Abstract:
A handwheel-operated device comprising a body, a handwheel and a chuck, the handwheel and the chuck being rotatable relative to the body, and the device further comprising a first motor operable to rotate the chuck, first sensor means responsive to rotation of the handwheel and first control means operable in conjunction with the first sensor means to cause the first motor to rotate the chuck in dependence upon an angular displacement and/or angular velocity of the handwheel.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to a handwheel-operated device and to a method of controlling a motor of a handwheel-operated device by sensing rotation of the handwheel and causing the motor to rotate a chuck in dependence upon the rotation of the handwheel.  
       BACKGROUND TO THE INVENTION  
       [0002]     Mechanical devices of the kind having a handwheel connected to a chuck through a gear train, so that rotation of the handwheel causes a corresponding rotation of the chuck are well known. Hand drills and hand whisks are examples of such devices. These handwheel-operated devices are popular because a handwheel affords a high degree of control over the speed of rotation of the chuck. However, the magnitude of the speed and/or torque that can be developed at the chuck is limited by the magnitude of the speed and/or torque applied to the handwheel, which must be provided by the user. Such devices are therefore unsuitable for use over long periods or by users who lack physical strength, or if high levels of both speed and torque are required.  
       SUMMARY OF THE INVENTION  
       [0003]     According to a first aspect of the invention there is provided a handwheel-operated device comprising a body, a handwheel and a chuck, the handwheel and the chuck being rotatable relative to the body, and the device further comprising a first motor operable to rotate the chuck, first sensor means responsive to rotation of the handwheel and -first control means operable in conjunction with the first sensor means to cause the first motor to rotate the chuck in dependence upon an angular displacement and/or angular velocity of the handwheel.  
         [0004]     The invention therefore provides a handwheel-operated device that is operable by a user in the same manner as a conventional handwheel-operated device, such as a hand drill or a hand whisk, but which, for a particular speed and/or torque applied to the handwheel, is capable of developing considerably more speed and/or torque at the chuck than would a conventional handwheel-operated device.  
         [0005]     The first control means may advantageously be operable to modulate a voltage applied to the first motor.  
         [0006]     The first control means may advantageously be operable to modulate the voltage applied to the first motor such that the magnitude of the voltage is substantially proportional to the angular velocity of the handwheel.  
         [0007]     This type of first control means is relatively straightforward to implement.  
         [0008]     The first control means is preferably operable to modulate the voltage applied to the first motor such that an angular displacement and/or angular velocity of the handwheel results in a corresponding angular displacement and/or angular velocity of the chuck.  
         [0009]     With this type of first control means, the response of the chuck to rotation of the handwheel is much closer to that of a conventional handwheel-operated device, where the handwheel and chuck are mechanically coupled to one another, for example by a gear train, because changes in the loading on (i.e. resistance to rotation of) the chuck do not alter the relationship between handwheel and chuck position and/or speed.  
         [0010]     The first control means is more preferably operable to modulate the voltage applied to the first motor in dependence upon the angular velocity of the handwheel such that the angular velocity of the chuck is non-linearly related to the angular velocity of the handwheel, the ratio of handwheel speed to chuck speed decreasing with increasing handwheel speed. An increase in handwheel speed causes a greater than proportionate increase in chuck speed, and this type of first control means therefore enables a user to obtain very precise control of the angular displacement of the chuck at low speeds of rotation of the handwheel, yet also to obtain high angular velocities of the chuck that would otherwise require speeds of rotation of the handwheel that would be difficult or impossible for the user to achieve or sustain.  
         [0011]     Precise control of the angular displacement of the chuck is useful where the device is used, for example, as a screwdriver, and a user wishes to align a screwdriver bit in the chuck of the device with a slot in the head of a screw.  
         [0012]     Preferably the first control means is operable to cause the polarity of the voltage applied to the first motor to be dependent on the sense of rotation of the handwheel so that changing the direction of rotation of the handwheel reverses the polarity of the voltage applied to the first motor, and hence reverses the direction of rotation of the chuck.  
         [0013]     The first control means may advantageously include a proportional-plus-integral (PI) controller. In that case, the first control means may advantageously be operable to turn off the PI controller if the speeds of rotation of the handwheel and chuck fall below respective first threshold speeds.  
         [0014]     Preferably the first control means is operable to turn on the PI controller if the speed of rotation of the handwheel rises above a second threshold speed. Preferably the second threshold speed is greater than the first threshold speed.  
         [0015]     Turning off the PI controller at low speeds of rotation of the handwheel has been found to be necessary to prevent “creep” of the chuck, that is slow rotation of the chuck when the handwheel is stationary, due to steady-state errors in the PI controller.  
         [0016]     The device may advantageously further comprise a variable low-pass signal filter operable to receive signals representative of the angular displacement and/or angular velocity of the handwheel from the first sensor means and to transmit signals below a cut-off frequency to the first control means and to attenuate signals above the cut-off frequency so as to prevent them from reaching the first control means, the cut-off frequency being determined by the angular velocity of the handwheel.  
         [0017]     Preferably the variable low-pass signal filter is operable to decrease the cut-off frequency with increases of angular velocity of the handwheel up to a threshold angular velocity, above which increases of angular velocity of the handwheel do not affect the cut-off frequency.  
