Abstract:
A sensor device for a fluid power apparatus and in particular a pneumatic cylinder comprises at least one sensor for producing at least one sensor value on the basis of a property or a condition of the fluid power apparatus, and a sensor communication means for the transmission of the at least one sensor value. As regards the sensor device there is a provision such that it includes a reading means for reading apparatus identification data characterizing the fluid power apparatus and the sensor device is adapted for the transmission of the apparatus identification data by way of the sensor communication means.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority based on German Application No. 10 2007 015 111.1 filed on Mar. 29, 2007, which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a sensor device for a fluid power apparatus and in particular a pneumatic cylinder with at least one sensor for producing at least one sensor value on the basis of a property or a condition of the fluid power apparatus, and a sensor communication means for the transmission of the at least one sensor value and to a fluid power apparatus fitted with such a sensor device. 
     2. Description of the Related Art 
     The fluid power apparatus can for example be a pneumatic cylinder, an electropneumatic hybrid drive or the like. The sensor is responsive to properties or operational states of the apparatus, as for example a position of the piston, pressures in chambers of the cylinder or the like. By way of the sensor communication means, as for instance a digital output interface, the sensor device transmits sensor values, as for example pressure values, position values or the like, of the fluid power apparatus, for example to a controller or regulator for the apparatus. The controller or regulator controls or regulates the apparatus on the basis of the sensor values. A position regulation means finds, on the basis of the sensor values, which constitute actual values, e. g. the desired target position of the piston. 
     In order to perform such regulation tasks the regulation means must be parameterized in an elaborate procedure. For this purpose for example sensor data, as for example measurement ranges of the sensor device, must be set in the regulation means by parameters. Furthermore elaborate parameterizing must be performed on the basis of physical properties of the fluid power apparatus to be controlled or regulated, as for example travel displacements, piston diameters or the like. 
     SUMMARY OF THE INVENTION 
     One object of the invention is to provide a simplified operational concept for a sensor device. 
     In order to achieve these and/or other objects appearing from the present specification, claims and drawings, in the present invention the sensor device includes a reading means for reading apparatus identification data characterizing the fluid power apparatus and the sensor device is adapted for the transmission of the apparatus identification data by way of the sensor communication means. Moreover a fluid power apparatus fitted with such a sensor device is suitable for achieving the object of the invention. 
     One basic principle of the invention is that the sensor device provides an additional functionality: addition to sensor values it also transmits apparatus identification data of the apparatus, whose operational states, properties or the like are sensed by it. The sensor communication means, which is in any case present, is utilized in addition for such communication tasks. For the communication of apparatus specific identification data no separate interface and no transmission means on the fluid power apparatus is needed. The sensor may for example include a position sensor, a pressure sensor a temperature sensor or a force sensor. 
     The apparatus identification data may for example comprise the type of the apparatus, a serial number of the apparatus, physical quantities as for example length, effective surface of an actuator member or a piston, pressure values and more particularly maximum pressures, rated operating pressures, force output values force output values as related to the pressures set, a working stroke or the like. Furthermore kinematic data of the fluid power apparatus, f. i. speed values such as a maximum speed or a rated operating speed, a braking distance or the like may represent apparatus identification data. 
     The apparatus identification data may for example be saved to a sensor memory. For instance the sensor device may have a micro-controller, which comprises a sensor memory. It is furthermore possible to use a sensor memory, such as a flash memory or an E(E)Prom for the storage of the apparatus identification data. 
     It is an advantage furthermore for sensor identification data, which characterize the sensor device, to be saved in the sensor memory. The sensor device is responsible for the output of such sensor identification data, also via the sensor communication means. The sensor identification data may for example comprise the sensor type, the serial number, measurement ranges of the sensor, resolution, zero point or the like. 
     The sensor memory is able to be programmed with the respective identification data (sensor identification data) and/or apparatus identification data. For instance it may be a question of the sensor memory&#39;S being a flash memory. 
     In the system of the invention the apparatus identification data are more or less saved on board the sensor device. On the fluid power apparatus itself no further means are necessary, as for example a storage chip for saving the apparatus identification data. However this possibility does exist. 
