Abstract:
A sensor system for monitoring surroundings on a mechanical component, includes at least one capacitive sensor element that is attachable to the surface of machines or machine parts, the at least one sensor element being constructed from a layered structure of flexible electrically conductive and electrically insulating plies, electrically conductive potential surfaces of one ply being disposed, laterally spaced apart via insulating plies located therebetween, in such a way that electric field lines form between the conductive potential surfaces and change measurably upon proximity and/or contact of a body or an object. The layered structure of a sensor element has at least two measuring elements operating separately from one another.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a sensor system for monitoring surroundings on a mechanical component, and further relates to a method for applying control to, and for evaluating, a sensor system according to the present invention. 
     2. Description of the Related Art 
     Published German patent application document DE 10 2009 029 021 A1 (which is not considered a prior art) discloses a sensor system, which is attachable to surfaces of machines or machine parts, and which has at least one sensor element made up of a layered structure of flexible electrically conductive and electrically insulating plies. The proximity and/or contact of a body or an object can be measured using such a sensor system, for example in order to stop the operation of an assembly robot having a sensor system. 
     It is furthermore known per se that for automatic proximity detection and/or collision detection, monitoring of the surroundings of the machine is performed using different sensor principles and sensors, for example optical sensors, ultrasonic sensors, or capacitive sensors, for example including contact-force sensing via the piezoelectric effect. Such sensors can as a rule be used in special cases, for example, in order to monitor machine parts having simple shapes and defined movement paths, so that upon detection of the proximity of a person, for example, reliable deceleration of the drive systems or processing equipment of the machine can be initiated. 
     If the hazardous machine part has a surface of relatively complex shape or a complex trajectory, on the one hand uninterrupted sensor-based surroundings monitoring is often possible only with a great deal of outlay or in some cases not at all. For example, optical sensing can be impeded by shadowing at edges and undercuts of the machine surface, or integration of sensors can also be impossible for lack of installation space. 
     For safe operation of machines it is usual, in order to meet safety standards, to utilize safety devices having two mutually independent safety channels with a diagnostic function, so that a single error in the system does not result in loss of safety. Failure of a safety channel is reliably detected and reported, while the second safety channel maintains the safety function. Dual sensor-based monitoring, embodied independently, is necessary for such applications. Sensors for safe configuration of machines having two safety channels that are flexibly adaptable to complexly shaped surfaces are not known. 
     Also known, from published utility model document DE 20 2005 002 475 U1, is a foamed-material cover, embodied especially to be used for collision detection with industrial robots, that is equipped with proximity-detecting, tactile, and capacitive sensors. Attachment of such an assemblage to different industrial robots is, however, often laborious. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is based on the object of embodying a sensor system, attachable in simple fashion to a wide variety of components or surfaces of machines or machine parts, that at the same time enables compliance with safety standards that require mutually independent safety channels with a diagnostic function. The underlying idea of the invention is to embody sensor elements with a layered structure of flexible electrically conductive and electrically insulating plies, electrically conductive potential surfaces of one ply being disposed, laterally spaced apart via insulating plies located therebetween, in such a way that electric field lines form between the conductive potential surfaces and change measurably upon proximity and/or contact of a body or an object, the layered structure of a sensor element having at least two measuring elements operating separately from one another. The flexible layered structure makes possible simple adaptation and attachment of the sensor element and sensor system onto moving components of machines or complexly shaped surfaces of the machines, and the provision of at least two measuring elements for each sensor element, operating separately from one another, simultaneously allows safety standards to be met. 
     An embodiment of the invention in which the sensor element encompasses means for separate application of control to and evaluation of the at least two measuring elements is particularly preferred. This ensures that even in the event of impairment of or damage to a measuring element, the respectively other measuring element can continue to operate. 
     In order to preclude mutual impairment of the measured values of the at least two measuring elements, provision is furthermore made that the means for separate application of control and evaluation apply control to the at least two measuring elements in chronologically consecutive fashion. 
     In order to enable particularly safe operation of machines in a manner corresponding to compliance with safety standards, thus precluding endangerment in particular of persons, provision is moreover made that evaluation means for evaluating the measured signals of the at least two measuring elements are provided; and that the evaluation means are at least indirectly operatively connected to the machines or machine parts and apply control thereto in such a way that operation of the machines or machine parts occurs only if the signals of the at least two measuring elements are within predetermined limit values. 