         [0018]     The effect of the variable low-pass signal filter is to cause the first control means to react relatively quickly to changes of angular displacement and/or angular velocity of the handwheel at low speeds of rotation of the handwheel, and relatively slowly to changes of angular displacement and/or angular velocity at higher speeds of rotation of the handwheel. This has been found to be necessary to give an accurate response of the speed of rotation of the chuck to changes of the speed of rotation of the handwheel at low speeds of rotation of the handwheel, which gives a user of the device the same impression of control of the speed of rotation of the chuck as is obtained with a conventional mechanical device, but avoids an overly abrupt response of the speed of rotation of the chuck to changes of the speed of rotation of the handwheel at high speeds of rotation of the handwheel. Such an abrupt response of the speed of rotation of the chuck to changes of the speed of rotation of the handwheel is generally prevented in a conventional mechanical device as a result of the inertia of the handwheel, gear train and chuck of the mechanical device.  
         [0019]     The first sensor means may advantageously comprise an angular displacement sensor. Suitable angular displacement sensors include a claw pole motor, an arrangement of a slotted disc rotatable relative to one or more optical sensors, or an arrangement of a multipole magnet rotatable relative to one or more Hall effect sensors and/or coils, which may be one or more printed coils on a printed circuit board. Where the arrangement of the multipole magnet and one or more coils is used, the first control means may be operable either to count pulses generated by the one or more coils, or to sample analogue voltage signals generated by the one or more coils. Typically the slotted disc or multipole magnet is mounted on a shaft of the angular displacement sensor. In that case, the handwheel may advantageously be attached to the shaft of the angular displacement sensor.  
         [0020]     Preferably, however, a first gear wheel is attached to the shaft of the angular displacement sensor, a second gear wheel is attached to the handwheel, and the first and second gear wheels are engageable with one another either directly or via one or more intermediate gears, so that each revolution of the second gear wheel causes the first gear wheel to rotate through more than 360°, preferably a plurality of revolutions.  
         [0021]     In this way, an inexpensive low-resolution angular displacement sensor, which produces, say, eight pulses during one revolution of its shaft, can be used, because each revolution of the handwheel will cause several revolutions of the shaft of the angular displacement sensor, and therefore a multiple of eight pulses during a revolution of the handwheel. Thus, provided that the ratio of the diameters of the first and second gear wheels is sufficiently large, the performance of an expensive high-resolution angular displacement sensor can be obtained using an inexpensive low-resolution angular displacement sensor.  
         [0022]     Alternatively or additionally, the first sensor means may advantageously comprise a second motor, a shaft of which is coupled for rotation to the handwheel, and measurement means for measuring one or more parameters related to a speed and direction of rotation of the shaft of the second motor, and computation means operable to derive a speed and direction of rotation of the shaft of the second motor, and hence a speed and direction of rotation of the handwheel, from the one or more measured parameters.  
         [0023]     Preferably the measurement means is operable to measure a back electromotive force (enf) generated by the second motor.  
         [0024]     Where the first sensor means includes both a second motor and an angular displacement sensor, the shaft of the angular displacement sensor may advantageously be coupled for rotation to the rotor of the second motor, and the first gear wheel be attached to the shaft of the second motor.  
         [0025]     The device may advantageously further comprise second sensor means operable to determine a torque developed by the first motor, torque feedback means coupled to the handwheel and second control means operable in conjunction with the second sensor means to cause the torque feedback means to oppose the rotation of the handwheel.  
         [0026]     In this way a user of the device may be provided with an indication of the torque developed by the first motor, which adds to the user&#39;s impression of a mechanical coupling between the handwheel and the chuck.  
         [0027]     The second sensor means may advantageously comprise a force sensor and the first motor be mounted in the body of the device such that, in use, a torque developed by the first motor causes a torsional reaction force to be exerted on the force sensor.  
         [0028]     The force sensor may advantageously be a piezoelectric crystal.  
         [0029]     Alternatively, the second sensor means may advantageously comprise measurement means for measuring one or more parameters related to the torque of the first motor, and computation means operable to derive a torque of the first motor from the one or more measured parameters.  
         [0030]     Preferably the measurement means is operable to measure a current supplied to the first motor.  
         [0031]     The torque feedback means may advantageously comprise a variable brake engageable with the handwheel under the control of the second control means.  
         [0032]     Where the first sensor means includes a second motor, the torque feedback means may more advantageously still comprise a second control means that is operable to supply current to the second motor so as to oppose the rotation of the handwheel.  
         [0033]     The device may advantageously further comprise a battery to allow the device to be operated cordlessly.  
         [0034]     In that case the device preferably further comprises third sensor means operable to determine an electromotive force (emf) developed by the battery, and the first control means is preferably operable in conjunction with the third sensor means to modulate the voltage applied to the first motor so that, at least until the battery is substantially discharged, decreases in the emf developed by the battery do not cause decreases of the speed of rotation of the chuck.  
         [0035]     The device may advantageously further comprise fourth sensor means operable to determine a magnitude of a current supplied to the first motor, and the first control means may advantageously be operable in conjunction with the fourth sensor means to limit the magnitude of the current supplied to the first motor if the magnitude of the current exceeds a threshold level.  
