Power tool with torque sensing control means

The present invention relates to motor-driven tools and in particular to a motor-driven tool with torque-dependent shut-off for precise control of the output torque of the tool.

Of the many requirements that must be met in the case of power tools, used for the transmission of torque to threaded fasteners in mass production, e.g.₄ in car manufacturing and the like, the accuracy and conformity of the torque socket are most important. As a result, various types of control devices and systems have emerged in an effort to achieve a uniform traction of the fasteners in the production belt.

While many of the torque-dependent devices and systems which have hitherto emerged have been largely satisfactory for the intended purpose, others, for various reasons, have not. Some of these causes have consisted of non-uniform control of the tool's dynamic peak torque output, difficult and / or complicated setting of the tool torque output, lag of peak torque values ​​resulting in the occurrence of undesirable, high torque reaction forces against the operator, large tool size and tool size.

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The power tool of the present invention is e.g. a portable nutrunner comprising a housing body with a motor and drive means connecting the motor to a torque emitting device and a torque sensing means in the form of an electronic transducer which emits a torque dependent electrical signal to automatically switch off the motor when the torque reaches a certain value.

What characterizes the invention is that the transducer is completely enclosed in the housing body and comprises a substantially annular member with a part immovably connected to the housing body at one end, an intermediate portion receiving torsional forces and a part at the other end with a member movable under torque the drive means formed the drive transmission, said means being arranged to absorb the reaction force of the drive means, which is proportional to the torque delivered at said device, and transmits the reaction force to the intermediate portion, the torsion of which is converted into an electrical signal.

In one embodiment of the invention, the torque actuated member is formed as a ring gear with internal teeth coupled to the drive means, while the intermediate portion carries torsional strain sensors which emit the torque dependent electrical signal which is proportional to the torsional voltage in the intermediate portion.

Other features of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: Fig. 1 is a side view showing the overall construction and arrangement of the various parts of the power tool together with the torque control system of the present invention. Fig. 2 is a slightly enlarged, divided, longitudinal view, partly in section, of the power tool of Fig. 1, with certain parts omitted for convenience. FIG. 3 Fig. 4 is a cross-sectional view taken along line 3-3 of Fig. 2. Fig. 4 is a plan view showing the mounting arrangement of and the electrical circuits between the torsional strain gauges of the torque actuated member according to Figs. the invention. Fig. 6 is a longitudinal section of one of the gear housings of the tool and showing the arrangement for pulling the power cables from the gear housing through other parts of the tool and to the handle, and fig. 7-10 shows a series of partial views taken along lines 7-7, 8-8, 9-9 resp. 10-10 in Fig. 6.

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In summary, the present invention includes a power tool capable of applying precise torque to a threaded fastener so that a uniform tightening of a plurality of fasteners can be achieved.

Fig. 1 shows a motor-driven tool T comprising the features according to the invention. In the example given, the tool T consists of one nut tightener with a pneumatic motor as the drive motor. Compressed air is thus supplied to the tool T through an air hose 11 which comprises a braided hose part 12 and an extension part 13 connected to a remotely regulated source of compressed air. A transducer, which will be described in detail below, is stored in the tool T and provides an electrical signal proportional to the output torque of the tool. A torque setting device which contains the electrical circuit of the control system, and which will be described in more detail below, is generally designated A.

The control device A is connected to the tool T by means of a multi-conductor power cable, a part 14 of which extends between the device A and a socket 15 on a splice connection 16 in the air hose 11. A socket 17 is mounted in the box 15 for receiving a plug 18 at the end of the cable 14 . The cable 14 enters the interior of the air hose 11 at the connection 16 and then continues through the part 12 to the tool T. A T-sleeve 19 is connected to the upstream side of the splice connection 16 to provide an inlet for one end of an oil line 22. The other end of the line 22 is connected to a suitable oil system (not shown) which supplies certain quantities of oil to the air hose 11 to lubricate it. the pneumatic motor in the tool T. A coupling 24 is placed between the T-sleeve 19 and the part 13 of the air hose 11.

Referring to Fig. 2 in combination with Fig. 1, the tool T comprises a substantially cylindrical tool body 30 with a handle 31 attached to one end thereof and a torque socket in the form of a right-angled nut tightener 32 attached to the opposite end of the body 30.