     The reading means of the sensor device for example comprises a receiving means for receiving of apparatus identification data transmitted by the fluid power apparatus. The reading means may be constituted by the receiving means or e comprised in the receiving means. Furthermore the reading means may be a separate means, as for example an optical reader or a wireless receiver connected to the receiving means. The apparatus identification data are stored in accordance with this part of the invention at least partly in a apparatus memory of the fluid power apparatus and are passed on to the sensor device, which communicates the apparatus identification data by way of the sensor interface. 
     It is admittedly possible for the receiving means to have a wired connection with the apparatus memory of the fluid power apparatus, as for example by way of electrical contacts. However it is advantageous to have a wireless connection, in the case of which the receiving means is joined in a wireless manner with the fluid power apparatus. Wireless for example means transmission by light, radio or the like. A so-called radio frequency identification (RFID) chip may be arranged on the fluid power apparatus. 
     Furthermore a hybrid design is possible, i. e. a part of the apparatus identification data are saved on board the sensor device in the sensor memory, whereas other data, as for example the type characteristic of the fluid power apparatus are saved in the apparatus memory. The fluid power apparatus then transmits the type characteristics to the sensor device, which then passes on such type characteristics in addition to other apparatus identification data, such as physical properties of the apparatus, by way of the sensor communication means. In this respect it is also possible for the sensor device to retrieve, on the basis of first apparatus identification data communicated by the fluid power apparatus, second apparatus identification data in its sensor memory. Accordingly the fluid power apparatus may communicate, for example, its type characteristic to the sensor device or the sensor device may read such type characteristic from the fluid power apparatus and on the basis of the type characteristic may find further apparatus identification data in the sensor memory, as for example physical properties assigned to the type characteristic, of the fluid power apparatus. 
     The sensor communication means preferably possesses at least one bus interface, as for example a field bus interface. It is an advantage for there also to be a second bus interface in the sensor device so that the sensor device may be concatenated with further components of the bus. Thus for example further sensor devices can be concatenated, f. i. sensor devices in accordance with the invention for the transmission of apparatus identification data or also prior art sensor devices not suitable for the transmission of apparatus identification data. 
     It is an advantage for the sensor device to transmit the apparatus identification data automatically, as for example as part a signing in procedure during coupling up with an automated system. The sensor device can however communicate the apparatus identification data as a response to interrogation, for example of a master control or regulation means. 
     Preferably the sensor memory is a non-volatile memory. Accordingly the apparatus identification data will be kept even upon a failure of the power supply. 
     It is an advantage however for the sensor device to have an electrical power storage means, and more particularly a long term storage means. Accordingly it is possible for the control means to be operated in a self-sustaining manner independent of an external power supply. The battery, as for example a battery with a long lifetime, is preferably able to be replaced. Owing to having the electrical energy storage means on board the sensor device simple installation is possible. Furthermore it is quite possible for the sensor device to be encapsulated so that it comes within a high electrical safety class and/or has a high degree of electromagnetic compatibility. Operation with the energy storage means is more particularly convenient in the case of a wireless sensor communication means. Accordingly no line connections are necessary in order to couple the sensor device with an automated system, a regulation system or the like. The electrical energy storage means may serve for saving the data held in the sensor memory, inter alia the apparatus identification data. In addition to the electrical energy storage means or as an alternative thereto it is possible to provide a local energy producing unit, as for example solar cells, an electrical generator operated with fluid, or the like, in the sensor device. The local energy producing unit will for example produce electric current, which is stored in a buffer storage means, as for example capacitor, of the sensor device. 
     For long term operation of the sensor device it is also advantageous for it also to have an energy economizing function. For instance the sensor device may after a predetermined time of inactivity switch over to an energy economy quiescent mode. On receiving an interrogating message, on a change in the condition of the fluid power apparatus to be sensed or the like, the sensor device will be reactivated and will communicate, for example sensor values, apparatus identification data or the like. 
     The sensor device may be an integral part of the fluid power apparatus, and for example can be integrated in its housing. For instance the sensor device may be mounted in an end plate of a pneumatic cylinder. 
