Patent Publication Number: US-9409302-B2

Title: Razors

Description:
TECHNICAL FIELD 
     This invention relates to razors, and more particularly to razors for wet shaving that include a battery-powered functionality. 
     BACKGROUND 
     Recently, some wet shaving razors have been provided with a battery-powered functionality. For example, the Gillette® M3 Power™ razor, sold by The Gillette Company, provides a vibrating function that is powered by a battery disposed in a chamber within the handle of the device. The battery is replaceable by the user, by removing a battery cover. It is desirable for safety and durability reasons that the handle of such a device be water-tight. 
     SUMMARY 
     The present invention provides razors having handles that are reliably water-tight and that can be readily sealed by the user when the battery cover is replaced by the user after changing the battery. 
     In one aspect, the invention features a razor handle for a razor having a battery-powered functionality, the handle including a unitary grip portion constructed to receive a razor head at one end thereof, and a battery cover, mounted on the grip portion, the grip portion and the battery cover, when joined, together defining a water-tight unit prior to mounting of the razor head on the grip portion. 
     Some implementations may include one or more of the following features. The razor handle may further include a plurality of components that provide the battery-powered functionality, and all components of the razor that provide the battery-powered functionality may be disposed within the grip portion. The razor handle may further include a razor head, fixedly mounted on the grip portion. The battery cover may be removably mounted on the grip portion, or, alternatively, may be permanently welded to the grip tube. The razor handle may further include a sealing member, e.g., an elastomeric seal, disposed at an interface between the battery cover and grip portion to provide a water-tight seal at the interface. The razor handle may further include a subassembly, disposed within the grip portion, including a carrier and a switch or electronic components mounted on the carrier. The carrier may include a portion constructed to receive a battery and provide electrical communication between the battery and electronic components. The carrier may also include a portion constructed to engage a corresponding portion of the battery cover. The handle may further include a sleeve, disposed inside the battery-receiving portion of the carrier and surrounding the battery. 
     In another aspect, the invention features a razor handle for a razor having a battery-powered functionality, the handle including: (a) a grip portion; (b) within the grip portion, components configured to provide the battery-powered functionality; (c) an actuator, mounted on the grip portion and positioned to be depressed by a user of the razor; and (d) an electronic switch, in electrical communication with the components, positioned to be actuated when the actuator is depressed. 
     Some implementations may include one or more of the following features. The electronic switch may require an actuation force of at least 4 N applied over about a displacement of about 0.25 mm. The grip portion may include a resilient membrane that is interposed between the actuator and the electronic switch. The resilient membrane may be configured to exert a restoring force on the actuator after the actuator is depressed and released. The actuator may include a button and an underlying cantilevered member supporting the button. The components may include a printed circuit board, and the electronic switch may be in communication with the printed circuit board to activate circuitry of the printed circuit board. The actuator may include a button, and an upper surface of the button may be substantially flush with an outer surface of the grip tube. The electronics may be configured to drive a vibrating function of the razor. 
     In some implementations, the razor handle may further include a closing system, including a first component within the battery cover, and a second component secured to the interior wall of the grip portion, the first component being configured to move axially within the battery cover during engagement of the battery cover with the grip portion, and being biased toward a predetermined axial position. The first and second components may be configured to engage each other by rotation of the battery cover relative to the housing. The first component may include a spring element configured to apply an axial force between the grip portion and battery cover when the first and second components are engaged. Engagement of the first and second components may provide an electrical connection between the first and second components. The handle may further include, within the grip tube, a pair of battery clamp fingers configured to exert a clamping force against the battery when the battery is in place in the razor. The grip tube may include a window, and the razor handle may further include an indicator, e.g., an LED or other light or display, beneath the window. 
     In other aspects, the invention features methods of manufacturing razor handles. In one such aspect, the invention features a method including: (a) forming a unitary grip tube having a closed end configured to receive a razor head; (b) inserting a battery and a carrier into an open opposite end of the grip tube, the carrier having electronic components mounted thereon; (c) sealing the open end of the grip tube; and (d) testing the electronic functionality of the resulting assembly. 
     Some implementations of this method may include one or more of the following features. The method may also include mounting, e.g., fixedly mounting, a razor head on the closed end if the testing step results in a determination that the electronics are functional. The sealing step may include mounting a removable battery cover on the open end. Mounting the battery cover on the open end may render the assembly water-tight. The razor head may in some cases be configured to receive a disposable razor cartridge. In other cases, the razor head and razor cartridge may be integral, e.g., if the razor is a disposable razor. Forming the unitary grip tube may, for example, include molding a grip tube preform having a window opening and welding a window into the opening. 
     In another aspect, the invention features a method of forming a plurality of razor products having a battery-powered functionality. The method includes (i) forming a plurality of substantially identical razor sub-assemblies, each sub-assembly including (a) a unitary grip tube having a closed end configured to receive a razor head, and (b) a battery and battery-powered components disposed within the grip tube, the grip tube being sealed in a water-tight manner; and (ii) mounting a first razor head on the closed ends of a first sub-set of the razor sub-assemblies to form a first product, and mounting a second, different razor head on the closed ends of a second sub-set of the razor sub-assemblies to form a second, different product. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a top view of a razor handle according to one embodiment. 
         FIGS. 1A and 1B  are cross sectional views of the razor handle of  FIG. 1 . 
         FIG. 2  is a bottom view of the razor handle of  FIG. 1 . 
         FIG. 3  is a partially exploded view of the razor handle of  FIG. 1 . 
         FIG. 4  is a perspective view of the head tube exploded from the grip tube of the razor. 
         FIG. 5  is a side view of the grip tube. 
         FIG. 6  is an exploded view of the grip tube showing the components contained therein. 
         FIGS. 7-7C  are exploded views illustrating the assembly of the components contained in the grip tube. 
         FIG. 8  is a perspective view of the grip tube with the LED window exploded from the tube and the actuator button omitted.  FIG. 8A  is a perspective view of the grip tube with the LED window welded in place and the actuator button exploded from the tube.  FIGS. 8B-8D  are enlarged perspective views of a portion of the grip tube, showing steps in assembly of the actuator button onto the tube. 
         FIG. 9  is a perspective view of a bayonet assembly used in the razor of  FIG. 1 .  FIG. 9A  is an enlarged detail view of area A in  FIG. 9 .  FIG. 9B  is an enlarged detail view of the bayonet assembly with the male and female components engaged and the bayonet and battery springs compressed. 
         FIG. 10  is a side view of the bayonet assembly shown in  FIG. 9 , rotated 90 degrees with respect to the position of the assembly in  FIG. 9 . 
         FIG. 11  is an exploded view of the lower portion of the bayonet assembly and the battery shell that contains the lower portion. 
         FIG. 12  is a cross-sectional view of the battery shell. 
         FIG. 13  is an exploded view of the venting components of the battery shell. 
       Like reference symbols in the various drawings indicate like elements. 
         FIG. 14A  shows a razor having a speed control switch. 
         FIG. 14B  shows a razor having a speed control switch and a memory for storage of preferred speeds. 
         FIG. 14C  shows a razor having an indirect power supply. 
         FIG. 14D  shows a voltage converter for the indirect power supply of  FIG. 14C . 
