Patent Publication Number: US-2009217531-A1

Title: Electric shaver

Description:
This application claims priority from Japanese Patent Application No. 2008-47093, filed Feb. 28, 2008, which is hereby incorporated by reference herein. 
     TECHNICAL FIELD 
     The present invention relates to electric shavers comprising a head having a blade unit and a handle supporting the head thereon tiltably. 
     BACKGROUND OF THE INVENTION 
     Electric shavers are available which comprise a head having a blade unit, and a handle tiltably supporting the head thereon so as to alter the angle of the razor blade relative to the handle (see, for example, Japanese Utility Model Publication No. 6372/1986). 
     With the electric shaver mentioned above, the head is very small in the maximum inclination from the handle, and the shaver is used with the handle pushed toward the head (hereinafter referred to as “pressure shaving.” 
     In pressure shaving, the blade tends to be pressed against the skin with a pressure greater than is necessary, causing the skin to feel irritated after shaving. Additionally, since the hand is moved with the elbow unconsciously raised nearly to the shoulder level, the user is likely to feel muscular fatigue. 
     The present invention provides an electric shaver which is usable for shaving by pulling (hereinafter referred to as “pull shaving”) like T-shaped safety razors, whereas this mode of shaving is inconceivable with conventional electric shavers. 
     SUMMARY OF THE INVENTION 
     The present invention provides an electric shaver comprising a head tiltably attached to one end of a handle, the head having a blade unit, 
     the head being tiltable with the handle thereby supported vertically until the blade unit is positioned sideways, the head being holdable as positioned sideways by lock means. 
     With the head positioned generally sideways relative to the handle, the electric shaver is usable for shaving by pulling the handle and slidingly moving the head along the face. 
     This mode of pull shaving eliminates the likelihood that the blade will be forced against the skin with a pressure greater than is needed, preventing the skin from smarting. The construction described reduces muscular burdens because there is no need to apply a force greater than is necessary and further because the shaver is usable without raising the elbow nearly to the level of the shoulder. 
     The head can be held tilted by the lock means, so the shaver is usable with safety without altering the angle of the head during use. 
     With the electric shaver described, the handle can be in the form of a shaft and enlarged into a generally T-shaped portion toward the head, the enlarged portion having bracket arms projecting respectively from opposite ends thereof, the head being provided between the bracket arms. 
     Since the handle of the shaver is in the form of a shaft, the shaver can be held like the conventional T-shaped safety razor when the shaver is used for shaving the underside of the chin or the side of the face by pulling the shaver upward from below. The shaver is therefore easy to use. 
     With the electric shaver described, the head can be locked in a plurality of tilted positions including a pull shaving tilted position which is a basic tilted position permitting the blade unit to be positioned sideways with the handle supported vertically and a border shaving tilted position permitting the blade unit to face generally upward. 
     When the head is in the border shaving tilted position, sideburns or like whiskers can be shaven off as by conventional electric shavers. 
     With the electric shaver described, the head in the pull shaving tilted position can be inclined through about 80 degrees from an extension of the axis P 1  of the handle extending through the head, and the head in the border shaving tilted position can be inclined through about 20 degrees from the extension. 
     When the head is brought to the border shaving tilted position, sideburns or like whiskers can be shaven off as by conventional electric shavers. 
     With the electric shaver described, the handle has an eccentric rotary shaft projecting from the end thereof and coupled to a motor, and the head is tiltably provided between bracket arms projecting respectively from opposite sides of the end of the handle, the head comprising a head body case having a bottom portion adjacent the handle and curved toward the direction of tilting of the head, an outer blade cassette removably provided in the head body case, a vibrator reciprocatingly movable in directions orthogonal to the handle and engaging with the eccentric rotary shaft as loosely inserted through a bottom plate of the head body case, and inner blades slidable in contact with outer blades of an outer blade cassette from inside thereof and attached to and reciprocatingly movable with the vibrator, the vibrator having parallel guide plates orthogonal to the directions of reciprocation of the vibrator, the eccentric rotary shaft being interposed between and slidable in contact with the guide plates, each of the guide plates having a circular-arc edge extending along the curve of the head body bottom portion, a closing piece projecting outward from each of the guide plates and extending along the circular-arc edge, the bottom plate of the head having a slip with a width to avoid the interference of the bottom plate with the eccentric rotary shaft, the closing piece serving to close the slit even when the vibrator oscillates widthwise of the slit. 