     In a design-related configuration of the sensor elements that enables adaptation of a sensor system, made up of multiple sensor elements, to a wide variety of surfaces of machines or machine components, it is proposed that the at least one sensor element have a base outline in the shape of a triangle or quadrangle; and that when multiple sensor elements are present, they be electrically and mechanically contactable to one another and preferably form a sensor skin. 
     A particularly compact and simple configuration of the sensor elements is moreover made possible when the measuring elements are disposed together on at least one layer, and are physically separated from one another. 
     The invention also encompasses a method for applying control to and evaluating a sensor system according to the present invention. Provision is made in this context that when multiple sensor elements are present, at least one electronic evaluation device having means be provided, which device cyclically addresses the sensor elements and checks whether a significant change in capacitance with respect to a reference value has taken place in the context of at least one sensor element; and that the means address the at least two measuring elements of a sensor element in chronologically successive fashion. Such a method operates particularly reliably and dependably, since mutual influencing of the measured values of the two measuring elements of a sensor element is avoided. 
     Particularly fast and thus reliable sensing of impending collisions is enabled if a measuring element of a first sensor element and another measuring element of another sensor element are addressed at the same point in time by the means. 
     The design outlay and the outlay necessary for wiring the measuring elements can be reduced if the sequence of the sensor elements is used to address linearly concatenated sensor elements, by the fact that the data are forwarded along the chain to the means via multiple sensor elements. 
     Also particularly preferred is a method in which, in a further cycle, each sensor element is subjected to a self-diagnosis, the sensor elements being acted upon by test voltages or by a characteristic signal pattern. Such a method makes it possible in particular to reliably detect damage to the sensor elements, thus enabling particularly reliable operation of a sensor system. 
    
    
     
       DETAILED DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified plan view of a single sensor element of a sensor system according to the present invention. 
         FIG. 2  is an exploded view of the structure of a sensor element according to  FIG. 1 . 
         FIG. 3  to  FIG. 5  are plan views of sensor elements having different shapes and modified with respect to  FIG. 1 . 
         FIG. 6  and  FIG. 7  are perspective views of a sensor element according to  FIG. 1  during application of control to its two measuring elements at different points in time. 
         FIG. 8  is a perspective view of a portion of a sensor skin using sensor elements connected to one another. 
         FIG. 9  is a block diagram to illustrate the application of control to the measuring elements of a sensor element. 
         FIG. 10  is a block diagram to depict a sensor system made up of multiple sensor elements. 
         FIG. 11  depicts the application of control to the different measuring elements of the sensor elements by different central units. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Identical components and components having the same function are labeled in the Figures with the same reference numbers. 
       FIGS. 1 and 2  depict a sensor element  10  as a component of a sensor system  100  to be explained in further detail later. Sensor system  100  or sensor element  10  serves to monitor surroundings on a mechanical component, for example on a moving robot arm of an industrial robot or the like. 
     As is evident in particular from  FIG. 2 , sensor element  10  has a layered structure made up of multiple interconnected flexible layers. This layered structure contains, by way of example and therefore not in limiting fashion, a base layer  11 , made for example of sponge rubber or rubber, having a thickness of, for example, 5 mm. Embodied within base layer  11  are two cutouts  12 ,  13  for the reception of an electronic system not depicted in  FIGS. 1 and 2 , or of electronic components. The underside of base layer  11  is disposed in abutment against, for example, the mechanical component. Disposed on the upper side of base layer  11  are two grounding surfaces  14 ,  15  that are separated from one another and are each triangular. The two grounding surfaces  14 ,  15  are each made, by way of example, of a nonwoven copper fabric having a thickness of 0.5 mm. The two grounding surfaces  14 ,  15  are covered, on the side located opposite base layer  11 , by an insulating layer  16  that is made, by way of example, of sponge rubber having a thickness of 1.5 mm. On the upper side of insulating layer  16 , the latter is connected to a total of four electrode surfaces  17  to  20 , made in particular of copper and constituting electrically conductive potential surfaces. While on the one hand electrode surfaces  17  and  19  are each embodied in the form of an angle member having two limbs of identical length, the other two electrode surfaces  18  and  20  are each of triangular configuration. In addition the two electrode surfaces  17  and  19  act as transmitting electrodes, while the two electrode surfaces  18  and  20  act as receiving electrodes. The two grounding surfaces  14  and  15 , on the other hand, act as shielding electrodes. It is also essential that electrode surfaces  17  to  20  are each disposed at a distance from one another. Electrode surfaces  17  and  18  form a first measuring element  21 , while the other two electrode surfaces  19  and  20  form a second measuring element  22 . 
