SHAVING APPARATUS WITH ELECTRICALLY ADJUSTABLE CUTTING UNIT

Abstract: A shaving apparatus (1, 105) with at least one adjustable cutting unit (11, 121) which comprises an external cutting member (13, 123) with at least one hair trap opening (17) and an internal cutting member (19, 125) which is rotatable inside the external cutting member (13, 123) by means of an electric motor (23, 127). The cutting unit (11, 121) is adjustable by means of an electrical actuator (91, 179) which is controllable by an electrical control unit (103, 191). In a first embodiment of the shaving apparatus (1), the external cutting member (13, 123) can be positioned relative to a holder (17) during a shaving operation by means of the actuator (91). In the second embodiment of the shaving apparatus (105), the external cutting member (123) is displaceable relative to the holder (111) under the influence of a skin contact force against a pretensioning force which has a value which is adjustable by means of the actuator (179). In both embodiments, the motor (23, 127) has a speed which is controlled by the control unit (103, 191). The control unit (103, 191) adjusts the cutting unit (11, 121) and the motor speed (23, 127) as a function of a measured skin contact force, a measured cutting frequency, a time which has elapsed during a shaving operation, and a balance between shaving performance and shaving comfort desired by the user. In a special embodiment, the control unit (103, 191) controls the cutting unit (11, 121) and the motor speed in accordance with an algorithm based on fuzzy logic. The shaving apparatus (1, 105) provides a user of the shaving apparatus (1, 105) with an optimum balance between the achieved shaving performance, i.e. skin smoothness and shaving speed, and the experienced shaving comfort, i.e. skin irritaion level, during a shaving operation.

Description: Shaving apparatus with electrically adjustable cutting unit. The invention relates to a shaving apparatus with at least one adjustable cutting unit which is provided with an external cutting member with at least one hair trap opening and an internal cutting member which is drivable relative to d e external cutting member by means of an electric motor. A shaving apparatus of the kind mentioned in the opening paragraph is known from European Patent 0 231 966. The known shaving apparatus comprises three round cutting units arranged in a holder. The external cutting members of the cutting units are detachably fastened to a common plate. The internal cutting members are each rotatable by means of a separate coupling shaft, which can be driven by the motor, and rest in the corresponding external cutting members under the influence of an elastic pretensioning force acting on the individual coupling shafts. A slidable adjustment ring is provided along a circumference of the holder, which ring is provided with three projections pointing inwards. The common plate has three stepped cams with which the plate rests on the three. projections of the adjustment ring under the influence of an elastic pretensioning force. Through shifting of the adjustment ring, it is possible to displace the common plate relative to the holder and to adjust a height over which the external cutting members project from the holder. If said height is comparatively small, the shaving comfort will be comparatively high, i.e. the skin irritation level will be comparatively low, whereas the shaving performance will be comparatively low, i.e. the speed of d e shaving process and die achievable skin smoothness are comparatively low. If said height is comparatively great, d e speed of d e shaving process and d e achievable skin smoothness are relatively high, but the skin irritation level is also comparatively high. A user of the known shaving apparatus may thus adjust a balance between the shaving comfort and die shaving performance desired by him through shifting of the adjustment ring. A disadvantage of the known shaving apparatus is that an adjustment of d e cutting units chosen by the user will be maintained during one or several shaving operations or will be changed only a very limited number of times. Since the shaving comfort and die shaving performance depend on a number of conditions such as, for example, me number of hairs per skin surface unit, the force with which the user presses th shaving apparatus against die skin, and d e time which has elapsed during a shaving operation, and since these conditions vary strongly over one or several shaving operations, the adjustment of the cutting units chosen by the user does not provide die user with an optimum balance between the shaving performance and d e shaving comfort experienced by the user during die shaving operation. It is an object of the invention to provide a shaving apparatus of the kind mentioned in die opening paragraph with which the balance between die shaving performanc and d e shaving comfort experienced by me user during d e shaving operation is improved. The invention is for diis purpose characterized in diat the cutting unit is adjustable by means of an electrical actuator which is controllable by an electrical control unit. Since the cutting unit is adjustable by means of die electrical actuator, die adjustment o me cutting unit can be changed automatically during a shaving operation. The actuator can b controlled and d e cutting unit can be adjusted d rough a suitable design of d e control unit such diat the user continuously experiences die shaving comfort desired by him during die shaving operation and die best possible shaving performance is provided in relation to diis desired shaving comfort. A special embodiment of a shaving apparatus according to die invention is characterized in that the cutting unit is arranged in a holder and is displaceable relative to die holder by means of d e actuator. The user's skin rests on die external cutting member of the cutting unit and on die holder during shaving. The shaving performance and die shaving comfort experienced by die user are dependent on die deformation of the skin around die cutting unit, which deformation depends on die adjustment position of the cutting unit relative to the holder. If d e actuator is controllable by means of a suitable control unit, a shaving comfort level desired by die user can be maintained during shaving in diat displacements of die cutting unit are generated by die actuator, while an optimum shaving performance in relation to this desired shaving comfort is provided. A further embodiment of a shaving apparatus according to die invention is characterized in that die actuator places die cutting unit in a rest position, in which the cutting unit is recessed in d e holder, when die electric motor is switched off. The cutting unit is d us protected by die holder when die shaving apparatus is not in use, so diat damage to the cutting unit dirough dropping of or impacts against the shaving apparatus is avoided much as possible. A yet further embodiment of a shaving apparatus according to d e invention is characterized in diat die external cutting member is displaceable relative to me holder by means of the acmator, while the internal cutting member is held in d e external cutting member under die influence of a pretensioning force of an elastically deformable element. The use of said elastically deformable element causes die internal cutting member remain in a desired position relative to d e external cutting member during displacements o me external cutting member, so mat the entire cutting element is displaceable in that exclusively d e external cutting member is adjusted by die acmator. A particular embodiment of a shaving apparatus according to die inventi is characterized in diat the external cutting member of the cutting unit is fastened to a displaceable carrier which is coupled to an adjustment member which is rotatable relative to the holder by means of the actuator, the carrier being displaceable dirough a rotation of the adjustment member. Owing to the use of the rotatable adjustment member, a simple, conventional electric motor may be used as die acmator by means of which the adjustment member can be driven into rotation. In a further embodiment of die shaving apparatus according to die invention, the carrier is a common carrier for at least two cutting units, while the acmator is a common acmator for me cutting units, so that a simple and effective construction of the shaving apparatus is provided. In a yet further embodiment of die shavi apparatus according to die invention, die carrier rests on a cam provided on die rotatable adjustment member under die influence of a further elastically deformable element. A transmission ratio obtaining between the acmator and die carrier is determined by a profile provided on die cam, while a suitable design of said profile leads to an accurate adjustabilit of die cutting element. A further embodiment of a shaving apparatus according to die invention characterized in that die electrical control unit has an electrical input which is connected to an electrical output of a position sensor which is capable of measuring a position of die cutting unit relative to the holder. Owing to the use of said position sensor, die control unit can detect a difference between an actual position of the cutting unit measured by d e position sensor and a desired position of die cutting unit determined by die control unit. Th measured position is rendered equal to die desired position in diat die acmator is controlled in a suitable manner, so mat an accurate adjustaient of me cutting unit is provided. A yet further embodiment of a shaving apparatus according to die invention is characterized in diat the position sensor is capable of measuring an angle of rotation of die adjustment member relative to die holder. Since the angle of rotation through which die adjustment member has been rotated relative to die holder determines the position of the external cutting member relative to the holder, die position of d e cutting unit can be measured in a simple and practical manner by means of said position sensor. A special embodiment of a shaving apparams according to die invention i characterized in diat d e cutting unit is arranged in a holder and is displaceable relative to di holder against a pretensioning force which has a value which is adjustable by means of die acmator. During shaving, die cutting unit is displaced relative to d e holder under die influence of a force exerted on die shaving apparams by the user. The shaving performance and d e shaving comfort experienced by die user depend on a pressure exerted on die skin b die cutting unit, which pressure depends on said pretensioning force. If the acmator can be controlled by a suitable control unit, a shaving comfort desired by die user can be maintaine during shaving through adjustment of die value of die pretensioning force by means of the acmator, and an optimum shaving performance can be achieved in relation to diis desired shaving comfort. A further embodiment of a shaving apparams according to die invention i characterized in mat me pretensioning force is exerted by an elastically deformable element which has a mechanical stiffness which is adjustable by means of die acmator. The cutting unit is displaceable relative to d e holder over a limited distance only. Owing to die use of die elastically deformable element, die pressure exerted on die skin by die cutting unit and dependent on die pretensioning force is determined by die distance over which the cutting unit is displaced relative to d e holder and by die value of d e mechanical stiffness of said element. Since the mechanical stiffness of die elastically deformable element is adjustable, a wide range of adjustment values for die pretensioning force is achieved in spite of the limite displaceability of the cutting unit. A yet further embodiment of a shaving apparams according to die invention is characterized in diat die elastically deformable element is coupled to die external cutting member, while the internal cutting member is held in die external cutting member under die influence of a pretensioning force of a further elastically deformable element. Coupling of me elastically deformable element to die external cutting member means that d e pretensioning force is exerted directly on d e external cutting member to be placed against die skin, while the