Abstract:
A modular safety switching device system for actuating actuators in a fail-safe manner. and a switching device system wherein a plurality of switching devices are connected in series and optically communicate with each other. The system includes a first and a second safety device. The first and second safety devices are connected to each other via an optical link. The optical link may be formed in a way that the first safety device comprises an optical transmitter and the second safety device comprises an optical receiver configured to receive information from the optical transmitter.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to European Patent Application No. EP10161648 filed on Apr. 30, 2010 and titled “Modular Safety Switching Device System With Optical Link” and the disclosure of which is incorporated herein. 
       BACKGROUND 
       [0002]    The present invention generally relates to a modular safety switching device system for actuating actuators in a fail-safe manner. In particular, the present invention relates to a switching device system wherein a plurality of switching devices are connected in series and communicate with each other for indicating the status of the safety switching devices of said system. 
         [0003]    Generally, safety relays are apparatuses intended to ensure the safety of humans working in the environment of an industrial process. Safety relays are used, for example, to detect the opening of emergency stop switches or other machine lock-out switches such as interlock switches guarding a gate or limit switches which, for instance, in the form of an optical curtain detect the presence of a human in a predefined hazardous region. Safety relays and safety devices, such as the above-mentioned switches, have to be designed to meet stringent requirements defined in world-wide adapted safety standards. These standards intend to achieve high reliability which is achieved particularly by applying redundancy, diversity, and monitoring principles. 
         [0004]    Safety relays, for example, provide internal checking of fault conditions, such as jammed, welded, or stuck contacts of safety switches. Moreover, safety switches, such as limit switches, which already have redundant, normally closed safety contacts for use with dual channel safety relays, are additionally provided with an auxiliary contact for status indication. 
         [0005]    Modular safety device systems may comprise a base module, at least one input module and at least one output module. The modules are arranged in a side-by-side fashion on a mounting rail. As for instance known from EP 1 645 922 B1, the modules are interconnected with each other by flat band cables through contact sockets, which are accessible from the outside. The flat band cable provides for the signal flow from the input modules via the base module to the output modules. 
         [0006]    The disadvantage of this solution is firstly to be seen in the fact that these flat band cables are accessible from outside and therefore may be tampered with in an unauthorized way. Further, open cables are prone to be influenced by electromagnetic disturbances. Finally, attaching the connecting cables represents a cumbersome additional mounting step. 
         [0007]    It is one aspect of the present invention to provide a modular safety device system, which can be assembled in a particularly easy and cost-effective way and, on the other hand, allows a high level of security for the communication between the individual safety devices. 
         [0008]    In particular, to link safety devices of known safety systems  200  ( FIG. 10 ) for logical functions, it is necessary to do that via terminals and wires with known systems. The safety device A, for example, is equipped with an output terminal to provide the own safety state. The safety device B is equipped with an input terminal that is connected via a cable  202  to the output terminal of device A. Thus, device B can read the safety information from device A and can control its own safety output by interpreting the information from device A and its own safety state. Logical AND/OR conjunctions are possible. Furthermore, a master device  204  may be provided for diagnosis and configuration of the individual safety devices. Regardless of the communication hierarchy, the various inputs and output of safety devices A and B are connected via terminals and/or wires that extend therefrom or therebetween. These connection methodologies unduly increase the installation and service requirements of such systems. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention provides a safety device system that overcomes one or more of the problems discussed above. One aspect of the invention dispenses with cables and wires common to prior art module systems and instead provides optical means for the logical link between the individual safety devices. 
