Abstract:
A method for operating a sensor system, having at least one capacitive sensor element, which is attachable to the surface of machines or machine parts, electrical field lines on the sensor element changing in the event of an approach and/or a contact of a body or object, and the at least one sensor element being connected to a control unit, which, based on the detected change of the field lines of the at least one sensor element, triggers a safety function on the machine or the machine part. The at least one sensor element has, in addition to fulfilling the safety function, an operating function, which is concluded from the location of the at least one sensor element and the time curve of the change of the field lines, and the safety function has priority over the operating function in a base state of the sensor system.

Description:
RELATED APPLICATION INFORMATION 
     The present application claims priority to and the benefit of German patent application no. 10 2012 211 231.6, which was filed in Germany on Jun. 29, 2012, and German patent application no. 10 2012 212 754.2, which was filed in Germany on Jul. 20, 2012, the disclosures of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a method for operating a sensor system and a sensor system. 
     BACKGROUND INFORMATION 
     A method for operating a sensor system and a sensor system are discussed in DE 10 2009 029 021 A1 of the applicant. It includes at least one capacitive sensor element, whose field lines generated thereby change in the event of an approach of a body or object, the change being able to be detected and analyzed with the aid of a control unit. The known sensor system is used in particular in handling robots or similar machines or devices for the purpose of switching the handling device into a safety mode, in the case of which the movement of the affected machine component is stopped, in the event of approach of a human or an (unexpected) approach of an object to a moving machine part, for example, a robot arm. In particular, injuries in the event of a collision of the handling device with a human or damage to objects or the handling device may thus be avoided or at least minimized. The known sensor system may include a plurality of planar sensor elements, which are arranged over the entire surface of the handling device like a sensor skin, for example, and are connected to one another by circuitry. 
     Applications in which handling devices collaborate with humans in a shared workspace will become more and more important in the future. Such applications occur, for example, in product manufacturing, for example, in assembly, during welding or lacquering, in the field of so-called service robots (for example, for pick-up and delivery services), cleaning robots, inspection robots, in the field of autonomous vehicles in the environment of humans, in the field of medical robots, which work closely with humans (for example, for angiography and tumor treatment), or other applications. The collaboration capability of such machines is essentially based on two basic functions, safe movement in the environment of humans and intuitive interaction with humans. 
     With respect to the interaction capability, it is typically implemented using classical operating elements such as buttons, switches, keyboards, rotating and sliding controllers, joysticks, computer mice, and touch screens. Speech recognition systems are also known, which react to spoken commands, and also visual systems, which recognize the movements of an operator (for example, in the form of gestures). In addition, various interaction technologies are known for controlling robots, e.g., indirect operation via classical operating elements, or direct operation, in the case of which the operator displaces the robot arm using his hands (detection of the operator command by measuring the motor current via the drive regulation or by additional torque sensors in the joints of the robot arm). 
     SUMMARY OF THE INVENTION 
     The present invention is based on the object of providing a method for operating a sensor system or a sensor system according to the descriptions herein so that it is suited to be used both as a safety system to avoid collisions of machines or machine components with humans or objects, and also as a system for interaction between a machine and an operator. 
     This object may be achieved in the case of a method for operating a sensor system having the features described herein essentially in that the sensor element has, in addition to a safety function, an operating function, an operating function is concluded from the location of the at least one sensor element and the time curve of the change of the field lines, and the safety function has priority over the operating function in a base state of the sensor system. In other words, this means that the same sensor element of a sensor system may be used in different ways, as a trigger for a safety function and as a switching element for an operating function. For safety reasons, it is provided that the safety function has priority over the operating function in a base state of the sensor system. This means that, for example, no gestures may be executed in direct proximity to the moving machine or the moving robot. If an operator attempts this, the safety function will decelerate the machine or the robot safely to a standstill. Only then may the operator retrieve the desired function using a gesture. In particular injuries to persons and damage to machines or objects are thus reliably. 
     Advantageous refinements of the method according to the present invention for operating a sensor system and a sensor system are set forth in the further descriptions herein. All combinations of at least two features which are disclosed in the claims, the description, and/or the figures fall within the scope of the present invention. Features disclosed with respect to the method are to be considered to be disclosed and claimable with respect to the device and features disclosed with respect to the device are simultaneously to be considered to be disclosed and claimable with respect to the method. 