internal cutting member remains in a desired position relative to die external cutting member during displacement of die external cutting member through the use of the further elastically deformable element. A particular embodiment of a shaving apparams according to die invention is characterized in diat die elastically deformable element is a mechanical blade spring which can be supported by a support element which is displaceable by means of me acmator. The mechanical stiffness of the blade spring depends on an effective lengdi of me blade spring, which effective lengdi is substantially equal to die length of an elastically deformable portion of the blade spring and is determined by the position of e support element. The effective length and d e mechanical stiffness of the mechanical blade spring are dius adjustable in a constructionally simple manner dirough displacement of die support element by means of the acmator. A further embodiment of a shaving apparams according to d e invention is characterized in that the support element cooperating with die cutting unit is provided on a displaceable carrier which is coupled to an adjusttnent member which is rotatable relative to the holder by means of die acmator, the carrier being displaceable dirough a rotation of the adjustment member. Owing to the use of die rotatable adjustment member, die acmator may be a simple, conventional electric motor by means of which the adjustment member can be driven into rotation. A further embodiment of die shaving apparams according to me invention comprises at least two cutting units, while the carrier is a common carrier for the support elements cooperating wim the cutting units, so diat die pretensioning force of the cutting units is adjustable by means of only one acmator, and a simple and effective construction of the shaving apparams is achieved. In a yet further embodiment of die shaving apparams according to die invention, the carrier rests on a cam provided on die rotatable adjustment member. A transmission ratio obtaining between die actuator and die carrier is determined by a profile provided on die cam, while an accurate adjustment possibility for the cutting elements is achieved dirough a suitable design of said profile. A yet further embodiment of a shaving apparams according to die invention is characterized in that the electrical control unit has an electrical input which is connected to an electrical output of a sensor capable of measuring the pretensioning force of the cutting unit. Owing to the use of die sensor, the control unit is capable of detecting a difference between an actual value of die pretensioning force measured by die sensor and a desired value of die pretensioning force determined by die control unit. The measured pretensioning force is rendered equal to die desired pretensioning force in that die acmator is controlled in a suitable manner, so that an accurate adjustment of e cutting unit is provided. A special embodiment of a shaving apparams according to die invention is characterized in that an angle of rotation of die adjustment member relative to d e holder is measurable by means of the sensor, while a further electrical input of die control unit is connected to an electrical output of a further sensor capable of measuring a position of die cutting unit relative to the holder. Since die mechanical stiffness of the blade spring is determined by d e position of die support element, which the position of die support element is determined by d e angle of rotation of the adjustment member, the mechanical stiffness can be measured by means of the sensor. Since die pretensioning force of the cutting unit is determined by die value of die mechanical stiffness of the blade spring and by die position of die cutting unit relative to die holder, which is measurable by means of d e further sensor, it is possible to measure the pretensioning force in a practical manner by means of said sensor, further sensor, and control unit. A further embodiment of a shaving apparams according to die invention is characterized in mat d e further sensor is a strain gauge sensor by means of which a deformation of a spring fastened between die external cutting member and die holder is measurable. Since die deformation of said spring is determined by die position of the external cutting member relative to the holder, die position of die external cutting member can be measured in a simple and practical manner by means of said further sensor. A still further embodiment of a shaving apparams according to the invention is characterized in that d e electric motor has a speed which is controllable by means of the electrical control unit. A comparatively high motor speed is required for achieving a desired shaving performance in die case of a comparatively great number of hairs per unit skin surface, while the same shaving performance can be achieved at a comparatively low motor speed in d e case of a comparatively small number of hairs per unit skin surface. Since me skin irritation level increases widi an increasing speed of the internal cutting member, and die shaving comfort is thus dependent on die speed of die electric motor, me balance between shaving performance and shaving comfort is further improved in that die motor speed is controlled in a suitable manner by means of me electrical control unit. A special embodiment of a shaving apparams according to d e invention is characterized in d at die electrical control unit has an electrical input which is connected to an electrical output of an operational member with which a desired balance between shaving performance and shaving comfort can be set. A user of die shaving apparams can adjust a balance between shaving performance, i.e. the speed of die shaving process and d e skin smoothness to be achieved, and shaving comfort, i.e. the acceptable skin irritation level, desired by him by means of said operational member. This balance is achieved in diat die control unit adjusts die cutting unit in a suitable manner during die shaving process. A further embodiment of a shaving apparams according to d e invention is characterized in that die electrical control unit has an electrical input which is connected to an electrical output of a timer capable of measuring a time which has elapsed during a shaving operation. The use of the timer renders it possible for die control unit to control die cutting unit as a function of the time which has elapsed during a shaving operation. Since the conditions which influence the shaving performance and die shaving comfort experienced by the user change during a shaving operation, die balance between shaving performance and shaving comfort can be further improved in that the cutting unit is controlled in a suitable manner as a function of die time which has elapsed during a shaving operation. A still further embodiment of a shaving apparams according to the invention is characterized in that die control unit is provided wid a calculation unit for calculating an average shaving time over a number of previous shaving operations, die control unit determining die time which has elapsed during a shaving operation in relation to die calculated average shaving time. Since the time which has elapsed during a shaving operation is determined in relation to the average shaving time, the cutting unit can be so controlled by d e control unit diat an optimum balance between a shaving performance and shaving comfort is achieved for die user, provided die shaving operation takes place in die average shaving time. Thus an optimum balance between shaving performance and shaving comfort is achieved botii for users widi a comparatively long average shaving time and for users widi a comparatively short average shaving time. A special embodiment of a shaving apparams according to d e invention is characterized in that die electrical control unit has an electrical input which is connected to an electrical output of a detector capable of measuring a number of hairs cut by the cutting unit per unit time. The use of said detector renders d e cutting unit controllable by the control unit during a shaving operation as a function of die number of hairs cut by the cutting unit per unit time, which number depends on die number of hairs per unit skin surface. Since the shaving performance and d e shaving comfort experienced by d e user depend on die number of hairs per unit skin surface, the balance between shaving performance and shaving comfort may be further improved by controlling die cutting unit in a suitable manner in dependence on d e number of hairs cut by die cutting unit per unit time. A further embodiment of a shaving apparams according to die invention is characterized in diat die detector is provided widi a microphone capable of detecting an acoustic signal produced by d e cutting unit, and widi an electrical filter capable of filtering a cutting frequency from the acoustic signal. The cutting frequency measured by means of the microphone and the filter is me number of individual hair cut operations canied out by die cutting unit per unit time, i.e. the number of hairs which the cutting unit cuts per unit time. The detector constructed in d is way is reliable and particularly suitable for incorporation in the limited space in d e shaving apparams. A yet further embodiment of a shaving apparams according to die invention is characterized in diat die electrical control unit has an electrical input which is connected to an electrical output of a force sensor capable of measuring a skin contact force exerted on die cutting unit. Owing to die use of said force sensor, die cutting unit is controllable by the control unit during a shaving operation as a function of the skin contact force exerted on d e cutting unit, which force is dependent on die force with which the user presses die shaving apparams against the skin. Since die shaving performance and die shaving comfort experienced by die user depend on said skin contact force, the balance between shaving performance and shaving comfort can be further improved by controlling die cutting unit in a suitable manner in dependence on die measured skin contact force. A particular embodiment of a shaving apparams according to die invention is characterized in mat the force sensor comprises a strain gauge sensor which is provided on an elastically deformable bridge, while the rotatable adjustment member rests on die bridge in a direction parallel to a force to be measured and has a mechanical stiffness in said direction which is comparatively small compared with a mechanical stiffness which the bridge has in said direction. A force can be measured by means of said strain gauge sensor which is exerted on die adjustment member by the carrier of the cutting unit. Since this force depends on die skin contact force exerted on die cutting unit, die skin contact force can be measured in a simple and practical manner by means of said strain gauge sensor. A further embodiment of a shaving apparams according to die invention is characterized in that die force sensor by which the skin contact force can be measured is die sensor by which the pretensioning force of die cutting unit can be measured. The force sensor dius has a dual function, whereby die number of sensors required is reduced. A yet further embodiment of a shaving apparams according to die invention is characterized in that the electrical control unit is provided widi means for controlling the electrical acmator, with a first electrical input which is connected to an electrical output of the force sensor, a second electrical input which is connected to die electrical output of the timer, a third electrical input which is connected to die electrical output of the operational member, a fourth electrical input which is connected to die electrical output of the detector, and an electrical output for supplying an output signal which corresponds to a desired position of d e cutting unit above die holder or a desired value of die pretensioning force of the cutting unit. Owing to the use of die four electrical inputs mentioned above, die cutting unit can be controlled by die acmator in dependence on d e balance between shaving performance and shaving comfort desired by die user, die time which has elapsed during a shaving operation, die number of hairs per unit skin surface, and die skin contact force exerted on d e