     The vibrator has parallel guide plates having the eccentric rotary shaft positioned therebetween and slidable in contact therewith. The guide plates each have a circular-arc edge which is curved in the direction of rotation of the head and opposed to the bottom plate of the head body case from inside. Since the bottom plate has a slit for preventing the bottom plate from interfering with the eccentric rotary shaft, the head is tiltable free of any trouble. 
     When the vibrator oscillates toward the slit portion, the closing pieces projecting from the respective guide plates cover the slit, obviating the likelihood of fragments of beard or like extraneous matter from moving into or out of the slit. 
     Furthermore, the closing pieces serve as reinforcement ribs for the guide plates, contributing to a reduction in the thickness of the guide plates. 
     With the handle positioned vertically and with the head on an upper end of the handle positioned sideways, the blade unit preferably has a border shaving outer blade, a rough shaving outer blade and a finish shaving outer blade which are arranged from below upward in this order, the outer blades having respective outer faces positioned generally on a plane F, and the plane F makes an angle of 10 to 20 degrees with an axis P 1  of the handle, the finish shaving outer blade being remotest in position from the axis P 1 . 
     In pull shaving, it is possible to shave off a twisted long beard with the border shaving outer blade first, to roughly shave off an ordinarily grown beard with the rough shaving outer blade and to use the finish shaving outer blade for finishing. This assures effective shaving with a reduced likelihood of leaving some beard unshaven. 
     The border shaving outer blade, rough shaving outer blade and finish shaving outer blade have their outer faces arranged generally in a plane F, and the plane F is inclined at an angle of 10 to 20 degrees from the axis P 1  of the handle so that the finish shaving outer blade is highest from the axis P 1 . Accordingly, all the blades are spontaneously brought into contact with the skin during pull shaving to realize an effective shave. 
     With the electric shaver described, the head body case preferably has a front wall facing toward the pull shaving tilted position and provided with a push knob for pushing up a border shaving outer blade to a border shaving position, and a rear wall provided with a washing window and a lid for closing the window. 
     When a flow of water is applied to the head body case from above with the washing window opened, the water is discharged from between the blades positioned sideways, whereby the shaver is washed effectively. 
     The border shaving outer blade has larger perforations than the rough shaving outer blade and finish shaving outer blade. Since the washing window is provided on the backside of the head body case, i.e., at a position remotest from the border shaving outer blade having the largest perforations, the flow of water applied to the head body case spreads over the entire interior of the body case to fully wash the shaver, and is then run off from the blade perforations and other clearances. This ensures effective cleaning by merely applying running water. 
     When the handle is grasped with its front side down and with the head in the border shaving tilted position, the washing window faces upward with the outer blades positioned sideways, so that the washings flow out sideways away from the handle. This eliminates the likelihood of the water splashing over the handle or the hand. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an electric shaver as it is seen from the front; 
         FIG. 2  shows a head in tilted positions, (a) being a tilted position for pull shaving, (b) being an intermediate tilted position, (c) being a border shaving tilted position; 
         FIG. 3  is a perspective view of the backside of the head of the shaver; 
         FIG. 4  is an exploded perspective view of the head; 
         FIG. 5(   a ) is a plan view of the head, and  FIG. 5(   b ) is a front view of the upper portion of a handle; 
         FIG. 6(   a ) is a side elevation of the head, and  FIG. 6(   b ) is a side elevation of the handle upper portion; 
         FIG. 7  is an exploded perspective view of lock means on the handle; 
         FIG. 8  is an exploded side elevation of the lower portion of the head; 
         FIG. 9  is an exploded perspective view of a blade unit; 
         FIG. 10  is a an exploded perspective view of an outer blade cassette; 
         FIG. 11  is a sectional view of the lock means in a head locking state; 
         FIG. 12  is a sectional view of the lock mans in a head unlocking state; 
         FIG. 13  is a perspective view of a vibrator as it is seen from below; 
         FIG. 14  is a sectional view showing the relationship between the vibrator and a slit in the head; 
         FIG. 15  is a sectional view showing the vibrator and the vicinity thereof; 
         FIG. 16(   a ) is a perforation pattern of an outer blade for finish shaving, and  FIG. 16(   b ) is an enlarged view of the perforation pattern; 
         FIG. 17(   a ) is a perforation pattern of rough shaving outer blade, and  FIG. 17(   b ) is an enlarged view of the perforation pattern; 
         FIG. 18  is an illustration of the shaver as it is used for the pull shaving of the lower part of the chin; 
         FIG. 19  is an illustration of the shaver as it is used for the pull having of one side the face; and 
         FIG. 20  is an illustration showing how to wash the interior of the head. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to  FIGS. 1 and 3 , the present invention provides an electric shaver, which comprises a head  2  having a blade unit  3  and tiltably supported between bracket arms  11 ,  11  projecting from opposite sides of one end of a handle  1 . The head  2  can be held in a plurality of tilted positions by lock means  6 . 