         [0036]     The device may advantageously further comprise biasing means and mechanical braking means, the biasing means being operable to urge the mechanical braking means into engagement with the handwheel so as to oppose the rotation of the handwheel.  
         [0037]     The mechanical braking means has been found to smooth the response of the chuck to rotation of the handwheel, and to prevent unintended rotation of the handwheel, for example rotation of the handwheel due to the weight of a handle attached to the handwheel, which would otherwise cause unintended movement of the chuck.  
         [0038]     Preferably the mechanical friction means is a felt-covered pad.  
         [0039]     The handwheel may advantageously be provided with a handle movable between a folded position and an extended position.  
         [0040]     The handwheel may advantageously further comprise latch means operable releasably to retain the handle in the extended position.  
         [0041]     The body of the device and the handle of the handwheel may advantageously be formed such that in the folded position the handle engages with the body so as to prevent rotation of the handle relative to the body.  
         [0042]     Preferably the device further comprises first switch means engageable with the handle, such that the first control means is operable to cause the first motor to rotate the chuck only when the handle is in the extended position.  
         [0043]     Alternatively or additionally, the device may advantageously further comprise a first further manual control (for example a trigger switch), movable between an “off” position and an “on” position, wherein movement of the first further manual control to the “on” position when the handle is in its folded position causes the first motor to rotate the chuck.  
         [0044]     Where the device includes both the first further manual control and the first switch means, the first control means may advantageously be operable to cause the first motor to rotate the chuck only when the handle is in the extended position and the first further manual control is moved to the “on” position. If the first further manual control includes biasing means operable to urge it into the “off” position, it may function as a “dead man&#39;s handle” such that if a user of the device drops the device in use, the first further manual control moves to the “off” position, in which position rotation of the handwheel does not cause rotation of the chuck.  
         [0045]     Where the device includes the first further manual control, it may advantageously further comprise a second further manual control movable between “clockwise”, “anti-clockwise” and “off” positions, wherein with the second further manual control in the “clockwise” or “anti-clockwise” positions, movement of the first further manual control to the “on” position when the handle is in its folded position causes the first motor to rotate the chuck clockwise or anti-clockwise, respectively.  
         [0046]     Where the device includes the first and second further manual controls and the first switch means, the first control means may advantageously be operable to cause the first motor to rotate the chuck only when the handle is in the extended position, the first further manual control is moved to the “on” position and the second further manual control means is moved to the “off” position.  
         [0047]     The body of the device may advantageously comprise a first portion to which the handwheel is attached and a second portion attached to, and movable between a first and a second position relative to, the first portion.  
         [0048]     In this way the device can be used by both left and right-handed users. In the first position of the second portion, the user can hold the second portion of the device in his left hand and operate the handwheel with his right hand. In the second position of the second portion, the user can hold the second portion of the device in his right hand and operate the handwheel with his left hand.  
         [0049]     Preferably the device further comprises switch means operable by the first or second portion such that the switch means is closed when the second portion is in the first position and open when the second portion is in the second position and the first control means is operable when the switch means is closed to cause the chuck to rotate in one sense when the handwheel is rotated in a first sense, and operable when the switch means is open to cause the chuck to rotate in the opposite sense when the handwheel is rotated in the first sense.  
         [0050]     Thus the response of the chuck to rotation of the handwheel is the same for both left and right-handed users of the device. That is, when the user rotates the handwheel away from him from top dead centre, the chuck rotates in a clockwise sense as seen from behind by the user, regardless of whether the second portion of the body is in the first or second position.  
         [0051]     Preferably the device is a power tool.  
         [0052]     In one embodiment of the invention the device is a cordless electric drill.  
         [0053]     In another embodiment of the invention the device is an electric food blender.  
         [0054]     According to a second aspect of the invention there is provided a method of controlling a motor of a handwheel-operated device, the device having a body, a handwheel, a chuck and a motor, the handwheel being rotatable relative to the body and the motor being operable to rotate the chuck relative to the body, the method comprising sensing rotation of the handwheel and causing the motor to rotate the chuck in dependence upon the angular displacement and/or angular velocity of the handwheel. 
