Abstract:
In a method for operating a safety device for a handling device, e.g., an industrial robot having a movable gripper device and at least one sensor device at least largely surrounding the gripper device for recognizing at least possible collisions with objects located in the motion path of the gripper device, a signal is output to a control unit upon recognizing a collision risk, resulting in a modified motion sequence of the gripper device on its motion path, which modified motion sequence is a controlled reduction in the motion velocity of the gripper device.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for operating a safety device for a handling device. Furthermore, the present invention relates to a safety device for a handling device and a handling device. 
     2. Description of the Related Art 
     A method of this type for operating a safety device for a handling device is already known from published German patent application document DE 10 2007 062 245 A1. Here, the safety device has a shell surrounding the handling device in the form of a fillable medium storage device, which is in operative connection with a pressure sensor. When a collision is recognized, the pressure sensor responds, whereupon the gripper arm is stopped or moved in an opposite direction. Since the safety device does not respond until contact or collision with an object, for example, an inanimate object or a person, has already occurred, the necessary change in motion or stopping must occur in an extremely short period of time in order to prevent damage or injury. Therefore, when a collision of this type is recognized, an “emergency stop” of the handling device or of the gripper arm is usually performed. An “emergency stop” of this type has, however, the disadvantage that the motion velocity is not reduced to the value zero in a controlled manner. After the collision risk has been eliminated, the gripper arm must be brought back into a certain position, for example, from which a predetermined motion sequence is possible or the control program must be resynchronized with the gripper arm motion. 
     Furthermore, it is known from published European patent application document EP 1 323 503 A2 to provide a multistage sensor system in order to make possible a risk-free operation of the handling device involving human interaction. The method is based on tactile function principles, although a capacitive sensor principle is described as a possible sensor principle. The capacitive sensor principle, however, has only a supplementary function, i.e., it is usable only together with additional safety mechanisms such as a foam padding or a tactile sensor system. A targeted, collision-free braking action is thus not provided. In the last-named safety device, a foam padding shell surrounding the handling device is, in particular, also used for dampening or absorbing the impact energy generated in the collision. 
     BRIEF SUMMARY OF THE INVENTION 
     An object of the present invention is to refine a method for operating a safety device for a handling device, in particular an industrial robot, in such a way that, in particular, simplified restart or continued operation of the handling device is possible when the collision risk no longer exists. The present invention is based on the idea that, when a collision risk is recognized, a modified motion sequence of the gripper arm is provided, the modified motion sequence being a controlled reduction of the motion velocity of the gripper arm. In other words, this means that, in contrast to the related art, no “emergency stop” operation takes place, but a controlled reduction of the motion velocity, this having the advantage that the instantaneous position of the gripper arm is reliably recognized, so that either continued operation of the handling device at reduced motion velocity of the gripper arm if necessary or stopping of the gripper arm up to a standstill takes place, the standstill position of the gripper arm being reliably recognized, so that starting directly from this position in the event of restart is possible. 
     In a first embodiment of the present invention it is provided that the reduction in the motion velocity occurs until standstill of the gripper device. In particular in the case where the object is a human person, a motion pattern of the gripper arm is thus achieved which is easily detected by the person. 
     Particularly preferred is a specific embodiment in which the reduction in the motion velocity occurs as a function of the particular detected distance of the object from the motion path of the gripper device. In other words, this means that, on the one hand, the operation of the handling device itself continues (at a reduced velocity) even in the event of an approaching object, whereby the productivity of the handling device is only relatively slightly affected and, on the other hand, this makes it possible to always provide an instantaneous motion velocity of the gripper device from which reliable stopping of the gripper device without the risk of a collision with the object is made possible, considering the instantaneous distance between the gripper device and the object. 
     Particularly preferred is furthermore that after a reduction in the motion velocity, the motion velocity of the gripper device is flexibly adapted to the detected distance from the object, i.e., if necessary, it is increased again to an original setpoint motion velocity. The performance of the handling device is thus optimized, i.e., in the case where a collision risk with the object no longer exists it resumes its original motion velocity and thus performs as it did originally. 