         [0010]    According to the present invention, all data transmission between the components is achieved via optical transferal with the advantage that no additional wiring for the link is necessary. 
         [0011]    According to another aspect of the present invention, the safety devices each have a housing and within the housing a small hole is provided. Behind the hole on one side of the housing an optical receiver, for instance an infrared photo transistor, is arranged, and behind a hole on the opposite side of the housing an optical transmitter, for instance, an infrared LED (light emitting diode) is arranged. The two openings are aligned to each other so that the transmitter of one safety device can communicate with the receiver of the adjacent safety device, when both devices are mounted on a mounting rail. 
         [0012]    The received optical data are converted into electrical data within the safety device and are read by an integrated microprocessor. This microprocessor interprets the information together with the own safety state of the respective safety device, and sends an electrical signal to the optical transmitter. The safety devices can be configured to an AND or an OR conjunction. Besides replacing the additional wiring, the optical communication according to the present invention has the advantage of enhanced elecromagnetic compatability (EMC) stability. 
         [0013]    According to another aspect of the present invention, there is not only provided a communication between individual safety devices, but also to a gateway which is able to convert the optical data into electrical data to be transmitted via a communication bus protocol. 
         [0014]    To the accomplishment of the foregoing and related ends, certain illustrative aspects of the disclosed innovation are described herein in connection with the following description and the annexed drawings. These aspects are indicative, however, of but a few of the various ways in which the principles disclosed herein can be employed as is intended to include all such aspects and their equivalents. Other advantages and novel features will become apparent from the following detailed description when considered in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  shows a perspective view of a first safety device according to the present invention; 
           [0016]      FIG. 2  shows a perspective view of a second safety device according to the present invention; 
           [0017]      FIG. 3  shows a front view of two safety devices when mounted in a communicating manner; 
           [0018]      FIG. 4  shows an example of a light signal sent from one safety device to another; 
           [0019]      FIG. 5  shows a schematic representation of a safety device which can be implemented in an optical bus system; 
           [0020]      FIG. 6  shows a schematic representation of a modular system of safety devices interconnected via an optical link and communicating via a gateway with another bus; 
           [0021]      FIG. 7  shows a perspective view of the gateway of  FIG. 6 ; 
           [0022]      FIG. 8  shows a block diagram of two communicating safety devices; 
           [0023]      FIG. 9  shows a flowchart of an automatic address assignment procedure; and 
           [0024]      FIG. 10  shows a perspective view of a known modular safety system comprising flat cable interconnections. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    The innovation is now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding thereof. It may be evident, however, that the innovation can be practiced without these specific details. In other instances, well known structures and devices are shown in block diagram form in order to facilitate a description thereof. 
         [0026]    As used in this application, the terms “component”, “system”, “equipment”, “interface”, “network” and/or the like are intended to refer to a computer related entity, either hardware a combination of hardware and software, software or software in execution. For example, a component can be, but is not limited to being, a process running on a processor, or a processor, a harddisk drive, multiple storage drives (of optical and/or magnetic storage medium), an object, an executable, a thread of execution, a program and/or a computer, an industrial controller, a relay, a sensor and/or a variable frequency drive. By way of illustration, both an application running on a server and a server can be a component. One or more components can reside within a process and/or thread of execution, and a component can be localized on one computer and/or distributed between two or more computers. 