         FIG. 14E  shows the signals output by the control logic and the oscillator, and their effect on the capacitor voltage. 
         FIG. 14F  shows another voltage converter for the indirect power supply of  FIG. 14C . 
         FIG. 14G  shows a circuit for supplying power to a load. 
         FIG. 15A  shows a blade-life indicator that counts the number of times a motor has started since blade replacement. 
         FIG. 15B  shows a blade-life indicator that accumulates motor-operating time since blade replacement. 
         FIG. 15C  shows a blade-life indicator that counts the number of strokes since blade replacement. 
         FIG. 15D  shows a blade-life indicator that accumulates stroke time since blade replacement. 
         FIG. 16A  shows a mechanical lock. 
         FIG. 16B  shows a locking circuit in which a lock signal disarms the razor. 
         FIG. 17A  shows a force-measurement circuit that senses variations in current drawn by the motor. 
         FIG. 17B  shows a force-measurement circuit that senses variations in motor speed. 
     
    
    
     DETAILED DESCRIPTION 
     Overall Razor Structure 
     Referring to  FIG. 1 , a razor handle  10  includes a razor head  12 , a grip tube  14 , and a battery shell  16 . The razor head  12  includes a connecting structure for mounting a replaceable razor cartridge (not shown) on the handle  10 , as is well known in the razor art. The grip tube  14  is constructed to be held by a user during shaving, and to contain the components of the razor that provide the battery-powered functionality of the razor, e.g., a printed circuit board and a motor configured to cause vibration. The grip tube is a sealed unit to which the head  12  is fixedly attached, allowing modular manufacturing and providing other advantages which will be discussed below. Referring to  FIG. 3 , the battery shell  16  is removably attached to the grip tube  14 , so that the user may remove the battery shell to replace the battery  18 . The interface between the battery shell and grip tube is sealed, e.g., by an O-ring  20 , providing a water-tight assembly to protect the battery and electronics within the razor. The O-ring  20  is generally mounted in groove  21  ( FIG. 5 ) on the grip tube, e.g., by an interference fit. Referring again to  FIG. 1 , the grip tube  14  includes an actuator button  22  that may be pressed by the user to actuate the battery-powered functionality of the razor via an electronic switch  29  ( FIG. 7A ). The grip tube also includes a transparent window  24  to allow the user to view a light  31  or display or other visual indicator ( FIG. 7A ), e.g., an LED or LCD, that provides a visual indication to the user of battery status and/or other information. The light  31  shines through an opening  45  ( FIG. 8 ) provided in the grip tube beneath the transparent window. These and other features of the razor handle will be described in further detail below. 
     Modular Grip Tube Structure 
     As discussed above, the grip tube  14  (shown in detail in  FIGS. 4 and 5 ) is a modular assembly, to which the razor head  12  is fixedly attached. The modularity of the grip tube advantageously allows a single type of grip tube to be manufactured for use with various different razor head styles. This in turn simplifies manufacturing of “families” of products with different heads but the same battery-powered functionality. The grip tube is water-tight except for the opening  25  at the end to which the battery shell is attached, and is preferably a single, unitary part. Thus, the only seal that is required to ensure water-tightness of the razor handle  10  is the seal between the grip tube and the battery shell, provided by O-ring  20  ( FIG. 3 ). This single-seal configuration minimizes the risk of water or moisture infiltrating the razor handle and damaging the electronics. 
     As shown in  FIG. 6 , the grip tube  14  contains a subassembly  26  (also shown in  FIG. 7C ) which includes a vibration motor  28 , a printed circuit board  30 , an electronic switch  29  and the light  31  mounted on the printed circuit board, and the positive contact  32  for providing battery power to the electronics. These components are assembled within a carrier  34  which also includes battery clamp fingers  36  and a male bayonet portion  38 , the functions of which will be discussed in the Battery Clamp and Battery Shell Attachment sections below. The assembly of all the functional electronic components of the razor onto the carrier  34  allows the battery-powered functionality to be pre-tested so that failures can be detected early, minimizing costly scrapping of completed razors. Subassembly  26  also includes an insulation sleeve  40  and mounting tape  42 , the function of which will be discussed in the Battery Clamp section below. 
     The subassembly  26  is assembled as shown in  FIGS. 7-7C . First, the positive contact  32  is assembled onto a PCB carrier  44 , which is then mounted on carrier  34  ( FIG. 7 ). Next, the printed circuit board  30  is placed in the PCB carrier  44  ( FIG. 7A ), and the vibration motor  28  is mounted on the carrier  34  ( FIG. 7B ) with lead wires  46  being soldered onto the printed circuit board to complete the subassembly  26  ( FIG. 7C ). The subassembly may then be tested prior to assembly into the grip tube. 
     The subassembly  26  is assembled into the grip tube so that it will be permanently retained therein. For example, the subassembly  26  may include protrusions or arms that engage corresponding recesses in the inner wall of the grip tube in an interference fit. 
     The grip tube also includes an actuator button  22 . The rigid actuator button is mounted on a receiving member  48  ( FIG. 8 ) that includes the window  24 , discussed above. The receiving member  48  includes a cantilevered beam  50  that carries an actuator member  52 . Actuator member  52  transmits force that is applied to the button  22  to an underlying resilient membrane  54  ( FIG. 8 ). Membrane  54  may be, for example, an elastomeric material that is molded onto the grip tube to form not only the membrane but also an elastomeric gripping portion. The cantilevered beam, acting in concert with the membrane, provides a restoring force to return the button  22  to its normal position after it is depressed by a user. When the button is depressed, the actuator member  52  contacts the underlying electronic switch  29 , which activates the circuitry of the PCB  30 . Activation may be by a “push and release” on/off action or other desired action, e.g., push on/push off. The electronic switch  29  makes an audible “click” when actuated, giving the user feedback that the device has been correctly turned on. The switch is preferably configured to require a relatively high actuation force applied over a small distance (e.g., at least 4 N applied over about an 0.25 mm displacement). This switch arrangement, combined with the recessed, low profile geometry of button  22 , tends to prevent the razor from being accidentally turned on during travel, or inadvertently turned off during shaving. Moreover, the structure of the switch/membrane/actuator member assembly provides the user with good tactile feedback. The actuator member  52  also holds the button  22  in place, the aperture  55  in the center of the actuator member  52  receiving a protrusion  56  on the underside of the button  22  ( FIG. 8B ). 
     Adjacent to the button  22  is the transparent window  24 , through which the user can observe the indications provided by the underlying light, which are described in detail in the Electronics section below. 
     Assembly of the window  24  and actuator button onto the grip tube, is illustrated in  FIGS. 8-8D . First, the receiving member  48 , carrying the window  24 , is sealingly mounted on the grip tube, e.g., by gluing or ultrasonic or heat welding ( FIG. 8 ), to form the unitary water-tight part discussed above. Next, the button  22  is slid into place and gently (preferably with less than 10 N force) pushed down into the opening in the receiving member, causing the protrusion  56  to engage the aperture  55  ( FIGS. 8A-8C ). 
     Battery Shell Attachment 
     As discussed above, the battery shell  16  is removably attached to the grip tube  14 , allowing removal and replacement of the battery. The two parts of the handle are connected, and electrical contact is established between the negative terminal of the battery and the electronic components, by a bayonet connection. The grip tube carries the male portion of the bayonet connection, while the battery shell carries the female portion. The assembled bayonet connection, with the grip tube and battery shell omitted for clarity, is shown in  FIGS. 9, 9A and 10 . 