     However a modular concept is also advantageous, that is to say the sensor device is a sensor module able to be arranged on the fluid power apparatus and more particularly detachably secured to it. The sensor device may for example be secured on an end plate or in a groove in the cylinder housing. Furthermore attachment by screwing, clipping or adhesive bonding is possible. The modular concept does however mean the advantage that the sensor device may be readily detached in the case of a failure or if it is required somewhere else. 
     The sensor device preferably has electrical contacts, which on arrangement on the fluid power apparatus provide a connection with the memory of the fluid power apparatus. Here, as explained above, the apparatus identification data are stored at least in part. It will be clear that wireless transmission between the apparatus memory and the sensor device arranged on the apparatus is possible. 
     Furthermore it is possible for the sensor module to be designed as a sort of intermediate module which while being able to be operated detached from the fluid power apparatus, nevertheless is responsive to its conditions and/or properties. More particularly in the case of this concept it is an advantage if the sensor device communicates in a wireless manner with a memory of the fluid power apparatus in order to read out the apparatus identification data from it, if the data are not alternatively held on board the sensor device in its sensor memory. The intermediate module may for example be a position measuring system, which is arranged at a certain distance from the fluid power apparatus. Furthermore it is possible for the intermediate module to be in the form of a pressure sensor which is arranged on a fluid line connected with the fluid power apparatus. 
     The fluid power apparatus may be designed in a variety of different forms. Thus it can for example be a power cylinder, as for example a piston rod-less power cylinder or one with a piston rod, a pneumatic servicing device, a vacuum means, as for example a suction means, a pneumatic valve or the like. The fluid power apparatus may however also be a so-called hybrid drive, that is to say a drive, which has a fluid power as for example a pneumatic, drive component or a functionally coupled electrical drive component. 
     In connection with the modular concept, in which the sensor device constitutes a separate unit, it is to be stressed that this configuration is also regarded as an invention in its own right in conjunction with exclusively electrical drives, that is to say as a patentable subcombination. The sensor device transmits apparatus identification data of the electrical drive by way of its sensor communication means. 
     It is an advantage for the sensor device to possess diagnostic means for diagnostic data concerning the fluid power apparatus, as for example wear data, data as regards the number of duty cycles, as regards pressure fluctuations indicative of an error or the like. The sensor device transmits the diagnostic data preferably by way of its sensor communication means. Furthermore a display provided on the sensor device, such as an LCD display, LED&#39;s or the like is an advantage. 
     Further advantageous developments and convenient forms of the invention will be understood from the following detailed descriptive disclosure of embodiments thereof in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  diagrammatically shows an automated system having two valve clusters and one central routing means. 
         FIG. 2  shows a fluid line with integrated electrical conductors for the connection of an actuator with a valve cluster in accordance with  FIG. 1 . 
         FIG. 3  shows a diagrammatic side elevation of a fluid power actuator with a sensor arrangement, which transmits apparatus identification data characterizing the actuator by way of a sensor communication means. 
         FIG. 4  shows an actuator with a sensor device constituting a separate unit and installed on the actuator, such sensor device also transmitting apparatus identification data of the actuator by way of a sensor interface. 
         FIG. 5  shows an actuator with a memory, in which apparatus identification data characterizing the actuator are stored, such data being transmitted by a sensor device constituting a separate unit and being installed on the actuator, via a sensor communication interface thereof. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The working embodiments of the invention include partially similar or functionally equivalent components which are not described twice over and are provided with the same reference numerals. 
     In the case of an automated system  10  valve clusters  11   a  and  11   b  are controlled by a central master control means  12 , as for example a routing computer  13 . The valve clusters  11   a  and  11   b  are connected with valve cluster communication means  14   a  and  14   b  for external communication on a system bus  15 , for example a field bus, by way of external interfaces  96 , for example bus interfaces. The control means  12  control the valve clusters  11   a  and  11   b  via the system bus  1 , which is connected in a wired or a wireless manner. 
     The valve clusters  11   a  and  11   b  comprise valve modules  16 , which are placed in a row with the communication means  14   a  and  14   b . The valve modules  16  serve for fluid control of the fluid power apparatus  17 , for example pneumatic actuators  18   a  and  18   b . The actuators  18   a  and  18   b  are pneumatic drive cylinders  66 , which as illustrated may have piston rods although designs without piston rods or with an additional electrical drive part are possible. The regulation modules  25   a  and  25   b  are also designed for the regulation of electrical or combined fluid power and electrical drives. Thus for example instead of the pneumatic actuator  18   d  an electrical drive could be provided. 
