Tyre changing apparatus for demounting and mounting a tyre of a vehicle wheel

Abstract

A tyre changing apparatus (1) for demounting and mounting a tyre relative to a respective rim of a vehicle wheel (2) includes: a frame (10); a chuck (11) rotating about an axis of rotation (A); a working tool (12), connected to the frame (10) and movable towards and away from the chuck; an electric motor (13), imparting to the chuck (11) a rotation speed and a working torque; a controller (14), including a power unit (141) supplying voltage and current as a function of a drive signal (101); a processing unit (142) generating the drive signal (101) and programmed to derive a control parameter (102) representing the working torque delivered to the electric motor (13) and to apply a torque-limiting function responsive to the control parameter (102). The processing unit (142) derives an activation parameter and, as a function of the activation parameter, enables and disables the torque-limiting function.

Claims

1. A tyre changing apparatus for demounting and mounting a tyre relative to a respective rim of a vehicle wheel comprising: a frame; a chuck, connected to the frame to rotate about an axis of rotation and connectable to the wheel to entrain it in rotation; a working tool, connected to the frame and movable towards and away from the chuck to interact with a bead of the tyre; an electric motor, connected to the chuck to apply a rotation speed and a working torque to the chuck; a controller configured to control the electrical motor, the controller receiving an electrical power input including: a power unit, wherein the power unit is powered through the electrical power input and delivers to the electric motor a supply voltage and a supply current as a function of a drive signal; a processing unit wherein the processing unit generates the drive signal and is programmed to: i) derive a control parameter, the control parameter representing the working torque applied by the electric motor, ii) set a torque-limiting function as a function of the control parameter, wherein the torque-limiting function prevents the electric motor from applying a working torque that is higher than a threshold value, wherein the processing unit includes an activated configuration, wherein the torque-limiting function is enabled, and a deactivated configuration, wherein the torque-limiting function is disabled, iii) derive an activation parameter and, iv) responsive to the activation parameter, commute between the activated configuration and the deactivated configuration.

2. The apparatus according to claim 1, wherein the activation parameter is associated with the rotation speed of the electric motor.

3. The apparatus according to claim 2, wherein the processing unit is programmed to enable the torque-limiting function when the activation parameter reaches or exceeds a threshold value representing an activation speed.

4. The apparatus according to claim 2, wherein the processing unit is programmed to derive the activation parameter as a function of a supply voltage frequency of the electric motor.

5. The apparatus according to claim 2, comprising a speed sensor, configured to detect a speed signal, representing the rotation speed of the electric motor, wherein the processing unit is configured to derive the activation parameter as a function of the speed signal.

6. The apparatus according to claim 1, comprising a control device which can be operated by a user to send control signals to the controller and wherein the controller is configured to generate the drive signals in response to the control signals.

7. The apparatus according to claim 1, wherein the processing unit is programmed to switch to the disabled configuration when a disable condition is reached.

8. The apparatus according to claim 7, wherein the disable condition is met by the rotation speed of the electric motor and includes resetting the rotation speed of the electric motor or changing the rotation direction of the electric motor.

9. The apparatus according to claim 1, wherein, for values of working torque greater than or equal to the threshold value, the processing unit, in the activated configuration, is programmed to generate the drive signal in such a way as to instruct the power unit to keep the working torque at a value that is constant at the threshold value.

10. The apparatus according to claim 1, wherein the processing unit is programmed to apply an additional torque-limiting function in order to prevent the electric motor from delivering a working torque that is higher than an additional threshold value, which is greater than the threshold value for the working torque.

11. The apparatus according to claim 1, wherein the activation parameter is representative of a control device selection among a plurality of control devices or is representative of an operative position of the control device, selected among a plurality of possible operative positions of the control device.

12. The apparatus according to claim 1, wherein the controller is configured to drive the electric motor to rotate at a first predetermined rotation speed and at a second predetermined rotation speed, respectively, the second rotation speed being higher than the first rotation speed, wherein the torque-limiting function is enabled responsive to selecting the second rotation speed.