     The male bayonet portion  38  of the carrier  34 , discussed above, provides the male portion of the bayonet connection. Male bayonet portion  38  carries a pair of protrusions  60 . These protrusions are constructed to be received and retained in corresponding slots  62  in a female bayonet component  64 , carried by the battery shell. Each slot  62  includes a lead-in having angled walls  66 ,  68  ( FIG. 9A ), to guide each protrusion into the corresponding slot as the battery shell is rotated relative to the grip tube. A detent area  65  ( FIG. 9A ) is provided at the end of each slot  62 . The engagement of the protrusions in the detent areas  65  ( FIG. 9B ) provides a secure, twist-on mechanical connection of the battery shell to the grip tube. 
     The carrier  34  and the female bayonet component  64  are both made of metal, and thus engagement of the protrusions with the slots also provides electrical contact between the carrier and the female bayonet component. The carrier is in turn in electrical contact with circuitry of the device, and the negative terminal of the battery is in contact with a battery spring  70  ( FIG. 9A ) that is in electrical communication with the female bayonet component, and thus contact of the spring members and electrical part ultimately results in contact between the battery and the circuitry of the device. 
     As shown in  FIG. 12 , the battery spring  70  is mounted on a spring holder  72 , which is in turn mounted fixedly to the inner wall of the battery shell  16 . The female bayonet component  64  is free to slide axially back and forth within the battery shell  16 . In its rest position, the female bayonet component is biased to the base of the battery shell by a bayonet spring  74 . The bayonet spring  74  is also mounted on the spring holder  72  and thus its upper end is fixedly mounted with respect to the inner wall of the battery shell. When the battery shell is twisted onto the grip tube, the engagement of the protrusions on the male bayonet component with the angled slots on the female bayonet component draws the female bayonet component forward, compressing the bayonet spring  74 . The biasing force of the bayonet spring then causes the female bayonet component to pull the male bayonet component and thus the grip tube toward the battery shell. As a result, any gap between the two parts of the handle is closed by the spring force and the O-ring is compressed to provide a water-tight sealing engagement. When engagement is complete and the protrusions  60  are received into the corresponding V-shaped detent areas  65  of the female bayonet slots  62  ( FIG. 9B ). This is perceived by the user as a clear and audible click, providing a clear indication that the battery shell has been correctly engaged. This click is the result of the action of the bayonet spring causing the protrusions to slide quickly into the V-shaped detent areas  65 . 
     This resilient engagement of the battery shell with the grip tube compensates for non-linear seam lines between the battery shell and grip tube and other geometry issues such as tolerances. The force applied by the bayonet spring also provides solid and reliable electrical contact between the male and female bayonet components. 
     The spring-loaded female bayonet component also limits the force acting on the male and female bayonet components when the battery shell is attached and removed. If, after the grip tube and battery shell contact each other, the user continues to rotate the battery shell, the female bayonet component can move forward slightly within the battery shell, reducing the force applied by the protrusions of the male bayonet component. Thus, the force is kept relatively constant, and within a predetermined range. This feature can prevent damage to parts due to rough handling by the user or large part or assembly tolerances. 
     To accomplish the resilient engagement described above, it is generally important that the spring force of the bayonet spring be greater than that of the battery spring. Generally, the preferred relative forces of the two springs may be calculated as follows: 
     1. Design the battery spring such that the contact force Fbatmin applied by the spring is sufficient for a minimum battery length. 
     2. Calculate the battery spring force Fbatmax that would be required for a maximum battery length. 
     3. Calculate the maximum force Fpmax that would be required to push the battery shell against the grip tube to overcome the friction of the o-ring. 
     4. Determine the minimum closing force Fclmin with which the battery shell should be pressed against the grip tube in the closed condition. 
     5. Calculate the force applied by the bayonet spring according to Fbayonet=Fbatmax+Fpmax+Fclmin. 
     As an example, in some implementations Fbatmax=4 N, Fpmax=2 N, and Fclmin=2 N, and thus Fbayonet=8 N. 
     Battery Clamp 
     As discussed above, carrier  34  includes a pair of battery clamp fingers  36  ( FIGS. 6, 10 ). These fingers act as two springs which exert a small clamping force against the battery  18  ( FIG. 3 ). This clamping force is sufficiently strong so as to prevent the battery from rattling against the inner wall of the grip tube or against other parts, reducing the noise generated by the razor during use. Preferably, the clamping force is also sufficiently strong so as to keep the battery from falling out when the battery shell is removed and the grip tube is inverted. On the other hand, the clamping force should be weak enough so that the user can easily remove and replace the battery. The male bayonet component  38  includes open areas  80  ( FIG. 4 ) through which the battery can be grasped by the user for removal. 
     The dimensions of the spring fingers and their spring force are generally adjusted to allow the spring fingers to hold the weight of the minimum size battery discussed above, to prevent it from falling out when the razor is held vertical, while also allowing the maximum size battery to be easily removed from the grip tube. To satisfy these constraints, it some implementations it is preferred that, with a coefficient of friction between the battery and foil of about 0.15-0.30, the spring force for one finger be about 0.5 N when a minimum size battery (e.g., having a diameter of 9.5 mm) is inserted and less than about 2.5 N when a maximum size battery (e.g., having a diameter of 10.5 mm) is inserted. In general, the spring fingers will perform the above functions if, when the razor is held with the battery opening pointing downwards, the minimum size battery will not fall out and the maximum size battery can be taken out easily. 
     Referring to  FIGS. 6 and 7C , a thin insulation sleeve  40 , e.g., of plastic foil, further damps vibration noise and provides safety against a short circuit if the battery surface is damaged. As shown in  FIG. 7C , the sleeve  40  is secured with tape  42  to the battery clamp fingers to hold the sleeve in place when the battery is removed and replaced. A suitable material for the insulation sleeve is polyethylene terephthalate (PET) film having a thickness of about 0.06 mm. 
     Venting Battery Compartment 
     Under certain conditions, hydrogen can accumulate in the interior of battery-powered appliances. The hydrogen may be released from the battery, or may be created by electrolysis outside the battery. Mixing of this hydrogen with ambient oxygen can form an explosive gas, which could potentially be ignited by a spark from the motor or switch of the device. Thus, any hydrogen should be vented from the razor handle, while still maintaining water tightness. 
     Referring to  FIG. 13 , a vent hole  90  is provided in the battery shell  16 . A microporous membrane  92  that is gas-permeable but impermeable to liquids is welded to the battery shell  16  to cover the vent hole  90 . A suitable membrane material is polytetrafluoroethylene (PTFE), commercially available from GORE. A preferred membrane has a thickness of about 0.2 mm. It is generally preferred that the membrane have a water-proofness of at least 70 kPa, and an air permeability of at least 121/hr/cm 2  at 100 mbar overpressure. 
     An advantage of the microporous membrane is that it will vent hydrogen by diffusion due to the difference in partial pressures of hydrogen on the two sides of the membrane. No increase in total pressure within the razor handle is required for venting to occur. 