cutting unit, so that die shaving performance and d e shaving comfort are adapted to me wishes and features of the user of the shaving apparams to a high degree. A special embodiment of a shaving apparams according to die invention is characterized in diat said means determine the output signal in accordance wid a first control rule according to which the desired position above die holder or die pretensioning force decreases when die measured skin contact force increases, and die desired position above die holder or die pretensioning force increases when an admissible skin deformation around die cutting unit increases, while said means determine die admissible skin deformation in accordance widi a second control rule. The skin deformation around die cutting unit is determined by the value of die skin contact force and by die position of die cutting unit above the holder or me pretensioning force of die cutting unit. The skin deformation increases when d e position above die holder or die pretensioning force increases at a constant skin contact force, or when the skin contact force increases at a constant position above the holder or constant pretensioning force. Since the admissible skin deformation is determined by die second control rule, the output signal corresponding to die desired position or pretensioning force of the cutting unit can be determined in a simple and practical manner by means of die first control rule as a function of die admissible skin deformation and die measured skin contact force. A further embodiment of a shaving apparams according to die invention is characterized in that, in accordance widi die second control rule, die admissible skin deformation decreases when a desired speed of die motor increases, and die admissible skin deformation increases when an admissible number of skin damage points per unit time increases, while the means determine the admissible number of skin damage points per unit time in accordance widi a diird control rule and die desired motor speed in accordance widi a fourth control rule. The number of skin damage points per unit time is determined by die deformation of the skin around die cutting unit and die speed of die internal cutting member, which is dependent on d e motor speed. The number of skin damage points per unit time increases when the skin deformation around d e cutting unit becomes greater at a constant motor speed, or when d e motor speed increases at a constant skin deformation around me cutting unit. Since the admissible number of skin damage points per unit time is determined by d e ird control rule and die desired motor speed by die fourth control rule, die admissible skin deformation can be determined in a simple and practical manner by means of said second control rule as a function of die admissible number of skin damage points per unit time and die desired motor speed. A yet further embodiment of a shaving apparams according to d e invention is characterized in diat, in accordance widi die d ird control rule, die admissible number of skin damage points per unit time increases widi an increase in die time which has elapsed during a shaving operation, die increase in the admissible number of skin damage points per unit time being comparatively small if the operational member is in a position in which a user of me shaving apparams wishes a comparatively high shaving comfort and comparatively low shaving performance, and being comparatively great if the operational member is in a position in which a user of die shaving apparams desires a comparatively low shaving comfort and comparatively high shaving performance. The cutting unit mainly cuts long hairs during an initial phase of die shaving process, die elapsed time then being comparatively short. By allowing only a small number of skin damage points in die initial phase, during which the comparatively long hairs are shortened, a reserve is built up for skin damage still admissible in an end phase of the shaving process, during which a desired smoothness is to be achieved dirough further shortening of die hairs. If the user wants a comparatively high shaving performance and a comparatively low shaving comfort, a comparatively great number of skin damage points per unit time is allowed in accordance widi d e diird control rule, so diat in accordance widi the second condrol rule a comparatively great skin deformation is allowed and according to die first control rule die cutting unit should be comparatively high above the holder or should have a comparatively strong pretensioning force. If the user wants a comparatively low shaving performance and a comparatively high shaving comfort, a comparatively small number of skin damage points per unit time is allowed according to die diird control rule, so diat according to die second control rule a comparatively small skin deformation is allowed, and according to me first control rule the cutting unit should be comparatively low above die holder or should have a comparatively weak pretensioning force. A special embodiment of a shaving apparams according to die invention is characterized in that, according to die fourth control rule, d e desired motor speed increases wid an increase in the measured number of hairs cut by the cutting unit per unit time, the desired motor speed decreases when die time which has elapsed during a shaving operation increases, and the increase in die desired motor speed widi an increase in me measured number of hairs cut by die cutting unit per unit time is comparatively small if the elapsed time is short, and is comparatively great if the elapsed time is long. If die number of hairs cut by the cutting unit per unit time (hair supply) is comparatively great, die internal cutting member is displaced relative to die external cutting member under die influence of the cutting forces which occur. The displacement of me internal cutting member relative to the external cutting member impairs the shaving performance. An increase in the motor speed at an increase in die hair supply renders die position of die internal cutting member in die external cutting member more stable, i.e. this position is less disturbed and die shaving performance is less impaired. Since me increase in die desired motor speed widi an increase in die measured number of hairs cut by the cutting unit per unit time is comparatively great if the elapsed time has been comparatively long, the needs of so-called local shavers are taken into account, i.e. of users who shave a portion of die skin until smooth each time and subsequently move to a yet unshaven portion. A further embodiment of a shaving apparams according to die invention is characterized in mat said means are provided widi a further electrical output for supplying a further output signal which corresponds to die desired motor speed determined in accordance widi die fourth control rule. Thus the control unit controls bodi die adjustment of die cutting unit and die speed of die motor as a function of the balance between shaving performance and shaving comfort desired by die user, d e time which has elapsed during a shaving operation, die number of hairs per unit skin surface, and die skin contact force exerted on die cutting unit. A yet further embodiment of a shaving apparams according to die invention is characterized in that the electrical control unit is provided widi means for controlling the speed of die electric motor, with a first electrical input connected to die electrical output of the timer, a second electrical input connected to die electrical output of the detector, and an electrical output for supplying an output signal which corresponds to a desired motor speed and which is determined by a control rule. The control of die motor speed by said means is not directly dependent on die control to be used for tine acmator which is to adjust the cutting unit. The said means for controlling the motor speed may ti us be applied in combination widi alternative means for controlling said acmator. A special embodiment of a shaving apparams according to die invention is characterized in diat, in accordance widi die control rule, die desired motor speed increases with an increase in die measured number of hairs cut by the cutting unit per unit time, the desired motor speed decreases as die time elapsed during a shaving operation increases, and the increase in d e desired motor speed widi an increase in die measured number of hairs cut by the cutting unit per unit time is comparatively small if the elapsed time is short, and comparatively great if the elapsed time is long. If die number of hairs cut by me cutting unit per unit time (hair supply) is comparatively great, the internal cutting member is displaced relative to me external cutting member under die influence of the cutting forces which occur. The displacement of die internal cutting member relative to die external cutting member impairs the shaving performance. By increasing the motor speed wid an increase in die hair supply, the position of die internal cutting member in the external cutting member becomes more stable, i.e. this position is less disturbed by die cutting forces occurring, and die shaving performance is less impaired. Since me increase in the desired motor speed with an increase in die measured number of hairs cut by the cutting unit per unit time is comparatively great if the elapsed time period is comparatively long, the needs of so-called local shavers are taken into account, i.e. of users who shave a portion of die skin until smooth each time and subsequently move to an as yet unshaven portion. A further embodiment of a shaving apparams according to die invention is characterized in diat die control rules determine die output signal in accordance wid an algoridim based on fuzzy logic. According to die algoritiim based on fuzzy logic, a range of each input quantity for each control rule is subdivided into a number of classes, and a membership of one of the classes is assigned to an instantaneous input quantity in accordance widi a membership function. The output quantity of die control rule is determined in accordance wid a logic rule as a function of a membership of the input quantities ascertained in accordance widi die membership function. A desired behaviour of die shaving apparams as a function of die input quantities can tiius be laid down in die control rules in a simple manner. In addition, die desired behaviour of the shaving apparams can be changed in a simple and flexible manner in a design phase if the knowledge of or insight into the operation of d e shaving apparams changes or if new input or output quantities are desired. The invention will be explained in more detail below widi reference to die drawing, in which Fig. la is a front elevation of a first embodiment of a shaving apparams according to die invention, Fig. lb is a side elevation of die shaving apparams of Fig. la, Fig. 2 is a cross-section taken on die line II-II in Fig. la, Fig. 3a shows a common closing plate of the shaving apparams of Fig. la, Fig. 3b shows a common carrier of the shaving apparams of Fig. la, Fig. 3c shows a common blade spring of die shaving apparams of Fig. la, Fig. 3d shows an adjustment member of the shaving apparams of Fig. la, Fig. 4 is a cross-section taken on the line IV-IV in Fig. 2, Fig. 5 shows a second embodiment of a shaving apparams according to die invention, Fig. 6 is a cross-section taken on die line VI- VI in Fig. 5, Fig. 7a shows a holder of die shaving apparams of Fig. 5, Fig. 7b shows a common closing plate of die shaving apparams of Fig. 5, Fig. 7c shows a common blade spring of me shaving apparams of Fig. 5, Fig. 7d shows a common carrier of the shaving apparams of Fig. 5, Fig. 7e shows a support ring of the shaving apparams of Fig. 5, Fig. 8 is a plan view of die closing plate of Fig. 7b, the blade spring of Fig. 7c, the carrier of Fig. 7d, and die support rings of Fig. 7e in d e mounted state, Fig. 9 is a cross-section taken on die line IX-IX in Fig. 6, Fig. 10 is a block diagram of a control unit of die shaving apparams of Fig. la or Fig. 5, Figs. 11a to lid show membership functions of input signals and output signals based on fuzzy logic of a first, a second, a diird, and a fourth sub-processor, respectively, of d e control unit of Fig. 10, and Figs. 12a to 12d contain Tables in which a class of the output signals assigned in accordance widi