13. The apparatus according to claim 12, comprising a first pedal and a second pedal, connected to the controller to set the first rotation speed or the second rotation speed, respectively.

14. The apparatus according to claim 12, comprising a pedal operable in a first operating position and in a second operating position, wherein the controller sets the first rotation speed or the second rotation speed, responsive to an operation of the pedal in the first operating position or in the second operating position, respectively.

15. The tyre changing apparatus according to claim 1, comprising a torque sensor, the torque sensor detecting a working torque of the chuck and being set up to send to the processing unit a control signal, wherein the processing unit determines the control parameter as a function of said control signal.

Description

(1) These and other features will become more apparent from the following detailed description of a preferred, non-limiting embodiment, illustrated by way of example in the accompanying drawings, in which:

(2) FIG. 1 illustrates a tyre changing apparatus to mount and demount a tyre relative to a corresponding wheel rim according to this disclosure;

(3) FIG. 2 schematically illustrates (at least part of) the tyre changing apparatus of FIG. 1:

(4) FIGS. 3A and 3B illustrate, respectively, a first and a second example of a characteristic curve of an electric motor of the apparatus of FIG. 1;

(5) FIGS. 3C, 3D and 3E illustrate characteristic curves of an electric motor of the apparatus of FIG. 1, according to a further example;

(6) FIG. 4 schematically illustrates a plurality of characteristic curves of an electric motor for different combinations of supply voltage amplitude and frequency of the electric motor;

(7) FIG. 5 schematically illustrates the steps of mounting and demounting a tyre relative to a corresponding wheel rim.

(8) With reference to the accompanying drawings, the numeral 1 denotes a tyre changing apparatus for mounting and demounting a tyre relative to a corresponding rim of a wheel 2. The apparatus 1 comprises a frame 10, which supports the apparatus 1 in a workroom. In an embodiment, the frame 10 comprises a first supporting member (a first structure) 10A and a second supporting member (a second structure) 10B.

(9) It should be noted that the embodiment illustrated represents an apparatus for mounting and demounting a tyre relative to a corresponding rim of a wheel 2 of a motorcar but without any intention of thereby excluding application of this disclosure to apparatuses for mounting and demounting a tyre relative to a corresponding rim of a wheel 2 of a heavy vehicle, such as a truck or a semitrailer.

(10) The first supporting member 10A rests on the floor, whilst the second supporting member 10B, which may be, for example, a supporting column, is mounted to the first supporting member 10A along a direction which may be parallel or perpendicular to the weight force.

(11) The apparatus 1 comprises a chuck 11. The chuck 11 is connected to the first supporting member 10A. The chuck 11 is configured to rotate about an axis of rotation A relative to the first supporting member 10A. The axis of rotation A is preferably parallel to the direction of the weight force but may, in some configurations of the apparatus 1, be perpendicular to the direction of the weight force.

(12) In an embodiment, the chuck 11 is movable on the first supporting member 10A along a direction of adjustment, perpendicular to the axis of rotation A.

(13) In an embodiment, the chuck 11 is connectable to the wheel 2 to entrain it in rotation about the axis of rotation A. The chuck 11 comprises a locking element, configured to engage the rim of the wheel 2 to lock it in rotation to the chuck 11.

(14) In an embodiment, the apparatus 1 comprises a tool 12.

(15) The tool 12 is configured to come into contact with the tyre of the wheel 2 to allow the apparatus to be mounted or demounted to or from the respective rim of the wheel 2. For this purpose, the tool 12 is movable towards and/or away from the wheel 2 (from the rim of the wheel 2), preferably along a direction parallel to the axis of rotation A.

(16) The tool 12 may be, for example, a demounting tool (preferably having the shape of a claw) 12, configured to engage a tyre bead or a bead breaker 12, configured to come into contact with the tyre sidewall.

(17) In an embodiment, the apparatus 1 comprises an operating arm 18, connected to the tool 12 and to the second supporting member 10B to support the tool 12 during mounting and demounting operations.