The body 30 comprises a pneumatic motor 35 and consists of a cylinder block 36 which is enclosed in and supported by a sleeve-like housing 37. A rotor 38 is rotatably mounted in the cylinder block 36 and a plurality of radially extending, longitudinally located slots (not shown) are arranged in the rotor for mounting a plurality of vanes 42. The vanes 42 are rotated radially outwards in the rotor slots and are in fluid 7406363-7:

pressure-sealing engagement with the inner wall of the cylinder block 36 with respect to * draining air from the air supply passages in the body 30. Skövlar- | the 42 thus delimits chambers between them for receiving pressure;

air from an air passage in the handle 31. The compressed air flows into the chambers of the engine 35 through a pair of circumferentially extending, axially spaced slots (not shown) in the cylinder block 36, which air communicates. with the inlet slots through connecting passages in the cylinder block 36 and a plurality of intermediate axial bores 41 (Fig. 7) in an end plate 43. The end plate 43 also serves to support a bearing assembly 44 for the rear or right end of the rotor 38, according to Figs. .

i Air exits radially outwards from the chamber 35 of the engine through a series of circumferentially extending, axially spaced slots (not shown) in cy- | the side wall of the linder block 36 at a distance from the inlet slots. The exhaust air then enters a space 45 between the cylinder block 36 and the sleeve 37, from where it finds its way to an annular clearance 46 around a sleeve 47 which supports the opposite end of the cylinder block 37. The sleeve 47 also serves to store another bearing assembly 48 for the rotor 38. From the annular clearance 46, the exhaust air continues through a plurality of circumferentially spaced, axially extending channels 49 (Figs. 2 and 7) into a gearbox housing 50. The exhaust air then continues through the space between the gears in a second stage of a reduction gear, to be described later, and then to an annular chamber 51 in another gearbox 52 at the left end of the tool body 30 according to FIG. 2. The exhaust air in the chamber 51 exits to the atmosphere through at least one air outlet opening in the gearbox 52. In the present case, this outlet opening consists of a ring of perpendicular bores 53 in the member 52.

The winding path of the exhaust air described above, which ends at the ring provided with bores 53 in the gearbox 52, effectively dampens the sound level of the exhaust air, so that no additional muffler is required.

It follows that neither the size, weight nor the price of the tool T changes as a result of the air discharge arrangement described above.

In order to increase the torque that can be taken out of the motor 35, a reduction gear is provided. According to the invention, this comprises a two-stage planetary gear with teeth 54 on the left end according to fig.

on the rotor 38, which engage with a plurality of idle or planetary gears 55. In the present case, four idle gears 55 engage with the teeth 54 and are rotatably mounted on pins 56, supported in holes

7406363-7 bearing 57 on another shaft 58. A bearing assembly 59 is mounted in the sleeve 47 and serves to support the adjacent end of the holder 57. The idle gears 55 engage teeth with teeth 60 formed in the interior of an axial extension 62 of the gearbox 50. This is fixedly placed in the tool body 30 by means of a plurality of screws 64, which extend through openings in a two-part housing body 65, the construction and function of which will be described in more detail below.

The second stage of the planetary reduction gear includes teeth 68 on the shaft 58, which teeth with a plurality of planetary or idle gears 72 located on pins 73 attached to a carrier 74 on another shaft 76. Four circumferentially spaced idler gears 72 are supported by the carrier 74, which gears 72 engage with teeth 71 on the inside of an axially outgoing portion 75 of the gearbox 52 and includes a crown gear in the second stage of the planetary gear. The right end of the shaft 76 according to fig. 2 is supported by a bearing assembly 77 mounted in the gearbox 50. The left end of the shaft 76 is rotatably mounted in another bearing assembly 78, which is supported in an axially extending, circumferentially divided flange portion 79 of the gearbox 52. The opposite left end of the shaft 76, according to Fig. 2, is externally knurled at 82 for grouting with the input shaft 83 of the perpendicularly arranged nut tightener 32.

The nutrunner 32 comprises a housing 84 in which the input shaft 83 is rotatably mounted. A torque emitting device 86 is also rotatably guided in the housing 84 with the geometric shaft arranged perpendicular to the input shaft 83. Conical gears 87 and 88 on the shafts 83 and 8, respectively. 86 serves to transmit torque from shaft 83 to actuator 86.

The rectangular nutrunner 32 is releasably connected to the tool body 30 by means of a sleeve 92 which cooperates through threads with a flange 79 in the gearbox 52. Locking screws 93 are provided to prevent the sleeve 92 from being threaded off from the body 30.