     To simplify the operation of a machine or a robot, for example, it may be provided that the safety function may be temporarily disabled by the operation of a safety switch. This means that by intentionally pressing a safety switch, the machine or the robot is immediately switched into an operating mode, in the case of which an approach of a human or an object to a sensor element is not classified as safety-relevant, so that, for example, the movement of the machine or the robot is not stopped. In this operating state, the operator assumes responsibility for the safe operation of the machine or the robot system. The safety switch may be configured in such a way that, when it is not being operated or pressed by an operator, it switches back into its original switching state, in which the sensor element of the machine or the robot is in its safety mode. 
     Another advantageous embodiment of the present invention provides that the safety function has three different switching states as a function of the detected distance of a body or an object from the machine or the machine part, that in the first switching state, which is designated as near range and which is assigned to a short distance (for example, less than 20 cm) of the body or object from the machine or the machine part, the movement is completely stopped by the safety function, that in a second switching state, which is designated as moderate range and which is assigned to a moderate distance (for example, between 20 cm and 40 cm) of the body or object from the machine or the machine part, the movement of the safety function is limited to a safe speed V1, and that in a third switching state, which is designated as far range and which is assigned to a long distance (for example, greater than 40 cm) of the body or object from the machine or the machine part, the movement of the safety function is limited to a safe speed V2, which may be greater than speed V1. The following is meant here: at close range, the safety function ensures a safe stop, so that a hazard for the operator no longer originates from the movement of the machine or the machine part and the operator may execute arbitrary gestures directly in front of the sensor elements. In the moderate range, only gestures may be executed, in the case of which the hand approaches not closer than up to a minimum distance of, for example, 20 cm to the moving machine or the machine part. This switching state may be used for the purpose, for example, of guiding a robot in a contactless way using a hand, in that the robot regulates its position so that its distance and its orientation to the hand always remain identical. At far range, there is no restriction for the execution of gestures. 
     In a simplified embodiment, the moderate range may be omitted, so that only a switching threshold of 20 cm exists, for example, which separates the near range from the far range. 
     Another advantageous embodiment of the method according to the present invention provides that the operating function has multiple operating modes, a first operating mode relating to teaching of a gesture by the sensor system, and a second operating mode relating to execution of a gesture, which was taught in the first operating mode, by the machine or a machine part. The first operating mode therefore means, for example, that a specific gesture is repeated multiple times in succession by an operator, and the sensor system stores the particular sensor values detected during the execution of the gesture. An “average” signal curve for a specific gesture may be ascertained from the stored sensor values, for example, which, subject to tolerance values, also allows the recognition of gestures which deviate from this “average” gesture, but are obviously to trigger the same function by the control unit. As soon as the teaching process or the first operating mode is completed, the sensor system operates in the second operating mode. If a gesture is executed, the control unit thus compares the average signal curves of stored gestures which are stored in the control unit to the currently detected signal curve of a gesture. If a correspondence is found, a specific gesture is concluded, which has the result that the control unit of the machine or the robot triggers a specific action, for example, a screwing process or the like. 
     A sensor system according to the present invention is distinguished in an advantageous embodiment in that in the operating mode, multiple sensor elements form an operating panel, the input values of the sensor elements, which are detected by the control unit, being able to be analyzed with the aid of a computer unit. 
     It particularly may be that when the sensor elements forming an operating panel represent a subset of all sensor elements situated on the machine or the machine part, and when the subset of the sensor elements may be selected from the total set of the sensor elements. The following is meant here: A machine or a machine component is covered with a plurality of sensor elements. For example, a matrix of 5×5 sensor elements arranged adjacent to one another forms an operating panel. This operating panel may be configured at an arbitrary point of the machine surface by an appropriate activation of corresponding sensor elements by the control unit. This means that, for example, the affected operating panel may either be formed on a robot arm, or in the area of a support element. With the aid of such an embodiment of the present invention, an operating panel of the sensor system may be freely adapted to greatly varying machines or machine components and also applications, without additional hardware devices having to be affected for this purpose. The assignment of the sensor elements to the operating panels is performed solely by software. 