     It is undesirable from an aesthetic standpoint for the user to see the vent hole and membrane. Moreover, if the membrane is exposed there is a risk that the pores of the membrane will become clogged, and/or that the membrane will be damaged or removed. To protect the membrane, a cover  94  is attached to the battery shell over the membrane/vent area, e.g., by gluing. So that gas can escape from under the cover  94 , an open area is provided between the inner surface of the cover and the outer surface  98  of the battery shell  16 . In the implementation shown in the Figures, a plurality of ribs  96  are provided on the battery shell adjacent the vent hole  90 , creating air channels between the cover and the battery shell. However, if desired other structures can be used to create the venting space, for example the cover and/or the grip tube may include a depressed groove that defines a single channel and the ribs may be omitted. 
     The height and width of the air channels are selected to provide a safe degree of venting. In one example (not shown), there may be one channel on each side of the vent hole, each channel having a height of 0.15 mm and width of 1.1 mm. 
     Cover  94  may be decorative. For example, the cover may carry a logo or other decoration. The cover  94  may also provide a tactile gripping surface or other ergonomic features. 
     Electronics 
     Variable Speed Control 
     A powered razor is often used to shave different types of hair at different locations on the body. These hairs have markedly different characteristics. For example, whiskers tend to be thicker than hair on the legs. These hairs also protrude from the skin at different angles. For example, stubble is predominantly orthogonal to the skin, whereas leg hairs tend to lay flatter. 
     The ease with which one can shave these hairs depends, in part, on the frequency at which the cartridge vibrates. Since these hairs have different characteristics, it follows that different vibration frequencies may be optimal for different types of hair. It is therefore useful to provide a way for the user to control this vibration frequency. 
     As shown in  FIG. 14A , the vibration frequency of the shaving cartridge is controlled by a pulse width modulator  301  having a duty cycle under the control of control logic  105 . As used herein, “duty cycle” means the ratio between the temporal extent of a pulse and that of the pause between pulses. A low duty cycle is thus characterized by short pulses with long waits between pulses, whereas a high duty cycle is characterized by long pulses with short waits between pulses. Varying the duty cycle varies the speed of the motor  306 , which in turn governs the vibration frequency of the shaving cartridge. 
     The control logic  105  can be implemented in a microcontroller or other microprocessor based system. Control logic can also be implemented in an application-specific integrated circuit (“ASIC”) or as a field-programmable gate array (“FPGA”). 
     The motor  306  can be any energy-consuming device that causes movement of the shaving cartridge. One implementation of a motor  306  includes a miniature stator and rotor coupled to the shaving cartridge. Another implementation of a motor  306  includes a piezoelectric device coupled to the shaving cartridge. Or, the motor  306  can be implemented as a device that is magnetically coupled to the shaving cartridge with an oscillating magnetic field. 
     In razors having variable speed control, the control logic  105  receives an input speed control signal  302  from a speed-control switch  304 . In response to the speed control signal  302 , the control logic  105  causes the pulse-width modulator  301  to vary its duty cycle. This, in turn, causes the motor speed to vary. The pulse-width modulator  301  can thus be viewed as a speed controller. 
     The speed-control switch  304  can be implemented in a variety of ways. For example, the speed-control switch can move continuously. In this case, the user can select from a continuum of speeds. Or, the speed-control switch  304  can have discrete stops, so that the user can select from a set of pre-defined motor speeds. 
     The speed-control switch  304  can take a variety of forms. For example, the switch  304  can be a knob or a slider that moves continuously or between discrete steps. The switch  304  can also be a set of buttons, with each one assigned to a different speed. 
     Or, the switch  304  can be a pair of buttons, with one button being assigned to increase and the other to decrease the speed. Or, the switch  304  can be a single button that one presses to cycle through speeds, either continuously or discretely. 
     Another type of switch  304  is a spring-loaded trigger. This type of switch enables the user to vary the vibration frequency continuously while shaving in the same way that one can continuously vary the speed of a chain saw by squeezing a trigger. 
     The actuator button  22  can also be pressed into service as a speed control switch  304  by suitably programming the control logic  105 . For example, one can program the control logic  105  to consider a double-click or a long press of the actuator button  22  as a command to vary the motor speed. 
     Among the available speeds is one that is optimized for cleaning the razor. An example of such a speed is the highest possible vibration frequency, which is achieved by causing the control logic  105  to drive the duty cycle as high as possible. Alternatively, the control logic  105  can operate in a cleaning mode in which it causes the motor  306  to sweep through a range of vibration frequencies. This enables the motor  306  to stimulate different mechanical resonance frequencies associated with the blades, the cartridge, and any contaminating particles, such as shaven whisker fragments. The cleaning mode can be implemented as a continuous sweep across a frequency range, or as a stepped sweep, in which the control logic  105  causes the motor  306  to step through several discrete frequencies, pausing momentarily at each such frequency. 
     In some cases, it is useful to enable the razor to remember one or more preferred vibration frequencies. This is achieved, as shown in  FIG. 14B , by providing a memory in communication with the control logic  105 . To use this feature, the user selects a speed and causes transmission of a memory signal, either with a separate control, or by pressing the actuator button  22  according to a pre-defined sequence. The user can then recall this memorized speed when necessary, again by either using a separate control or by pressing the actuator button  22  according to a pre-defined sequence. 
     As shown in  FIGS. 3A-3B , the razor features an indirect switching system in which the actuator button  22  controls the motor  306  indirectly through control logic  105  that operates the pulse-width modulator  301 . Thus, unlike a purely mechanical switching system, in which the state of the switch directly stores the state of the motor  306 , the indirect switching system stores the state of the motor  306  in the control logic  105 . 
     Since the actuator button  22  no longer needs to mechanically store the state of the motor  306 , the indirect switching system provides greater flexibility in the choice and placement of the actuator button  22 . For example, a razor with an indirect switching system, as disclosed herein, can use ergonomic buttons that combine the advantages of clear tactile feedback and shorter travel. Such buttons, with their shorter travel, are also easier to seal against moisture intrusion. 
     Another advantage to the indirect switching system is that the control logic  105  can be programmed to interpret the pattern of actuation and to infer, on the basis of that pattern, the user&#39;s intent. This has already been discussed above in connection with controlling the speed of the motor  306 . However, the control logic  105  can also be programmed to detect and ignore abnormal operation of the actuator button  22 . Thus, an unusually long press of the actuator button  22 , such as that which may occur unintentionally while shaving, will be ignored. This feature prevents the annoyance associated with accidentally turning off the motor  306 . 
     Voltage Controller 
     The effectiveness of the razor depends in part on the voltage provided by a battery  316 . In a conventional motorized wet razor, there exists an optimum voltage or voltage range. Once the battery voltage is outside the optimum voltage range, the effectiveness of the razor is compromised. 
     To overcome this difficulty, the razor features an indirect power supply, shown in  FIG. 14C , that separates the voltage of the battery  316  from the voltage actually seen by the motor  306 . The voltage actually seen by the motor  306  is controlled by the control logic  105 , which monitors the battery voltage and, in response to a measurement of battery voltage, controls various devices that ultimately compensate for variations in battery voltage. This results in an essentially constant voltage as seen by the motor  306 . 
     The method and system described herein for controlling the voltage seen by a motor  306  is applicable to any energy-consuming load. For this reason,  FIG. 14C  refers to a generalized load  306 . 