     As is evident in particular from  FIGS. 6 and 7 , upon application of a voltage respectively to first measuring element  21  and to second measuring element  22 , a respective electric field having respective field lines  1  and  2  forms between the respective electrode surfaces  17  and  18 , and  19  and  20 . In other words, this means that first measuring element  21  and second measuring element  22  each constitute a capacitive sensor whose respective field lines  1  and  2  change at the proximity of an object or a person, for example starting at a distance of less than 30 to 60 mm. This change in field lines  1 ,  2  results in a change in the capacitance of the two respective measuring elements  21  and  22 , which is sensed by sensor element  10 . 
     In order to prevent mutual influencing of the measurement results of the two measuring elements  21 ,  22  of sensor element  10  that would exist as a result of field lines  1 ,  2  that are present simultaneously, provision is made according to the present invention that the two measuring elements  21 ,  22  have control applied to them in chronologically successive fashion. This situation is depicted in  FIGS. 6 and 7 : in  FIG. 6 , by way of example, first measuring element  21  having field lines  1  is activated, while the other measuring element  22  is deactivated. In  FIG. 7 , conversely, second measuring element  22  is activated so that field lines  2  are formed, while first measuring element  21  is deactivated. 
     Sensor element  10  depicted in  FIG. 1  has in plan view a square base outline having, by way of example, an edge length of approximately 60 mm.  FIGS. 3 and 4  depict modified sensor elements  10   a  and  10   b  that each have a rectangular base outline. Sensor element  10   a  has edge lengths of, by way of example, 40 mm and 60 mm, while sensor element  10   b  has edge lengths of 30 mm and 60 mmm. In sensor elements  10   a  and  10   b , electrode surfaces  17   a ,  17   b ,  18   a ,  18   b ,  19   a ,  19   b , and  20   a ,  20   b  are each of rectangular or ribbon-shaped configuration, and are disposed in alternately spaced-apart fashion on the upper side of the respective sensor element  10   a ,  10   b . Sensor element  10   c  depicted in  FIG. 5 , on the other hand, has a triangular shape in plan view, the edge length of the two short limbs being, by way of example, 60 mm in each case. While one the one hand electrode surfaces  17   c  and  19  are each of ribbon-shaped configuration, the two other electrode surfaces  18   c  and  20   c  each have a triangular shape. 
       FIG. 8  depicts a portion of a sensor skin  25  that is made up of a plurality of sensor elements each configured, in the exemplifying embodiment, in square fashion. Sensor elements  10  are connected to one another at their lateral surfaces both mechanically, e.g. in the form of gripping strips, and electrically, for example in the form of plug connections (not depicted). What is essential here is that in the context of the electrical connection of sensor elements  10 , the respective first measuring elements  21  and the respective second measuring elements  22  are electrically connected to one another. A connection in the form of a linear concatenation of sensor elements  10  thus takes place. 
     It is of course conceivable and usual in practice, as a modification of the exemplifying embodiment depicted in  FIG. 8 , to mechanically and electrically interconnect differently shaped sensor elements  10 ,  10   a ,  10   b ,  10   c  so as thereby to constitute a sensor skin  25  that is adapted to the shape of the machine part to be monitored, for example an arm of an industrial robot, in such a way that sensor skin  25  can, for example, be placed around the robot arm. Provision is likewise made for this purpose that the machine part to be monitored by sensor skin  25 , and sensor skin  25 , are connected to one another, for example, once again using gripping elements. Gripping elements of this kind allow sensor skin  25  to be rapidly placed onto and removed from the machine component. In addition, sensor skin  25  can be covered with a nonconductive, for example textile, protective layer that keeps moisture, dirt, and other physical or chemical disrupting influences away from sensor skin  25 . Field lines  1 ,  2  penetrate through this protective layer, so that the sensor function is not impaired. 