     
    
     BRIEF DESCRIPTION OF DRAWING FIGURES  
       [0055]     The invention will now be described by way of illustrative example and with reference to the accompanying drawings, in which:  
         [0056]      FIG. 1  is a perspective view of a first cordless drill in accordance with the first aspect of the invention;  
         [0057]      FIG. 2  is a schematic sectional view of the drill of  FIG. 1 ;  
         [0058]      FIG. 3  is a partial schematic sectional view of the drill of  FIGS. 1 and 2  along the line A-A;  
         [0059]      FIG. 4  is a block diagram of a first control scheme for the drill of FIGS.  1  to  3 ;  
         [0060]      FIG. 5  is a block diagram of a second control scheme;  
         [0061]      FIG. 6  is a block diagram of a third control scheme;  
         [0062]      FIG. 7  is a block diagram of a fourth control scheme;  
         [0063]      FIG. 8  is a graph of amplifier gain and hence angular velocity of the chuck of the drill against angular velocity of the handwheel;  
         [0064]      FIG. 9  is a block diagram of a detail of the fourth control scheme;  
         [0065]      FIG. 10  is a block diagram of a fifth control scheme;  
         [0066]      FIG. 11  is a sectional view of the handwheel with the handle in a folded position;  
         [0067]      FIG. 12  is a sectional view of the handwheel with the handle in an extended position;  
         [0068]      FIG. 13  is a side view of an electric whisk in accordance with the first aspect of the invention;  
         [0069]      FIG. 14  is a block diagram of a motor model used in the fifth control scheme;  
         [0070]      FIG. 15  is a graph of cut-off frequency of a variable filter against angular velocity of the handwheel;  
         [0071]      FIG. 16  is a sectional view of a handwheel and a mechanical brake assembly;  
         [0072]      FIG. 17  is a perspective view of a second cordless drill in accordance with the first aspect of the invention;  
         [0073]      FIG. 18  is a sectional view of the drill of  FIG. 17 ;  
         [0074]      FIG. 19  is a perspective view of a third cordless drill in accordance with the first aspect of the invention;  
         [0075]      FIG. 20  is a partially cut away top view of a fourth cordless drill in accordance with the first aspect of the invention with one of two handwheels in an extended position;  
         [0076]      FIG. 21  is a sectional view of the drill of  FIG. 19 ;  
         [0077]      FIG. 22  is a partially cut away side view of a fifth cordless drill in accordance with the first aspect of the invention; and  
         [0078]      FIG. 23  is a top view of the drill of  FIG. 20  with both handwheels in the extended position. 
     
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
       [0079]     The cordless drill  10  of  FIG. 1  comprises a body  12 , a handwheel  14  and a chuck  16 . Except for the handwheel, the drill  10  superficially resembles a conventional drill, with a pistol grip  18 , trigger switch  20  located in the pistol grip, and forward housing portion  22  located in front of the trigger. The handwheel  14  is attached to the portion  22 . A rechargeable battery  24  is removably attached to the base of the body.  
         [0080]     Turning to  FIG. 2 , from which the battery  24  has been omitted for the purpose of clarity, the body  12  contains a first motor  26 , a first rotary encoder  28 , a gearbox  30 , a second motor  32 , a second rotary encoder (not shown), and first and second gear wheels  34  and  36 , respectively. The body  12  further contains first control means in the form of a programmed microprocessor (not shown). The first rotary encoder  28  is made up of a multipole magnet and three Hall effect detectors and is attached to a first end of the spindle of the first motor  26 . The gearbox  30  is coupled to a second end of the spindle of the first motor  26  and to the chuck  16 .  
         [0081]     It will be appreciated by those skilled in the art that it may not be necessary to have a separate rotary encoder to implement the first rotary encoder  28 , and that an arrangement, for example, of a magnetised gear wheel forming part of the gearbox  30  and three Hall effect detectors could be used instead to implement the first rotary encoder  28 .  
         [0082]     Moreover, it will be apparent to those skilled in the art that it is not essential that the first rotary encoder be attached to an end of the spindle of the first motor  26 . Indeed, with very minor modifications to the drill, the rotary encoder could be placed at any point of the drive train comprising the first motor  26 , gearbox  30  and chuck  16 .  
         [0083]     The first gear wheel  34  is attached to the spindle of the second motor  32 . The second gear wheel  36  is attached to the handwheel  14  and to a spindle on which the handwheel rotates. The second motor  32  and the spindle on which the handwheel rotates are so located that the first and second gear wheels engage with one another, such that when the handwheel is rotated, the second motor is driven. The second gear wheel has a diameter that is between three and four times the diameter of the first wheel. For each revolution of the handwheel, therefore, the first gear wheel makes between three and four rotations, which increases the effective resolution of the second rotary encoder by between three and four times.  
         [0084]     The handwheel  36  has a folding handle  38 , which is shown in an extended position in  FIGS. 1 and 2 . The handle can be moved into a folded position, and is engageable with a microswitch (not shown) in the folded position, which microswitch disconnects the second rotary encoder from the microprocessor.  
         [0085]     The first motor and gearbox are secured in the body by resilient mounts, which allow a small amount of torsional movement of the motor and gearbox relative to the body. The gearbox is formed with a radially outwardly projecting member  40 . A piezoelectric crystal (not shown) is located to either side of the member  40  such that if torsional movement of the motor and gearbox relative to the body occurs, a force is exerted on one or other piezoelectric crystal.  
         [0086]     The arrangement of the member  40  and the piezoelectric crystals is shown more clearly in  FIG. 3 , in which the piezoelectric crystals are denoted by reference numerals  42  and  44 .  FIG. 3  is a sectional view along the line A-A of  FIG. 2 .  
         [0087]      FIG. 4  shows a first control scheme for the drill in which the speed of rotation of the handwheel is measured and a pulse width modulated (PWM) voltage of magnitude proportional to the speed of rotation of the handwheel is applied to the first motor. As the handwheel is rotated, pulses are generated by the second rotary encoder (not shown). A first clock  46  determines the frequency of the pulses and generates a signal representative of the speed of rotation of the handwheel. The signal representative of the speed of rotation of the handwheel is used to generate a PWM voltage which drives a first field effect transistor (FET) h-bridge  48 . The first motor  26  is connected across the first h-bridge  48 .  