     In one embodiment, the motor  306  is designed to operate at an operating voltage that is less than the nominal battery voltage. As a result, when a new battery  316  is inserted, the battery voltage is too high and must be reduced. The extent of the reduction decreases as the battery  316  wears down, until finally, no reduction is necessary. 
     Voltage reduction is readily carried out by providing a voltage monitor  312  in electrical communication with the battery  316 . The voltage monitor  312  outputs a measured battery voltage to the control logic  105 . In response, the control logic  105  changes the duty cycle of the pulse-width modulator  301  to maintain a constant voltage as seen by the motor  306 . For example, if the battery voltage is measured at 1.5 volts, and the motor  306  is designed to operate at one volt, the control logic  105  will set the duty cycle ratio to be 75%. This will result in an output voltage from the pulse-width modulator  301  that is, on average, consistent with the motor&#39;s operating voltage. 
     In most cases, the duty cycle is a non-linear function of the battery voltage. In that case, the control logic  105  is configured either to perform the calculation using the non-linear function, or to use a look-up table to determine the correct duty cycle. Alternatively, the control logic  105  can obtain a voltage measurement from the output of the pulse-width modulator  301  and use that measurement to provide feedback control of the output voltage. 
     In another embodiment, the motor  306  is designed to operate at an operating voltage that is higher than the nominal battery voltage. In that case, the battery voltage is stepped up by increasing amounts as the battery  316  wears down. This second embodiment features a voltage monitor  312  as described above, together with a voltage converter  314  that is controlled by the control logic  105 . A suitable voltage converter  314  is described in detail below. 
     A third embodiment combines both of the foregoing embodiments in one device. In this case, the control logic  105  begins by reducing the output voltage when the measured battery voltage exceeds the motor operating voltage. Then, when the measured battery voltage falls below the motor operating voltage, the control logic  105  fixes the duty cycle and begins controlling the voltage converter  312 . 
     In a conventional powered razor, the motor speed gradually decreases as the battery  316  wears down. This gradual decrease provides the user with ample warning to replace the battery  316 . However, in a powered razor with an indirect power supply, there is no such warning. Once the battery voltage falls below some lower threshold, the motor speed decreases abruptly, perhaps even in the middle of a shave. 
     To prevent this inconvenience, the control logic  105 , on the basis of information provided by the voltage monitor  312 , provides a low-battery signal to a low-battery indicator  414 . The low-battery indicator  414  can be a single-state output device, such as an LED, that lights up when the voltage falls below a threshold, or conversely, that remains lit when the voltage is above a threshold and goes out when the voltage falls below that threshold. Or, the low-battery indicator  414  can be a multi-state device, such as a liquid crystal display, that provides a graphical or numerical display indicative of the state of the battery  316 . 
     The voltage monitor  312 , in conjunction with the control logic  105 , can also be used to disable operation of the razor completely when the battery voltage falls below a deep-discharge threshold. This feature reduces the likelihood of damage to the razor caused by battery leakage that may result from deep-discharge of the battery  316 . 
     A suitable voltage converter  312 , shown in  FIG. 14D , features a switch S 1  that controls an oscillator. This switch is coupled to the actuator button  22 . A user who presses the actuator button  22  thus turns on the oscillator. The oscillator output is connected to the gate of a transistor T 1 , which functions as a switch under the control of the oscillator. A battery  316  provides a battery voltage V BAT . 
     When the transistor T 1  is in its conducting state, a current flows from the battery  316  through an inductor L 1 , thus storing energy in the inductor L 1 . When the transistor is in its non-conducting state, the current through the inductor L 1  will continue to flow, this time through the diode D 1 . This results in the transfer of charge through the diode D 1  and into the capacitor C 1 . The use of a diode D 1  prevents the capacitor C 1  from discharging to ground through the transistor T 1 . The oscillator thus controls the voltage across the capacitor C 1  by selectively allowing charge to accumulate into the capacitor C 1 , thereby raising its voltage. 
     In the circuit shown in  FIG. 14D , the oscillator causes a time-varying current to exist in the inductor L 1 . As a result, the oscillator induces a voltage across the inductor L 1 . This induced voltage is then added to the battery voltage, with the resulting sum being available across the capacitor C 1 . This results in an output voltage, at the capacitor C 1  that is greater than the voltage provided by the battery alone. 
     The capacitor voltage, which is essentially the output voltage of the voltage converter  312 , is connected to both the control logic  105  and to the pulse-width modulator  301  that ultimately drives the motor  306 . When the capacitor voltage reaches a particular threshold, the control logic  105  outputs an oscillator control signal “osc_ctr” that is connected to the oscillator. The control logic  105  uses the oscillator control signal to selectively turn the oscillator on and off, thereby regulating the capacitor voltage in response to feedback from the capacitor voltage itself. The set point of this feedback control system, i.e. the voltage across the capacitor C 1 , is set to be the constant operating voltage seen by the motor  306 . 
     A resistor R 1  disposed between the oscillator and ground functions as part of a decoupling circuit to selectively transfer control of the oscillator from the switch S 1  to the control logic  105 . Before initialization of the control logic, the port that carries the oscillator control signal (the “oscillator control port”) is set to be a high-impedance input port. As a result, it is the switch S 1  that controls the operation of the oscillator. The resistor R 1  in this case prevents a short circuit from the oscillator control port to ground. Following initialization, the oscillator control port becomes a low-impedance output port. 
     Eventually, the user will complete shaving, in which case he may want to turn off the motor  306 . With the control logic  105  now controlling the oscillator, there would be no way to turn off the shaver without removing the battery  316 . To avoid this difficulty, it is useful to periodically determine the state of the external switch S 1 . This is achieved by configuring the control logic  105  to periodically cause the oscillator control port to become a high-impedance input port, so that the voltage across the resistor R 1  can be sampled. 
     In certain types of switches, the state of the switch indicates the user&#39;s intent. For example, a switch S 1  in the closed position indicates that the user wishes to turn on the motor  306 , and a switch S 1  in an open position indicates that the user wishes to turn off the motor  306 . If the voltage thus sampled indicates that the user has opened the switch S 1 , then, when the oscillator control port again becomes a low-impedance output port, the control logic  105  causes the oscillator control signal to shut down the oscillator, thereby shutting down both motor  306 . In doing to, the control logic  105  also shuts down its own power supply. 
     In other types of switches, closing of the switch S 1  indicates only that the user wishes to change the state of the motor from on to off or vice versa. In embodiments that use such switches, the voltage across the resistor R 1  changes only briefly when the user actuates the switch S 1 . As a result, the control logic  105  causes the voltage across the resistor R 1  to be sampled frequently enough to ensure capturing the user&#39;s momentary actuation of the switch S 1 . 
       FIG. 14E  shows the interaction between the oscillator control signal, the oscillator output, and the capacitor voltage. When the capacitor voltage falls below a lower threshold, the oscillator control signal turns on, thereby turning the oscillator on. This causes more charge to accumulate in the capacitor C 1 , which in turn raises the capacitor voltage. Once the capacitor voltage reaches an upper threshold, the oscillator control signal turns off, thereby turning off the oscillator. With no more charge accumulating in the capacitor C 1  from the battery  316 , the accumulated charge begins to drain away and the capacitor voltage begins to decrease. It does so until it reaches the lower threshold once again, at which point the foregoing cycle repeats itself. 