     Sensor system  100  has, besides the previously described sensor elements  10 ,  10   a ,  10   b , and  10   c , two central units  50 ,  60  for monitoring the two measuring elements  21 ,  22  of sensor elements  10 ,  10   a ,  10   b ,  10   c , which units will be described in further detail below. Sensor system  100  furthermore encompasses a computer software program for application and maintenance of sensor system  100 , and accessory material, for example cables, gripping tape, and installation material, in order to fasten sensor system  100  on the component to be monitored. The component to be monitored, for example a part of an industrial robot, has a controller  30  depicted in  FIG. 9  that, in the case of an industrial robot, encompasses at least a robot controller  31  and a safety controller  32 . It is also evident from  FIG. 9  that sensor system  100  is operatively connected both to robot controller  31  and to safety controller  32 .  FIG. 9  depicts sensor system  100  using the example of a single sensor element  10  with its two measuring elements  21  and  22 . It is evident that each of the two measuring elements  21 ,  22  has a respective input stage  33 ,  34  associated with it. Input stages  33 ,  34  are, in particular, a component of the electronic system of sensor element  10  disposed in cutouts  12 ,  13 . The two input stages  33 ,  34  are operatively connected to an evaluation stage  35 ,  36  that is a component of central units  50 ,  60 . The two output stages  35 ,  36  each have a Go/No Go output  37  that is connected to robot controller  31 , while an Err/No Err output  38  is operatively connected to safety controller  32 . 
     As already explained, the two measuring elements  21  and  22  of each sensor element  10  have control applied to them in chronologically successive fashion. In this context, the capacitance of electrode surfaces  17 ,  18  and  19 ,  20  is respectively sensed and is compared to a predetermined limit value or values. In the presence of a specific rate of change in the capacitance, or if the capacitance exceeds or falls below the previously discussed limit values, a collision-risking proximity between sensor element  10  and an object, for example a person, is inferred therefrom. In this case a No Go signal is generated at the respective Go/No Go output  37  of the respective measuring element  21 ,  22 , and is delivered to robot controller  31  as an input value. Robot controller  31  thereupon reacts, for example, with a decrease in the motion speed, or a stoppage, of the handling robot. It is sufficient for this if a corresponding signal is generated at one of the two measuring elements  21 ,  22  of a sensor element  10 . In addition, as will be explained in further detail below, the two measuring elements  21 ,  22  are subjected to a cyclically repeating self-diagnosis whose result is outputted at Err/No Err output  38  of the respective measuring element  21 ,  22 . If an error of measuring element  21 ,  22  is inferred within the self-diagnosis at first measuring element  21  or at second measuring element  22 , a corresponding signal is generated at Err/No Err output  38  and is delivered to safety circuit  32  as an input signal. Safety controller  32  thereupon reacts, for example, by once again stopping or restricting the operation of the industrial robot. What takes place is therefore a two-channel, mutually independent checking of the surroundings in terms of proximity events, as well as corresponding self-diagnosis. 
     As already explained, evaluation stages  35 ,  36  are a component of the respective central unit  50 ,  60 .  FIG. 10  now depicts the situation in which an arbitrary number of sensor elements  10  are electrically (and mechanically) interconnected in the form of a chain. It is also evident in particular that the respective input stages  33 ,  34  of the respective measuring elements  21 ,  22  are connected to one another. The two central units  50 ,  60  successively cyclically query the respective measuring elements  21 ,  22  of sensor elements  10 , provision preferably being made that each of sensor elements  10  has a specific address on the basis of which the respective sensor element  10  can be identified in terms of its position in sensor skin  25 . The two central units  50 ,  60  are connected and synchronized with one another via a connection  39  in such a way that the querying or addressing of the individual sensor elements  10  by central units  50 ,  60  occurs successively. It is moreover evident that the two central units  50 ,  60  are each identically configured and have a voltage supply  40 , a serial interface  41  for optional connection of a PC, outputs  42 ,  43  as respectively a Go and No Go signal for robot controller  31 , outputs  44 ,  45  as respectively an Err and No Err signal for safety controller  32 , a connector  47  for a loudspeaker, and an input  48  that is connected to robot controller  31 . 