     According to the exemplary embodiments and/or exemplary methods of the present invention, it may be provided that at least one sensor element in the operating mode acts as a digital switch or as an analog switch, for example, like a slide controller. This means that in the operating mode, for example, if a specific threshold value is exceeded at the sensor element, the control unit turns a specific machine element on or off, regardless of the value by which the threshold value was exceeded. Alternatively thereto, however, the absolute level of the detected measured value of the sensor element may also be used for the purpose of being converted into a corresponding speed signal for operating a machine element, for example, so that the level of the sensor signal corresponds to a specific analog value (for the speed of the machine component). 
     In order to give an operator feedback as to whether, for example, a gesture executed by him was correctly detected or interpreted by the sensor system, it may be provided in another embodiment of the present invention that at least one visual, acoustic, or other display element is provided, with the aid of which the control unit outputs a signal in the operating mode. For example, this display element may be a monitor, which signals the detected gesture or a specific operator command by a corresponding visual display as feedback to the user. Alternatively thereto, for example, it may be communicated to the operator by an acoustic signal that the control unit has unambiguously recognized a specific gesture or also if a gesture was not recognized. Other types of elements, for example, LEDs, may also be used for such feedback for the operator. 
     In addition, it particularly may be that if the at least one sensor element acting in the operating mode is visually marked on the machine or the machine component. It is thus signaled to the operator at which point he is to execute a gesture, for example, so that it may be recognized as easily and unambiguously as possible by the sensor system. It is conceivable, for example, to perform such a marking with the aid of a light, which is only recognizable in the operating mode of the machine. However, printed markings or the like may also be used, so that the operator recognizes the area of the sensor elements via which an input of gestures is made possible, for example. 
     Further advantages, features, and details of the exemplary embodiments and/or exemplary methods of the present invention result from the following description of exemplary embodiments and on the basis of the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic view of a handling robot during the transfer of an object by an operator. 
         FIG. 2  shows the fundamental structure of an interaction system, in which an operating panel constructed from 24 sensor elements is used to recognize a gesture. 
         FIG. 3  shows a view to illustrate an exemplary mode of operation of a virtual operating element for detecting a keypress. 
     
    
    
     DETAILED DESCRIPTION 
     Identical elements or elements having an identical function are provided with identical reference numerals in the figures. 
       FIG. 1  shows a machine in the form of a handling robot  100 . Handling robot  100  includes a machine base  101 , which carries a robot arm  103 , which is rotatably mounted in a first axis  102 . Robot arm  103  has three arm sections  104  through  106 , which are in turn each mounted so they are pivotable in one axis  107  through  109  in the direction of the double arrows shown. Arm section  106  carries a gripping mechanism  110  for gripping an object  1 . Such a handling robot  100  thus described is suited for the purpose of receiving object  1  within the range of robot arm  103  at an arbitrary location and delivering it at a second, also arbitrary location. 
     At least areas of handling robot  100  are covered by a sensor skin (not shown in detail) having sensor elements  10 , which are each configured as capacitive sensor elements  10 . Sensor elements  10  form a sensor system. Sensor elements  10  may each be configured identically; however, they may also be configured differently or have different sizes. With respect to a fundamental construction of such a sensor element, reference is made to DE 10 2009 029 021 A1 of the applicant, which is thus to be part of this application. 
     Sensor elements  10  are connected to a control unit  20  of handling robot  100 . In control unit  20  of handling robot  100 , the particular locations of sensor elements  10  on handling robot  100  are stored. For example, some of sensor elements  10  are used according to the present invention in such a way that the control of a function or an operation of handling robot  100  may be performed via these sensor elements. For this purpose, multiple virtual operating panels  11  through  14  are generated on the surface of handling robot  100 , sensor elements  10  assigned to individual operating panels  11  through  14  being freely assignable as a subset to all of sensor elements  10  situated on handling robot  100  via an input unit (not shown), for example. Operating panels  11  through  14  described hereafter are only to represent possible variants, the number and configuration of which are variable to a high degree. 