     Another embodiment of a voltage converter  312 , shown in  FIG. 14F  is identical to that described in connection with  FIG. 14D  with the exception that the diode D 1  is replaced by an additional transistor T 2  having a gate controlled by an RC circuit (R 2  and C 2 ). In this embodiment, when the oscillator is inactive, the voltage between the emitter and the base (V BE2 ) of the additional transistor T 2  is zero. As a result, current flow through the additional transistor T 2  is turned off. This means that no charge is being provided to the capacitor C 1  to replace charge that is being drained from the capacitor C 1 . When the oscillator is active, and the oscillator frequency is greater than the cut-off frequency of the RC circuit, then the voltage between the emitter and the base V BE2  will be approximately half the battery voltage V BAT . As a result, the additional transistor T 2  functions as a diode to pass current to the capacitor C 1 , while preventing the capacitor C 1  from discharging to ground. 
     Another notable feature of the circuit in  FIG. 14F  is that the pulse-width modulator  301  is supplied with a voltage directly from the battery  316 . As a result, the output voltage of the pulse-width modulator  301  can be no higher than the battery voltage. Thus, in  FIG. 14F , the motor  306  is powered by a step down in voltage, whereas the stepped up voltage, which is the voltage across the capacitor C 1 , is used to power the control logic  105 . However, the circuit shown in  FIG. 14F  can also feature a pulse-width modulator  316  that takes its input from the voltage across the capacitor C 1 , as shown in  FIG. 14D . 
       FIG. 14G  shows a circuit for driving a voltage converter  312  of the type shown in  FIG. 14F  in greater detail. The oscillator is shown in greater detail, as are the connections associated with the control logic  105 . However, the circuit shown in  FIG. 14G  is otherwise essentially identical to that described in connection with  FIG. 14D  modified as shown in  FIG. 14F . 
     As described herein, a voltage control system provides a constant operating voltage to a motor  306 . However, a powered razor may include loads other than a motor. Any or all of these loads may likewise benefit from a constant operating voltage as provided by the voltage control system disclosed herein. 
     One load that may benefit from a constant operating voltage is the control logic  105  itself. Commercially available logic circuits  105 , are typically designed to operate at a voltage that is higher than the 1.5 volts available in a conventional battery. Hence, a voltage control system that provides a step up in voltage to the control logic is useful to avoid the need for additional batteries. 
     Cartridge Lifetime Detection 
     In the course of slicing through hundreds of whiskers on a daily basis, the blades of a razor cartridge inevitably grow duller. This dullness is difficult to detect by visual inspection. As a rule, dull blades are only detected when it is too late. In too many cases, by the time a user realizes that a blade is too dull to use, he has already begun what will be an unpleasant shaving experience. 
     This final shave with a dull blade is among the more unpleasant aspects of shaving with a razor. However, given the expense of shaving cartridges, most users are understandably reluctant to replace the cartridge prematurely. 
     To assist the user in determining when to replace a cartridge, the razor includes a blade lifetime indicator  100 , shown in  FIG. 15A , having a counter  102  that maintains a count indicative of the extent to which the blades have been already used. The counter is in communication with both the actuator button  22  on the handle  10 , and with a cartridge detector  104 , mounted at the distal end of the razor head  12 . A suitable counter  102  can be implemented in the control logic  105 . 
     A cartridge detector  104  can be implemented in a variety of ways. For example a cartridge detector  104  may include a contact configured to engage a corresponding contact on the cartridge. 
     Razor cartridges can include one, two, or more than two blades. Throughout this description, a single blade is referred to. It is understood, however, that this blade can be any blade in the cartridge, and that all the blades are subject to wear. 
     In operation, when the user replaces the cartridge, the cartridge detector  104  sends a reset signal to the counter  102 . Alternatively, a reset signal can be generated manually, for example by the user pressing a reset button, or by the user pressing the actuator button according to a predetermined pattern. This reset signal causes the counter  102  to reset its count. 
     The ability to detect the cartridge can be used for applications other than resetting the count. For example, the cartridge detector  104  can be used to determine whether the correct cartridge has been used, or whether a cartridge has been inserted improperly. When connected to the control logic  105 , the cartridge detector  104  can cause the motor to be disabled until the condition is corrected. 
     When the user shaves, the counter  102  changes the state of the count to reflect the additional wear on the blade. There are a variety of ways in which the counter  102  can change the state of the count. 
     In the implementation shown in  FIG. 15A , the counter  102  changes the count by incrementing it each time the motor is turned on. For users whose shaving time varies little on a shave-to-shave basis, this provides a reasonably accurate basis for estimating blade use. 
     In some cases, the number of times the motor has been turned on may misestimate the remaining lifetime of a blade. Such errors arise, for example, when a person “borrows” one&#39;s razor to shave their legs. This results in the shaving of considerable acreage with only a single activation of the motor. 
     The foregoing difficulty is overcome in an alternative implementation, shown in  FIG. 15B , in which the actuator button  22  and the counter  102  are in communication with a timer  106 . In this case, the actuator button  22  sends signals to both the control logic  105  and the timer  106 . As a result, the counter  102  maintains a count indicative of the accumulated motor-operating time since the last cartridge replacement. 
     The accumulated motor-operating time provides an improved indicator of blade wear. However, as a rule, the blade does not contact the skin at all times that the motor is operating. Thus, an estimate based on the motor&#39;s operating-time cannot help but overestimate blade wear. In addition, the motor switch may be inadvertently turned on, for example when the razor is jostled in one&#39;s luggage. Under those circumstances, not only will the battery be drained, but the counter  102  will indicate a worn blade, even though the blade has yet to encounter a single whisker. 
     Another implementation, shown in  FIG. 15C , includes a counter  102  in communication with a stroke-detector  108 . In this case, the actuator button  22  signals both the stroke detector  108  and the control logic  105 . Thus, turning on the motor also turns on the stroke-detector  108 . 
     The stroke-detector  108  detects contact between the blade and the skin and sends a signal to the counter  102  upon detecting such contact. In this way, the stroke-detector  108  provides the counter  102  with an indication that the blade is actually in use. In the implementation of  FIG. 15C , the counter  102  maintains a count indicative of the accumulated number of strokes that the blade has endured since the cartridge was last replaced. As a result, the counter  102  ignores time intervals during which the motor is running but the blade is not actually in use. 
     A variety of implementations are available for the stroke-detector  108 . Some implementations rely on the change between the electrical properties on or near the skin and electrical properties in free space. For example, the stroke-detector  108  can detect skin contact by measuring a change in resistance, inductance, or capacitance associated with contacting the skin. Other implementations rely on the difference between the acoustic signature of a blade vibrating on the skin and that of a blade vibrating in free space. In these implementations, the stroke-detector  108  can include a microphone connected to a signal processing device configured to distinguish between the two signatures. Yet other implementations rely on changes to the motor&#39;s operating characteristics when the blade touches the skin. For example, because of the increased load associated with skin contact, the motor&#39;s appetite for current may increase and the motor&#39;s speed may decrease. These implementations include ammeters or other current indicating devices, and/or speed sensors. 