a logic rule is represented as a function of the input signals of the sub-processors of die control unit of Fig. 10. A first embodiment of a shaving apparams 1 according to me invention shown in Figs. 1 to 4 comprises a housing 3 with a handle 5 for a user of die shaving apparams 1. The housing 3 has a holder 7 in which three round openings 9 are provided in triangular arrangement, a cutting unit 11 being positioned in each opening 9. The cutting units 11 each comprise an external cutting member 13, which is provided widi an annular rim 15 in which slotted hair trap openings 17 are provided. As is visible in Fig. 2, d e cutting units 11 further comprise an internal cutting member 19 widi a rim of cutters 21 which are present in die rim 15 of the external cutting member 13. The internal cutting members 19 are rotatable in die external cutting members 13 by means of an electric motor 23 arranged in d e housing 3, comprising an output shaft 25 with a gear 27, and fastened to a motor frame 29. In the motor frame 29, furthermore, three gears 31 have their rotation bearings, which gears are in engagement widi die gear 27 of die output shaft 25. The gears 31 are each coupled to a hollow drive shaft 33 for a respective internal cutting member 19, which drive shafts 33 are slidable relative to the gears 31 in a direction parallel to an axial direction X shown in Fig. 2. A pretensioned mechanical helical spring 35 is fastened between the gears 31 and die drive shafts 33, whereby the internal cutting members 19 are held in the external cutting members 13 under die influence of a pretensioning force of me helical springs 35. It is noted d at Fig. 2 shows only one gear 31, one drive shaft 33, one internal cutting member 19, and one external cutting member 13 in cross-section. As is visible in Fig. 2, a common closing plate 37, a common carrier 39, and a common blade spring 41 for the d ree external cutting members 13 are present in die holder 7. The closing plate 37, the carrier 39 and die blade spring 41 are separately depicted in Figs. 3a, 3b and 3c. As Fig. 2 shows, die closing plate 37, the carrier 39, and die blade spring 41 are fastened around a central fastening pin 43 of the holder 7 under d e influence of a pretenionsing force of a mechanical spring 45 which is tensioned between the blade spring 41 and a blocking stud 47 which can be screwed onto die fastening pin 43. As Fig. 3b shows, die carrier 39 comprises three carrier rings 49 which are fastened to a star-shaped central portion 51 of die carrier 39 by means of elastic bridges 53, each of which has an opening 55. The use of die elastic bridges 53 and a favourable choice of die dimensions of me carrier rings 49 render die carrier rings 49 flexible relative to die central portion 51. Only one of die carrier rings 49 is visible in cross-section in Fig. 2. As Fig. 3c shows, die common blade spring 41 comprises three pairs of flexible strips 57 which each have a raised end 59. In die mounted state shown in Fig. 2, die raised ends 59 of d e blade spring 41 are present in die openings 55 of die carrier 39, while the external cutting members 13 each rest on one pair of raised ends 59 and on a ridge 61 of one of d e carrier rings 49 visible in Fig. 3b. In Fig. 2, die raised ends 59 are not visible, while only one ridge 61 is visible in cross-section. The external cutting members 13 are held in position relative to d e carrier rings 49 by the common closing plate 37 shown in Fig. 3a, which is provided widi tiiree closing rings 63. Only one of the closing rings 63 is visible in cross- section in Fig. 2. As Fig. 2 shows, the external cutting members 13 have a flanged rim 65 with which me external cutting members 13 in me unloaded state bear on die closing rings 63 under d e influence of a pretensioning force of die common blade spring 41. When die user applies d e shaving apparams 1 against his skin, die skin exerts a skin contact force on die external cutting members 13. The external cutting members 13 are individually displaceable relative to die holder 7 under the influence of said skin contact force, whereby the carrier rings 49 and me strips 57 of the blade spring 41 are bent relative to the central portion 51 of d e carrier 39 over a distance which is dependent on die value of die skin contact force. The internal cutting members 19 follow the external cutting members 13 during d is widi die drive shafts 33 moving relative to me gears 31 parallel to the axial direction X. As Fig. 3a shows, a wire spring 67 is provided around each closing ring 63 of the closing plate 37. Only one of die wire springs 67 is visible in Fig. 2. As Fig. 2 shows, each wire spring 67 in die mounted state rests on a protrusion 69 provided in me holder 7, so diat die wire springs 67 in the mounted state exert a pretensioning force on die closing plate 37. The closing plate 37 rests on die carrier 39 under die influence of the pretensioning force of the wire springs 67. As Fig. 3b further shows, d e carrier 39 is provided with tiiree support plates 71. Under die influence of me pretensioning force of die wire springs 67, the carrier 39 bears with the tiiree support plates 71 via three pins 73 on three cams 75 which belong to an adjustment member 77 shown in Fig. 3d. It is noted diat Fig. 2 shows only one of tiie support plates 71, one of the pins 73 and one of die cams 75 in cross-section. The pins 73 are guided so as to be displaceable parallel to die axial direction X in a channel 79 which is provided in a first intermediate plate 81 belonging to die housing 3, while the adjustment member 77 is journalled in a second intermediate plate 83 belonging to die housing 3 and extending parallel to the first intermediate plate 81. As Fig. 3d shows, the adjustment member 77 has three arms 85, the cams 75 being arranged at die ends of die arms 85. It is noted d at d e arms 85 are not visible in Fig. 2. One of the cams 75 is provided wid a tootiied rim 87 on an inside, which toothed rim is in engagement widi a pinion 89 provided on an output shaft of an electrical actuator 91 fastened to die second intermediate plate 83, as is shown in Fig. 4. The cams 75 each have an oblique profile on an upper side. When die adjustment member 77 is rotated relative to die holder 7 by means of die acmator 91, die carrier 39 and closing plate 37 resting on me cams 75 via the pins 73 are displaced parallel to die axial direction X relative to die holder 7 under elastic deformation of the wire springs 67, so that a height H shown in Fig. 2 over which die external cutting members 13 project from die holder 7 in die unloaded state changes. As Figs. 2 and 4 show, a strip-shaped elastically deformable bridge 93 is present below each cam 75 of d e adjustment member 77. Only one of the bridges 93 is shown in cross-section in Fig. 2. As Fig. 4 shows, die cams 75 rest on first ends 95 of die bridges 93, d e ends 95 being arranged below d e pins 73. Second ends 97 of die bridges 93 are fastened to the second intermediate plate 83. The bridges 93 have a mechanical stiffness parallel to die axial direction X which is comparatively great in relation to a mechanical stiffness of me arms 85 of the adjustment member 77 in said direction. A strain gauge sensor 99 which is known er se and generally used, is provided on each bridge 93. A skin contact force exerted on die external cutting members 93 is transmitted dirough the common carrier 39, the pins 73, and the cams 75 to the bridges 93, which are elastically deformed under die influence of die skin contact force. Since die mechanical stiffness of the bridges 93 parallel to die X-direction is comparatively great in relation to die mechanical stiffness of die arms 85, the deformation of the bridges 93 is determined substantially solely by die value of die skin contact force, so that die skin contact force can be measured by means of said strain gauge sensors 99. As Fig. 4 further shows, a position sensor 101 is present near one of tiie cams 75 such as, for example, a digital position detector which is known per se and generally used, whereby an angle of rotation of die adjustment member 77 relative to the holder 7 can be measured. Since die cams 75 have a defined shape, d e height H can be derived from a measured angle of rotation of die adjustment member 77, H being the height over which the external cutting members 13 project from the holder 7 in the unloaded state. The shaving apparams 1 is provided widi an electrical control unit 103 widi which the actuator 91, i.e. the height H over which the external cutting members 13 project from the holder 7 in die unloaded state, and die speed of die motor 23 can be controlled in a manner yet to be described further below. The shaving performance of the shaving apparams 1, i.e. the speed of die shaving process and die achievable skin smoothness, and die shaving comfort experienced by die user during d e shaving process, i.e. the skin irritation level, depend on said height H and die speed of d e motor 23. When die height H is comparatively small, the deformation of die skin around die external cutting members 13 is comparatively small. In this condition, die skin penetrates die hair trap openings 17 of die external curring members 13 to a comparatively small deptii, so that the shaving comfort is comparatively great, but me shaving performance comparatively low. If said height H is comparatively great, the skin deformation around die external cutting members 13 is comparatively great. In mis condition, d e skin penetrates the hair trap openings 17 over a comparatively great deptii, so that die shaving performance is comparatively high but the experienced skin comfort comparatively small. Furthermore, the skin irritation level is greater at a comparatively high speed of die motor 23 than at a comparatively low speed of d e motor 23. The shaving performance and shaving comfort further depend on a number of conditions which change in me course of a shaving operation or a number of shaving operations such as, for example, die hair supply, i.e. the number of hairs per unit skin surface to be cut, or the skin contact force referred to above. Since d e height H and die speed of die shaving apparams 1 can be controlled by die control unit 103, die height H and d e speed, i.e. the shaving performance and shaving comfort, can be made variable during die shaving operation when said conditions change during die shaving operation. In this manner, a particularly favourable balance between the achieved shaving performance and die experienced shaving comfort is obtained tiiroughout the shaving operation. A second embodiment of a shaving apparams 105 according to die invention shown in Figs. 5 to 9 comprises a housing 107 which is also provided widi a handle 109 for a user of die shaving apparams 105. The housing 107 has a holder 111 which is shown in detail in Fig. 7a and in which three openings 113 are provided in triangular arrangement. As Fig. 7a shows, a frame 115 is fastened in each opening 113, which frame is pivotable relative to the holder 111 about a pivot axis 117. The frames 115 adjoin one another two-by-two by their sides 119 which are arranged relative to one anotiier in a star shape. The sides 119 are in engagement widi one anotiier, so that the frames 115 can pivot jointly only about the pivot axes 117. As is visible in Figs. 5 and 6, a cutting unit 121 is arranged in each frame 115 with an external cutting member 123 and an internal cutting member 125 provided dierein. The external cutting member 123 and internal cutting member 125 correspond to die external and internal cutting members 13 and 19 of die shaving apparams 1 described above. The internal cutting members 125 can be driven into rotation by means of an electric motor 127 via a transmission which corresponds to diat of d e shaving apparams 1 , while the internal cutting members 125 are each coupled to a drive shaft 129 which is slidable parallel to an axial X-direction against a pretensioning force of a mechanical spring 131. Only one frame 115, one external cutting member 123, one internal cutting member 125 and one drive shaft 129 are visible in cross-section in Fig. 6. As is visible in Figs. 6 and 8, die following are present in the holder 111: a common closing plate 133, a common blade spring 135, and a common carrier 137 for the three external cutting members 123. The closing plate 133, die blade spring 135, and die