         [0088]      FIG. 5  shows a second control scheme in which the speed of rotation of the handwheel is measured and a feedback loop is used to ensure that the speed of rotation of the chuck is proportional to that of the handwheel. With only minor changes it would be possible instead to measure the angular displacement of the handwheel from a reference orientation and use the feedback loop to ensure that the angular displacement of the chuck from a reference orientation is proportional to that of the handwheel.  
         [0089]     The first clock  46  determines the frequency of the pulses generated by the second rotary encoder to generate a signal representative of the speed of rotation of the handwheel. At the same time a second clock  52  determines the frequency of pulses generated by the first rotary encoder to generate a signal representative of the speed of rotation of the chuck. The signals representative of the speeds of rotation of the chuck and handwheel are compared by a microprocessor  50  to generate a speed error signal. The microprocessor generates a PWM voltage to drive the first h-bridge  48  and control the speed of rotation of the first motor so as to reduce the magnitude of the speed error signal.  
         [0090]      FIG. 6  shows the control scheme of  FIG. 5  modified by a further feedback loop, which enables a retarding force to be applied to the handwheel, which retarding force is approximately proportional to the torque developed by the first motor  26 . The control scheme shown in  FIG. 6  is as described in relation to  FIG. 5 . However, a voltage developed by one of the piezoelectric crystals  42  and  44 , which is subjected to a compressive force due to the reaction torque on the motor, is applied to a microprocessor  54 . The microprocessor  54  generates a PWM voltage to drive a second FET h-bridge (not shown). The second motor  32  is connected across the second h-bridge and the PWM voltage generated by the microprocessor  54  causes the second motor to generate a torque which opposes the rotation of the handwheel.  
         [0091]      FIG. 7  shows a control scheme similar to that shown in  FIG. 6 , but with a further feedback loop to ensure that the torque generated by the second motor to oppose the rotation of the handwheel is proportional to the torque generated by the first motor.  
         [0092]     In the control scheme of  FIG. 7  the handwheel  14  is rotated and causes the spindle of the second motor  32  to rotate and the second rotary encoder  56  to generate pulses. The first clock  46  measures the frequency of the pulses from the second rotary encoder and generates a signal representative of the speed of rotation of the handwheel. An amplifier  58  applies a gain to the signal representative of the speed of rotation of the handwheel to generate an amplified speed signal. The gain of the amplifier increases with the magnitude of the signal representative of the speed of rotation of the handwheel.  FIG. 8  shows the gain characteristic  63  of the amplifier  58  with gain plotted against magnitude of the signal representative of the speed of rotation of the handwheel. Gain is plotted on the y-axis  65  and magnitude of the handwheel speed signal on the x-axis  67 . The gain of the amplifier therefore determines the ratio of the speeds of rotation of the chuck and the handwheel. The amplified speed signal is applied to a first proportional plus integral (PI) controller  60 .  
         [0093]     The spindle of the first motor  26  rotates and causes the first rotary encoder  28  to generate pulses. A third clock  62  measures the frequency of the pulses and generates a signal representative of the speed of rotation of the first motor. The signal representative of the speed of rotation of the first motor is applied to the PI controller  60 . A current sensor (not shown) measures the current flowing through the first motor and generates a signal representative of the current flowing through the first motor. The current sensor transmits the signal to the first PI controller  60 . The first PI controller  60  generates a PWM voltage to drive the first h-bridge  48  to cause the spindle of the first motor to rotate at the speed determined by the gain of the first amplifier  58 , whilst ensuring that the current flowing through the motor remains below a safe limit. The current limiting operation of the first PI controller  60  is explained in more detail below in relation to  FIG. 9 . The battery  24 , which was omitted from FIGS.  4  to  6  for the purpose of clarity, is shown in  FIG. 7  connected to the first h-bridge  48  and the second h-bridge  64  across which the second motor  32  is connected.  
         [0094]     The piezoelectric crystal  42  generates a voltage proportional to the torque developed by the first motor  26 . An attenuator  66  attenuates the voltage generated by the crystal  42  to generate a signal representative of a fraction of the torque developed by the first motor  26 . The attenuated torque signal is applied to a second PI controller  68 . A current sensor  70  generates a signal representative of the current flowing through the second motor  32  from the second h-bridge  64 . A second microprocessor  72  generates a signal representative of an estimated torque developed by the second motor  32  and applies this signal to the second PI controller  68 . The second PI controller generates a PWM voltage to drive the second h-bridge  64  so as to cause the second motor  32  to generate a torque equal to the fraction of the torque generated by the first motor  26 .  
         [0095]     Turning to  FIG. 9 , the current limiting operation of the first PI controller  60  is shown. The PI controller  60  in fact comprises an outer, relatively slow PI controller  74 , a current limiter  76  and an inner, relatively fast PI controller  78 . In  FIG. 9  the first h-bridge  48 , first motor  26 , first rotary encoder  28 , second clock  62  and current sensor of  FIG. 7  are represented by the functional block  80 .  