(18) In an embodiment, the operating arm 18 is movable on the second supporting member 10B along a direction parallel to the axis of rotation A to move the tool 12 towards and/or away from the wheel 2.

(19) In an embodiment, the apparatus 1 comprises an electric motor 13. The electric motor 13 preferably runs on alternating current power but, in some embodiments, a direct current power supply is also possible. The electric motor 13 is connected to the chuck 11 to impart a rotation speed and a working torque to it. In an embodiment, the electric motor 13 comprises a gear motor configured to vary (adapt) the rotation speed and working torque.

(20) The electric motor may be disposed (contained) inside the first supporting member 10A or it may be outside of it. In some embodiments, the apparatus 1 comprises a transmission system (for example, a belt and/or a gear train), configured to transmit rotation and torque from the electric motor 13 to the chuck 11.

(21) In an embodiment, the electric motor comprises a controller 14. In an embodiment, the controller 14 is an inverter, configured to control the electric motor 13 by varying the power supply parameters.

(22) The power supply parameters (of the motor) include one or more of the following parameters: supply voltage; supply voltage frequency; intensity of a supply current.

(23) In an embodiment, the controller 14 comprises a power unit 141. In an embodiment, the controller 14 comprises a processing unit 142. The power unit is configured to receive electric power 100 from an external power supply: for example, mains or battery.

(24) The power unit 141 is configured to condition the electric power 100 received and to deliver electric power having a supply voltage and a supply frequency. The power unit 141 is configured to deliver electric power having a supply voltage and a supply current as a function of a drive signal 101.

(25) In other words, in an embodiment, the power unit 141 controls electrical power components (for example, power transistors or switches) as a function of the drive signal 101 in such a way as to condition the electric power 100 and to deliver the required supply voltage and supply frequency to the electric motor 13.

(26) With reference to FIG. 4, note, for example, how a characteristic curve of the motor varies with the variation of the supply voltage (amplitude) and the supply voltage frequency (the curve shows the different types of control that can be implemented). The graph can be divided into two zones: a first zone, corresponding to a rotation speed that is higher than a preset rotation speed, where the frequency increases with the resistant load, while the amplitude of the supply voltage remains constant; a second zone, corresponding to a rotation speed that is lower than the preset rotation speed, where the working torque is maintained at the maximum deliverable value, keeping a constant ratio between the supply voltage amplitude and the supply frequency.

(27) In an embodiment, the processing unit 142 is configured to generate the drive signal 101.

(28) The processing unit 142 is configured to derive a control parameter 102. The control parameter 102 is a parameter by which the processing unit 142 performs feedback control to set the power supply parameters of the electric motor 13. In an embodiment, the control parameter 102 represents the working torque. In an embodiment, the control parameter 102 represents the resistance torque. In an embodiment, the control parameter 102 represents the rotation speed or any quantity to be controlled by feedback.

(29) In an embodiment, the apparatus 1 comprises a control device 17. The control device 17 is configured to send control signals 104, entered by a user, to the processing unit 142.

(30) In an embodiment, the control signal 104 represents a rotation speed of the electric motor 13.

(31) The processing unit is configured to generate the drive signal 101 as a function of the control parameter 102 and/or as a function of the control signal 104.

(32) In an embodiment, the control device 17 comprises a first control element. The first control element may be a first pedal 17A, for example. In an embodiment, the control device 17 comprises a second control element. The second control element may be a second pedal 17B, for example. According to an aspect of this disclosure, the first pedal 17A is configured to be operated by a user to send a first set of control signals to the processing unit 142. The processing unit 142 is configured to generate the drive signal 101 as a function of the first set of control signals, to control the motor according to a first working curve L1, having a first maximum rotation speed ?.sub.1max. The second pedal 17B is configured to be operated by a user to send a second set of control signals to the processing unit 142. The processing unit 142 is configured to generate the drive signal 101 as a function of the second set of control signals, to control the motor according to a second working curve L2, having a second maximum rotation speed ?.sub.2max. In an embodiment, the second rotation speed ?.sub.2max is higher than the first maximum rotation speed ?.sub.1max.