carrier 137 are individually shown in Figs. 7b, 7c and 7d. As Fig. 6 shows, die closing plate 133 and die blade spring 135 are fastened around a central fastening pin 143 of the holder 111 by means of a blocking smd 139 and a closing ring 141. As Fig. 6 further shows, each external cutting member 123 is closed up between one of die frames 115 and a support ring 145 shown in Fig. 7e. Only one support ring 145 is visible in cross-section in Fig. 6. As Figs. 6 and 7e show, d e support rings 145 each comprise two support arms 147 on which the relevant external cutting member 123 rests, and two journals 149 which are clamped in between die closing plate 133 and die blade spring 135 under die influence of a pretensioning force of the blade spring 135 in a manner yet to be described below. Fig. 6 shows only one of die journals 149 of die support ring 145 represented. As Fig. 7c shows, die blade spring 135 has tiiree pairs of flexible strips 151 which each have an end 153 bent in the plane of die blade spring 135. As Fig. 7b shows, die closing plate 133 has tiiree forked arms 155 each provided widi two tapering seats 157. In a mounted state shown in Figs. 6 and 8, die journals 149 of each support ring 145 are present in two mutually opposed seats 157 of two different arms 155 of the closing plate 133. The journals 149 are supported tiien by two mutually opposed ends 153 of two strips 151 of the blade spring 135 belonging to two different pairs. In Fig. 6, only one journal 149, one seat 157, and one strip 151 with bent end 153 are visible. The external cutting members 123 and die support rings 145 are individually displaceable relative to die holder 111 and die frames 115 against me pretensioning force of the blade spring 135 under die influence of a skin contact force exerted on d e external cutting members 123. Furthermore, the external cutting members 123 and die support rings 145 are pivotable relative to the holder 111 about a pivot axis 159 shown in Fig. 8, which extends dirough die journals 149 and runs parallel to die pivot axis 117 of the relevant frame 115, under die influence of a skin contact force. As Fig. 7b further shows, die closing plate 133 comprises three flexible hooks 161. Only one hook 161 is visible in Fig. 6. Said common carrier 137 is connected to the closing plate 133 by means of the hooks 161, tiie carrier 137 being displaceable between die blade spring 135 and die ends of die hooks 161. As Fig. 7d shows, the common carrier 137 comprises three support plates 163 and tiiree pairs of support elements 165 which are each provided near one of d e support plates 163. Via three pins 167, tiie three support plates 163 bear on tiiree cams 169 which belong to an adjustment member 171 visible in Fig. 9 and corresponding to the adjustment member 77 shown in Fig. 3d. Only one of die support plates 163, one of the support elements 165, one of die pins 167, and one of die cams 169 are visible in Fig. 6. The pins 167 are each guided so as to be displaceable parallel to die axial direction X in a channel 173 provided in a first intermediate plate 175 belonging to the housing 107, while die adjustment member 171 is journalled in a second intermediate plate 177 belonging to the housing 107 and extending parallel to die first intermediate plate 175. In an uppermost position of the carrier 137 and die support elements 165 shown in Fig. 6, die flexible strips 151 of the blade spring 135 are each supported by one of d e support elements 165. Only one support element 165 is visible in Fig. 6. As can be seen in Fig. 8, the strips 151 are supported near a central portion where die strips 151 are bent. Since the support rings 145 and die external cutting members 123 are supported by die bent ends 153 of d e strips 151, the pretensioning force of die strips 151 in the uppermost position of the canier 137 is determined by an effective lengdi L, of the strips 151 shown in Fig. 8. In a bottom position of tiie carrier 137 and die support elements 165, the flexible strips 151 are not supported by die support elements 165 both in a condition in which the external cutting members 123 are unloaded and in a condition in which the external cutting members 123 are substantially sunken into die frames 115 under d e influence of a comparatively great skin contact force. The pretensioning force of die strips 151 in die bottom position of die carrier 137, accordingly, is determined by an effective lengdi L 2 shown in Fig. 8 which is greater than die effective length L, mentioned above. When die carrier 137 and die support elements 165 are in an intermediate position between the uppermost and bottom position, die effective length of the strips 151 is equal to Lj when tiie external cutting members 123 are unloaded or are subjected to a comparatively small skin contact force, and die effective lengdi is equal to L< when die external cutting members 123 are subjected to a comparatively great skin contact force. Widi the carrier 137 in die uppermost position, die snips 151 have a comparatively great mechanical stiffness as a result of die comparatively small effective length L, of the strips 151, so that the pretensioning force of the strips 151 is also comparatively great. With die carrier 137 in the bottom position, the strips 151 have a comparatively small mechamcal stiffness as a result of die comparatively great effective lengdi L 2 , so that die pretensioning force of tiie strips 151 is comparatively small. In me intermediate position of die carrier 137, die pretensioning force of die strips 151 is comparatively small in an unloaded state of the external cutting members 123 and widi comparatively small skin contact forces, whereas die pretensioning force of die strips 151 is comparatively great for comparatively great skin contact forces. As Fig. 9 shows, die adjustment member 171 is rotatable relative to the holder 111 in a manner similar to that of the adjustment member 77 of the shaving apparams 1 by means of an electrical acmator 179 fastened to d e second intermediate plate 177. The value of die pretensioning force of die blade spring 135 is tiius adjustable dirough rotation of die adjustment member 171 by means of the acmator 179. As is visible in Fig. 9, a position sensor 181 corresponding to die position sensor 101 of die shaving apparams 1 is present near one of die cams 169 of d e adjustment member 171. A rotational angle of die adjustment member 171 relative to the holder 111 is measurable by means of die position sensor 181. Since die cams 169 have a defined shape, die support elements 165 of the carrier 137 have a defined position in a direction parallel to die axial direction X as a function of said rotational angle of die adjustment member 171, so that the mechanical stiffness of tiie strips 151 is indirectly measurable by means of me position sensor 181. Fig. 8 further shows that tiiree strip-shaped springs 183 are present in die holder 111. The strip-shaped springs 183 are each fastened to die housing 107 by means of a hook 185 and are each provided widi two raised ends 187 by means of which the springs 183 each rest under a pretension against die bent ends 153 of die strips 151 of the blade spring 135. Two strain gauge sensors 189, which are known er se and generally used, are provided on each strip-shaped spring 183. When die external cutting members 123 are displaced relative to d e holder 111 under the influence of a skin contact force, die strip-shaped springs 183 resting against die strips 151 are deformed. Since die deformation of the strip-shaped springs 183 is determined by die position of die external cutting members 123, the position of tiie external cutting members 123 can be measured by means of the strain gauge sensors 189. The pretensioning force of die strips 151, which follows from the mechanical stiffness of tiie strips 151 and die position of the external cutting members 123, can be derived in a manner to be described further below from the mechanical stiffness value of tiie strips 151 measured by means of the position sensor 181 and die position of die external cutting members 123 measured by means of die strain gauge sensors 189. As Fig. 5 further shows, the shaving apparams 105 is provided widi an electrical control unit 191 widi which the acmator 179, i.e. the mechanical stiffness of tiie strips 151 and d e pretensioning force of tiie blade spring 135, as well as the speed of die motor 127, can be controlled in a manner to be described further below. The shaving performance of tiie shaving apparams 105 and d e shaving comfort experienced by die user of die shaving apparams 105 during a shaving operation depend on die pretensioning force of the blade spring 135 and d e speed of die motor 127. It has been explained above wid reference to the shaving apparams 1 how the shaving performance and die shaving comfort depend on die speed of d e motor 23, 127. When the pretensioning force of die blade spring 135 is comparatively small, the external cutting members 123 are displaced over a comparatively great distance relative to die holder 111 as a result of a skin contact force exerted on die cutting members 123, so that the external cutting members 123 will lie comparatively deeply recessed in die holder 111 under d e influence of die skin contact force and die deformation of the skin around die external cutting members 123 will be comparatively small. Under tiiese circumstances, die skin will penetrate die hair trap openings of tiie external cutting members 123 over a small distance only, so diat die shaving comfort is comparatively high but the shaving performance comparatively low. When the pretensioning force of the blade spring 135 is comparatively great, die external cutting members 123 are displaced relative to die holder 111 over a comparatively small distance as a result of die skin contact force, so that in spite of the skin contact force die external cutting members 123 project comparatively far from the holder 111, and die skin deformation around die external cutting members 123 is comparatively great. Under tiiese circumstances, tiie skin penetrates comparatively deeply into me hair trap openings of die external cutting members 123, so that the shaving performance is comparatively high but the experienced shaving comfort is comparatively low. The shaving performance and shaving comfort of the shaving apparams 105 also depend on otiier conditions, as in die case of die shaving apparams 1, such as the value of the skin contact force and die time which has elapsed during a shaving operation. Since d e pretensioning force of die blade spring 135 and die speed of die motor 127 can be controlled by die control unit 191, said pretensioning force and speed, i.e. the shaving performance and shaving comfort, are adjustable during die shaving operation when said conditions change during die shaving operation. Thus a particularly favourable balance is achieved between die shaving performance of the shaving apparams 105 and die shaving comfort experienced by die user tiiroughout the shaving operation. It is apparent from the preceding descriptions of die first embodiment of die shaving apparams 1 and d e second embodiment of die shaving apparams 105 that the shaving performance and d e shaving comfort are qualitatively equally influenced by an increase or decrease in d e height H of the external cutting members 13 above the holder 7 of d e shaving apparams 1 and by an increase or decrease in die pretensioning force of the blade spring 135 of d e shaving apparams 105. The control unit 103 of die shaving apparams 1 and die control unit 191 of die shaving apparams 105, accordingly, are essentially die same. The block diagram shown in Fig. 10 therefore relates both to the control unit 103 of tiie shaving apparams 1 and to die control unit 191 of the shaving apparams 105. As Fig. 10 shows, the control unit 103, 191 has a first electrical output 193 for supplying a first electrical output signal u H or u E , corresponding to a desired height H of the external cutting members 13 of the shaving apparams 1 or to a pretensioning force of tiie blade spring 135 of the shaving apparams 105 as determined by die relevant control unit 103, 191. The control unit 103, 191 further comprises a second electrical output 195 for supplying a second electrical output signal u R which corresponds to a desired speed of die motor 23, 127 determined by die control