     An estimate that relies on the number of strokes may nevertheless be inaccurate because not all strokes have the same length. For example, a stroke down a leg may wear the blade more than the several strokes needed to shave a moustache. The stroke-detector  108 , however, cannot tell the difference between strokes of different lengths. 
     Another implementation, shown in  FIG. 15D , includes both a stroke-detector  108  in communication with the actuator button  22  and a timer  106 . The timer  106  is in communication with the counter  102 . Again, the actuator button signals both the stroke detector  108  and the control logic  105 . The stroke detector  108  stops and starts the timer  106  in response to detecting the beginning and end of a stroke respectively. This implementation is identical to that in  FIG. 15C  except that the counter  102  now maintains a count indicative of the accumulated time that the cartridge has been in contact with the skin (referred to as “stroke time”) since the last cartridge replacement. 
     A stroke-detector  108  in conjunction with a timer  106  as described in connection with  FIG. 15D  has applications other than providing information indicative of blade wear. For example, the absence of a stroke for an extended period of motor operation may indicate that the motor has been turned on or left on inadvertently. This may occur when the razor is jostled in one&#39;s luggage. Or it may occur because one has absent-mindedly overlooked the need to turn off the motor after shaving. 
     In the embodiments of  FIGS. 1A-1D , the counter  102  is in communication with a replacement indicator  110 . When the count reaches a state indicative of a worn blade, the counter  102  sends a replacement signal to the replacement indicator  110 . In response, the replacement indicator  110  provides the user with a visual, audible, or tactile cue to indicate that the blade is worn out. Exemplary cues are provided by an LED, a buzzer, or a governor that varies the motor speed, or otherwise introduces an irregularity, such as a stutter, into the operation of the motor. 
     The counter  102  includes an optional remaining-lifetime output that provides a remaining-life signal indicative of an estimate of the remaining life of the blade. The remaining-life estimate is obtained by comparing the count and an expected lifetime. The remaining life signal is provided to a remaining-life indicator  112 . A suitable remaining-life indicator  112  is a low-power display showing the expected number of shaves remaining before the worn-out signal activates the worn-out indicator. Alternatively, the remaining lifetime estimate may be shown graphically, for example by flashing a light with a frequency indicative of a remaining lifetime estimate, or by selectively illuminating several LEDs according to a pre-defined pattern. 
     Travel Lock 
     In some cases, it is possible to inadvertently turn on the motor of a powered wet razor. This may occur, for example, during travel when other items in a toilet kit shift and press the actuator button  22 . If this occurs, the motor will draw on the battery until the battery runs down. 
     To avoid this difficulty, the razor can include a lock. One such lock is a mechanical lock  200  on the actuator button  22  itself. An example of a mechanical lock  200  is a sliding cover, as shown in  FIG. 16A , that covers the actuator button  22  when the razor is put away. Other examples of mechanical locks are associated with a holder for the razor, rather than with the razor itself. For example, the switch can be configured to cover the actuator button  22  when the razor is stowed in the holder. 
     Other locks are electronic in implementation. One example of an electronic lock is a locking circuit  202 , as shown in  FIG. 16B , that receives a switch signal  204  from the actuator button  22  (labeled “1/0” in the figure) and an arming signal  206  from an arming circuit  208  (labeled “arming-signal source” in the figure). The locking circuit  202  outputs a motor control signal  210  to the control logic  105  in response to the states of the switch signal  204  and the arming signal  206 . 
     The arming circuit  208  is said to arm and disarm the locking circuit  202  using the arming signal  206 . As used herein, the locking circuit  202  is considered armed when pressing the actuator button  22  starts and stops the motor. The locking circuit  202  is considered disarmed when pressing the actuator button  22  fails to operate the motor at all. 
     Arming circuits  208  and locking circuits  202  typically include digital logic circuits that change the state of their respective outputs in response to state changes in their respective inputs. As such, they are conveniently implemented within the control logic  105 . However, although digital logic elements provide a convenient way to build such circuits, nothing precludes the use of analog or mechanical components to carry out similar functions. Examples of arming circuits  208 , or portions thereof, are described below. 
     One example of an arming circuit  208  includes an arming switch. In this implementation, the user operates the arming switch to change the state of the arming signal  206 . The user then presses the actuator button  22  to start the motor. After shaving, the user again presses the actuator button  22 , this time to stop the motor. He then operates the arming switch to disarm the locking circuit  202 . 
     Alternatively, the arming circuit  208  can be configured to disarm the locking circuit automatically upon detecting that the motor has been turned off. In this case, the arming circuit  208  will generally include an input to receive a signal indicating that that the motor has been turned off. 
     As used herein, “switch” includes buttons, levers, sliders, pads, and combinations thereof for effecting a change in the state of a logic signal. Switches need not be actuated by physical contact but can instead be activated by radiant energy carried, for example, optically or acoustically. A switch can be directly user-operable. One example of such a switch is the actuator button  22 . Alternatively, the switch can be operated by a change in the disposition of the razor, for example by replacing a razor in its holder, or by removing and installing a cartridge. 
     As suggested by  FIG. 16B , the locking circuit  202  can be viewed abstractly as an “AND” gate. Although the locking circuit can be implemented as an “AND” gate, any digital logic circuit with a suitable truth table can be used to carry out the arming function of the locking circuit  202 . For example, the locking circuit  202  can be implemented by placing an arming switch in series with the actuator button  22 . 
     In another implementation, the arming circuit  208  includes a timer. The output of the timer causes the arming circuit  208  to initially arm the locking circuit  202 . Upon the lapse of a predetermined shaving interval, the timer causes the arming circuit  208  to disarm the locking circuit  202 , thereby turning off the motor. The length of the shaving interval corresponds to a typical shaving time. A suitable length is between about five and seven minutes. 
     In this implementation, upon pressing the actuator button  22 , the motor will run either until the actuator button  22  is pressed again, or until the lapse of the shaving interval. Should the user take longer than the shaving interval to shave, the motor will turn off, in which case, the user must press the actuator button  22  again to restart the motor and complete the shave. To avoid this, the arming circuit  208  can be provided with an adaptive feedback loop that extends the default shaving interval in response to “extensions” requested by the user. 
     When the arming circuit  208  includes a timer, a reset input on the timer is connected to either the output of the locking circuit  202  or to the actuator button  22 . This enables the timer to reset itself in response to a change in the state of the switch signal  204 . In particular, the timer resets itself whenever the switch signal  204  turns off the motor. This can occur when either the user presses the actuator button  22  prior to the lapse of the shaving interval, or upon the lapse of the shaving interval. 
     In another implementation, the arming circuit  208  includes a decoder having an input connected to either the actuator button  22  or to a separate decoder input-button. In this case, the state of the arming signal  206 , which depends on the decoder&#39;s output is controlled manually by the user, either by pressing the actuator button  22  according to a predefined pattern, or, in the alternative implementation, by operating the decoder input-button. 
     For example, in the case in which the decoder takes its input from the actuator button  22 , the decoder may be programmed to respond to an extended press of the actuator button  22  or a rapid double-click of the actuator button  22  by causing a change to the state of the arming signal  206 . Alternatively, in the case in which the decoder accepts input from a separate decoder input-switch, the user need only operate the decoder input-switch. There is no need for the user to remember how to lock and unlock the motor with the actuator button  22 . 