(33) In other embodiments, the control device 17 may also comprise a single control element: for example, a single pedal. In these embodiments, the single pedal includes a plurality of operating positions. Depending on the operating position of the single pedal, the control device is configured to send to the processing unit 142 respective control signals, as a function of which the processing unit 142 generates the drive signal. The electric motor 13 is therefore operated according to the first working curve L1 at a first operating position of the single pedal and according to the second working curve L2 at a second operating position of the single pedal.

(34) In an embodiment, the control device 17 is configured to adjust a rotation direction of the chuck. More specifically, in an embodiment, the control device 17 is configured to instruct the chuck to rotate in a first rotation direction. For example, but with no limitation of scope implied, the chuck rotates in the first rotation direction when the pedal is raised. In an embodiment, the control device 17 is configured to instruct the chuck to rotate in a second rotation direction. For example, but with no limitation of scope implied, the chuck rotates in the first rotation direction when the pedal is pressed down.

(35) In an embodiment, the processing unit 142 is configured to run a transient by which the rotation speed changes from the first maximum rotation speed ?.sub.1max to the second maximum rotation speed ?.sub.2max. More specifically, during the transient, the processing unit 142 is configured to operate the chuck at the first maximum rotation speed ?.sub.1max for a predetermined length of time and to then automatically bring the speed up to the second maximum rotation speed ?.sub.2max.

(36) In an embodiment, the processing unit 142 is programmed to apply a torque limiting function. In other words, the processing unit 142 is programmed to generate the drive signal 101 in such a way as to prevent the working torque from exceeding a threshold value C.sub.s. The processing unit 142 is programmed to apply the torque-limiting function as a function of the control parameter 102. In short, the processing unit 142 is programmed to check that the control parameter remains below a value corresponding to the threshold value C.sub.s of the working torque. For example, the processing unit 142 is configured to compare the value of the intensity of the supply current (which may be measured on a shunt resistor in series with the electric motor) with the current value corresponding to the threshold value C.sub.s, which corresponds to the working torque not to be exceeded. In other embodiments, the apparatus comprises a torque sensor 15. The torque sensor 15 is configured to detect a working torque of the chuck. In an embodiment, the torque sensor 15 is configured to detect a working torque directly at the electric motor, thus avoiding measurements affected by the efficiency of the gear motor. The torque sensor 15 is configured to send to the processing unit 142, a control signal 102, as a function of which the processing unit determines the control parameter 102.

(37) In an embodiment, the processing unit 142 can be switched between an activated configuration, in which the torque-limiting function is enabled, and a deactivated configuration in which the torque-limiting function is disabled. In other words, the processing unit 142 is programmed to apply a conditional torque limiting function, that is to say, a torque limiting function that is enabled only if an activation condition is met.

(38) In an embodiment, the processing unit 142 is configured to derive an activation parameter. In an embodiment, the processing unit 142 is programmed to switch as a function of the control parameter 102. In an embodiment, the processing unit 142 is in the activated configuration when the activation parameter meets the activation condition.

(39) In an embodiment, the activation parameter represents the rotation speed of the electric motor 13. In an embodiment, the processing unit 142 is programmed to derive the activation parameter as a function of the rotation speed of the electric motor 13. In an embodiment, the processing unit 142 is programmed to derive the activation parameter as a function of the supply voltage frequency of the electric motor 13.

(40) In short, in the preferred embodiment, the processing unit 142 is programmed to access the value of the supply voltage frequency, as a function of which it is programmed to derive the activation parameterfor example, the corresponding rotation speed of the electric motor 13. Lastly, the processing unit 142 is programmed to process the rotation speed of the electric motor 13 to check that it meets the activation condition.

(41) In an embodiment, the activation condition is met when the activation parameter reaches or exceeds a threshold value. In an embodiment, the activation condition is met when the rotation speed of the electric motor 13 reaches or exceeds an activation speed ?.sub.s.

