Abstract:
A gripping device for positioning a component ( 47 ) on a substrate, comprising three fingers ( 1, 2, 3 ) arranged in a triangle ( 7 ), and a drive device for moving the fingers along parallel paths ( 4, 5, 6 ) relative to each other to grip or release a component. A middle finger ( 2 ) is movable in opposite directions with respect to the outer fingers ( 1, 3 ).

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a gripping device for placing a component on a substrate, which gripping device comprises movable fingers and means for making the fingers move relative to each other so as to grip and release the component. 
     Such a device is known from DE-A1-3704402. This known device comprises two fingers which are arranged right opposite to each other and which can be moved towards each other and away from each other, and by means of which a component can be gripped and released. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a gripping device in accordance with the first paragraph, by means of which components can be reliably and properly gripped. 
     To achieve this, the gripping device in accordance with the invention is characterized in that three fingers are present, which are arranged in a triangle and which are movable in parallel paths relatively to each other, and in that, viewed in the direction of movement of the fingers, the central finger can be moved in opposite directions with respect to the outer fingers. By arranging the fingers in a triangle, a component is gripped at three locations. As a result, the gripping operation is statically determined. The risk that rotational forces develop which act on the component is small. The component is gripped in a stable and reliable manner. Such a gripping device can be used to grip electric components, but also other components or objects, for example, framework-shaped accessories for electric components, which are to be placed on a substrate or printed circuit board. 
     A gripping device which is preferably used is characterized in that the distance between the fingers, viewed in the direction of movement of the fingers, is adjustable. By virtue of the adjustability, it becomes possible to adapt the distance between the fingers to the component to be gripped. In general, a component will be gripped on the outside thereof, i.e. the fingers will be moved towards each other in the gripping operation. It is alternatively possible, however, to move the fingers relative to each other such that a component can be gripped on an inside thereof, while for gripping and also for releasing the component, the fingers move in the same direction. The means for driving the fingers do not have to be adjusted. 
     A further embodiment is characterized in that each finger can be moved by means of two parallel leaf springs. By virtue thereof, the movement of the fingers is substantially without friction. 
     Yet another embodiment is characterized in that a cap is present which is arranged over the gripping device and which has a wall, wherein parallel grooves are formed through which the fingers project, and which wall serves as a stop for a component to be gripped. As a result, after a component has been placed on a substrate, it is clamped between the wall of the cap and the substrate, and only then the fingers are moved away from each other (or towards each other) to release the component. This leads to a reduction of the risk that, during placing the component, the component is slightly moved when it is released, which could result in an incorrect placement of the component. 
     These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     In the drawings: 
     FIG. 1 is a perspective view of a gripping device in accordance with the invention, 
     FIG. 2 is a perspective view of the gripping device in a realistic embodiment in accordance with FIG. 1, the cap being removed, 
     FIG. 3 diagrammatically shows, partly in section and partly in a front view, the gripping device shown in FIG. 2, 
     FIG. 4 is a plan view of the gripping device shown in FIG. 3, and 
     FIG. 5 shows a situation wherein the gripping device places a component on a substrate. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a gripping device comprising three fingers  1 ,  2 ,  3  which are movable in parallel paths  4 ,  5 ,  6  with respect to each other. In operation, the central finger  2  always moves in an opposite direction with respect to the outer fingers  1 ,  3 . The direction of movement of the fingers is indicated by means of an arrow P. The fingers are arranged in a triangle  7 . As a result, a component is gripped at three locations. The fingers are each secured onto a respective slide bar  8 ,  9 ,  10 . A cap  11  is arranged over the gripping device, and is provided with three parallel grooves through which the fingers  1 ,  2 , 3  project. 