unit 103, 191. The first output signal u H , u E is offered to an electrical supply unit 197 of the acmator 91, 179. As Fig. 10 shows, the supply unit 197 comprises a comparator 199 which compares the first output signal u H , u E with an output signal u φ H , u ψ E , supplied by die position sensor 101, 181 and corresponding to a measured height H of the external cutting members 13 and to a measured mechanical stiffness of die blade spring 135, respectively. The supply unit 197 further comprises a controller 201, which is known er se and in general use, which drives die acmator 91, 179 such that a differential signal δu H = u H - or όu E = u E - u φ E supplied by die comparator 199 becomes equal to zero, so diat die measured height H of the external cutting members 13 or the measured mechanical stiffness of die blade spring 135 are equal to the desired height H and d e desired mechanical stiffness, respectively. The second output signal u R is applied to an electrical supply unit 203 of die motor 23, 127. The supply unit 203 also comprises a comparator 205 which compares the second output signal u R with an output signal U RR supplied by a motor speed sensor which is known per se and generally used, which is depicted in Figs. 2 and 6, and which measures a speed of d e output shaft 25 of the motor 23, 127. The supply unit 203 further comprises a controller 209, which is known er se and generally used, which controls the motor 23, 127 such that a differential signal δu R = u R - U RR supplied by die comparator 205 becomes equal to zero, i.e. the measured speed of die motor 23, 127 is then equal to tiie desired speed. As Fig. 10 further shows, die control unit 103, 191 has a first electrical input 211 for receiving a first electrical input signal u F which corresponds to a measured skin contact force exerted on die external cutting members 13, 123, a second electrical input 213 for receiving a second electrical input signal u τ which corresponds to a measured time which has elapsed during a shaving operation, a diird electrical input 215 for receiving a diird electrical input signal u s which corresponds to a desired ratio between shaving performance and shaving comfort set by the user, and a fourth electrical input 217 for receiving a fourth electrical input signal u M which corresponds to a measured cutting frequency, i.e. a number of hairs cut by the cutting units 11, 121 per unit time. The control unit 103, 191 controls the acmator 91, 179 and d e speed of die motor 23, 127 in a manner yet to be described below in dependence on die four input signals u F , u τ , u s and u M , so that d e shaving performance and shaving comfort are adapted to the wishes and properties of die user and to die manner in which the user uses die shaving apparams 1, 105. An optimum balance between shaving performance and shaving comfort is thus obtained for die user. The first electrical input signal u F is supplied by a processor 219. In die first embodiment of die shaving apparams 1, the input signal u F corresponds to an average of tiiree signals u F1 , u^ and u F3 , each corresponding to a skin contact force measured by one of die tiiree strain gauge sensors 99, which average is calculated by die processor 219. In die second embodiment of die shaving apparams 105, the output signal u F corresponds to a measured average skin contact force calculated by die processor 219 as a function of die output signal u φ E supplied by die position sensor 181 and corresponding to d e measured mechanical stiffness of die blade spring 135, and of tiiree signals u H1 , u^ and u^, each corresponding to a position of the external cutting members 123 as measured by one of die three pairs of strain gauge sensors 189. The output signal u ΦE of the position sensor 181 tiius forms an input signal for die comparator 199, with which the desired and measured mechanical stiffnesses of die blade spring 135 are compared, as well as an input signal for die processor 219 widi which the skin contact force is calculated. The number of sensors required is limited tiiereby. In Fig. 10, tiie input signals u φ E , u H1 , u m and u^ of the processor 219 in tiie second embodiment of the shaving apparams 105 have been indicated by means of broken lines. The second electrical input signal u τ is supplied by a timer 221 which measures the time which has elapsed from a moment at which the shaving apparams 1, 105 was switched on by die user by means of a switching button 223 visible in Figs, la and 5. The timer 221 for this purpose comprises an electrical input 225 which is connected to die switching button 223. The input signal u τ is offered to a calculation unit 227 of d e control unit 103, 191. The calculation unit 227 comprises a memory 229 in which the total shaving time of a number of preceding shaving operations, for example ten operations, is stored. The calculation unit 227 calculates an average shaving time of said preceding shaving operations. An output signal u %τ of the calculation unit 227 corresponds to die quotient of d e time elapsed during a shaving operation (input signal u τ ) and die calculated average shaving time. The third electrical input signal u s is supplied by an operational member 231 shown in Figs, la and 5 which is provided on die housing 3, 107 of the shaving apparams 1, 105. By means of die operational member 231, the user of die shaving apparams 1, 105 may set a balance desired by him between die shaving performance and the shaving comfort. The operational member 231 comprises a slide 233 for diis purpose, which may be moved into any of a number of positions by die user. The fourth electrical input signal u M , finally, is supplied by a detector 235 which is capable of measuring a number of hairs cut by me cutting units 11, 121 per unit time (cutting frequency). The detector 235 for diis purpose comprises a microphone 237 such as, for example, an electret microphone which is known er se and generally used, which is provided on die first intermediate plate 81, 175, as is evident from Figs. 2 and 6. The microphone 237 supplies an acoustic signal u N which corresponds to die sound produced by die cutting units 11, 121 during die operation of cutting hairs offered dirough die hair trap openings 17. The acoustic signal u N is applied to an electrical filter 239, known er se and generally used, of die detector 235, which filters the cutting frequency (input signal u M ) from the acoustic signal u N , i.e. the number of hairs cut by the cutting units 11, 121 per unit time. As Fig. 10 shows, the control unit 103, 191 comprises a first sub- processor 241 which determines the first electrical output signal u H or u E , as applicable, as a function of tiie first input signal u F , and a first intermediate signal u D supplied by a second sub-processor 243 of die control unit 103, 191 and corresponding to an admissible skin deformation around die external cutting members 13, 123. An electrical filter 245 is furthermore connected between die first input 211 and die first sub-processor 241, filtering out comparatively short-period changes in die input signal u F , so that die shaving apparams 1, 105 does not react immediately to fast and transient changes in die skin contact force. The skin deformation around die external cutting members 13, 123 is determined in the case of shaving apparams 1 by tiie value of the skin contact force and die height H of the external cutting members 13 above the holder 7, and in the case of shaving apparams 105 by the value of the skin contact force and by die value of die pretensioning force of die blade spring 135. The skin deformation becomes greater when, given a constant skin contact force, die height H or the pretensioning force increases, or, given a constant height H or a constant pretensioning force, tiie skin contact force increases. The desired height H (output signal u H ) and d e desired pretensioning force (output signal u E ) may thus be determined when the skin contact force and die admissible skin deformation are known. The first sub-processor 241 determines die output signal u H , u E in accordance widi a first control rule, tiierefore, according to which d e desired height H or the desired pretensioning force (output signal u H , u E ) decreases when die measured skin contact force (input signal u F ) increases, so that die skin deformation remains substantially constant, and according to which die desired height H or the pretensioning force (output signal u H , u E ) increases at a constant skin contact force (input signal u F ) when die admissible skin deformation (intermediate signal u D ) increases. In the first embodiment of die shaving apparams 1, the first sub-processor 241 has a further electrical input 242 which is connected to the switch button 223. The further input 242 is indicated wid a broken line in Fig. 10. When die shaving apparams 1 is switched off wid the switching button 223, tiie control unit 103 and die acmator 91 bring me external cutting embers 13 into a position in which the external cutting members 13 are completely recessed in die holder 7 (H = 0). In die switched-off state of the shaving apparams 1, therefore, the cutting units 11 are less sensitive to damage, while in addition die switched-off state of the shaving apparams 1 is better recognizable for die user of die shaving apparams 1. As Fig. 10 further shows, the second sub-processor 243 determines die first intermediate signal u D which corresponds to an admissible skin deformation as a function of a second intermediate signal Uj supplied by a diird sub-processor 247 and corresponding to a number of skin damage points admissible per unit time, and of d e second output signal u R supplied by a fourth sub-processor 249. The number of skin damage points caused by die cutting units 11, 121 per unit time is determined in botii shaving apparatuses 1, 105 by the skin deformation around d e external cutting members 13, 123 and by die rotational speed of die internal cutting members 19, 125, which again is determined by die speed of motor 23, 127. The number of skin damage points caused per unit time increases when, at a constant motor speed, die skin deformation around die external cutting members 13, 123 increases, or when, at a constant skin deformation, the speed of die motor 23, 127 increases. The admissible skin deformation (intermediate signal u D ) can tiius be determined when die speed of d e motor 23, 127 and die admissible number of skin damage points per unit time are known. The second sub-processor 243 determines me intermediate signal u D in accordance widi a second control rule, tiierefore, according to which the admissible skin deformation (intermediate signal u D ) decreases when die desired motor speed (output signal u R ) increases, so diat the number of skin damage points caused per unit time remains substantially constant, and according to which the admissible skin deformation (intermediate signal u D ) at a constant desired motor speed (output signal u R ) increases when die admissible number of skin damage points per unit time (intermediate signal u,) increases. As Fig. 10 further shows, the third sub-processor 247 determines the second intermediate signal U[ which corresponds to an admissible number of skin damage points per unit time as a function of the output signal u %τ of the calculation unit 227 and of die diird input signal u s . The admissible number of skin damage points per unit time is determined by die balance desired by die user between die shaving performance and the shaving comfort, which shaving comfort depends not only on die number of skin damage points per unit time but also on the cumulative number of skin damage points during a shaving operation. When only a comparatively small number of skin damage points per unit time is allowed in an initial phase of the shaving operation, when me hairs are still comparatively long, so that d e hairs are only shortened d e first time, a comparatively great reserve is still present for yet admissible skin damage points in an end phase of die shaving operation, when die desired shaving performance (smoothness) is to be achieved in d at die hairs are shortened further. The intermediate signal u, is determined by die sub-processor 247 in accordance widi a diird control rule, tiierefore, according to which the admissible number of skin damage points per unit time (intermediate signal u,) increases