(42) In an embodiment, the processing unit 142 is programmed to derive the activation parameter by processing an enable signal (that is, a signal used by the processing unit to derive the activation parameter) received from a sensor of the apparatus 1.

(43) To obtain the enable signal, the apparatus 1 comprises a speed sensor, configured to detect a signal representing the rotation speed of the chuck.

(44) In an example embodiment, the apparatus 1 comprises a (first) speed sensor 16, configured to detect the rotation speed of the electric motor 13 (upstream of the gear motor) and to generate a corresponding speed signal 103. The speed sensor 16 is configured to send the speed signal 103 to the processing unit 142. In an embodiment, the speed sensor 16 may be an encoder.

(45) In an example embodiment, the apparatus 1 comprises a (second) speed sensor 16, configured to detect the rotation speed of the chuck (for example, an encoder associated with the chuck 11) and to generate a corresponding (second) speed signal 103.

(46) The processing unit 142 is programmed to derive the activation parameter as a function of the speed signal 103 and/or 103 received from the speed sensor 16 and/or 16.

(47) In an embodiment, the processing unit 142 is programmed to switch to the disabled configuration when a disable condition is reached by the apparatus 1. In an embodiment, the processing unit 142 is programmed to switch to the disabled configuration when a disable condition is reached by the activation parameter. In an embodiment, the processing unit 142 is programmed to switch to the disabled configuration when a disable condition is reached by the rotation speed of the electric motor 13. In an embodiment, the disable condition is met when the electric motor 13 switches off (rotation speed of the chuck 11 is zero) or when the rotation direction of the motor 13 is reversed. In other embodiments, the disable condition can be obtained by operating or not operating a dedicated control with which the user can switch the processing unit 142 between the activated configuration and the deactivated configuration.

(48) It should be noted that in some embodiments, the apparatus 1 comprises a resetting element. The resetting element is programmed to send a reset signal to the processing unit 142. In some embodiments, the processing unit 142 is programmed not to switch to the activated configuration until after receiving the reset signal. This embodiment is just an example of how a resetting procedure can be implemented. In effect, in other embodiments, the disable condition also causes automatic resetting of the apparatus 1 which is thus made ready to switch to the activated configuration once again. In an embodiment, the apparatus is equipped with a signalling device for indicating to the user the activated/deactivated configuration state. In an embodiment, the signalling device is an optical device, such as a flashing light, for example; in another embodiment, the signalling device is an acoustic device.

(49) In an example embodiment, the processing unit 142 is configured to apply an additional torque limiting function. In other words, the processing unit 142 is programmed to generate the drive signal 101 in such a way as to prevent the working torque from exceeding an additional threshold value C.sub.s. In an embodiment, the additional threshold value C.sub.s is the value of the maximum torque deliverable by the electric motor 13. The processing unit 142 is programmed to apply the additional torque-limiting function as a function of the control parameter 102. In short, the processing unit 142 is programmed to check that the control parameter 102 remains below a value corresponding to the additional threshold value C.sub.s of the working torque. In an embodiment, the additional threshold value C.sub.s is greater than the threshold value C.sub.s.

(50) According to one aspect of it, this disclosure provides a method for mounting or demounting a tyre to or from the respective rim of a wheel 2.

(51) The method comprises a step of preparing a frame 10.

(52) The method comprises a step F1 of locking the wheel 2 to a chuck 11 of the frame 10. The method comprises a step F2 of rotating the chuck 11 about an axis of rotation A by means of an electric motor 13. In the step of rotating, the electric motor 13 imparts a rotation speed and a working torque to the chuck 11.

(53) The method comprises a step F3 of moving a (working) tool 12 towards and/or away from the chuck 11, preferably along a direction parallel to the axis of rotation of the chuck 11. The tool 12 moves towards the tyre to interact with it, in particular to engage the tyre bead or to press against the sidewall of the tyre to break the bead. The tool can come into contact with the tyre when the electric motor 13 is stationary as well as when it is set in rotation.