It is clear that other types of fasteners, e.g. screwdriver or the like, can be attached to the body 30 of the tool T and driven by the shaft 76 instead of the nutrunner 32.

The handle 31 of the tool 10 consists of an extended part 102 which is releasably connected to the right end of the body 30, according to Figs. 1 and 2, by means of a threaded sleeve 103. The sleeve 103 is threaded on the right end of the engine cylinder 37. Setting marks (not shown) are provided to

7406363-7 show the correct orientation of the housing 102 in relation to the motor housing 37. The right end of the handle 31 according to Figs. 1 and 2 is threaded to receive a hose coupling 104 on the connecting part 12 of the air hose 11. through channels in the handle of a throttle valve 105 (Fig. 3). The throttle valve 105 comprises a cylindrical body 106 which is reversibly mounted in a bushing 107 and normally pressed to the closed position by means of a spring 108. The valve 106 is manually reversed to the open position by means of a lever 109 which is pivotally mounted in the housing 102 on a pin 112. Therefore, when the lever 109 is pushed downward by the operator to perform a torque operation, the valve body 106 is pressed downward in its bushing 107 and allows air under pressure from the air hose 11 to flow through the channels in the handle to a chamber 113 at the lower end of the valve body 106. through port openings (not shown) into the bushing 107 to a chamber 114 which communicates with a shut-off valve, generally designated 120 in Fig. 2.

The shut-off valve 120 comprises a control valve 121 and a shut-off valve part 122. The control valve 121 consists of a cylindrical valve body 123 which is reversibly mounted in a bore 124 in an elongate bushing 125. The bushing 125 is in turn mounted in a bore 126 in the handle housing 102, which bore extends across the axis of the housing 102. A pair of port openings 127 and 128 intersect the bore 124 and are axially offset relative to the axis of the bore. The communication between the port openings 127 and 128 is controlled by the upper larger diameter portion 131 of the valve 123, according to Fig. 2.

The control valve 123 is normally kept closed as in Fig. 2 by means of the coil spring 132 whose inner end abuts the valve and whose outer end abuts the inner surface of a housing 133 which is threaded on an extended part of the bushing 125. Opposite transverse bores 134 and 136 in the bushings 125, respectively, the housing 133 ensures the free movement of the valve 123 in its bore 124.

The upward movement of the valve 123 in its bore 124 to a position which allows communication between the port openings 127 and 128 is effected by means of a solenoid 140 located in a drill recess 142 in the end portion 143 of the bushing 125 opposite the end portion 137. The inner end 144 of the solenoid 140 is enclosed in a diameter, and a housing 146 is threaded onto the end portion 143 of the bushing 124 to close the bore 142 and provide dust protection.

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The piston 147 of the solenoid 140 according to Fig. 2 affects the lower end surface of the control valve 123 and has the purpose of moving the control valve upwards to provide communication between the port openings 127 and 128, when the solenoid 140 is activated. The power lines of the solenoid 140 are indicated by 152 and 153 in Fig. 2.

The sub-valve 122 of the shut-off valve 120 comprises a shut-off means 155 which is also cylindrical and which serves to regulate the communication between the chamber 114 and a substantially axially extending passage 156 in the handle housing 102. The passage 156 communicates with the plate 43 (Fig. 7) through the axial bore 41 and thus also with the inlet port openings in the engine block 36 of the engine 35, as previously described.

As shown in Fig. 2, the shut-off valve 155 is mounted in a bushing 157 located close to the bushing 125 of the control valve with the shaft parallel to the axis of the bushing 125. The shut-off valve 155 comprises a pair of spaced collars 162 and 163 of substantially the same outer diameter, and a reduced diameter connecting member 164 defines an annular space between them. The lower collar 163 of FIG. 2 is cup-shaped to allow a protruding portion or stop 167 on a plug 168 inserted into the housing 102 to extend into the collar 163 and cooperate with the inner end surface 166 of the cavity. The stop 167 thereby restricts the downward movement of the valve 155.

The upper part 172 of the bore in the bushing 157 according to Fig. 2 has a slightly larger diameter than the parts of the bore where the collars 162 and 163 are mounted, and a cup-shaped cover 173 is slidably mounted in the drill part 172 for co-operation with an upward or downward spindle. 174 on the valve collar 162. The arrangement is such that when the cover 173 and the valve 155 are inverted upwards to their full extent according to fig. 2, the collar 163 wants to prevent the compressed air in the chamber 114 from flowing through a ring of port openings 176 in the lower end of the sleeve 157 according to Fig. 2 and thus to the passage 156.