         [0096]     The outer PI controller  74  receives signals representative of a demanded motor speed from the amplifier  58  and signals representative of the actual motor speed from the first rotary encoder  28  and third clock  62  and generates a signal representative of a demanded current. The demanded current is that which will cause the actual motor speed to approach the demanded motor speed. The signal representative of the demanded current is transmitted to the current limiter  76 , which either transmits the signal representative of the demanded current to the inner PI controller  78 , or if the signal representative of the demanded current exceeds a threshold value, transmits a signal representative of a limited demanded current to the inner PI controller  78 .  
         [0097]     The inner PI controller  78  receives the signal representative of the demanded current (whether or not limited) and a signal representative of the actual motor current from the current sensor. The inner PI controller generates a PWM voltage to drive the first h-bridge so as to cause the actual current flowing through the motor to approach the demanded current.  
         [0098]      FIG. 10  shows a variation of the control scheme shown in  FIG. 7 , in which a torque developed by the first motor is calculated from parameters of the first motor related to torque, rather than measured directly. The operation of the first motor  26 , first rotary encoder  28 , second motor  32 , second rotary encoder  56 , first clock  46 , amplifier  58 , first PI controller  60 , first h-bridge  48 , attenuator  66 , second PI controller  68 , current sensor  70 , microprocessor  72  and third clock  62  is as previously described in relation to  FIG. 7 . However, the first PI controller  60  receives the signals representative of the first motor current from voltage and current sensors  82  operable to generate signals representative of the voltage developed across, and current flowing in, the first motor  26 .  
         [0099]     The voltage and current sensors  82  transmit signals representative of the voltage developed across, and current flowing in, the first motor  26  to a second microprocessor  84 . The second microprocessor also receives pulses from the first rotary encoder  28  and generates a signal representative of the load torque developed by the first motor  26 , which is transmitted to the attenuator  66 . The second microprocessor  84  implements a model of the motor, which is explained in greater detail below with reference to  FIG. 14 . The attenuated torque signal is transmitted to the second PI controller  68  to cause the second motor  32  to generate a torque proportional to the load torque generated by the first motor, which torque opposes the rotation of the handwheel  14 , as previously described.  
         [0100]     Turning to  FIG. 14 , this shows the model implemented by the second microprocessor  84 . In the following description it is to be assumed that signals representative of a particular variable are signals representative of the Laplace transform of that variable. The second microprocessor receives a signal representative of the voltage applied to the first motor  26 , and the current through it and a signal representative of the angular displacement of the rotor of the first motor from a reference orientation. From previous angular displacement signals the second microprocessor determines the actual speed of rotation of the rotor of the first motor. Using the model an estimate of the motor current and speed may be made. The estimated speed of the motor enables a signal representative of the back emf generated by the first motor to be generated. The back emf signal is subtracted from the motor voltage signal to generate a signal representative of the estimated voltage across the windings of the first motor. The second microprocessor uses the estimated windings voltage signal to generate a signal representative of the motor current and of the total electrical torque generated by the first motor  26 . The second microprocessor also generates a signal representative of a predicted load torque generated by the first motor by comparing the actual current and speed against the estimates and subtracts the signal representative of the predicted load torque from the signal representative of the total electrical torque to generate a signal representative of the accelerating torque developed by the first motor. The second microprocessor generates a signal representative of the estimated speed of rotation of the rotor of the first motor from the accelerating torque signal, from which the back emf signal referred to earlier is generated.  
         [0101]     The second microprocessor generates from the estimated rotor speed signal a signal representative of the estimated angular displacement of the rotor from the reference orientation and compares the estimated angular displacement signal with a signal representative of the actual angular displacement of the rotor generated by the first rotary encoder  28 . The second microprocessor adjusts the predicted load torque signal to reduce the difference between the actual and estimated angular displacement signals and the difference between the actual and estimated motor current.  
         [0102]     The variables shown in the model of  FIG. 14  are as follows:  
         [0103]     V drive (S)˜Laplace transform of the voltage applied to the first motor  26 ;  
         [0104]     K I ˜torque constant of the first motor;  
         [0105]     R˜armature resistance of the first motor;  
         [0106]     L˜armature inductance of the first motor;  
         [0107]     s˜the Laplace variable;  
         [0108]     T elec (s)˜Laplace transform of the total electrical torque of the first motor;  
         [0109]     T load (s)˜Laplace transform of the load torque of the first motor;  
         [0110]     T accel (s)˜Laplace transform of the accelerating torque of the first motor;  
         [0111]     b˜friction coefficient of the first motor and gearbox;  
         [0112]     J˜inertia of the rotor of the first motor and gearbox;  
         [0113]     θ(s)˜Laplace transform of the estimated angular displacement of the rotor of the first motor;  
         [0114]     K ω ˜electric constant of the first motor; and  
         [0115]     V bemf ˜Laplace transform of the estimated back emf of the first motor.  
