GB2052333A - Power tool with marking device - Google Patents

Abstract

A power tool comprises a motor, a drive shaft (3) rotatable by the motor and coupled to a torque sensor (6) input (5). A sensor output (6) is coupled to a wrench socket (10) for engaging a workpiece (12), and a marking punch (11) is operable in response to the torque in the drive shaft by actuation of a sensor coupled electrical circuit (14) to mark the workpiece when a predetermined torque load has been applied thereto. An electric arc or paint spray may provide the marking device. <IMAGE>

Description

SPECIFICATION Power tool This invention relates to power tools.

Power tools such as those used in production-line assembly of motor vehicles comprise a motor, which is usually driven pneumatically, and a drive shaft which is rotatable by the motor and which, in use, carries a tool for engaging a workpiece, for example a screwdriver or a socket for engaging a hexagonal vly-headed nut or bolt. In certain applications it is desirable to mark the workpiece to indicate that a predetermined operation has been performed on the .workpiece by the power tool. For example it may be desirable to mark certain nuts or screws in a motor vehicle when they have been tightened by the power tool to a predetermined torque. One known pneuma tically operated power tool of this type is provided with marking means for automatically marking the workpiece when the desired operation has been completed.In this equipment, the torque applied by the drive shaft is controlled by the pneumatic pressure fed to the Motor, and this pressure can be adjusted to produce a desired torque. When the applied pressure reaches the desired level, the drive shaft stops rotating. The resulting back-pressure in the pneumatic feed line for the motor is used to trigger the marking means which may, for example be in the form of a paint spray mounted on the tool.

The marking means thus produces a visible indica tion for quality control purposes that the required torque has been applied by the powertool.

Since the marking means is operable in response to a back-pressure in the pneumatic line, it is possible for the marking means to mark the work piece even though the desired torque has not been applied to it. For example a sudden reduction in the line pressure may cause the drive shaft to cease rotating, with the result that a back-pressure is built up in the tool sufficient to operate the marking means.

According to the present invention there is pro vided a power tool comprising a motor, a drive shaft rotatable by the motor and adapted to carry a tool for engaging a workpiece and marking means mounted on the tool for marking the workpiece when a predetermined operation has been performed on the workpiece, characterised in that the marking means is operable in response to the torque in the drive shaftto mark the workpiece when a predetermined torque load has been applied thereto.

Since the marking means operates directly in response to the torque load applied to the drive shaft, the pressure of a mark on the workpiece is a reliable indication that the required load has been applied to it.

The power tool motor may be operated electrical ly, but in the preferred embodiment of the invention, it is operated pneumatically.

The marking means may be of any suitable construction. For example it may include a paint spray, or a mechanical marker such as a stamp.

Alternatively the marking means may apply an electrical etch mark to the workpiece, eg. by momentarily generating an electrical arc between the tool and the workpiece.

Any suitable device may be used for sensing the torque in the drive shaft. For example the drive shaft may carry an electrical transducer which generates an electrical signal the strength of which alters in accordance with the torque in the drive shaft. This signal can then be used to trigger the marking means.

A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying schematic drawing which is an "exploded" view of a power tool in accordance with the invention.

Referring to the drawing, a pneumatically-drive, hand-held power tool 1 incorporates a conventional pneumatic motor which rotates a drive shaft in the tool. The drive shaft terminates in a coupling head 3 of square cross section which is received in a socket 4 in an input shaft 5 to a sensor unit 6. The sensor unit 6 incorporates an output shaft 7 which is driven by the input shaft 5. Within the sensor unit, the input and output shafts are connected together by a resilient coupling. Relative movement of the input and output shafts about their common axis of rotation 8 is detected by a transducer which generates an electrical signal the strength of which varies in accordance with the extent of the relative movement of the input and output shafts 5, 7.Since the relative movement of the shafts is directly proportional to the torque applied to the shafts, the electrical signal from the transducer will be representate of the torque in the output shaft 7.

The output shaft 7 terminates in a driving head 9 of square cross section upon which a tool 10, for example a socketfortightening hexagonally-headed nuts and bolts, may be mounted. The coupling head 3, and the input and output shafts 5 and 6 all define a passage which is coaxial with the axis of rotation 8 of the input and output shafts 5, 7. A punch 11 extends along the passage from the coupling head 3 and through the sensor unit 6 and projects into the tool 10 to lie adjacent the workpiece engaged by the tool 10, namely an hexagonally headed bolt 12. The punch 11 is reciprocable within the passage by means of pneumatic pressure applied to the end of the punch in the head 3.The application of pneumatic pressure to the punch 11 is controlled by a valve in the body of the power tool, the valve being electrically operable in response to a signal generated by an electrical control unit 14.

The control unit is arranged to receive the electrical signal from the sensor unit 6 and to generate an output signal to operate the valve controlling the punch 11 when the signal from the sensor unit 6 indicates thatthe torque in the shaft 7 has reached a desired value. The size of which may be selected by adjustment of the control unit 14.

In use, the control unit 14 is adjusted to trigger the punch 11 when a required torque is detected in the shaft 7. The tool 10 is then mounted on the shaft 7 and fitted over the head of the bolt 12. The power tool is then switched on, causing the head 3, and therefore the shafts 6 and 7 to rotate. As the bolt 12 is tightened, the torque applied by the power tool causes the input shaft 6 to rotate relative to the output shaft 7, generating an electrical signal which causes the control unit 14 to actuate the punch 11 when the torque reaches the predetermined level.

The punch 11 is then reciprocated axially into engagement with the bolt 12 impressing therein an identifying mark, as indicated at 15. The pressure of this mark can later be used during quality control to confirm that the bolt 12 has been correctly tightened.

Claims (4)

1. A powertool comprising a motor, a drive shaft rotatable by the motor and adapted to carry a tool for engaging a workpiece and marking means mounted on the tool for marking the workpiece when a predetermined operation has been performed on the workpiece, characterised in that the marking means is operable in response to the torque in the drive shaft to mark the workpiece when a predetermined torque load has been applied thereto.

2. A power tool according to Claim 1 wherein the motor is operable pneumatically.

3. A power tool according to Claim 1 or Claim 2 wherein the marking means is operable in response to an electrical signal generated by a transducer mounted on the drive shaft.

4. A power tool substantially as hereinbefore described and as illustrated in the drawing.