         [0027]    In addition to the foregoing, it should be appreciated that the claimed subject matter can be implemented as a method, apparatus, or article of manufacture using typical programming and/or engineering techniques to produce software, firmware, hardware, or any suitable combination thereof to control a computing device, such as a variable frequency drive and controller, to implement the disclosed subject matter. The term “article of manufacture” as used herein is intended to encompass a computer program accessible from any suitable computer-readable device, media, or a carrier generated by such media/device. For example, computer readable media can include but are not limited to magnetic storage devices (e.g., hard disk, floppy disk, magnetic strips . . . ), optical disks (e.g., compact disk (CD), digital versatile disk (DVD) . . . ), smart cards, and flash memory devices (e.g., card, stick, key drive . . . ). Additionally it should be appreciated that a carrier wave generated by a transmitter can be employed to carry computer-readable electronic data such as those used in transmitting and receiving electronic mail or in accessing a network such as the Internet or a local area network (LAN). Of course, those skilled in the art will recognize many modifications may be made to this configuration without departing from the scope or spirit of the claimed subject matter. 
         [0028]    Moreover, the word “exemplary” is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects or designs. Rather, use of the word exemplary is intended to present concepts in a concrete fashion. As used in this application, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or”. That is, unless specified otherwise, or clear from context, “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, if X employs A; X employs B; or X employs both A and B, then “X employs A or B” is satisfied under any of the foregoing instances. In addition, the articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from context to be directed to a singular form. 
         [0029]    Furthermore, the terms to “infer” or “inference”, as used herein, refer generally to the process of reasoning about or inferring states of the system, environment, and/or user from a set of observations as captured via events and/or data. Inference can be employed to identify a specific context or action, or can generate a probability distribution over states, for example. The inference can be probabilistic—that is, the computation of a probability distribution over states of interest based on a consideration of data and events. Inference can also refer to techniques employed for composing higher-level events from a set of events and/or data. Such inference results in the construction of new events or actions from a set of observed events and/or stored event data, whether or not the events are correlated in close temporal proximity, and whether the events and data come from one or several event and data sources. 
         [0030]    Referring to the drawings,  FIG. 1  depicts a first safety device  102  according to the present innovation. As can be seen from  FIG. 1 , the safety device  102  has an opening  106  within its housing  103  through which an optical signal  108  can be emitted. This optical signal  108  can for instance be a pulsed infrared radiation. For performing a communication with a second safety device  102 , the first safety device  102  is mounted on a mounting rail  110 , which can for instance be a so-called top hat rail or DIN rail. A second safety device  104  is mounted adjacently to the first safety device  102  at the mounting rail  110 , as shown in  FIG. 2 . Safety device  104  has a corresponding opening  112  for receiving the optical signal  108  from the first safety device  102 . 
         [0031]    As shown in  FIG. 3 , safety devices  102  and  104  are mounted on the mounting rail  110  preferably in a way that they touch each other, so that no scattered ambient light can interfere with the optical signal  108 , transmitted from one safety device to the other. Preferably, the opening  106  and  112  are arranged to align with each other. 
         [0032]      FIG. 4  shows a possible sample of a pulse train for the optical signal  108 . As shown in the following table 1, the safety devices can be configured according to an “and” or an “or” conjunction. 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Logic 
                 Optical Input 
                 Safety input 
                 Safety output 
                 Optical output 
               