     First operating panel  11  is situated in the area of third arm section  106  of robot arm  103  on a lateral surface and acts as a digital switching element, so that if the hand of an operator  30  approaches, for example, gripping unit  110  is opened or closed. Operating panel  12  is situated on second arm section  105  of robot arm  103  and includes six sensor elements  10 , for example, which are used for the sequence control of the operation of handling robot  100 , so that if the hand of operator  30  approaches a specific sensor element  10  in operating panel  12  of handling robot  100 , for example, a stored operating program starts or is executed. Operating panel  13  is situated on first arm section  104  of robot arm  103  and is used as a virtual proximity surface for guiding robot arm  103 . In particular, if an identical operating panel  13  is situated on the opposite side of first arm section  104  on robot arm  103 , which is parallel to the plane of the drawing of  FIG. 1 , robot arm  103  may be caused to rotate in first axis  102  in the desired direction, in order to teach a specific movement sequence of robot arm  103 , by the approach of the hand to one or the other operating panel  13 . Finally, an operating panel  14  is situated on machine base  101 , which is used for data input in the form of a virtual keyboard, and includes a plurality of sensor elements  10  situated adjacently to one another and one over another. 
     To make operating panels  11  through  14  identifiable for operator  30 , it may be provided that operating panels  11  through  14  are emphasized by appropriate markings or visual aids. 
     Sensor elements  10  shown in  FIG. 1  in operating panels  11  through  14  are used, like sensor elements  10  (not shown in  FIG. 1 ) distributed over the surface of handling robot  100 , which are not situated in operating panels  11  through  14 , for stopping the movement of handling robot  100  during the operation of handling robot  100  in the so-called safety mode in the event of an imminent collision of handling robot  100  with a human or an object, in order to prevent injuries or damage. For this purpose, control unit  20  analyzes the input signals generated by individual sensor elements  10 . In addition to the safety-relevant function of sensor elements  10 , they are used, as explained above, in operating panels  11  through  14  for the purpose of interacting with operator  30  (operating mode). 
     The safety mode has priority over the operating mode. This means that, for example, if operator  30  approaches handling robot  100 , which is recognized by sensor elements  10 , initially the speed of robot arm  103  is throttled to a safe value, so that contact with moving robot arm  103  is precluded. Sensor elements  10  situated within operating panels  11  through  14  are then ready to recognize gestures of operator  30 . If the robot receives a command at any time to move toward an object or a human, to fall below the preset safety distance, or to exceed the maximum speed corresponding to the distance, the execution of the command is prevented by the priority of the safety mode. 
     Manually pressing an optional safety switch  15 , which is connected to control unit  20  of handling robot  100 , by operator  30  causes the approach of a human or an object to be classified as not safety-relevant, while the recognition of gestures is still active. In this operating state, the operator assumes responsibility for the safe operation of the robot system. 
     As long as safety switch  15  is pressed, control unit  20  of handling robot  100  or its sensor elements  10  switch from the safety mode into the operating mode, in the case of which in particular sensor elements  10  situated within operating panels  11  through  14  are used to recognize gestures of operator  30  or inputs. It may also be provided that in the event of an approach of operator  30  to sensor elements  10 , control unit  20  initially switches into a mode in which sensor elements  10  in the area of operating panels  11  through  14  are used to recognize gestures, for example, while the movement of handling robot  100  is simultaneously performed at reduced speed in comparison to normal operation. Upon further approach of operator  30  to sensor elements  10 , in the case of which the distance falls below a specific minimum distance of, for example, 10 cm, control unit  20  switches handling robot  100  over into the safety mode, during which any movement of handling robot  100  or its robot arm  103  is stopped. 
     In order to provide operator  30  with feedback about inputs made by hand via operating panels  11  through  14 , a visual, acoustic, or other display unit  16  may be provided, which receives a corresponding signal from control unit  20  if, for example, a specific gesture of operator  30  was correctly recognized (or was not recognized at all), or if, for example, a gesture is to be repeated. 
