Abstract:
A device for changing the rotational angle position of a pneumatic tire relative to a rim, on which the pneumatic tire is fitted to the rim, includes a manipulating device with a gripper adapted to be rotated by a positionable rotary drive mechanism and having radially adjustable gripper fingers with oppositely facing lift-off devices. Via the gripper it is possible to load a wheel into a clamping fixture, and following unseating of the tire beads from the clamped rim the pneumatic tire can be rotated relative to the rim through a computed angular difference.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Applicants claim priority under 35 U.S.C. §119 of German Patent Application No. 10 2010 017 031.3 filed May 19, 2010. 
     FIELD OF THE INVENTION 
     This invention relates to a device and a method for changing the rotational angle position of a pneumatic tire relative to a wheel rim, with the pneumatic tire being fitted to the rim and resting with its tire beads against seating surfaces of the rim. The device comprises a clamping fixture for holding the rim, a measuring device for measuring and storing the rotational angle position of markers on the rim and on the pneumatic tire, an evaluating and control unit which computes an angle of rotation, and a positionable rotary drive mechanism which is controllable by the evaluating and control unit. 
     DESCRIPTION OF PRIOR ART 
     Devices of the type referred to are used for lining the pneumatic tire up with the wheel rim, which is referred to as matching. Matching is a process used in tire fitting to optimize the true running properties of the wheel. In manufacture, markers referred to as match points are applied to the tires and the wheel rims to identify the extreme positions of the radial run-out measured. On the pneumatic tire the match point identifies the maximum of the first harmonic radial-force variation, and on the wheel rim the position of the radial run-out with the smallest radius. When the marker on the tire is lined up with the marker on the rim, the true-running properties of the wheel attain a favorable value. 
     In volume production of vehicle wheels, matching of tire and rim is performed if so required to satisfy the quality demands. To perform the matching operation, DE 10 2004 006 822 A1, for example, discloses a machine on which the rim of a fitted wheel is clamped by means of a clamping unit, the markers on tire and rim are sensed by a camera system, the tire beads are detached from the rim by forcing in the tire sidewalls, following which the rim is rotated through a calculated angle of rotation by means of the rotary clamping unit so that the markers on tire and rim lie on the same rotational angle position. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a device of the type initially referred to, which affords economy of manufacture, ease of integration into a facility for the mass production of vehicle wheels and which simplifies the matching-related conveying tasks. 
     According to the present invention, the device for changing the rotational angle position of a pneumatic tire relative to a wheel rim, in which the pneumatic tire is fitted to the rim and rests with its tire beads against seating surfaces of the rim, comprises a clamping fixture for holding the rim, a measuring device for measuring and storing the rotational angle position of markers on the rim and on the pneumatic tire, an evaluating and control unit which computes an angle of rotation, a positionable rotary drive mechanism which is controllable by the evaluating and control unit, and a manipulating device with a gripper movable relative to the clamping fixture and having radially adjustable gripper fingers, with the gripper fingers having oppositely facing lift-off devices for urging the tire beads away from the seating surfaces of the rim. 
     To change the rotational angle position of the pneumatic tire, it is possible with the device of the invention to load a wheel into a clamping fixture for holding the rim, to detach the tire by pushing off the tire beads after the rim is clamped and held in position, then to rotate the wheel and transfer it, for example, to an inflating station or an outgoing conveyer unit. On the other hand, it is also possible for the device of the invention to be used to advantage without applying the conveying function of the gripper when suitable conveying devices are present to load the wheel into, and unload it from, the clamping fixture. The device of the invention is simple because the movement functions of the gripper and the manipulating device are also utilized for performing the matching operation. 
     Advantageously, the clamping fixture is fixed in place and the rotary drive mechanism enables the gripper to be positioned relative to the manipulating device about a central axis. This permits a very simple configuration of the clamping fixture and the use of prior installed clamping fixtures which are not equipped with a positionable rotary drive mechanism. 