The shut-off valve 155 is kept in its open position according to Fig. 2 by the pressure in a chamber 177 partly formed by the outer or end surface 175 of the valve cover 173. Air with substantially the same pressure as in the chamber 114 communicates with the chamber 177 through a transverse bore 178 in the handle housing 102, and a connecting bore 179 having a sufficiently small diameter to prevent rapid airflow through the drill

7406363-7 .8 'ing 178 and into the chamber 177.

A short transverse bore Γ82 in the housing portion 180 of the shut-off valve 120 intersects a longitudinal bore 183 therein, one end of the bore 183 cooperating with the port opening 127 in the control valve portion 121._z and the opposite end of the bore 183 is closed by a threaded plug 184. The chamber 177 will thus be open to the atmosphere through the bores 182 and 183 and the port openings 127 and 128 in the control valve part, 121 when the control valve 123 is reversed to its open position by the solenoid 140. When this occurs, the rapid discharge of the compressed air from the chamber 177 to the atmosphere will cause the shut-off valve 155 to be rapidly reversed to its closed position, as a result of the pressure in the chamber 114 acting against the end surfaces of the collar 163. As a result, the compressed air flow to the engine 35 is shut off within a few milliseconds and the output torque of the engine is thereby reduced to substantially zero within the same amount of time.

The activation of the solenoid 140 of the shut-off valve 120 by current supply through the lines 152 and 153 is regulated by means of an electric current circuit in the torque setting device A (Fig. 1). Before the solenoid 140 is activated, however, a control signal of a certain size must be received by the device A. This signal, which is a function of the torque to be assigned to the output shaft 86 of the tool T, is transmitted from a transmission system in the tool T.

With reference to. Figs. 4-6 and also Fig. 2, the tool T comprises a torque sensing means in the form of a transducer 200, for generating a signal proportional to the output torque of the device 86. Such a signal affects circuits in the control device A for activating the solenoid 140 in the shut-off valve 120, for limiting a torque operation when the output torque at the shaft 86 reaches a dynamic peak value. The transducer 200 consists of a torsional force receiving intermediate portion 201, and at least one or preferably a plurality of torsionally actuated elements 202 for emitting a signal and placed on the intermediate portion 201.

The intermediate portion 201 in the present case consists of a ring^:formed, thin-walled portion of the gear member 52 between the crown gear 75 and the body portion of the member. Since the crown gear 75 and the thin-walled part 201 are made in one piece with the gear member 52, the thin-walled part 201 is subjected to the reaction torque from the crown gear 75 when the tool T is actuated.

7406363-7 as well. It follows that the intermediate portion 201 is rotated directly in proportion to the reaction torque imposed on the crown gear 75 and the torsional stress in the portion 201 will always be a direct function of the output torque at the shaft 86 and thus also the torque applied to a nut or other fastener connected to the shaft 86 .

The torsionally sensitive signal emitting elements 202 comprise at least one, and in the present case eight, wire strain sensors 211-218, Figs. 4 and 5.

Each of the wire elongation sensors 211-218 in the present example is preferably of the blade type and has a nominal resistance of 350 ohms plus or, minus 0.2% and an elongation factor of 2.095 plus or minus 0.5%.

According to an embodiment of the arrangement with the wire strain gauges 211-218, the outer periphery of the intermediate portion 201 is provided with eight flat surface parts 221-228 for mounting respective wire strain gauges. In other words, the intermediate portion 201 has an octagonal cross section, as shown in Fig. 4. The previously mentioned difference between the outer and inner peripheries of the portion 201 (octagonal and circular, respectively) provides a significant advantage in that the wall thickness of the portion 201 at the center of each of the flat surface portions 221-228 is thinner than at the corners of said surface portions. It follows that the largest torsional bending of the material 201 of the portion takes place at the center of the flat surface parts 221-228. This is desirable because the wire strain gauges 211-218 are located centrally on the surface portions 221-228.

It should also be noted that the wire strain gauges 211-218 are located on the surface portions 221-228 in such a way that their lines of maximum deflection are substantially parallel to the lines of maximum torsional stress of the material in the intermediate portion 201. In other words, the wire strain gauges 211-218 are oriented in 45 ° angle in relation to the axis of the intermediate portion 201.