         [0116]     Returning to  FIGS. 11 and 12 , the handwheel assembly of the drill of  FIGS. 1 and 2  comprises the handwheel  14 , folding handle  38 , spindle  86  to which the handwheel is attached, circular thrust plate  88  through which the spindle  86  passes, and microswitch  90 . The folding handle  38  is pivotally attached to the handwheel  14  and is formed with a cam  92 . In the folded position (as shown in  FIG. 11 ) the cam does not engage with the thrust plate  88 , which is biased towards the handwheel  14  by the microswitch. In the extended position, however, (as shown in  FIG. 12 ) the cam engages with the thrust plate  88 , which causes the microswitch to be depressed, closing the microswitch. The second rotary encoder  56  is connected to the first clock  46  by the microswitch such that the handwheel is operable to control the rotation of the chuck only when the handle  38  is in the extended position and the microswitch closed. When the handle  38  is in the folded position (and therefore inoperable to control the rotation of the chuck, the rotation of the chuck may be controlled by the trigger switch  20 , in the manner known from conventional cordless drills.  
         [0117]      FIG. 13  shows a hand whisk  94  in accordance with the first aspect of the invention. It will be appreciated that the electric hand whisk has two chucks (not shown in  FIG. 13 ), one for each whisking element  96  and  98 . The hand whisk  94  has a handwheel and a handle  102 . In this embodiment of the invention the handle  102  is not foldable, since the whisk can be disabled simply by unplugging it from the mains electricity outlet to which it is connected.  
         [0118]      FIG. 15  shows the frequency response of a variable frequency digital low-pass filter with cut-off frequency plotted against magnitude of a signal representative of the speed of rotation of the handwheel. Cut-off frequency is plotted on the y-axis  106  and magnitude of the handwheel speed signal on the x-axis  108 . The variable frequency digital low-pass filter could be used in any of the control schemes described above. In the control scheme shown in  FIG. 4 , for example, the variable frequency low-pass filter would be interposed between the clock  46  and the h-bridge  48 .  
         [0119]     The filter, the frequency response of which is shown in  FIG. 15 , is designed to be used in a control scheme that defines a maximum speed of rotation of the handwheel, such that increases of speed of rotation of the handwheel above the maximum speed do not cause a corresponding increase in the speed of rotation of the chuck. This is not an essential feature of the filter, however.  
         [0120]     As can be seen from  FIG. 15 , the filter passes all signals with frequencies below 50 Hz for speeds of rotation of the handwheel up to five percent of the maximum speed. For speeds of rotation of the handwheel between five and ten percent of the maximum speed the filter passes all signals with frequencies below 12 Hz. For speeds of rotation of the handwheel between ten and one hundred percent of the maximum speed the filter passes all signals with frequencies below 3 Hz.  
         [0121]     The effect of this is to slow the speed of response of the drill motor controller with increasing speed of the drill motor. This arrangement has been found to give very sensitive control of the speed of the chuck at low speeds of rotation of the chuck, for which a high speed of response of the drill motor controller is required, and relatively insensitive control of the speed of the chuck at high speeds of rotation of the chuck. It is important that the control of the speed of rotation of the chuck at high speeds of rotation of the chuck be relatively insensitive, since it is difficult for a user to maintain a constant, high speed of rotation of the handwheel, and the speed of rotation of the chuck would otherwise be variable to a degree that would irritate the user. This is because the user would be used to conventional mechanical drills, in which the inertia of the handwheel, gear train and chuck tend to prevent or reduce sudden variations in the user&#39;s speed of rotation of the handwheel.  
         [0122]      FIG. 16  shows an improved arrangement of a handwheel that forms part of a cordless drill. The handwheel  110  is mounted on a shaft that is attached to the body of the drill. A portion of the body is shown in  FIG. 16 , denoted by reference numeral  114 . A compression spring  115  is accommodated in a recess in the body and acts on a brake block  116 . The brake block is covered by a felt pad  118  and arranged such that the action of the spring urges the felt pad  118  into engagement with a rear face of the handwheel  110 .  
         [0123]     In addition to preventing movement of the handwheel  110  due to the weight of a handle  120  attached to the handwheel, the brake block assists the smooth operation of the drill by the user, since the brake block resists abrupt changes of the speed of rotation of the handwheel by the user.  
         [0124]      FIG. 17  shows a drill  122  that is suitable for use by both left and right-handed users. The body of the drill is provided with symmetrically disposed sockets on opposite sides of the body. One such socket is shown in  FIG. 17 , denoted by reference numeral  124 . The drill  122  is provided with a single, detachable handle  126  that can be placed into either of the sockets, depending on the handedness of the user. The handle contains a multipole magnet that, in conjunction with three Hall effect sensors (not shown) in the body of the drill, is used to detect rotation of the handwheel relative to the body of the drill. The body of the drill also contains a ferromagnetic keeper (not shown) adjacent to each socket that is acted on by the magnet in the handle to retain the handle in whichever socket it has been placed.  
         [0125]     Turning to  FIG. 18 , this shows a section through the drill  122  along a line of symmetry of the handwheel  126 . The multipole magnet in the handwheel  126  is shown in  FIG. 18 , denoted by reference numeral  128 . Microswitches  130  and  132  are contained in each of the sockets and one of the microswitches is closed by insertion of the handwheel into the socket. In  FIG. 18  the microswitch  130  has been closed by insertion of the handwheel into the socket. The motor controller (not shown) of the drill determines into which socket the handwheel  126  has been inserted by determining which of the switches  130  and  132  has been closed. The motor controller controls the motor in response to rotation of the handwheel such that when the user holds the drill in one hand with the chuck pointing away from him, rotation of the handle of the handwheel towards the chuck (with the handle of the handwheel at top dead centre) causes clockwise rotation of the chuck (as seen by the user). This is regardless of whether the handwheel is on the left or right-hand side of the drill.  