     The valve clusters  11   a  and  11   b  are run on compressed air, for example from a compressed air source  19 . The compressed air source  19  supplies, for example, servicing apparatus  20 , as f. i. filters and oilers, which prepare compressed air for the valve clusters  11   a  and  11   b . The servicing apparatus  20  is in the present case separate from the valve clusters  11   a  and  11   b , although it could for example constitute components of the valve cluster  11   b.    
     From the central control means  12  the valve modules  16  receive control instructions for the pneumatic control of the actuators  18   a  and  18   b  via the system bus  15 . The communication means  14   a  and  14   b  transmit the control instructions so received by way of internal communication buses  21  to the valve modules  16 . The communication buses  21  serve for internal communication of the valve clusters  11   a  and  11   b.    
     While the valve cluster  11   a  is controlled exclusively externally by way of the system bus  15 , the valve cluster  11   b  has a local control competence in the form of control means  22 . The control means  22  are designed in the form of control modules, which are placed in circuit between the valve modules  16  and the communication means  14   b  in the form of a communication module. 
     Optionally it is possible for the valve cluster  11   b  to have a local control means  94  for its control, f. i. of the valve modules  16 , as for example a separate control module. The communication means  14   b  as well can be designed in the form of such a local control means  94  for the valve cluster  11   b . For this purpose the communication means  14   b  will then for example have a processor  95 , which transmits control instructions by way of communication bus  21 , for example to the valve modules  16 . 
     The control means  22  control valve means  23 , which for their part control actuators  18   c  and  18   d . The actuators  18   c  and  18   d  constitute, for example, servo drives. Admittedly the actuators  18   c  and  18   d  could constitute two drives independent of each other. However the actuators  18   c  and  18   d  are mechanically coupled with each other. In the drawing this is diagrammatically indicated since the actuator  18   d  is arranged on a force output means of the actuator  18   c  for example on its piston rod. A mechanical coupling may however be realized indirectly, for example if the actuators  18   c  and  18   d  constitute the drives of a gantry or carriage traveling in the X and the Y directions. 
     The valve means  23  are valves separate from the valve cluster  11   b  and connected with a compressed air network  24  supplied by the compressed air source  19  with compressed air. The valve means  23  control the compressed air supply to the actuators  18   c  and  18 d, which are for example pneumatic drive 
     cylinders. The valve means  23  and the actuators  18   c  and  18   d  also consitute fluid power apparatus  17 . 
     The control means  22  regulate the actuators  18   c  and  18   d  by control of the valve means  23  for regulation. The control means  22  are for example regulation modules  25   a  and  25   b . The regulation modules  25   a  and  25   b  fit in well with the modular concept of the valve cluster  11   b . They are able to be placed in line with the valve modules  16  and the communication means  14   b . The regulation modules  25   a  and  25   b  are coupled at internal bus interfaces  26  with the internal communication bus  11   b . The regulation modules  25   a  and  25   b  may receive messages by way of the communication bus  21 , as for example control instructions from the control means  12  and may transmit messages, as for example indications, which the communication means  14   b  passes on to the control means. 
     For their regulation tasks the regulation modules  25   a  and  25   b  have separate regulation communication interfaces  27  for the issue of target values  28  and the reception of actual values  29 . The communication interfaces  27  are real time interfaces. The communication interfaces  27  comprise digital bus interfaces  27   a . The valve means  23  are connected by way of bus lines  30   a  and  30   b  with the communication interfaces  27  so that each fluid power unit to be regulated comprising a respective valve means  23  and one of the actuators  18   c  and  18   d  has a separate regulator bus line  30   a  or  30   b  available for it. Accordingly rapid communication is possible between the units to be regulated and the assigned regulation module  25   a  and  25   b . Between each regulation module  25   a  and  25   b  and its arrangement to be regulated  23  and  18   c  or  23  and  18   d  there is a separate physical connection. The actual values  29  are then transmitted by these connections. 