widi an increase in the time elapsed during a shaving operation (signal u %τ ), the increase in the admissible number of skin damage points per unit time (intermediate signal u,) being comparatively small when me operational member 231 is placed in a position (C) in which the user desires a comparatively high shaving comfort and a comparatively low shaving performance, and being comparatively great when the operational member 231 is placed in a position (P) in which the user desires a comparatively low shaving comfort and a comparatively high shaving performance. Since die signal u %τ corresponds to die quotient of tiie time elapsed during a shaving operation and die average shaving time over a number of previous shaving operations, die admissible number of skin damage points per unit time (intermediate signal u,) is so determined by die diird sub-processor 247 diat the user is given an optimum balance between shaving performance and shaving comfort, provided d e shaving operation takes place in the average shaving time. An optimum balance between die shaving performance and the shaving comfort experienced is tiius achieved botii for users witii a comparatively long average shaving time and for users widi a comparatively short average shaving time. As Fig. 10 further shows, die fourth sub-processor 249 determines die second output signal u R which corresponds to die desired speed of die motor 23, 127 as a function of me output signal u %τ of the calculation unit 227 and die fourth input signal u M . Between die fourth input 217 and die fourth sub-processor 249 tiiere is a further electrical filter 251 which filters comparatively short-period changes in die input signal u M , so that the shaving apparams 1, 105 does not react immediately to fast and transient changes in die measured cutting frequency. The desired motor speed is determined by die sub-processor 249 in accordance wid a fourth control rule, according to which d e desired motor speed (output signal u R ) increases widi an increase in d e measured cutting frequency (input signal u M ). When the cutting frequency is comparatively high, die internal cutting members 19, 125 are displaced relative to die external cutting members 13, 123 under die influence of cutting forces exerted on die internal cutting members 19, 125. Since d e motor speed is comparatively high at comparatively high cutting frequencies, die internal cutting members 19, 125 have a comparatively high mechanical angular momentum at high cutting frequencies, so diat the rotational movement of tiie internal cutting members 19, 125 is comparatively stable and displacements of the internal cutting members 19, 125 relative to the external cutting members 13, 123 under die influence of me cutting forces are limited as much as possible. In accordance widi the fourth control rule, furthermore, the desired motor speed decreases as die time elapsed during a shaving operation increases, and die increase in d e desired motor speed at a given increase in me cutting frequency is comparatively small when the elapsed time is short, and comparatively great when die elapsed time is long. This takes into account me wishes of users who shave a comparatively small portion of die skin smooth each time and subsequently shave an as yet unshaven portion of die skin, in which case the measured cutting frequency fluctuates strongly during die shaving operation. The four control rules mentioned, according to which the control unit 103, 191 determines me output signals u H or u E , and u R as a function of die input signals u F , u τ , u s and u M each comprise an algoritiim based on so-called fuzzy logic. According to tiiese algorithms, a range of each of die input signals and output signals of the relevant sub- processors 241, 243, 247, 249 is divided into a number of classes for each sub-processor 241, 243, 247 and 249 of the control unit 103, 191. Figs. 11a to lid show an embodiment of die classes into which the input signals and output signals of die respective sub-processors 241, 243, 247 and 249 are subdivided. As Fig. 11a shows, die input signal u F of the first sub-processor 241 is divided into the classes L (low) and H (high), while the intermediate signal u D is divided into the classes L (low), L/M (low to medium), M (medium), M/H (medium to high) and H (high). The output signal u H or u E is subdivided into classes 1 (smallest height H or pretensioning force) up to 9 (greatest height H or pretensioning force). Each of the signals u F and u D occurring during a shaving operation is continuously assigned a membership of one of me relevant classes by the sub-processor 241 in accordance widi a membership function. The membership functions of the signals u F and u D are shown in Fig. 11a. The class to which the output signal u H or u E belongs during die shaving operation is determined by the sub-processor 241 in accordance widi a logic rule as a function of die classes of the signals u F and u D determined in accordance widi die membership functions. Fig. 12a shows a Table in which the class assigned to d e output signal u H or u E in accordance widi said logic rule is plotted as a function of the classes assigned to die signals u F and u D . It is noted d at Fig. 12a exclusively shows simations in which the signals u F and u D each belong to only one class according to die membership functions. However, the signals u F and u D may also belong to two classes. Fig. 11a shows, for example, that die signal u F belongs botii to class L and to class H when die signal u F lies between the limit values u FI and u F3 . In these simations, too, tiie sub-processor 241 determines to which class or classes the output signal u H or u E belongs in a usual manner known per se from fuzzy logic. The sub-processor 241 determines die value of die output signal u H or u E in a usual manner known per se from fuzzy logic also when tiie output signal u H or u E belongs to two classes. As Fig. lib shows, tiie intermediate signal u,, which forms an input signal for the second sub-processor 243, is divided into die classes L (low), M (medium), and H (high), while the output signal u R , which also forms an input signal for tiie second sub-processor 243, is divided into classes 1 (low speed), 2 (medium speed), and 3 (high speed). Fig. lib also shows die membership functions in accordance to which a membership of one of said classes is assigned to die signals u, and u R . The membership function of die intermediate signal u D , which forms an output signal of die second sub-processor 243, is identical to die membership function of the intermediate signal u D depicted in Fig. 11a. Fig. 12b is a Table in which the class assigned to d e intermediate signal u D by the second sub- processor 243 is listed in relation to the classes assigned to die signals u, and u R . As Fig. lie shows, the signal u %τ , which forms an input signal for tiie third sub-processor 247, is divided into classes B (initial phase) and E (end phase), while the input signal u s , which also forms an input signal for me third sub-processor 247, is divided into classes P (high shaving performance) and C (high shaving comfort). Fig. lie also shows the membership functions in accordance widi which a membership of one of said classes is assigned to die signals u %τ and u s . The classes and membership function of die intermediate signal u,, which forms an output signal of die third sub-processor 247, are identical to d e classes and membership function of die intermediate signal u t shown in Fig. lib. Fig. 12c is a Table in which the class assigned to die intermediate signal u, by the third sub-processor 247 is indicated in relation to the signals u %τ and u s . Fig. lid finally shows that the input signal u M , which is an input signal for the fourth sub-processor 249, is divided into classes L (low) and H (high). The classes and membership functions of die signal u %τ , which also forms an input signal for the fourth sub-processor 249, and of die output signal u R , which is an output signal of die fourth sub- processor 249, are identical to die respective classes and membership functions of the signals u %τ and u R shown in Figs, lie and lib. Fig. 12d is a Table in which the class assigned to me output signal u R by the fourth sub-processor 249 is given as a function of the signals u %τ and u M . It is noted diat the ranges of die input signals and output signals of die sub-processors 241, 243, 247, 249 may alternatively be subdivided into more classes than tiiose described above, and diat die sub-ranges of die classes may also be distributed differently. The desired behaviour of die shaving apparams 1, 105 may be further refined thereby. The desired behaviour of die shaving apparams 1, 105 may be laid down in a simple and visual manner in the control rules of the sub-processors 241, 243, 247, 249 owing to the use of said algoritiims based on fuzzy logic. The desired behaviour of the shaving apparams 1 , 105 may in addition be changed in a simple and flexible manner during a design phase if die knowledge about die operation of die shaving apparams 1, 105 or about characteristics of the user thereof should change. It is noted diat the shaving apparatuses 1, 105 described above are each provided widi tiiree external cutting members and tiiree internal cutting members which are rotatable inside die external cutting members. The invention, however, is equally applicable to shaving apparatuses having an external cutting member and an internal cutting member which performs a vibratory or oscillatory movement relative to die external cutting member. The invention further also applies to shaving apparatuses comprising a different number of cutting units, for example, only one or two. It is further noted diat die height H of the cutting units 11 is adjustable in die first embodiment of the shaving apparams 1, while in the second embodiment of the shaving apparams 105 the pretensioning force of die cutting units 121 is adjustable. The invention is also applicable to shaving apparatuses with a cutting unit which is adjustable in a different manner and in which the shaving performance and shaving comfort are influenced by the adjustment of the cutting unit. Thus, for example, in the case of a shaving apparams in which the external cutting member is a flexible foil with hair trap openings and in which the internal cutting member is a row of cutters oscillating along die foil, a contact force of the internal cutting member against the external cutting member may be adjustable by means of an acmator controlled by a control unit. Alternatively again, die contact force of the internal cutting member in tiie external cutting member may be adjustable by means of an acmator controllable by a control unit in a shaving apparams which is provided widi a rotatable internal cutting member, as are the shaving apparatuses 1, 105 described above. It is further noted that die mechanical stiffness of the cutting units 121 may also be adjustable by means of a construction in which the flexible strips 151 bear continuously on tiie support elements 165 and in which die support elements 165 are movable along die flexible strips 151, whereby die mechanical stiffness of me strips 151 can be adjusted steplessly. Instead of die flexible strips 151, an alternative type of spring may be used, for example, in which the mechanical stiffness can be changed by a displacement or change in a clamping point of the spring. It is finally noted d at a different type of control unit compared widi die control unit 103, 191 may be used for controlling die acmator 91, 197. Instead of a control unit based on control rules according to fuzzy logic, for example, control rules may be used based on usual mathematical equations. Furthermore, for example, alternative input signals may be used, or a different number of input signals, while also a different relation between die input signals and output signals may be chosen. Furthermore, for example, the control of die acmator 91, 179 may alternatively be used in a shaving apparams in which the motor speed has a conttolled, constant value or in which the voltage across or current through the motor is constant, and die motor speed depends on die load on die cutting units. In diat case, die signal u R in Fig. 10 corresponds to d e desired constant motor speed or to die measured actual motor speed, respectively.