The wire strain gauges are connected in one circuit with a Wheatstone bridge, the various branch lines of the network being connected to four contacts 231, 232, 233 and 234, respectively. Two pairs of tuning resistors 236 and 237 are connected in the sensor circuit to facilitate the calibration of the transducer 200, before it is connected with the tool.

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T, which will be described in more detail below.

The wire strain gauges 211-218 are attached to the flat, outer surface of the intermediate portion 201 by means of some conventional adhesive, e.g. by applying some adhesive to the flat surface and then placing the sensors on the same cover with successive layers of protective material.

After the wire strain gauges 211-218 are encapsulated, the gear member 52 is placed in a voltage tester and the voltage versus the torsional load of the transducer 200 is plotted. Any variations of the curve compared to a standard curve are then adjusted by setting the tuning resistors 236 and 237. The voltage tester is also used to check the torque marking in the window 235 of the device A, The sensitivity of the transducer 200 can be increased by milling or otherwise removing material from the inner surface of the portion 201.

After the transducer has been calibrated, the gear members 52 are inserted into the body 30 of the tool T according to Fig. 2 and fastened by means of the screws 64. The wires of the cable 14 are then connected to the contacts 231-234 by, for example, soldering.

The power cable 14 is passed through the interior of the tool T in the manner shown in Fig. 6 for the purpose of improving the safe operating properties of the tool and preventing the cable from being damaged. For this purpose, the cable 14 extends backwards or to the right in Figs. 2 and 6 from the gear member 52 between the outside of the parts 201 and 75 and the inner surface of the housing 65. The cable then extends through one of the axially extending semicircular recesses 49 (Fig. 6 and 10) in the periphery of the gear member 50.

From the gear member 50, the cable 14 extends into the space 46 between the outer periphery of the bearing sleeve 47 and the housing 65 and then passes through a bore 238 (Fig. 9) in the sleeve 47 and inwards from its right end surface according to Figs. 2 and 6. The bore 238 is aligned with another axially running bore 239 (Figs. 8 and 9) in the cylinder block 36 of the engine 35.

The cable 14 then extends through a drilled hole 242 in the engine end plate 43 from which the cable 14 passes through another axial hole 243 in the hollow end wall 244 of the handle housing 102. A sealing bushing 246 prevents the pressure fluid from escaping between the cable 14 and the hole 243.

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The outer or right end of the hole 243 communicates with the chamber 114 so that the cable 14 passes through this chamber and around the bushings 157 and 125 of the shut-off valve 120 in the manner shown in Fig. 2. The cable then continues through a further bushing seal 247 in the handle housing 102, before it enters the hose coupling 104 and the air hose 11.

The previously mentioned two-part construction of the housing 65 facilitates the assembly of the tool T and keeps its components in proper mutual position. The housing 65 also facilitates the attachment of the cable 14 wires to the connectors 231-234 in the transducer 200 during assembly and disassembly of the tool. It prevents the cable 14 from being subjected to stretching due to the mutual rotation between the different parts of the tool. The housing 65 thus includes a pair of semicircular members 247 and 248 (Figs. 1, 2 and 4), with radially inwardly extending flanges 249 and 250 at the opposite ends. The flanges 249 and 250 extend into annular grooves 251 and 252 in the gear member 52 and the motor housing 37, respectively, when the housing parts 247 and 248 are assembled. This assembly takes place by radially displacing the housing parts 247 and 248 to engage the other parts of the tool body 30 with a gripping cup movement, and fixing the parts by means of the screws 64. A similar movement is performed when the housing parts 247 and 248 are to be disassembled.

After the transducer 200 has been calibrated and the gear member 52 has been stored in the tool T according to the foregoing, the tool is ready for use. It is assumed that the compressed air source to which the air hose 11 is connected is adjusted and set to provide the required pressure in the tool T and provide the desired output torque at the shaft 86 during the turning operation. It was further assumed that the control device A was activated and set for the torque reading. The operation begins when the operator presses down the lever 108 to open the valve 106 in the throttle assembly 105 and thereby allow air to flow through the passages in the handle 31 to the motor 35 in the tool body 30. The air flow flows through the passages in the handle housing 102, through the throttle valve 105 and into the chamber 114 (Figs. 2 and 3), which extends around the control valve bushing 125 and communicates with the ring with inlet openings 176 in the shut-off valve bushing 157. The compressed air in the chamber 114 then flows through the inlet port openings 176 around the reduced diameter portion 164 of the shut-off valve 155 and then through the passage 156 to the inlet bore 41 (Fig. 7) in the engine end plate 43. The air then enters the chambers of the engine 35 to drive

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this and cause the rotation of the rotor 38. The torque socket from the shaft 38 is increased by the two-stage planetary reduction gear 54, 55, 62 and 68, 72, 75. The torque socket from the second stage in the planetary gear is transmitted by the shaft 76 to a torque bracket connected to the tool body 30, in this case the right-angled nut tightener 32.