               
                   
               
             
             
               
                 AND 
                 false 
                 false 
                 OFF 
                 OFF 
               
               
                 AND 
                 false 
                 true 
                 OFF 
                 OFF 
               
               
                 AND 
                 true 
                 false 
                 OFF 
                 OFF 
               
               
                 AND 
                 true 
                 true 
                 ON 
                 ON 
               
               
                 OR 
                 false 
                 false 
                 OFF 
                 OFF 
               
               
                 OR 
                 false 
                 true 
                 ON 
                 ON 
               
               
                 OR 
                 true 
                 false 
                 ON 
                 ON 
               
               
                 OR 
                 true 
                 true 
                 ON 
                 ON 
               
               
                   
               
             
          
         
       
     
         [0033]    The optical serial transmission signal can have the following states: light constantly ON, light constantly OFF, or pulsed light pattern, for instance, short ON, short OFF, short ON, short OFF, long ON, long OFF, and repeat this pattern from the beginning. This signal pulse train is shown in  FIG. 4 . 
         [0034]    The receiving device  104  interprets these states to the following results: 
         [0035]    Light constantly ON: safety state from the transmission device is OFF 
         [0036]    Light constantly OFF: safety state from the transmission device is OFF 
         [0037]    Light pattern as shown in  FIG. 4 : safety state from the transmission device is ON 
         [0038]    By using such a light pattern, static states of the light never run into dangerous situations and therefore, the safety requirements for such a data transmission can be met. 
         [0039]    Of course, any number of devices  102 ,  104 , in which a state of the safety devices is transmitted unidirectionally, can be assembled in line with  FIG. 3 . Furthermore, the devices have to be configured whether an AND or an OR conjunction has to be interpreted. 
         [0040]    According to a further embodiment of the present invention, not only a unidirectional but also a bidirectional, for instance, a ring-shaped communication of a plurality of safety devices can be achieved. 
         [0041]    As shown schematically in  FIG. 5 , each safety device  100  can be equipped with two openings at each sidewall of the housing  103  for sending and receiving optical signals indicative of the safety status of the respective safety device  100 . As shown in  FIG. 6 , a plurality of such safety devices  100  with a bidirectional optical link can be joined to form a modular safety device system  114 . The light emitting device  106  can be an infrared light emitting diode, LED, and the light receiving device  112  can be a photo transistor sensitive for infrared radiation. Other optical wavelengths besides infrared radiation are of course also usable, as well as different receiver principles, such as photodiodes or photo resistors, can be used. Furthermore, instead of light emitting diodes also laser diodes can be applied. 
         [0042]    According to the present innovation, the optical data transmission within the modular safety device system is used for diagnosis and configuration of the safety devices  100 . To this end, a gateway  116  is provided for converting the data coming from a bus or PC or other control units into an optical signal. 
         [0043]    The gateway  116  works as a master in the safety device system  114  and controls the communication. For the communication, for example, a so-called MODBUS protocol can be used. 
         [0044]    MODBUS is as serial communication protocol for use with programmable logic controllers (PLC), in particular, it is used for transmitting information over serial lines between electronic devices. The device requesting information is called the MODBUS master and the devices supplying information are MODBUS slaves. In a standard MODBUS network, there is one master and up to 247 slaves, each with a unique slave address from one to 247. The master may also write information to the slaves. 
         [0045]    MODBUS is an open protocol; therefore, it has become a standard communications protocol in industry by being the most commonly available means of connecting industrial electronic devices. The official MODBUS specification can be found at www.modbus-ida.org. However, other bus protocols are of course also applicable with the present invention. 
         [0046]    The gateway  116  sends a query to a member  100  of the safety system  114  and the asked device replies with the diagnostic data. On the other hand, the master or gateway  116  can also send configuration data to the member  100 . In this case, the device replies thereto with a confirmation of the data. For that kind of communication, each member  100  of the system needs to have a unique address. This address can either be set by hardware switches or can be given automatically as will be set forth in the following with reference to  FIG. 9 . 
         [0047]      FIG. 7  shows a perspective view of the gateway  116  with a respective optical transmitter and receiver in the sidewall of the housing  103 . An electrical connector  117  to be connected to another than optical bus  115  is provided at the front of gateway  116  in order to be accessible for an operator. However, a wireless connection for instance via Bluetooth is also possible. 
         [0048]      FIG. 8  shows a block diagram of a safety device  100  according to the present innovation. As can be derived from  FIG. 8 , the safety outputs  118  communicate with two microcontrollers  120  and  122 . Microcontroller A receives data only from microcontroller B  122  and the safety outputs. Microcontroller B, on the other hand, is responsible for the conversion of optic signals into electric signals and vice versa. Furthermore, an input shift register  124  receives the signals from the safety inputs and communicates same via, for instance, a serial peripheral interface, SPI, bus. From the output shift register  126  status indicating LEDs provided at the housing and being visible for a user, are activated as well as the microcontroller B  122 . Microcontroller B processes the information from the output shift register  126  and provides the necessary information for the safety outputs  118 . 
         [0049]    This highly redundant architecture enhances significantly the safety of the modular safety device system according to the present innovation. 
         [0050]    Tables 2 to 5 summarize examples of communication codes for the communication using a simplified MODBUS protocol. If a safety device  100 , representing a member of the bus system, receives data that are not addressed to same, the device  100  forwards those data without any changes to the next device within the line. 
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Code 
                 Name 
                 Meaning 
               
               
                   
               
             
             
               
                 0x01 
                 Illegal Function 
                 The function code is not supported by the 
               
               
                   
                   
                 Device 
               
               
                 0x02 
                 Illegal Data Address 
                 The data address in the query is not allowed 
               
               
                   
                   
                 for the Device 
               
               
                 0x03 
                 Illegal Data Value 
                 The data value in the query is not valid 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                 Code 
                 Name 
                 Meaning 
               
               
                   
               
             
             
               
                 0x03 
                 Read Multiple Registers 
                 Reads the contents of a sequence of 
               
               
                   
