conductive tracks  82  and  84 . When the pair of sliding contacts  104  is located in an angle range above the diagonal  108  shown in FIG. 5, this produces a conductive connection between the otherwise conductively isolated conductive tracks  78  and  80 . In this case, the input switch  12  between the contact pins  72  and  73  is closed. 
     When, in contrast, the pair of sliding contacts  104  are located in an angle position which is underneath the diagonal  108  shown in FIG. 5, there is no conductive connection between the conductor tracks  78  and  80 , so that the switch between the contact pins  72  and  73  is open. 
     The same applies in an identical manner to the pair of sliding contacts  106 , which interact with the conductive tracks  82  and  84 . The conductive tracks  78  to  84  are in this case arranged with respect to one another on the circuit board  76  such that the input switches  12  and  14  produced in this way in each case switch at the same time and redundantly with respect to one another. 
     As can easily be seen, the switching logic for the input switch unit  70  is provided primarily by the arrangement of the conductive tracks  78  to  84  on the circuit board  76 . The present exemplary embodiment has in this case been chosen deliberately to be simple, in order to explain the invention. However, it is self-evident that redundant multiposition switches can also be produced by suitable choice of the conductive track structure. 
     The input switch unit  70  is one particularly preferred exemplary embodiment of a safety switching device  10  according to the invention. As can be seen from FIG. 3, the pairs of sliding contacts  104 ,  106  as well as the conductive track structures  78  to  84 , that is to say all the switching contacts of the two input switches  12  and  14 , are in this case located within a common plane  110 . However, it is not absolutely essential to use a two-button switch of the illustrated type in order to implement the invention in this case. In alternative exemplary embodiments of the invention, the mounting disk  86  may for example also be adjusted via a shaft  62  and a rotary knob  64 , as is known from the safety switching device  40 . 
     When using multiposition switches for the input switches  12  and  14 , the number of contact pins required increases in principle twice as quickly as the number of desired switch positions. Furthermore, the factor of two also applies to the redundant design of the safety switching device  10 . Thus, if  16  switch positions were required, it would intrinsically be necessary to have  64  contact pins, and corresponding connection options. This number can be reduced by suitable coding of the switch positions, by means of a matrix structure. 
     FIG. 6 shows a preferred exemplary embodiment of a matrix structure  120  for the input switches  12  and  14 . The matrix structure  120  in this case has four connecting contacts  122 , which are supplied in parallel to switching contacts  124 ,  126  of the two input switches  12  and  14 . In the present exemplary embodiment, the mutually associated switching contacts  124 ,  126  are in each case shifted by one step with respect to one another, that is to say the uppermost switching contact  124  of the input switch  12  in FIG. 6 is in this case connected to the second switching contact  126  from the top of the input switch  14  in FIG.  6 . As an alternative to this, the switching contacts  124 ,  126  of the two input switches  12  and  14  may, however, also be connected to one another shifted by different step widths. In this case, a step width of zero, that is to say a mirror-image association between the switching contacts  124 ,  126  with respect to one another, is also possible. 
     The output-side switching contacts  132 ,  134  of the two input switches  12  and  14  are connected to output-side connecting contacts  136 ,  138  separately from one another. By virtue of the matrix arrangement, it is in this case possible to determine the respective current switch positions of the input switches  12  and  14  by comparison and evaluation of the signals at the input-side connecting contacts  122  and at the output-side connecting contacts  136 ,  138 . In this case, by virtue of the common input-side connecting contacts  122  and the separate output-side connecting contacts  132 ,  134 , the illustrated matrix structure  120  allows fail-safe evaluation with a minimal number of connecting contacts.