     A power supply switch  10  is provided at an upper portion of center of the front wall of the handle  1 . 
       FIG. 2  shows the tilted rocked positions of the head  2 . According to the embodiment, the head  2  can be locked in three tilted positions. 
       FIG. 2(   a ) shows the basic position of the head  2  while the electric shaver of the present invention is in use. The head  2  is in a pull shaving tilted position in which the head  2  is positioned generally sideways.  FIG. 2(   c ) shows the head  2  in a border shaving tilted position, wherein the head  2  faces generally upward.  FIG. 2(   b ) shows an intermediate tilted position between the two tilted positions. 
     As shown in  FIG. 20  and described previously, the tilted position of  FIG. 2(   c ) for border shaving is suitable also for washing the interior of the shaver head  2 . 
     The intermediate tilted position is suitable for pressure shaving because the elbow then need not be raised. 
     A line extending from the axis P 1  of the handle  1  and passing through the head  2  makes with a tilt axis P 2  of the head  2  an angle, which is about 80 degrees in the pull shaving tilted position, about 50 degrees in the intermediate tilted position, or about 20 degrees in the border shaving tilted position. 
     The axis P 1  of the handle is the center of the tubular shaft serving as the handle  1 . 
     The tilt axis P 2  of the head  2  is an axis extending through the center of rotation (the center of tilting) of the head  2  and through the midpoint of the width of a rough shaving outer blade  33  positioned in the center of the head  2  to be described later. 
     With reference to  FIG. 1 , the handle  1  is in the form of a hollow shaft and enlarged into a generally T-shaped portion toward the head  2 . The handle  1  is slender and rounded over the entire periphery thereof so as to be gripped like a pen. 
     The handle  1  is provided on each of its opposite sides with a grip portion  17  gently recessed in a circular-arc form and extending from the base end of the bracket arm  11  toward the base end of the handle  1 . 
     When the handle  1  is to be gripped at the portion thereof close to the bracket arms  11  from the backside of the handle  1 , one of the grip portions  17  bears on the protuberance of the thumb, and the other grip portion  17  bears on the protuberances of the first and second fingers as shown in  FIGS. 18 and 19 . 
     The grip portions  17  are made of a nonslip material and/or have projections or indentations for preventing slippage. 
     The handle  1  is so shaped that the electric shaver can be held like the conventional T-shaped razor when the underside of the chin is to be shaved by pulling the shaver as shown in  FIG. 18  or when the face side is to be similarly shaved as seen in  FIG. 19 . The shaver is therefore easy to use. 
     Between the bracket arms  11 ,  11 , the handle  1  is provided at its upper end with a recessed circular-arc face  14  extending along the direction of rotation of the head  2  and with an eccentric rotary shaft  16  projecting upward and positioned slightly closer to the handle backside at the midportion of width of the handle end. The shaft  16  is eccentrically rotatable to oscillate a vibrator  4  reciprocatingly laterally. 
     With reference to  FIG. 4 , the head  2  comprises a head body case  21 , and the vibrator  4 , inner blades  35 ,  35  and an outer blade cassette  30  which are housed in the head body case  21 . 