     As an alternative the regulation module  25   a  could be a regulator for two actuators and regulate both arrangements  23 ,  18   c  and  23  and  18   d  via the bus line  30   a  and an optional bus line  30   c  leading to the regulation module  25   a  in lieu of the bus line  30   b.    
     The actual values  29  contain pressure sensor values  33  for example, which are generated by pressure sensors  31  of a sensor arrangement  32  of the valve means  23 . The pressure sensors  31  are for example arranged on ports of pressure lines, by which the actuators  18   c  and  18   d  are joined with the valve means  23 . To this extent the valve means  23  constitute sensor means. The valve means  23  transmit the pressure sensor values  33  by means of a bus coupler  34  which to this extent constitutes a sensor communication interface, on the respective bus line  30   a  or  30   b  to the regulation module  25   a  or  25   b.    
     Sensor means  35   c  and  35   d  arranged on the actuators  18   c  and  18   d  produce further sensor values as actual values  29 , for example pressure values, temperature values and/or position values  36 . 
     The sensor means  35   c  and  35   d  are coupled serially with the valve means  23  via bus lines  37   a  and  37   b . For this purpose it is however also possible for the connection contacts for the valve means  23  to have separate bus couplers. It is however possible for the bus lines  37   a  and  37   b  at the valve means  23  to be looped through to the corresponding connection contacts of the bus couplers  34 . In any case the connection of the sensor devices  35   c  and  35   d  and of the valve means  23  is simplified because these means are coupled with each other in series because only one connection line leads to the regulation or communication interfaces  27 . 
     The adjustment of parameters, in particular regulation parameters and/or a selection of the type of regulation (position regulation, pressure regulation, position regulation with slave pressure regulation) and/or a diagnosis of the modules of the valve cluster  11   b , f. i. of the regulation modules  25   a  and  25   b , may be undertaken at some central position using a user device  57 , as for example a notebook. The user device  57  is able to be connected with a user device interface  58  of the communication means  14   b  and is thus able to be connected with the internal communication bus  21 . Then parameters may be loaded from the user device  57  to the valve cluster  11   b , for example the regulation modules  25   a  and  25   b  or any other modules. Furthermore a diagnosis is possible using the user device  57 . Thus for example the regulation modules  25   a  and  25   b  can transmit failure messages, indications as regards a number of duty cycles already performed or other diagnostic data to the user device  57 . 
     It will be clear that wireless operation or diagnosis is also possible, for example using a user device  59 , which communicates with the communication means  14   b  in a wireless fashion. 
     The putting into operation of the automated system  10  and diagnosis and/or parameterizing of the regulation modules  25   a  and  25   b  is simplified by an auto-identification concept. The fluid power apparatus  17  or means assigned to it, as for example sensor means  35   a .  35   b  and  35   c  assigned to the actuators  18   a  through  18   c , comprise or constitute ident data transmission means  60 , which transmit apparatus identification data  61   a ,  61   b ,  61   c ,  61   d  and  62  to receiving means  63  for the identification data  61   a  through  61   c  and  62  of the valve clusters  11   a  and  11   b . The identification data  61   a  through  61   d  characterize the pneumatic actuators  18   a ,  18   b ,  18   c  and  18   d . The identification data  62  characterize the valve means  23 . 
     The apparatus identification data  62  of the valve means  23  are saved in an optionally present memory  64 . In the case of the valve means  23  assigned to the actuator  18   d  in addition the apparatus identification data  61   d  can be saved as well, which characterize the actuator  18   d . The actuator  18   d  has f. i. no memory of its own for saving its identification data and furthermore no interface to transmit such data to the valve cluster  11   b.    
     The valve means  23  responsible for fluid control of the actuator  18   c  communicates the apparatus identification data  16   c  thereof, which it receives by way of the line  37   b , via the bus line  30   b  on to the regulation communication interface  27 . 