                   
                 registers 
               
               
                 0x06 
                 Write Single Register 
                 Writes a value to a single register 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                 Fieldname 
                 Example 
               
               
                   
               
             
             
               
                 Query 
                   
               
               
                 Slave Address 
                 0x01 
               
               
                 Function Code 
                 0x03 
               
               
                 Start Address (High byte) 
                 0x00 
               
               
                 Start Address (Low byte) 
                 0x02 
               
               
                 Number of registers (High byte) 
                 0x00 
               
               
                 Number of registers (Low byte) 
                 0x02 
               
               
                 CRC (High byte) 
                 0x65 
               
               
                 CRC (Low byte) 
                 0xCB 
               
               
                 Response 
               
               
                 Slave Address 
                 0x01 
               
               
                 Function Code 
                 0x03 
               
               
                 Byte Count 
                 0x04 
               
               
                 Data (High byte) 
                 0x1F 
               
               
                 Data (Low byte) 
                 0x70 
               
               
                 Date (High byte) 
                 0xC0 
               
               
                 Data (Low Byte) 
                 0x94 
               
               
                 CRC (High byte) 
                 0xAD 
               
               
                 CRC (Low byte) 
                 0xFF 
               
               
                 Error Response 
               
               
                 Slave Address 
                 0x01 
               
               
                 Function Code 
                 0x83 
               
               
                 Exception Code 
                 (see supported exception codes) 
               
               
                 CRC (High byte) 
                 0x . . . 
               
               
                 CRC (Low byte) 
                 0x . . . 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 5 
               
               
                   
                   
               
               
                   
                 Fieldname 
                 Example 
               
               
                   
                   
               
             
             
               
                   
                 Query 
                   
               
               
                   
                 Slave Address 
                 0x01 
               
               
                   
                 Function Code 
                 0x06 
               
               
                   
                 Start Address (High byte) 
                 0x00 
               
               
                   
                 Start Address (Low byte) 
                 0x03 
               
               
                   
                 Data (High byte) 
                 0x00 
               
               
                   
                 Data (Low byte) 
                 0x02 
               
               
                   
                 CRC (High byte) 
                 0xF8 
               
               
                   
                 CRC (Low byte) 
                 0x0B 
               
               
                   
                 Response 
               
               
                   
                 Slave Address 
                 0x01 
               
               
                   
                 Function Code 
                 0x03 
               
               
                   
                 Start Address (High byte) 
                 0x00 
               
               
                   
                 Start Address (Low byte) 
                 0x03 
               
               
                   
                 Data (High byte) 
                 0x00 
               
               
                   
                 Data (Low byte) 
                 0x02 
               
               
                   
                 CRC (High byte) 
                 0x34 
               
               
                   
                 CRC (Low byte) 
                 0x0B 
               
               
                   
                 Error Response 
               
               
                   
                 Slave Address 
                 0x01 
               
               
                   
                 Function Code 
                 0x86 
               
               
                   
                 Exception Code 
                 (see supported exception codes) 
               
               
                   
                 CRC (High byte) 
                 0x . . . 
               
               
                   
                 CRC (Low byte) 
                 0x . . . 
               
               
                   
                   
               
             
          
         
       
     
         [0051]      FIG. 9  shows an exemplary flow chart of assigning the addresses of the individual safety devices  100  during power up. In the first step the safety device sends a request to the module on the right-hand side. In the next step, each device checks what signal was received from the left-hand side. In case that no signal came from the lefthand side, the respective module/model must have been the first device in the row and accordingly sets a bit indicating that it is the first device. This first device sends a signal indicating that it is the first device to the adjacent safety device and sets its address to 0x01. 
         [0052]    In this case, the first device has found its address. Alternatively, if the respective safety device receives a message from the left module, it sets a bit for “middle devices” and proceeds to checking whether it received an address from the left module. If not, an error had occurred and the procedure must start again or a warning has to be output. If yes, the slave chooses and address which is one integer higher than the one assigned to the left-hand module and informs the right-hand side device about this address. If all middle devices and the first device have assigned their addresses, the address finding process of  FIG. 9  is finished.