     The manipulating device may be a robot with a jointed arm movable about several axes and having the gripper arranged at is free end. Furthermore, the rotary drive mechanism designed to rotate the gripper may be arranged at the free end of the jointed arm. Alternatively, the gripper may be prevented from rotating about its central axis, and the clamping fixture may be rotatable and positionable by the rotary drive mechanism. The latter variant is advantageous when a manipulating device is used which is not equipped with a suitable rotary drive mechanism for rotating and positioning the gripper. 
     According to another proposal of the invention, the lift-off device may include rigid lift-off elements, with the gripper being movable up against the rim axially by means of the manipulating device for unseating a tire bead. This is a low-cost configuration using the movability and force of the manipulating device to advantage. 
     Furthermore, at least the lift-off devices arranged on one side of the tire may include lift-off elements movable up against the tire by means of actuators. The use of these movable lift-off elements not only enables a tire bead to be disengaged from the seating surface of the rim but also enables the tire, in cooperation with the lift-off elements, to be held locked against rotation on the opposite side of the tire in such a way that its rotational angle position relative to the gripper is not changed when the gripper or the rim is rotated. 
     In an advantageous embodiment, the gripper includes a body and at least two gripper arms movable radially to the central axis of the gripper, with the gripper arms being coupled to a synchronizing device which synchronizes the radial movement of the gripper arms. It is thereby ensured that the gripper, on opening and closing its gripper arms, does not alter its central position relative to the held wheel or tire, which simplifies the precise control of the gripper movement considerably. 
     The gripper fingers are preferably arranged at the free ends of movable gripper arms and include retaining plates arranged parallel to the central axis of the gripper and having portions configured for engagement with the tread of a pneumatic tire. According to the invention, the free ends of the retaining plates may include a bend which extends at right angles to the gripper centre and is provided with preferably rigid lift-off elements. 
     Moreover, the gripper fingers may include plates extending at a distance from the bends and parallel thereto in the direction of the gripper centre, with actuators and lift-off elements movable thereby being attached to said plates. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be explained in greater detail in the following with reference to one or more embodiments illustrated in the accompanying drawing. In the drawing, 
         FIG. 1  is a side view of a device of the invention including manipulating robot, gripper and clamping fixture; and 
         FIG. 2  is a sectional view of the gripper of the device of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The device shown in  FIG. 1  comprises a manipulating robot  1  and a gripper  2  movable thereby which is configured for gripping and holding pneumatic tires. The manipulating robot  1  is composed of a stationary base  3  on which a carousel  4  having a swivel  5 , an arm  6  and a robot hand  7  rotates about a vertical axis A 1 . The swivel  5  is mounted for rotation on the carousel  4  about a horizontal axis A 2 , and the arm  6  is mounted for rotation on the swivel  5  about a horizontal axis A 3 . The arm  6  is comprised of two parts which are rotatable relative to each other about an axis A 4  extending in the longitudinal direction of the arm  6 . The robot hand  7  is connected to the arm  6  for rotation about an axis A 5  extending transversely to the longitudinal axis of the arm  6 . The robot hand  7  has at its free end a flange  8  rotatable about an axis A 6 . All the axes A 1  to A 6  of the manipulating robot  1  are adapted to be driven by controlled servomotors. Integrated into the servomotors are brakes and resolvers for measuring the angle of rotation. The robot is equipped with a freely programmable controller by means of which each of the aforementioned axes is individually movable into any angular position and lockable therein. 