The drive from the shaft 76 takes place through grooves 82 on its outer or left end according to Fig. 2, Over an input shaft 83 in the bracket 32, conical.

gears 87 and 88 and then to the socket shaft 86.!

As the tightener to which the tool T is attached increases the tightening, the reaction force in the power transmission mechanism, including the crown gear 75 in the gear member 52, will increase. Such a torque reaction causes a certain torsional deformation of the intermediate portion 201 in the transducer 200, which deformation is directly proportional to the torque socket at the shaft 86. The torque deformation of the portion 201 causes a change of the resistance of the wire strain gauges 211-218. This resistance change is sensed in the circuit of the wire strain sensors in the device A and results in a control signal which serves to activate another circuit in the device A to generate a current supplied to the solenoid 140 in the shut-off valve 120, when the torque at shaft 86 reaches a certain dynamic peak value. The activation of the solenoid 140 causes the control valve 123 to be moved rapidly upwards in its bore 124, = according to Fig. 2. It follows that the door openings 127 and 128 are caused to | communicate so that the compressed air in the chamber 177 ΐ of the shut-off valve 122 exits to the atmosphere through the bores 182 and 183 in the shut-off valve housing 180. The venting of the chamber 177 allows the air in the chamber 114 to act only on the end portions of the collar 173 in the shut-off valve 155, so that it is quickly reversed upwards in the bushing 157 to a position which prevents further flow of compressed air to the outlet passage 156 in the handle 31. This stops the tool T motor 35 immediately. This rapid shut-off of the air flow to the engine 35 prevents any torque kickback through the handle 31 to the operator.

Assuming that the dynamic peak torque applied to the tightener remains within permissible limits, the operator only needs to remove the tool from the tightener and then release the throttle lever 109 so that it is moved to the position in Figs. 1 and 3. When the lever 109 is moved to this position, the piston 254 (Figs. 1 and 3) is reset by the switch 255 in a control circuit to its closed position. The switch 255 is connected by a pair of wires 256 and 257, respectively

7406363-7 ka may be part of the cable 14, to the circuit of the control device A. This circuit interrupts the current to the solenoid 140 of the shut-off valve 120. It follows that the control valve 123 is reversed to the position in Fig. 2, so that the chamber 177 is no longer vented to the atmosphere. The pressure is rebuilt in the chamber 177 as a result of draining air to the same through the passages 178 and 179, and the shut-off valve 155 is then moved to its open position according to fig. 2, after which the tool T is ready for a new operation.

For periodic checking of the precision of the torque stroke on the screen 235 while the tool is in operation and after assembly, a locking arrangement is provided for temporarily locking the rotor 38 of the motor 35, so that the tool can be placed in a voltage tester analyzer and a known load applied to the shaft 86 to check the torque deflection of this load on the screen 235. This locking arrangement in the present case comprises a radial bore 262 (fig. 2) in the side wall of the motor housing 37 and a coaxial bore in the side wall of the cylinder block 36. These bores 262 and 263 allow a suitable locking in that a pin or a rod (not shown) can be inserted through them and into one of the chambers between a pair of the vanes 42 of the motor 35. The rotor 38 will thereby be locked against rotation and a known load can be applied to the shaft 86 by the voltage tester. If the curve on the screen 235 does not coincide with the torque supplied from the voltage tester, the curve can be corrected by means of a trimming potentiometer (not shown) in the device A.

After the curve on the screen 235 has been adjusted to correspond to the known load applied to the shaft 86, the tool T is ready to be used again. The opposite holes 262 and 263 can be closed by means of stop screws 264 when not in use.

When the tool T is to be used in a production series where a central computer is used to control additional tools in the series, the control device A can be simplified by eliminating the torque control screen 235 and circuits other than those required to provide an analog signal.

It is clear that while the present invention has been described in connection with a tool T driven by a pneumatic. motor as a power source, the torque sensing and regulating construction according to the invention is also useful in connection with electric motor driven tools. Such devices are therefore accommodated within the scope of the invention.