(54) The method comprises a step F4 of feeding the electric motor 13. In the step of feeding the electric motor, a controller 14 delivers a supply voltage and a certain supply frequency to the electric motor 13. The controller 14 receives electric power 100 from the mains from an external power source.

(55) The step F4 of feeding comprises a step F42 of generating a drive signal 101 through a processing unit 142 of the controller 14. The drive signal 101 is sent to a power unit 141 of the controller 14, which conditions the electric power 100 as a function of the drive signal 101 in order to obtain the required supply voltage and current.

(56) In an embodiment, the step F4 of feeding comprises a step F41 of delivering the supply voltage and supply voltage frequency of the electric motor 13 as a function of the drive signal 101.

(57) In an embodiment, the step F4 of feeding comprises a step of deriving a control parameter 102. Through the control parameter 102, the processing unit 142 performs a feedback control to generate the drive signal 101 and to set power supply parameters (supply voltage frequency, supply voltage and electric current) of the electric motor 13. In an embodiment of the method, the control parameter 102 represents the working torque and/or the rotation speed or any quantity to be controlled by feedback.

(58) In an embodiment, the method comprises a step F6. of controlling. In the step F6 of controlling, a control device 17 sends a control signal 104, entered by a user, to the processing unit 142. Preferably, the control signal 104 represents a rotation speed of the electric motor 13.

(59) In the step of generating the drive signal 101, the processing unit generates the drive signal 101 as a function of the control parameter 102 and/or as a function of the control signals 104.

(60) In an embodiment, in the step F6 of controlling, a first control element 17A of the control device 17 is operated by a user and sends a first set of control signals to the processing unit 142. In an embodiment, in the step F6 of controlling, a second control element 17B of the control device 17 is operated by a user and sends a second set of control signals to the processing unit 142. In an example embodiment, the processing unit 142 generates the drive signal 101 as a function of the first set of control signals, to control the electric motor 13 according to a first working curve L1, having a first maximum rotation speed ?.sub.1max.

(61) In an embodiment, the processing unit 142 generates the drive signal 101 as a function of the second set of control signals, to control the electric motor 13 according to a second working curve L2, having a second maximum rotation speed ?.sub.2max. In an embodiment, the second rotation speed ?.sub.2max is higher than the first maximum rotation speed ?.sub.1max.

(62) In an embodiment, in the step F6 of controlling, a single pedal of the control device 17 is moved between a plurality of operating positions. For each operating position, the single pedal sends a respective set of control signals, corresponding to respective working curves of the electric motor. The electric motor 13 is therefore operated according to the first working curve L1 at a first operating position of the single pedal and according to the second working curve L2 at a second operating position of the single pedal.

(63) In an example embodiment, the single pedal has a third operating position, at which the electric motor 13 is driven in the direction opposite to that of the first working curve L1.

(64) In an embodiment, the method comprises a step F43 of limiting torque. The processing unit 142 generates the drive signal 101 in such a way as to prevent the working torque from exceeding a threshold value C.sub.s. The processing unit 142 limits the working torque as a function of the control parameter 102. In the step of limiting torque, the processing unit 142 checks that the control parameter remains below a value corresponding to the threshold value C.sub.s of the working torque. For example, the processing unit 142 compares the value of the intensity of the current (which may be derived in real time from the drive signal) with the threshold value C.sub.s, which corresponds to the working torque not to be exceeded.

(65) In other embodiments, the method comprises a step F51 of detecting a control signal, where a torque sensor 15 detects a control signal 102 representing the working torque of the chuck 11. The torque sensor 15 sends to the processing unit 142, a control signal 102 used by the processing unit to determine the control parameter 102 (and thus to generate the drive signal 101).