Claims: CLAIMS: ~ 1. A shaving apparams with at least one adjustable cutting unit which is provided widi an external cutting member wid at least one hair trap opening and an internal cutting member which is drivable relative to d e external cutting member by means of an electric motor, characterized in diat d e cutting unit is adjustable by means of an electrical acmator which is controllable by an electrical control unit. 2. A shaving apparams as claimed in Claim 1, characterized in that die cutting unit is arranged in a holder and is displaceable relative to d e holder by means of the acmator. 3. A shaving apparams as claimed in Claim 2, characterized in mat the acmator places the cutting unit in a rest position, in which the cutting unit is recessed in die holder, when d e electric motor is switched off. 4. A shaving apparams as claimed in Claim 2 or 3, characterized in that die external cutting member is displaceable relative to die holder by means of the acmator, while the internal cutting member is held in the external cutting member under die influence of a pretensioning force of an elastically deformable element. 5. A shaving apparams as claimed in Claim 4, characterized in that die external cutting member of the cutting unit is fastened to a displaceable carrier which is coupled to an adjusttnent member which is rotatable relative to the holder by means of me acmator, the carrier being displaceable dirough a rotation of the adjustment member. 6. A shaving apparams as claimed in Claim 2, 3, 4 or 5, characterized in diat the electrical control unit has an electrical input which is connected to an electrical output of a position sensor which is capable of measuring a position of me cutting unit relative to the holder. 7. A shaving apparams as claimed in Claim 5 and 6, characterized in that the position sensor is capable of measuring an angle of rotation of die adjustment member relative to die holder. 8. A shaving apparams as claimed in Claim 1, characterized in diat die cutting unit is arranged in a holder and is displaceable relative to die holder against a pretensioning force which has a value which is adjustable by means of d e actuator. 32 9. A shaving apparams as claimed in Claim 8, characterized in diat the pretensioning force is exerted by an elastically deformable element which has a mechamcal stiffness which is adjustable by means of die acmator. 10. A shaving apparams as claimed in Claim 9, characterized in diat die elastically deformable element is coupled to die external cutting member, while the internal cutting member is held in the external cutting member under die influence of a pretensioning force of a further elastically deformable element. 11. A shaving apparams as claimed in Claim 9 or 10, characterized in diat the elastically deformable element is a mechanical blade spring which can be supported by a support element which is displaceable by means of die acmator. 12. A shaving apparams as claimed in Claim 11, characterized in diat the support element cooperating widi die cutting unit is provided on a displaceable carrier which is coupled to an adjustment member which is rotatable relative to the holder by means of die acmator, die carrier being displaceable dirough a rotation of die adjustment member. 13. A shaving apparams as claimed in Claim 8, 9, 10, 11 or 12, characterized in diat the electrical control unit has an electrical input which is connected to an electrical output of a sensor capable of measuring die pretensioning force of die cutting unit. 14. A shaving apparams as claimed in Claims 12 and 13, characterized in diat an angle of rotation of the adjustment member relative to the holder is measurable by means of the sensor, while a further electrical input of the control unit is connected to an electrical output of a further sensor capable of measuring a position of the cutting unit relative to die holder. 15. A shaving apparams as claimed in Claim 14, characterized in that the further sensor is a strain gauge sensor by means of which a deformation of a spring fastened between die external cutting member and d e holder is measurable. 16. A shaving apparams as claimed in any one of die preceding Claims, characterized in that the electric motor has a speed which is controllable by means of the electrical control unit. 17. A shaving apparams as claimed in any one of me preceding Claims, characterized in that die electrical control unit has an electrical input which is connected to an electrical output of an operational member wid which a desired balance between shaving performance and shaving comfort can be set. 18. A shaving apparams as claimed in any one of die preceding Claims, characterized in that the electrical control unit has an electrical input which is connected to an electrical output of a timer capable of measuring a time which has elapsed during a shaving operation. 19. A shaving apparams as claimed in Claim 18, characterized in diat d e control unit is provided with a calculation unit for calculating an average shaving time over a number of previous shaving operations, the control unit determining me time which has elapsed during a shaving operation in relation to die calculated average shaving time. 20. A shaving apparams as claimed in any one of d e preceding Claims, characterized in mat d e electrical control unit has an electrical input which is connected to an electrical output of a detector capable of measuring a number of hairs cut by the cutting unit per unit time. 21. A shaving apparams as claimed in Claim 20, characterized in d at die detector is provided widi a microphone capable of detecting an acoustic signal produced by the cutting unit, and widi an electrical filter capable of filtering a cutting frequency from the acoustic signal. 22. A shaving apparams as claimed in any one of die preceding Claims, characterized in mat the electrical control unit has an electrical input which is connected to an electrical output of a force sensor capable of measuring a skin contact force exerted on d e cutting unit. 23. A shaving apparams as claimed in Claims 5 and 22, or as claimed in Claims 12 and 22, characterized in that die force sensor comprises a strain gauge sensor which is provided on an elastically deformable bridge, while the rotatable adjustment member rests on die bridge in a direction parallel to a force to be measured and has a mechanical stiffness in said direction which is comparatively small compared widi a mechanical stiffness which the bridge has in said direction. 24. A shaving apparams as claimed in Claims 13 and 22, characterized in that die force sensor by which the skin contact force can be measured is die sensor by which the pretensioning force of tiie cutting unit can be measured. 25. A shaving apparams as claimed in Claim 22, 23 or 24, with Claim 22 being at least dependent on Claim 17, Claim 18 or 19, and Claim 20 or 21, characterized in diat d e electrical control unit is provided widi means for controlling die electrical acmator, with a first electrical input which is connected to an electrical output of the force sensor, a second electrical input which is connected to die electrical output of the timer, a third electrical input which is connected to die electrical output of die operational member, a fourth electrical input which is connected to die electrical output of die detector, and an 34 electrical output for supplying an output signal which corresponds to a desired position of die cutting unit above die holder or a desired value of die pretensioning force of the cutting unit. 26. A shaving apparams as claimed in Claim 25, characterized in diat said means determine the output signal in accordance wid a first control rule according to which the desired position above die holder or d e pretensioning force decreases when the measured skin contact force increases, and the desired position above d e holder or die pretensioning force increases when an admissible skin deformation around die cutting unit increases, while said means determine me admissible skin deformation in accordance widi a second control rule. 27. A shaving apparams as claimed in Claim 26, characterized in diat, in accordance with d e second control rule, die admissible skin deformation decreases when a desired speed of die motor increases, and die admissible skin deformation increases when an admissible number of skin damage points per unit time increases, while said means determine die admissible number of skin damage points per unit time in accordance widi a third control rule and die desired motor speed in accordance widi a fourth control rule. 28. A shaving apparams as claimed in Claim 27, characterized in tiiat, in accordance widi die tiiird control rule, the admissible number of skin damage points per unit time increases with an increase in me time which has elapsed during a shaving operation, die increase in the admissible number of skin damage points per unit time being comparatively small if the operational member is in a position in which a user of die shaving apparams wishes a comparatively high shaving comfort and comparatively low shaving performance, and being comparatively great if the operational member is in a position in which a user of the shaving apparams desires a comparatively low shaving comfort and comparatively high shaving performance. 29. . A shaving apparams as claimed in Claim 27, characterized in tiiat, according to die fourth conttol rule, the desired motor speed increases with an increase in the measured number of hairs cut by die cutting unit per unit time, the desired motor speed decreases when die time which has elapsed during a shaving operation increases, and die increase in die desired motor speed widi an increase in me measured number of hairs cut by die cutting unit per unit time is comparatively small if die elapsed time is short, and is comparatively great if die elapsed time is long. 30. A shaving apparams as claimed in Claims 16 and 27, Claims 16 and 28, or Claims 16 and 29, characterized in tiiat said means are provided widi a further electrical output for supplying a further output signal which corresponds to die desired motor speed determined in accordance widi die fourth control rule. 31. A shaving apparams as claimed in Claim 20 or 21, with Claim 20 being at least dependent on Claim 16 and Claim 18 or 19, characterized in mat the electrical control unit is provided with means for controlling tiie speed of die electric motor, with a first electrical input connected to die electrical output of the timer, a second electrical input connected to die electrical output of the detector, and an electrical output for supplying an output signal which corresponds to a desired motor speed and which is determined by a control rule. 32. A shaving apparams as claimed in Claim 31, characterized in that, in accordance widi the control rule, the desired motor speed increases with an increase in the measured number of hairs cut by die cutting unit per unit time, the desired motor speed decreases as me time elapsed during a shaving operation increases, and die increase in die desired motor speed widi an increase in tiie measured number of hairs cut by die cutting unit per unit time is comparatively small if the elapsed time is short, and comparatively great if the elapsed time is long. 33. A shaving apparams as claimed in Claim 26, 27, 28 or 29, characterized in mat the control rules determine d e output signal in accordance widi an algoritiim based on fuzzy logic. 34. A shaving apparams as claimed in Claim 31 or 32, characterized in that the control rule determines d e output signal in accordance with an algorithm based on fuzzy logip.

Inventors: DE BOER JAN REINDER, DE POOTER PIETER, DEKKER JACOBUS NICOLAAS, REEDER ANDRIES THEUNIS, VAN DER BORST ALBERTUS JOHANNE, DE BOER, JAN, REINDER, DE POOTER, PIETER, DEKKER, JACOBUS, NICOLAAS, REEDER, ANDRIES, THEUNIS, VAN DER BORST, ALBERTUS, JOHANNES, CORNELIS
Applicants: PHILIPS ELECTRONICS NV, PHILIPS NORDEN AB, PHILIPS ELECTRONICS N.V.
Application year: 1995
Main classification: B26B19
IPC codes: B26B19