       FIG. 2  shows an operating panel  18 , including  24  sensor elements  10 . Sensor elements  10  are situated in the form of a 4×6 matrix in operating panel  18  and are connected to a central unit  19 , which is part of a computer unit. Operating panel  18  thus formed detects the gestures of operator  30 . For this purpose, each of sensor elements  10  delivers a measured value D i , which varies with the distance of the finger of operator  30  from particular sensor element  10 . Central unit  19  takes over the cyclic request and processing of measured values D i  of all sensor elements  10  and also the output thereof via an interface. A control computer  25  having an integrated software interaction module  27 , which is connected to central unit  19 , reads in measured values D i  of all sensor elements  10  as a time series and analyzes them in the following way, as an example: 
     preprocessing of measured values D i    
     recognition of taught patterns in the data, for example, with the aid of correlation functions 
     classification of the patterns according to operating elements and gestures 
     assignment of the recognized gestures to commands, and 
     command execution in step  28  (for example, by retrieval of functions, output of signals). 
       FIG. 3  shows an example of the mode of operation of a virtual operating element having six sensor elements  10  arranged adjacent to one another. In this case, the operating element is used to detect a keypress. The index finger of an operator  30  is guided in the X direction of the arrow shown. The diagram shown below six sensor elements  10  schematically shows the measured value curve of all six sensor elements  10 , as a function of the X position of the finger. Each sensor element  10  has a characteristic curve similar to a Gaussian curve, the Gaussian curves of adjacent sensor elements  10  typically overlapping. The X position of the finger of operator  30  may be derived from six measured values D 1  through D 6  with the aid of interpolation functions. The resolution of the finger position is not linked to the width of sensor element  10  or the width of the finger. If adjacent sensor elements  10  are provided, different finger positions may also be detected within a sensor element  10  by interpolation. This measurement principle is transferred to flatly situated sensor elements  10 , in order to detect the finger position in both spatial directions (i.e., in parallel and perpendicularly to the plane of the drawing of  FIG. 3 ). In a similar way, the distance of the finger of operator  30  may also be detected on the basis of characteristic sensor data, so that the spatial position of the finger of operator  30  may be ascertained. 
     If gestures are to be recognized with the aid of sensor elements  10 , these gestures are transformed as a result of the input signals of sensor elements  10  into a chronological sequence of sensor data. One task of control computer  25  shown in  FIG. 2  is to take over the back transformation, i.e., to recognize gestures in the chronological sequence of sensor data. Furthermore, module  27  situated in control computer  25  has the two operating modes “configure” and “execute.” In the operating mode “configure,” the virtual operating elements (operating panels  11  through  14 ) are configured by an operator  30  before handling robot  10  is put into operation. This is carried out in the following steps, for example: 
     a. Visualization of the operating elements (operating panels  11  through  14 ) on the surface of handling robot  100 , for example, by stickers or in the form of LEDs delimiting operating panels  11  through  14 . 
     b. “Demonstration” of the gesture at the operating element by operator  30 . The gesture is stored as a chronological sequence of characteristic sensor data. Permissible variations of the gesture are subsequently also demonstrated. 
     c. Teaching of the gesture: The stored sensor data are reduced to characteristic features. A teachable classifier is trained using these features. The classifier is multiclass capable, i.e., it may recognize all taught gestures again and assign them separately. In the case of analog gestures, it is capable of determining the analog value of the gesture (for example, the distance between the hand of an operator  30  and a sensor element  10 ). 
     d. Linking the gestures to functions: Operator  30  assigns each taught gesture to a function or a sequence of functions, which is to be automatically executed upon recognition of the gesture. For example, this may be a function sequence on control computer  25  or a command which is transmitted via a communication interface to peripheral units. 
     In the operating mode “execute”, the measured values of sensor elements  10  are continuously cyclically read in and the characteristic features are calculated. The previously taught classifier continually checks whether a taught gesture was executed. If so, control unit  20  triggers the execution of the function linked thereto. 
     The method thus described for operating the sensor system including sensors  10  may be altered or modified in manifold ways, without deviating from the exemplary embodiments and/or exemplary methods of the present invention. In particular, the use of such a sensor system is not necessarily restricted to the use in handling robots  100 , but rather may also be applied in the case of other machines or machine components.