     The regulator communication interfaces  27  constitute or include receiving means  63  for the apparatus identification data  62  and  61   c  and also apparatus identification data  61   d  of the actuator  18   d . On the basis of such apparatus identification data, which for example comprise the working strokes of the actuators  18   c  and  18   d , the regulator modules  25   a  and  25   b  regulate the actuators  18   c  and  18   d . In this respect it is possible for the regulator modules  25   a  and  25   b  to directly evaluate the apparatus identification data  61   c ,  61   d  and  62  for the generation of regulation parameters. Accordingly for example maximum pressures may serve for example for the limitation of pressure of the compressed air by pressure regulation. Furthermore it is possible, using the internal communication infrastructure, namely the internal communication bus  21  and the communication  14   b  means  14   b , for the regulation modules  25   a  and  25   b  to transmit the respective apparatus identification data  61   b ,  61   d  and  62  to the user device  57 , which generates the regulation parameters therefrom and transmits same to the regulation modules  25   a  and  25   b  using the said communication path. 
     The sensor means  35   a  transmits the apparatus identification data  61   a  in a wireless fashion to a receiving means  63  comprised in the valve cluster communication means  14   a.    
     The actuator  18   b  is connected by a conventional pressure line  86  and a fluid connection line  87 , which has a fluid duct  88  and data lines  89 , with the valve cluster  11   b . The data lines  89  are for example arranged in a casing  90  encircling the fluid duct  88 . On plugging in the fluid connecting line  87  contacts (not illustrated) of the valve cluster  11   b  and of the sensor means  35   b  are connected with the data lines  89  so that simultaneously a fluid connection and a data connection are produced between the valve cluster  11   b  and the sensor device  35   b  and also the actuator  18   b.    
     The sensor device  35   b  transmits the apparatus identification data  61   b  in a wired manner, f. i. by way of the data lines  89 , to a receiving means  63 , which for example is comprised in the valve module  16  driving the actuator  18   b.    
     For saving and transmitting the apparatus identification data  61   a  through  61   d  and  62  different transmission concepts and memory concepts are possible. In the case of the automated system  10  it is preferred for sensor means to transmit the apparatus identification data  61   a ,  61   b ,  61   c ,  61   d  and  62  to the receiving means  63 . 
     The valve means  23  comprises the pressure sensors  31  and to this extent constitutes a sensor device. Its bus coupler  34  to this extent constitutes a sensor communication means and the memory  64  with the apparatus identification data  62  and/or  61   d  constitutes a sensor memory. 
     The apparatus identification data  61   c  are not transmitted by the actuator  18   c  itself but by the sensor device  35   c  assigned to it. The sensor device  35   c  is arranged on the housing of the actuator  18   c , for example in the longitudinal direction on the side and comprises a position sensor  65  which transmits position values  36  of an actuator member  67   c  of the actuator  18   c  by way of sensor communication interface  68   c . The sensor communication interface  68   c  comprises a bus interface  81 , for example a bus coupler, for a bus connection by way of the valve means  23  to the regulation communication interface  27 . 
     The apparatus identification data  61   c , which characterize the actuator  18   c  and for instance comprise the diameter of the actuator member  67   c , the travel displacement of the actuator member  67   c  in a housing  69   c  of the actuator  18   c  or the like, are saved in a sensor memory  70   c . The memory  70   c  is preferably programmable, for example by way of a programming interface  71  able to be connected with the user device  57 . The sensor communication means  68   c  comprises electrical read contact as a reading means  76   c  for reading the sensor memory  70   c.    
     The actuator  18   c  need not have any intelligence of its own for saving the apparatus identification data  61   c.    
     The sensor means  35   c  may be supplied with electrical power for example by way of its sensor communication interface  68   c , i. e. a bus coupler. 
     The sensor means  35   a  on the contrary, which also comprises a position sensor  65 , has an electrical long term energy storage means  72 , for example a lithium battery, for long term service independent of an external power supply. Furthermore for data transmission, as for example for the transmission of position values produced by a position sensor  65 , no line connections are necessary either. The sensor device  35   a  has a wireless communication means  68   a , which for example with the Wireless Fidelity (WiFi) standard. 
