Modular Safety Switching Device System With Optical Link

Description

CROSS REFERENCE TO RELATED APPLICATIONS

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

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.

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.

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.

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.

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.

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.

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

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.

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.

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.

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.

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.

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

FIG. 1 shows a perspective view of a first safety device according to the present invention;

FIG. 2 shows a perspective view of a second safety device according to the present invention;

FIG. 3 shows a front view of two safety devices when mounted in a communicating manner;

FIG. 4 shows an example of a light signal sent from one safety device to another;

FIG. 5 shows a schematic representation of a safety device which can be implemented in an optical bus system;

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;

FIG. 7 shows a perspective view of the gateway of FIG. 6;

FIG. 8 shows a block diagram of two communicating safety devices;

FIG. 9 shows a flowchart of an automatic address assignment procedure; and

FIG. 10 shows a perspective view of a known modular safety system comprising flat cable interconnections.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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.

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.

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.

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.

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.

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.

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.

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.

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

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.

The receiving device 104 interprets these states to the following results:

Light constantly ON: safety state from the transmission device is OFF

Light constantly OFF: safety state from the transmission device is OFF

Light pattern as shown in FIG. 4: safety state from the transmission device is ON

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

This highly redundant architecture enhances significantly the safety of the modular safety device system according to the present innovation.

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.

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

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

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 . . .

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 . . .

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.

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.

Claims

1. Modular safety switching device system for actuating actuators in a fail-safe manner, said system comprising: at least one first safety device;at least one second safety device; andwherein said first and second safety devices are connected to each other via an optical link.
2. The system according to claim 1, wherein each safety device has a housing, and wherein the at least one first safety device comprises an optical transmitter arranged in a first opening of said housing, and wherein the at least one second safety device comprises an optical receiver arranged in a second opening of said housing.
3. The system according to claim 2, wherein said optical receiver comprises at least one of an infrared phototransistor or a photo diode, and wherein said optical transmitter comprises an infrared light emitting diode (LED).
4. The system according to claim 1, wherein said at least one first safety device and at least one second safety device are arranged on a mounting rail.
5. The system according to claim 1, further comprising a plurality of safety transmitters, each for generating a safety switching event; wherein said first and second safety devices comprise: a plurality of input modules for fail-safely evaluating said safety switching events and for generating output signals;a plurality of output modules for fail-safely actuating an actuator in response to the output signals; anda control module for controlling said input modules and output modules.
6. The system according to claim 1, further comprising a gateway module that connects the optically linked first and second safety devices with a non-optical bus.
7. The system according to claim 1, wherein said first and second safety devices are coupled serially in a way that an optical signal is passed from a first to a last safety device through all safety devices in one direction and back again from the last to the first safety device, in order to form a ring shaped data transmission system.
8. The system according to claim 7, wherein each safety device comprises means for converting a received optical signal into an electric signal and further comprises means for converting an electric signal into an optical output signal.
9. The system according to claim 8, wherein each safety device comprises at least one microprocessor for converting the optical data into electrical data and for processing the electrical data together with a safety state of the respective safety device, and for generating an electrical signal to be output via the optical link.
10. The system according claim 9, wherein each safety deviceis operable to set their addresses automatically during a power-up procedure.
11. The system according to claim 1, wherein each safety device comprises hardware means to set their addresses.
12. The system according to claim 1, wherein each safety device comprises: a first microprocessor being coupled with safety inputs receiving signals from said safety transmitters and for generating output signals to be output by at least one safety output; anda second microprocessor for converting the optical data into electrical data and for processing these data together with a safety state of the respective safety device, and for generating an electrical signal to be output via the optical link, wherein said second microprocessor is coupled to said first microprocessor.
13. A module for a safety device switching system comprising: a housing having a first side shaped to cooperate with a rail and a second side facing a user opposite the first side;a passage formed though the housing; andan optical link disposed in the housing and aligned with the passage for communicating an optical signal indicative of an operating condition of the module beyond the housing between adjacent modules.
14. The module of claim 13 wherein the rail is further defined as one of a top hat rail or a DIN rail.
15. The module of claim 13 wherein the passage is formed in a side of the housing that is oriented in a crossing direction relative to a longitudinal axis of the rail.
16. The module of claim 13 wherein the optical link further comprises an optical signal generator and an optical signal receiver.
17. The module of claim 13 further comprising an indicator visible through the second side of the housing.
18. A method of monitoring a modular safety switching system comprising: mounting a first module on a rail;mounting a second module on the rail in proximity to the first module; andoptically communicating information between the first module and the second module.
19. The method of claim 18 further comprising providing each module with an optical signal generator and an optical signal receiver.
20. The method of claim 18 further comprising forming a passage in each module that is aligned with a passage in adjacent modules and communicates an optical signal between adjacent modules.

Priority Claims (1)

Number	Date	Country	Kind
EP10161648	Apr 2010	EP	regional

Modular Safety Switching Device System With Optical Link

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Priority Claims (1)