         [0126]     In  FIG. 18 a  dust cover  134  is shown inserted into the spare socket. Insertion of the dust cover  134  into the socket does not close the microswitch  132 .  
         [0127]     It will be appreciated by those skilled in the art that, by having a set of three Hall effect sensors for each socket, the microswitches  130  and  132  can be dispensed with, because the motor controller can determine into which socket the handle has been inserted by the set of Hall effect sensors from which it receives signals produced by rotation of the handle, and control the direction of rotation of the chuck accordingly.  
         [0128]      FIG. 19  shows another drill  136  suitable for use by both left and right-handed users. The body of the drill includes a rotatable collar  138  to which a handwheel  140  is attached. The collar is rotatable through  180  degrees relative to the rest of the body, so that the handwheel is disposed either on the left or right-hand side of the body.  
         [0129]     Turning to  FIG. 21 , this shows a section through the drill  136  along a line of symmetry of the handwheel  140 . The internal surface of the collar  138  is provided with first and second inwardly projecting lugs  142  and  144 . The lugs are engageable with respective first and second microswitches  146  and  148  that are disposed inside the body of the drill. In  FIG. 21  the second lug  144  is shown engaged with the second microswitch  148 .  
         [0130]     Engagement of a lug with its respective microswitch closes the microswitch. The motor controller (not shown) is operable to determine to which side of the drill the user has rotated the collar by whichever of the microswitches  146  and  148  is closed and to control the motor so that, whichever side of the body the handwheel is disposed, rotation of the handle of the handwheel away from top dead centre towards the chuck causes the chuck to rotate clockwise as seen from behind by the user.  
         [0131]     Turning to  FIG. 20 , this shows another drill  150  suitable for both left and right-handed users. The drill  150  is provided with two handwheels  152  and  154  disposed symmetrically on the left and right-hand sides of the drill. The handwheels are fitted with respective handles  156  and  158  that are movable between extended and closed positions. The handle  156  of the handwheel  152  is shown in  FIG. 20  in the extended position and the handwheel  158  of the handwheel  154  is shown in the closed position.  
         [0132]     As described in relation to  FIGS. 11 and 12 , the handles  156  and  158  are formed with respective cam surfaces  160  and  162 . The drill  150  further comprises a toggle switch  164  and a yoke  166  that is engageable with the toggle switch  164  and the cam surfaces  160  and  162  of the handles. In  FIG. 20 , the cam surface  160  of the handle has engaged with the yoke  166  as a result of the handle being moved to the extended position. This has caused the yoke to close the toggle switch  164 . If the handle  156  were to be moved to the closed position and the handle  158  moved to the extended position, the cam surface  162  of the handle  158  would engage with the yoke  166  and cause the yoke to open the toggle switch  164 .  
         [0133]     A motor controller (not shown) of the drill  150  is operable to determine from whether the toggle switch  164  is open or closed, whether the user of the drill is using the handwheel  152  or  154 , and, as explained above, to ensure that forward rotation of the handwheel used by the user causes clockwise rotation of the chuck of the drill.  
         [0134]      FIG. 23  shows the drill  150  of  FIG. 20  with both of the handles  156  and  158  of the handwheels  152  and  154  in their extended positions. In practice, this situation would not arise, because the yoke  166  shown in  FIG. 20  would prevent the other handle from being moved to the extended position when one handle was already in the extended position.  
         [0135]     Turning finally to  FIG. 22 , this also shows a drill  168  suitable for both left and right-handed users. The body of the drill comprises a housing  170  to which a handwheel  172  is attached and a handgrip  174  that is pivotally attached to the housing  170 . The handgrip  174  is rotatable relative to the housing  170  between a first, left-handed position (shown by a dotted line and denoted by reference numeral  176 ) and a second, right-handed position (shown also by a dotted line and denoted by reference numeral  178 ). The handgrip  174  is formed with a lug  180  and is engageable with a first microswitch  182  in the first position and with a second microswitch  184  in the second position. When engaged with a microswitch, the lug closes the microswitch.  
         [0136]     A motor controller (not shown) of the drill  168  is operable to determine which of the microswitches  182  and  184  is closed and hence whether the handgrip is in the first or the second position. A right-handed user of the drill would hold the handgrip in his left hand and operate the handwheel  172  with his right hand with the handgrip in the first position. A left-handed user would hold the handgrip in his right hand and operate the handwheel  172  with his left hand with the handgrip in the second position. The motor controller is operable by determining which of the microswitches  182  or  184  is closed to control the motor of the drill (not shown) in response to rotation of the handwheel  172  such that with the chuck  186  pointing away from the user, rotation of the handwheel towards the chuck with the handle of the handwheel (not shown) at top dead centre causes clockwise rotation of the chuck as seen from the rear end of the chuck by the user.  
         [0137]     It will be apparent that although the foregoing description relates to several embodiments of the invention, the invention encompasses other embodiments as defined by the foregoing statements of the invention.