     In order to ensure reliable recognition of possible collisions, according to another preferred method, it is proposed that the signals of multiple sensor elements be processed, at least two of the sensor elements having the same detection area. This means that the different signals may be compared to each other, so that even in the event of failure of one sensor element, the control unit is, for example, still able to recognize a possible collision risk and respond accordingly. 
     It may be furthermore provided that the signals of multiple sensor elements are processed, at least two of the sensor elements working by different measurement principles. This also makes, in particular, an always reliable operation of the safety device possible even under varying environmental conditions. 
     In another embodiment of the present invention, it is provided that the change in motion velocity of the gripper device is controlled as a function of the approach velocity between the gripper device and the object. This means that in the case of a relatively high approach velocity, a relatively rapid and abrupt braking of the gripper device occurs in order to avoid a possible collision. In contrast, in the case of a relatively low approach velocity, an appropriately slighter reduction in the motion velocity of the gripper device is effected. 
     The present invention also includes a safety device for a handling device, in particular an industrial robot having at least one sensor device for recognizing possible collisions and a control unit for operating the safety device. It is provided here that the gripper device has gripper fingers, which are designed to yield, in the event of a collision, in the direction of the collision. This makes an interactive operation between a person and an industrial robot possible, in which the operator shifts or removes an object shortly before the gripper arm grips it, there being a risk, due to the short distance between the operator&#39;s hand and the gripper fingers, that the gripper fingers grip or injure the operator&#39;s hand. Due to the very high approach velocity between the operator&#39;s hand and the gripper fingers, known sensor principles or security measures often fail in this case. In order to still avoid or at least alleviate injury to the operator, the gripper fingers are designed to yield in the direction of the collision. 
     In another, particularly preferred embodiment of the present invention, it is provided that the gripper device is surrounded by an impact-absorbing padding, whose thickness is adapted to a braking distance of the gripper arm up to a standstill. 
     Further advantages, features, and details of the present invention are derived from the following description of preferred exemplary embodiments and the drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a simplified illustration of an industrial robot situated in a work area and having a safety device according to the present invention. 
         FIG. 2  shows a block diagram for illustrating the method according to the present invention for operating the safety device. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Identical components or components having identical functions are provided with identical reference numerals in the figures. 
       FIG. 1  shows, in a highly simplified form, a handling device  10  in the form of an industrial robot  100 . Handling device  10 , i.e., industrial robot  100 , has a multi-axis gripper device  11 . Gripper device  11  includes a column  12 , which is connected to two movably situated carriers  13 ,  14 . At the end of one carrier  14 , three gripper fingers  15  through  17  are situated, as an example, using which an object or a component  1 , which is symbolically illustrated in  FIG. 1  and situated on a table  2 , may be gripped. 
     Column  12  and carriers  13 ,  14  are mounted in rotating or swiveling shafts not described or illustrated in greater detail, so that gripper device  11  or gripper fingers  15  through  17  may move to reach any point in space located within work area  5 . Work space  5  thus forms the system boundary of gripper device  11 . This makes it possible in particular, for example, to pick up component  1  from table  2  and to transport it to another point within work space  5 , where, for example, component  1  is assembled with other components (not illustrated). 
       FIG. 1  shows the case where gripper fingers  15  through  17  approach component  1 , which is illustrated by a first path section  18 . After gripping component  1 , the gripper device moves to the discussed point within work space  5 , which is to be indicated by a second path section  19 . The two path sections  18 ,  19  form a motion sequence stored in handling device  10  or a motion path of gripper device  11 ; gripper device  11  and gripper fingers  15  through  17  may be moved at different velocities on the motion path. 
     Handling device  10  is surrounded, at least in the area of column  12  and carriers  13 ,  14 , by an impact-absorbing padding  22 , whose thickness is adapted or dimensioned in such a way that in the event of a possible collision with an object  3 , e.g., an operator, gripper device  11  may be stopped on the motion path, without damaging object  3 . 
     Furthermore, handling device  10  includes a sensor device  25 , which has, for example, a plurality of individual sensor elements  26 ,  27  having detection areas  28 ,  29 . Sensor device  25  is situated, as an example, on the outside of padding  22  in such a way that, when gripper device  11  is moved, sensor elements  26 ,  27  are able to detect any point in space located on the motion path. 