     In those implementations that rely on the user to change the state of the arming signal  206 , it is useful to provide an indicator, such as an LED, that provides the user with feedback on whether he has successfully changed the state of the arming signal  206 . 
     In other implementations, the arming circuit  208  relies on the disposition of the razor to determine whether it should disarm the locking circuit  202 . For example, the arming circuit  208  may include a contact switch that detects the installation and removal of a shaving cartridge. When the cartridge is removed, the arming circuit  208  disarms the locking circuit  202 . Alternatively, the arming circuit  208  can include a contact switch that detects whether or not the razor has been stowed in its holder. In this case, when the arming circuit  208  detects that the razor has been stowed in its holder, it disarms the locking circuit  202 . 
     In the case in which the arming circuit  208  responds to the presence of a cartridge, a user prevents the motor from accidentally turning on by removing the cartridge from the handle. To operate the razor normally the user re-installs the cartridge on the handle. 
     In the case in which the arming circuit  208  responds to the presence of a holder, the user prevents the motor from accidentally turning on by stowing it in its holder. To operate the razor normally, the user removes it from its holder, which is something he would have to do in any case. 
     While the embodiment described herein controls the operation of a motor, the disclosed methods and devices can be used to prevent battery drain from inadvertent consumption of energy by any load. 
     Shaving Force Measurement 
     During the course of a shave, the user applies a force that presses the blade against the skin. The magnitude of this shaving force affects the quality of the shave. A shaving force that is too low may be insufficient to force the whiskers into an optimum cutting position. One that is too high may result in excessive skin abrasion. Because of the varying contours of the face, it is difficult for the user to maintain even a constant shaving force, much less an optimal shaving force. 
     This difficulty is overcome in razors that include force-measurement circuits  400  as shown in  FIGS. 4A and 4B . The illustrated force-measurement circuits  400  exploit the fact that in a motorized razor, the shaving force governs, in part, the load applied to the motor  306  that drives the blade. The operating characteristics of this motor  306  thus change in response to the shaving force. 
     The force-measurement circuit  400  shown in  FIG. 17A  exploits the change in the current drawn by the motor  306  in response to different loads. As the shaving force increases, the motor  306  draws more current in response. The implementation in  FIG. 17A  thus features a current sensor  402  that senses the magnitude of the current drawn by the motor  306 . The current sensor provides a force signal  408  to the control logic  105 . 
     The force-measurement circuit shown in  FIG. 17B  exploits the change in motor speed that results from different loads on the motor  306 . As the shaving force increases, the motor speed decreases. The implementation shown in  FIG. 17B  thus features a speed sensor  410  for sensing the motor speed. This speed sensor provides a force signal  408  to the control logic  105 . 
     The control logic  105  receives the force signal  408  and compares it with a nominal force signal indicative of what the force signal would be under a known load. Typically, the known load is selected to correspond to a razor vibrating in free space, without contacting any surface. Alternatively, the control logic  105  compares the force signal  408  with a pair of nominal force signals corresponding to a razor vibrating with two known loads, one corresponding to a minimum shaving force and another corresponding to a maximum shaving force. 
     The control logic  105  then determines whether the applied shaving force falls outside the band defined by the upper and lower shaving force thresholds. If the applied shaving force falls outside the band, the control logic  105  sends a correction signal  412  to an indicator  414 . The indicator  414  then transforms the correction signal  412  into an observable signal that is observable by the user, either because it is visible, audible, or provides some tactile stimulation. 
     For an acoustic observable signal, the indicator  414  can be a speaker that provides an audible signal to the user. For an optically observable signal, the indicator  414  can be an LED that provides a visible signal to the user. For a tactile observable signal, the motor  306  itself is used as an indicator  414 . Upon detecting an incorrect shaving force, the control logic  105  sends a correction signal  412  to the motor  306  to introduce a disturbance into its normal operation. For example, the control logic  105  might send a correction signal  412  that causes the motor  306  to stutter. 
     In all the foregoing cases, the signal for an insufficient shaving force can differ from that for an excessive shaving force so that the user will know how to correct the applied shaving force. 
     A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. 
     For example, while the razors described above include a vibration motor and provide a vibrating functionality, other types of battery-operated functionality may be provided, such as heating. 
     Moreover, while in the embodiment described above a receiving member containing a window is welded into an opening in the grip tube, if desired the window may be molded into the grip tube, e.g., by molding a transparent membrane into the grip tube. 
     In some implementations, other types of battery shell attachment may be used. For example, the male and female portions of the battery shell and grip tube may be reversed, so that the battery shell carries the male portion and the grip tube carries the female portion. As another example, the battery shell may be mounted on the grip tube using the approach described in copending U.S. Ser. No. 11/115,885, filed on Apr. 27, 2005, the complete disclosure of which is incorporated herein by reference. Other mounting techniques may be used in some implementations, e.g., latching systems that are released by a push button or other actuator. 
     Additionally, in some implementations the razor may be disposable, in which case the battery shell may be permanently welded to the grip tube, as it is not necessary or desirable that the consumer access the battery. In disposable implementations, the blade unit is also fixedly mounted on the razor head, rather than being provided as a removable cartridge. 
     Other venting techniques may also be used, for example venting systems that employ sealing valve members rather than a microporous membrane. Such venting systems are described, for example, in U.S. Ser. No. 11/115,931, filed on Apr. 27, 2005, the complete disclosure of which is incorporated herein by reference. 
     Some implementations include some of the features described above, but do not include some or all of the electronic components discussed herein. For example, in some cases the electronic switch may be replaced by a mechanical switch, and the printed circuit board may be omitted. 
     Accordingly, other embodiments are within the scope of the following claims. 
     A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. 
     For example, while the razors described above include a vibration motor and provide a vibrating functionality, other types of battery-operated functionality may be provided, such as heating. 
     Moreover, while in the embodiment described above a receiving member containing a window is welded into an opening in the grip tube, if desired the window may be molded into the grip tube, e.g., by molding a transparent membrane into the grip tube. 
     In some implementations, other types of battery shell attachment may be used. For example, the male and female portions of the battery shell and grip tube may be reversed, so that the battery shell carries the male portion and the grip tube carries the female portion. As another example, the battery shell may be mounted on the grip tube using the approach described in copending U.S. Ser. No. 11/115,885, filed on Apr. 27, 2005, the complete disclosure of which is incorporated herein by reference. Other mounting techniques may be used in some implementations, e.g., latching systems that are released by a push button or other actuator. 
     Additionally, in some implementations the razor may be disposable, in which case the battery shell may be permanently welded to the grip tube, as it is not necessary or desirable that the consumer access the battery. In disposable implementations, the blade unit is also fixedly mounted on the razor head, rather than being provided as a removable cartridge. 
     Other venting techniques may also be used, for example venting systems that employ sealing valve members rather than a microporous membrane. Such venting systems are described, for example, in U.S. Ser. No. 11/115,931, filed on Apr. 27, 2005, the complete disclosure of which is incorporated herein by reference. 
     Some implementations include some of the features described above, but do not include some or all of the electronic components discussed herein. For example, in some cases the electronic switch may be replaced by a mechanical switch, and the printed circuit board may be omitted. 
     Accordingly, other embodiments are within the scope of the following claims.