     The gripper  2  shown in  FIG. 2  in greater detail has a cruciform body  10  with four arms  11  extending radially outwardly from a central annular body  12 . Pivotally mounted on the radially outer ends of the arms  11  by means of rotary joints  13  are outer links  14  of gripper arms  15 . Gripper fingers  17  are pivotally mounted on the free ends of the links  14  by means of rotary joints  16 . The axes of the rotary joints  13  and  16  of each link  14  are parallel and extend tangentially relative to the central axis of the gripper  2  and in a radial plane. On the side of the links  14  facing the gripper centre, inner links  18  are arranged at a parallel distance thereto, which have one end connected to a gripper finger  17  by a rotary joint  19  while the other end is connected to an arm  11  by a rotary joint  20 . The distance between the rotary joints  19  and the axis of the rotary joints  16  equals the distance between the rotary joints  20  and the axis of the rotary joints  13 . Moreover, the relative distance of the rotary joints  19  and  20  is substantially equal to the relative distance of the axes of the rotary joints  13  and  16 . As a result, the links  14 ,  18  form a pivotal parallel guide by means of which the gripper finger  17  connected with the links maintains its predetermined orientation to the central axis of the gripper  2  when the gripper  2  is opened and closed. 
     Each of the gripper fingers  17  includes a retaining plate  21  aligned substantially parallel to the central axis of the gripper  2  and extending in a direction away from the axis of the rotary joint  16 . The retaining plate  21  has a studded portion  22  close to the axis for abutment with the tread of a pneumatic tire, and a portion  23  remote from the axis. The free end of the portion  23  is provided with a bend  24  extending at right angles towards the gripper center and carrying a plate-shaped lift-off element  25  extending towards the body. Formed on the mounting end of the retaining plate  21  is a seating surface  26  which extends radially inwardly and perpendicularly thereto and enables the gripper to take support upon a sidewall of a pneumatic tire. 
     Secured to the gripper fingers  17  in close proximity to the rotary joints  16 ,  19  are furthermore plates  27  which extend in the direction of the gripper centre and carry actuators  28  and lift-off elements  29  movable thereby in the direction of the lift-off elements  25 . The actuators  28  may be pneumatic cylinders, hydraulic cylinders or electrically powered linear motors. 
     To open and close the gripper it is necessary for the gripper arms  15  to be moved towards or from each other in synchrony. To produce this synchronous movement, a rotary disc  30  is provided which is mounted for rotation in the central opening of the annular body  12  by means of a four-point rolling-contact bearing  31 . The disc  30  is connected to each gripper arm  15  by a rod-shaped coupling member  32 . The coupling members  32  are of equal length, mounting on their ends joints  33 ,  34  having at least two degrees of freedom, in particular ball-and-socket joints. The joint  33  secures the coupling members  32  to the disc  30 . In this arrangement, the joints  33  are arranged at an angular distance of 90° and at the same distance from the axis of rotation of the disc  30 . The joints  34  secure the coupling members  32  to the outer links  14  at a distance from the axis of the rotary joints  13 . When the disc  30  is rotated, the coupling members  32  move in radial direction relative to the adjacent arms  11  of the body  10 , as a result of which the gripper arms  15  mounted on the arms  11  perform a pivotal movement in the corresponding direction. 
     In order to grip a wheel, the gripper  2  is moved to an open position by controlled rotation of the disc  30  by means of a servo drive mechanism not shown, in which position the relative distance of the oppositely facing lift-off elements  25  is greater than the outer diameter of the wheel&#39;s pneumatic tire to be gripped. Owing to the parallel guide of the gripper fingers  17 , the retaining plates  21  are aligned parallel to the gripper central axis, regardless of the opening position of the gripper  2 , so that they come to rest uniformly against the circumferential surface of the tire when the gripper  2  is closed. In order to bring the retaining plates  21  into contact with the tire, the servo drive mechanism rotates the disc  30  in the opposite direction. This causes the gripper arms  15  to move synchronously in the direction of the central axis of the gripper  2  until they reach a position in which the seating surfaces  26  and the retaining plates  21  make engagement with the portions  22  on the pneumatic tire. 
     The gripper  2  is arranged on the robot hand  7  in such a way as to enable it to be rotated relative to the robot hand  7  about its central axis congruous to axis A 6  and to be positioned at the correct angle of rotation with precise accuracy. To this effect, the annular body  12  of the gripper  2  is secured to the flange  8  of the robot hand  7 , which flange is movable by means of the servomotor arranged on the robot hand  7  into any desired angular position and can be locked in these positions. In this way it is possible for the gripper  2  to rotate a tire held by it about its axis of rotation into a specific angular position, rotating, for example, a match point marked on the tire into the same angular position which a match point occupies on the assigned rim. 