       FIG. 11  depicts the sequence over time of a possible application of control to sensor elements  10  by central units  50 ,  60 . It is evident in particular that in a context of, for example, six sensor elements  10 , the one central unit  50  applies control to the respective first measuring elements  21  successively, beginning with the first sensor element  10 . Second central unit  60 , on the other hand, applies control to fourth sensor element  10  at its second measuring element  22  at a point in time at which first central unit  50  is applying control to first measuring element  21  of first measuring element  10 . Control is then applied to the fifth and sixth sensor element  10 , and then to the first three sensor elements  10 . In other words, this means that although both central units  50 ,  60  are each applying control at one and the same time to a sensor element  10  at its respective measuring element  21 ,  22 , control is nevertheless never being applied simultaneously by the central units to both measuring elements  21 ,  22  at one and the same sensor element  10 . 
     The respective sensor elements  10  are addressed by central units  50 ,  60  electronically, by way of a shift register. After each cycle of a main program loop, each sensor element  10  is read out once and stored in the RAM region of the microcontroller. 
     All sensor elements  10 , connecting cables, and the microcontroller are subjected to a cyclic self-diagnosis so that, for example, the industrial robot can be reliably shut down in the event of malfunction. While central units  50 ,  60  and their connector cables are usually mounted immovably in an electrical cabinet, sensor elements  10  and their connecting cables are exposed to the movement of, for example, the robot arm and to possible collisions. Each sensor element  10  is completely checked by the self-diagnosis several times per second. Interruptions, shorts to ground, shorts to operating voltages, a failure of electronic components, and further errors are detected. The errors are diagnosed, for example, on the basis of six diagnostic criteria. These diagnostic criteria can be generated, for example, after applying test voltages or characteristic signal patterns to sensor elements  10 ; it is sufficient for one of the six diagnostic criteria to respond in order to generate a corresponding error signal in the context of self-diagnosis. 
     Sensor system  100  so far described, as well as sensor elements  10 ,  10   a ,  10   b ,  10   c  and the connection to a controller, can be varied or modified in many ways without deviating from the idea of the invention. For example, it is conceivable in particular for sensor elements  10 ,  10   a ,  10   b ,  10   c  to have different dimensions or different shapes. Differently embodied electrode surface dispositions are likewise conceivable. It is moreover conceivable for digital signal transfers from sensor element  10 ,  10   a ,  10   b ,  10   c  to the respective central units  50 ,  60  to take place, instead of analog measured values or signal transfers. 
     Instead of a modular structure of sensor skin  25  from base elements or individual sensor elements  10 ,  10   a ,  10   b ,  10   c  that are interconnected, it is possible to use a monolithic manufacturing method with which a complete sensor skin  25  can be produced as a single piece (e.g. by injection embedding, production as extruded goods). In addition, in order to enhance safety in the context of the operation of sensor system  100 , each of sensor elements  10 ,  10   a ,  10   b ,  10   c  can have, instead of two mutually independently operating measuring elements  21 ,  22 , a larger number of measuring elements, for example three or four measuring elements. 
     The system can be used in a variety of application sectors, for example on industrial robots or service robots, mobile platforms, vehicles (in particular unmanned), in medical technology, or in the entertainment industry. 
     In addition to the safety function, sensor system  10  can take on different or additional surroundings monitoring functions. For example, the interaction of a robot with its surroundings, or gesture recognition, can occur by the fact that a controller combines the sensor data with information regarding the physical disposition of sensor elements  10 ,  10   a ,  10   b ,  10   c  and interprets it. The evolution of the sensor data over time can also supply useful information in this regard. 
     In a modification, a capacitance measurement can be carried out by distributing transmission operation and reception operation over two or more sensor elements  10 ,  10   a ,  10   b ,  10   c . Field lines  1 ,  2  of the measurement field then extend over a greater baseline distance; as a result, range is increased and possible gaps between sensor elements  10 ,  10   a ,  10   b ,  10   c  are closed.