     FIG. 2 shows the gripping device in a realistic form, the cap  11  being removed. The gripping device is composed of a support  12  on which a supporting plate  13  is secured, a frame  14  comprising the slide bars  8 ,  9 ,  10  with the fingers  1 ,  2 ,  3 , and a drive unit  15  for driving the slide bars. The frame  14  is provided with a supporting element  16  which is secured onto the supporting plate  13 . Between ends of each slide bar  8 ,  9 ,  10  and the supporting element  16 , there are arranged parallel pairs of leaf springs  17 ,  18 ;  19 ,  20 ;  21 ,  22 , as shown in FIG.  3  and FIG. 4, which also show further details of the gripping device. The leaf springs  17 ,  18  are secured to one outer slide bar  8 , the leaf springs  21 ,  22  are secured to the other outer slide bar  10 , and the leaf springs  19 ,  20  are secured to the central slide bar  9 . The drive unit  15  comprises a cylinder block  23  with a cylinder space  24  and a piston  25  which is movable in the cylinder space. The outer slide bars  8 ,  10  are coupled to the piston  25  by means of a fork  26 . For this purpose, the piston is provided with a pin  27  which is oriented transversely to the direction of movement of the piston and which projects, through an elongated hole  28  of the cylinder block  23 , beyond the cylinder block. The fork  26  is coupled to the pin  27 . The cylinder space  24  is closed on either side by an end plate  29 ,  30 . At least one compression spring  31  is compressed between the end plate  30  and the piston  25 , which compression spring presses the piston to one side, in FIG. 3 the left side. The cylinder block  23  further comprises an air-supply channel  32  which opens into the part of the cylinder space  24  which is situated on the side of the piston  25  opposite the side where the spring  31  is located. The outermost slide bars  8 ,  10  are connected to each other by means of a bridging piece  33 . As a result, the slide bars move simultaneously. The central slide bar  9  is coupled to the outermost slide bar  8 . For this purpose, the bridging piece  33  is provided with an opening  34  accommodating a rocker arm  35 . This rocker arm  35  can be pivoted about a shaft  36  which is connected to the cylinder block  23 . Ends of the rocker arm  35  are provided with a fork  37 ,  38 . The slide bar  8  is provided with a pin  39 , and the slide bar  9  is provided with a pin  40 . The pin  39  is coupled to the fork  37 , and the pin  40  is coupled to the fork  38  of the rocker arm. By virtue of this construction, the central slide bar  9  always moves in the opposite direction relative to the outermost slide bars  8 ,  10 . The fingers  1 ,  2 ,  3  are each L-shaped and secured onto the slide bar by means of an adjusting screw  41 ,  42 ,  43 , which fits in elongated holes  44 ,  45 ,  46 , respectively, of one of the limbs of the fingers. This enables the fingers to be adjusted with respect to each other in the direction of the paths  4 ,  5 ,  6 , so as to adapt the distance between the fingers to the component  47  to be gripped. 
     The operation of the gripping device is as follows: The spring  31  presses the piston  25  to one side, in FIG. 3 the left side. By means of the fork-pin  26 - 27  construction, the outermost slide bars  8 ,  10  are also pressed to the left, while the central slide bar  9  is pressed to the right by means of the rocker arm construction  35 - 40 . The fingers  1 ,  2 ,  3  move in a corresponding direction, so that the component  47  can be clamped between the fingers. If, subsequently, compressed air is connected to the supply channel  32 , which exerts a greater pressure on the left side of the piston  25  than the pressure exerted on the right side of the piston by the spring  31 , then the piston will move to the right and the outer fingers  1 ,  3  will move to the left and the central finger  2  will move to the right, as indicated by means of an interrupted line. The component  47  is released. 
     In the above description of the operation of the gripping device, a component is gripped at the outer surfaces of the component. It is alternatively possible to grip a component or a specific accessory for a component at the inner surfaces. For this purpose, the position of the fingers on the slide bars is changed, as indicated by means of interrupted lines in FIG.  4 . The L-shaped fingers  1 ,  3  are rotated through 180° and secured onto the slide bar  8 ,  10 , at a location further to the left, while the L-shaped finger  2  is also rotated through 180° and secured onto the slide bar  9 , at a location further to the right. The movements of the fingers for gripping or releasing a component are the same as the movements described in the preceding paragraph. 
     Apart from a protective function, the cap  11  also has a stop function (see FIG.  5 ). When a component  47  is lifted up, an outer surface  48  of the component engages the wall  49  of the cap  11 . When the component is placed, for example, on a printed circuit board  50 , the component is clamped for a short period of time between the wall  49  of the cap and the surface  51  of the printed circuit board. Only then is the component released by the fingers, and subsequently the gripping device is moved away from the printed circuit board. In this manner, it is precluded that during placing a component on a printed circuit board, said component could still be moved by the moving fingers. 
     It is also possible to provide the gripping device with a built-in detection system by means of which it can be detected whether a component has been lifted up improperly or not at all. As indicated in FIG. 3 by means of an interrupted line, this may be achieved, for example, by providing an air suction channel  52  which extends to the space of the cylinder  24  where the spring  31  is situated, i.e. on the other side of the piston  25 , opposite to where the supply channel  32  is situated. The piston  25  is provided with a foil-like shut-off element  53  by means of which the suction channel  52  can be closed. In FIG. 3, a component  47  is gripped by the fingers. A vane closes the opening  54  of the suction channel. The partial vacuum in the suction channel does not have any effect on gripping the component. However, if there is no component, then the spring  31  presses the piston further to the left, so that the shut-off element  53  no longer closes the opening  54 . By means of a pressure measurement, it can be determined whether a component has been properly gripped, improperly gripped, or not gripped at all. The detection means for measuring a pressure difference are not shown in greater detail. These means are known per se.