     A clamping fixture  36  for clamping a rim is shown in  FIG. 1  schematically. Arranged on a table  37  is a column-type post  38  mounting on its upper end a chuck  39  having radially movable jaws  40 . The chuck has on its upper side a seating surface  41  and a central locating mandrel  42  engaging in the rim hole. The jaws  40  are actuated by a pneumatic reciprocating cylinder arranged in the post  38  via an inner lying chucking wedge and engage the inner surface of the rim dish. 
     With the device described, the process referred to as matching can be performed by selectively changing the angular position of a pneumatic tire relative to the rim on which it is mounted as follows: 
     The wheel comprised of rim and pneumatic tire is initially loaded into a clamping fixture for clamping and holding the rim. The rim clamping fixture may involve a simple chuck having several elastically deformable plastic jaws pressed on the inside against the rim dish. It will be understood, of course, that other rim clamping fixtures may also be used, for example, of the type which clamp the rim in the centre hole. Loading the wheel into the clamping fixture may be performed by means of the gripper  2  and the manipulating robot  1 , but other loading devices, for example, a vertical step conveyer, may also serve this purpose. 
     Once the rim is held clamped, a measuring device, for example, a camera system, measures the position of the match points on tire and rim and calculates the angular difference between the match points by means of an evaluating and control unit. In cases where the wheel was previously loaded into the clamping fixture by means of the gripper  2 , it is necessary to remove the gripper  2  from the wheel for this measurement. 
     In the next step, the manipulating robot  1  guides the gripper  2  centrically above the wheel and in axial direction into a position in which the lift-off elements  25 ,  29  of the gripper  2  are outside the lateral boundary planes of the wheel. By synchronous movement of the gripper arms  15  and gripper fingers  17  in the direction of the gripper centre, the gripper is adjusted to the diameter of the rim such that the lift-off elements  25 ,  29  are spaced from the rim edge in a position suitable for lift-off. The gripper  2  is then moved by the manipulating robot  1  in an axial direction such that the body  10  of the gripper  2  moves a predetermined distance away from the wheel. This causes the rigid lift-off elements  25  to make engagement with the adjacent tire bead, urging it away from its seating surface on the rim. As soon as the lift-off position is reached, the gripper stands still, and the actuators  28  of the lift-off elements  29  are set in operation next. This causes the lift-off elements  29  to unseat the adjacent second tire bead from its seating surface on the rim. The pneumatic tire is then held solely by the gripper  2  with the aid of the lift-off elements  25 ,  29  and can therefore be rotated easily by means of the gripper  2 . 
     In the next step, the evaluating and control unit drives the servomotor in the robot hand  7 , and the gripper  2  is rotated about the angular difference previously calculated on account of the detected match points, so that after rotation both match points occupy the same angular position. With the gripper  2  in this position, the actuators  28  are reversed to return the lift-off elements  29  to their initial position. At the same time, the manipulating robot  1  moves the gripper  2  back into the initial position in which the rigid lift-off elements  25  are lifted clear of the pneumatic tire. For a subsequent check of the matching operation, the gripper  2  is reopened and removed from the wheel by the manipulating robot  1 . If the check measurement finds that the result of the matching operation is correct, the clamping fixture is released from the rim and the wheel is unloaded from the clamping fixture, which task may be performed by the gripper and the manipulating robot or any other conveying device. 
     The device described distinguishes itself by a straightforward and economical machine design which utilizes the functions of a manipulating robot of conventional construction, enabling the loading of the wheel into the matching station and the movement functions in the matching station to be performed with the same device, that is, the gripper moved by the manipulating robot. To clamp the rim, a simple clamping fixture without elaborate drive mechanism is sufficient, as it also finds application in tire fitting.