     In a sensor memory  70   a  of the sensor device  35   a  sensor identification data  73  are held, as for example the resolution of the position sensor  65 , an initial position and an end position of the measurement range of the position sensor  65 . Apparatus identification data  61   a  of the fluid power apparatus  17 , as for example the diameter of the actuator member  67   a , the maximum force available at a force output of the actuator  67   a  (f. i. at the piston rod) or the like are saved in an apparatus memory  74  of the fluid power apparatus. The apparatus memory  74  is mounted f. i. in a cover  75   a  of the housing  69   a  and includes a rewritable memory, f. i. an EEPROM. The apparatus memory  74  is programmed during manufacture of the fluid power apparatus  17  so that its apparatus identification data  61   a  are available and for example may be read out by a reading apparatus, as for example the user device  59 . 
     It is an advantage to use a sensor communication interface for the transmission of the apparatus identification data stored in the fluid power apparatus, for example the actuator  18   a . A reading means  76   a , for example a data interface with electrical contacts of the sensor communication means  68   a , reads the apparatus memory  74  via electrical connections  77 . 
     The electrical connections  77  are automatically made during arrangement or assembly of the sensor means  35   a  designed in the form of a sensor module  78 . A housing  79  of the sensor device  35   a  extends as far as the housing cover  75   a  so that contacts  80  of the sensor device  35   a  and of the actuator  18   a  touch and produce the electrical connections  77 . 
     Alternatively a wireless concept is possible, in which the apparatus identification data  61  are for example saved in an apparatus memory  75 ′ able to be read in a wireless manner, for example in a radio frequency identification (RFID) module. The reading means  76  is in this case a wireless reading interface, for example an RFID reading device. A transmission means of the apparatus memory  74 ′ gets the transmission power, necessary for the transmission of the apparatus identification data)  61   a , through the sensor device  35   a , for example by way of an electrical connection (not illustrated) or as transmission energy transmitted by the transmission of an interrogation message on the part of the reading means  76 . 
     The apparatus identification data  61   a  read from the apparatus memories  74  or  74 ′ may also be first apparatus identification data, on the basis of which the sensor device  35   a  finds second apparatus identification data  61   a ′ in its sensor memory  60   a . The identification data  61   a ′ are for example data, which complement the identification data  61   a . Thus for example the apparatus identification data  61   a  may include the type characteristic of the actuator  18   a , on the basis of which the sensor device  35   a  finds further characteristics of the actuator  18   a , as for example its mechanical properties. Furthermore in the case of every sensor device in accordance with the invention, as for example in the case of the sensor device  35   a , it is possible for the sensor device to convert or complement the sensor values on the basis of the apparatus identification data. Thus for example the sensor device  35   a  may provide the position values  36  with particulars in metric units, when it has found the specific travel displacement of the actuator member  67   a  on the basis of the apparatus identification data  61   a . The sensor device  35   b  can specifically find a force output of the actuator  82   a  on the basis of the pressure sensor values  85  and provide an output thereof in f. i. newtons as force values. 
     While the sensor devices  35   a  and  35   c  constitute sensor modules  78  able to be detachably arranged on the actuators  18   a  and  18   c  and therefore in case of need may be replaced by other different types of sensor devices preferably in accordance with the invention, which for example comprise pressure sensors or the like, one sensor device  35   b  is an integral part of the actuator  18   b.    
     The sensor device  35   b  has a position sensor  65  and also pressure sensors  84 , which for example are arranged at gcompressed air ports  83   a  and  83   b . A sensor communication means  68   b  transmits position values  36  and pressure sensor values  85  of the pressure sensor  84  in a wired manner. In principle separate data lines could be provided for this. The sensor communication means  68   b  is however connected with the data lines  89  of the fluid connection line  87 . 
     By way of data lines  89  the sensor device  35   b  transmits the position sensor values  36  and the pressure sensor values  85  and furthermore, for example on signing up with the valve cluster  11   b  or on interrogation from the valve cluster  11   b , the apparatus identification data  61   b  characterizing the actuator  18   b . The apparatus identification data  61   b  are saved in a sensor memory  70   b  of the sensor device  35   b.    
     The sensor device  35   b  furthermore has a processor  91 , which for example counts the duty cycles of the actuator  18   b  and/or detects trouble conditions on the basis of the pressure sensor values  84 , or the like. The processor constitutes a component of a diagnostic facility  93  and transmits such information as diagnostic data  92  by way of sensor communication means  68   b .