Method and device for position locked power tool operation for correction of unacceptable screw joint tightening results
View Patent ↗A method and a device are provided for locking the operation of a power wrench to the location of an unacceptably tightened screw joint or object with a sensor for at least one tightening parameter. A position sensing system is provided for indicating continuously the position of the power wrench during tightening operations, and a control unit includes a unit for comparing obtained tightening parameter values with predetermined limit values and to provide an OK or a NOK signal in response to those limit values being passed or not for each screw joint. A locking device is provided to lock the power wrench operation to the very position of the screw joint or the object for which a NOK signal has been issued until the unacceptably tightened screw joint has been attended to and the NOK signal is removed.
1. A control device for a power wrench arranged to prevent negligence of at least one unacceptably tightened screw joint on an assembled object, the power wrench comprising at least one operation parameter indicating unit, and the control device comprising:
a position sensing system configured to continuously indicate an actual multi-dimensional position of the power wrench during tightening of the at least one screw joint on the object to be assembled; and
a control unit configured to compare obtained operation parameter values indicated by said at least one operation parameter indicating unit at each tightening operation with predetermined operation parameter limit values, and to issue an OK or an NOK signal indicating whether or not a tightening result of each screw joint is acceptable depending on whether or not said limit values are passed for each screw joint;
wherein said control unit is configured to lock operation of the power wrench to an object position for which an NOK indicated screw joint tightening result has been indicated, and to enable the power wrench for tightening operations on other objects than the object position for which said NOK indicated screw joint tightening result has been indicated only when said NOK indication is removed.
2. The control device according to claim 1 , wherein said position sensing system comprises (i) an identity providing unit located on the power wrench and (ii) at least one stationary position scanning device connected to the control unit and arranged to communicate with said identity providing unit via wireless transmission.
3. The control device according to claim 2 , wherein said identity providing unit comprises an RFID tag.
4. The control device according to claim 3 , wherein the object is supported on a moving carrier of an assembly line, and the control unit is configured to compensate for movement of said carrier.
5. The control device according to claim 2 , wherein the object is supported on a moving carrier of an assembly line, and the control unit is configured to compensate for movement of said carrier.
6. The control device according to claim 1 , wherein said control unit is configured to lock the operation of the power wrench to a screw joint position or positions for which a NOK result has been indicated until the NOK indication has been removed.
7. The control device according to claim 6 , wherein the object is supported on a moving carrier of an assembly line, and the control unit is configured to compensate for movement of said carrier.
8. The control device according to claim 1 , wherein the object is supported on a moving carrier of an assembly line, and the control unit is configured to compensate for movement of said carrier.
9. The control device according to claim 1 , wherein said position sensing system comprises a movable arm connected to a stationary structure at one end thereof and to the power wrench at an opposite end thereof, and wherein said arm comprises one or more links interconnected by movable joints each provided with an angle sensor.
10. The control device according to claim 1 , wherein the at least one operation parameter indicating unit is configured to indicate at least one of a torque and an angle of a tightening operation of the power wrench on the at least one screw joint on the object to be assembled.
11. A method for ensuring correction of occurring non-acceptably tightened screw joints on objects to be assembled by utilizing a power wrench having at least one operation parameter indicating unit, and a position sensing system for indicating an actual position of the power wrench, the method comprising:
continuously indicating the actual position of the power wrench during tightening of the screw joints on the objects to be assembled;
providing a tightening result as indicated by the operation parameter indicating unit in terms of OK and NOK signals indicating whether or not the tightening result of each screw joint is acceptable in relation to predetermined tightening parameter limit values;
locking operation of the power wrench to an object for which an NOK indication for at least one screw joint of the object has been received, the operation of the power wrench being locked to a screw joint position or positions on the object for which the NOK indication has been received; and
enabling the power wrench for operation on other objects only when the NOK indication for the at least one screw joint of the object has been removed.
12. The method according to claim 11 , further comprising performing position indication via wireless communication between an RFID tag mounted on the power wrench and at least two stationary scanning devices.
13. The method according to claim 11 , wherein the tightening result indicated by the operation parameter indicating unit indicates at least one of a torque and an angle of a tightening operation of the power wrench on the at least one screw joint on the object to be assembled.