(66) In an embodiment, the method comprises a step F7 of switching. In the step F7 of switching, the processing unit 142 switches between an activated configuration, in which the step of limiting torque is enabled, and a deactivated configuration in which the step of limiting torque is disabled. In other words, the processing unit 142 applies the torque limiting function in a conditional manner, that is to say, the torque limiting function is enabled only if an activation condition is met.

(67) In an embodiment, therefore, the apparatus is operated in a deactivated configuration and, after checking that an enable condition is met, switches to an activated configuration. For example, the apparatus starts with the chuck stationary and the torque limiting function initially disabled and then enabled when the threshold speed is exceeded.

(68) In an embodiment, the method comprises a step of deriving an activation parameter. In an embodiment, the processing unit 142 performs the step of switching as a function of the control parameter. In an embodiment, the processing unit 142 is in the activated configuration when the activation parameter meets the activation condition. In an embodiment, the processing unit 142 derives the activation parameter as a function of the rotation speed of the electric motor 13, preferably as a function of the supply voltage frequency of the electric motor.

(69) In short, in the preferred embodiment, the processing unit 142 accesses the value of the supply voltage frequency of the motor and derives the activation parameterfor example, the corresponding rotation speed of the electric motor 13. Lastly, the processing unit 142 processes the rotation speed of the electric motor 13 to check that it meets the activation condition.

(70) In an embodiment, the activation condition is met when the activation parameter reaches or exceeds a threshold value. More specifically, in an embodiment, the activation condition is met when the rotation speed of the electric motor 13 reaches or exceeds an activation speed ?.sub.s.

(71) In an embodiment, the processing unit 142 derives the activation parameter by processing an enable signal received from a sensor of the apparatus 1.

(72) In an embodiment, the method comprises a step F52 of detecting an enable signal, preferably a speed signal. In the step F52 of detecting, a (first) speed sensor 16 detects the rotation speed of the drive shaft of the electric motor 13 and generates a corresponding (first) speed signal 103. In the step F52 of detecting, a (second) speed sensor 16 detects the rotation speed of the chuck 11 and generates a corresponding (second) speed signal 103. In an embodiment, the processing unit 142 derives the activation parameter as a function of the speed signal 103 received from the speed sensor 16.

(73) In an embodiment, the method (the step of switching) comprises a step of deactivating (disabling), in which the processing unit 142 switches to the deactivated configuration when the apparatus meets a disable condition, preferably when the activation parameter meets the disable condition. In an embodiment, the processing unit 142 switches to the deactivated configuration when a disable condition is reached by the rotation speed of the electric motor 13. In an embodiment. the disable condition is met (occurs) when the electric motor 13 switches off (rotation speed of the electric motor 13 is zero) or when the rotation direction of the motor (that is, of the chuck 11) is reversed. In other embodiments of the method, the step of disabling can be carried out by the user through a dedicated control with which the user can switch the processing unit 142 between the activated configuration and the deactivated configuration.

(74) In an embodiment, the method comprises a step of resetting, in which a resetting element sends a resetting signal to the processing unit 142. In some embodiments, the processing unit 142 does not switch to the activated configuration until after receiving the reset signal. In other words, the apparatus 1 is operated with the processing unit 142 in the deactivated configuration. Next, after reaching the activated condition, the processing unit 142 changes over to the activated configuration. When the motor switches offfor example, because the value of the working torque exceeds the threshold value C.sub.sthe processing unit 142 switches back to the deactivated configuration. At this point, when the apparatus 1 is next operated, the processing unit 142 will be programmed to switch to the activated configuration only after it receives the resetting signal. This embodiment is just an example of how a resetting procedure can be implemented. In effect, in other embodiments, the disable condition also causes automatic resetting of the apparatus 1.

(75) In an embodiment, the method comprises an additional step of limiting torque, in which the processing unit 142 generates the drive signal 101 in such a way as to prevent the working torque from exceeding an additional threshold value C.sub.s. The processing unit 142 applies the additional torque-limiting function as a function of the control parameter 102. In short, the processing unit 142 checks that the control parameter remains below a value corresponding to the additional threshold value C.sub.s of the working torque.