     Capacitive sensor elements  26 ,  27 , which emit an appropriate signal to a control unit  30  of handling device  10  when a relative approach occurs between sensor elements  26 ,  27  and object  3 , are used, in particular, as sensor elements  26 ,  27 . However, different measurement principles for sensor elements  26 ,  27  are basically conceivable. For example, sensor elements  26 ,  27  operating on an ultrasound or a radar basis may also be used. What is essential is only that an object  3  is detected or found within detection areas  28 ,  29  with the aid of sensor elements  26 ,  27  before object  3  collides with or contacts handling device  10 . 
     Sensor elements  26 ,  27  described so far form, together with control unit  30 , a safety device  50  for handling device  10 . Their mode of operation is now elucidated in greater detail with reference to  FIG. 2 : it is apparent that sensor elements  26 ,  27  are connected to control unit  30  in a signal-conducting manner. An anticollision program or a corresponding algorithm, which processes the signals received, preferably continuously, by sensor elements  26 ,  27  regarding the existence of an object  3  within detection area  28 ,  29 , is stored in control unit  30 . In a first program step  52 , it is queried whether a signal regarding an object  3  located in detection area  28 ,  29  is being reported by sensor elements  26 ,  27 . If this is not the case, a certain motion sequence or a certain motion path  20  of gripper device  11  is followed according to second program step  53 , i.e., handling device  10  works in its normal operation in which parts  1  are handled in the desired manner. 
     In contrast, if, in first program step  52 , one of sensor elements  26 ,  27  reports an object  3  within detection area  28 ,  29 , the corresponding sensor element  26 ,  27 , is located, if necessary, in another program step  54 . Since sensor elements  26 ,  27  preferably generate appropriate signals in equally long time intervals, a corresponding approach velocity between object  3  and sensor element  26 ,  27  or handling device  10  may be additionally inferred, for example, from the particular signal intensities. It is also possible to ascertain, from the detected or transmitted signals of sensor elements  26 ,  27  whether or not a potential collision of object  3  with gripper device  11  may occur in the area of motion path  20 . 
     If there is the risk of a potential collision, in a next program step  55 , a controlled reduction in the motion velocity of gripper device  11  is carried out in such a way that, depending on the instantaneous distance between object  3  and motion path  20  or on the approach velocity between object  3  to motion path  20 , a reduction in the velocity, to the value zero, if needed, occurs at the potential contact point. It is essential here that this is a controlled reduction in the motion velocity of gripper device  11 , i.e., control unit  30  is able to detect the exact location of gripper device  11  or of gripper fingers  15  through  17  at any given point in time. 
     It is particularly preferred that the change or reduction in the motion velocity of gripper device  11  occurs as a function of the particular distance between object  3  and handling device  10  or of the corresponding approach velocity. This means that in the case where the distance between object  3  and handling device  10  increases again on its motion path, the motion velocity of gripper device  11  is increased again, possibly to a setpoint velocity corresponding to normal operation of gripper device  11 . A velocity or performance optimization of handling device  10  thus occurs as soon as an object  3  is at a possible collision risk with handling device  10 . 
     However, it may also be provided that, when an object is detected by one of sensor elements  26 ,  27 , a controlled reduction in the motion velocity of gripper device  11  up to a standstill occurs. As soon as no object is detected, the motion velocity is increased again to its original value. 
     It is also pointed out that safety device  50  or handling device  10  described so far may be modified in multiple ways without deviating from the inventive idea. It is particularly advantageous to use, as sensor elements  26 ,  27 , sensor elements working by different measurement principles (for example, capacitively working sensor elements  27  and sensor elements  27  working by the ultrasound principle). It is furthermore conceivable and advantageous, for increasing operational reliability, if at least two sensor elements  26 ,  27  both have an identical detection area  28 ,  29  in such a way that the same area in work space  5  is monitored with the aid of corresponding detection area  28 ,  29 . In addition, it is also possible that gripper fingers  15  through  17  are situated or fastened in a force-fitted manner on carrier  14  in such a way that in the case where, for example, an operator grips component  1 , gripper fingers  15  through  17  may get into contact with the operator&#39;s hand, but they are designed to yield in the direction of the collision, so that at least serious injuries to the operator may be ruled out.