     The head body case  21  comprises a lower case member  21   a  positioned on the handle  1  and pivotably provided between the bracket arms  11 ,  11 , and a head upper case member  5  placed on the lower case member  21   a  and joined thereto. 
     With reference to  FIGS. 8 and 14 , the lower case member  21   a  is in the form of a laterally elongated case which is open at its upper side, and has a bottom plate  22  in the form of a circular-arc wall centered about the center of rotation of the head  2  and shaped to extend along the recessed circular-arc face  14  at the upper end of the handle  1 . The bottom plate  22  has a slit  28  extending in the direction of the circular arc for the eccentric rotary shaft  16  to loosely fit in. 
     The slit  28  extends over such a range that the bottom plate  22  will not interfere with the eccentric rotary shaft  16  when the head  2  is shifted from the pull shaving tilted position to the border shaving tilted position. 
     The lower case member bottom plate  22  has recessed step portions  29  lower than the inner surface of the plate  22  and extending over the entire length of the plate edges defining the slit  28 . 
     With reference to  FIGS. 8 and 11 , each of opposite ends of the lower case member  21   a  has a partitioned small compartment  27 , and a circular recessed step portion  24  is concentrically formed in an end plate  23  of the case member  21   a.  A circular hole  25  is formed in the center of the step portion  24 . 
     The hole  25  has cutouts  25   a,    25   a  positioned symmetrically as spaced apart by 180 degrees about the center. 
     Guide holes  26  spaced apart by 180 degrees are formed symmetrically in the step portion  24  on opposite sides of the hole  25 . 
     As shown in  FIG. 8 , the vibrator  4  coupled to the eccentric rotary shaft  16  is disposed in the lower case member  21   a.    
     As in conventional electric shavers, the vibrator  4  has an inner blade mount  41  and flexible arm pieces  42 ,  42  at opposite ends of the mount  41 . The arm pieces  42 ,  42  are fastened at their free ends to a mount boss (not shown) on the lower case member  21   a  with screws. 
     Projecting from the bottom of the inner blade mount  41  are parallel guide plates  42 ,  42  which are arranged orthogonal to the directions of reciprocation of the vibrator  4 , with the eccentric rotary shaft  16  disposed slidably between the guide plates  42 ,  42 . 
     The guide plates  43 ,  43  have respective circular-arc edges  43   a  extending along the curve of the bottom plate  22  of the lower case member  21   a.  Projecting outward from each of the guide plates  43  is a closing piece  44  extending along the circular-arc edge  43   a.    
     The circular-arc edges  43   a  of the guide plates  43  fit in the recessed step portions  29  on opposite sides of the slit  28  in the bottom plate  22  of the lower case member  21   a.    
     The guide plates  43 ,  43  are pushed laterally leftward or rightward by the eccentric rotation of the rotary shaft  16 , whereby the vibrator  4  is oscillated longitudinally of the lower case member  21   a.  Despite the oscillation of the vibrator  4 , the closing pieces  44 ,  44  close the recessed step portions  29 , consequently closing the slit  28  and preventing extraneous matter from moving in or out through the slit  28 . 
     The upper opening of the lower case member  21   a  is provided with a vibrator cover  46  for closing the opening. The cover  46  has an opening  46   a  corresponding in position to the vibrator  4  and provided with a rubber cap (not shown). 
     The vibrator  4  has a connector  45  disposed at an upper portion thereof and extending through the rubber cap. 
     With reference to  FIG. 9 , the connector  45  has two mount legs  45   a,    45   a  for mounting the inner blades  35 ,  35 , and an engaging portion  45   b  for driving an outer blade  32  for border shaving. 
     As shown in  FIG. 9 , the blade unit  3  comprises two inner blades  35 ,  35  to be removably mounted on the legs  45   a,    45   a  of the connector  45 , the outer blade cassette  30  including two outer blades  33 ,  34  fittable over the inner blades  35 ,  35  and the border shaving outer blade  32 , and the head upper case member  5  on the lower case member  21   a.    
     Each inner blade  35  is a known one and comprises a blade plate prepared from a metal sheet having a row of slits by curving the blade plate to an inverted U shape in cross section (see, for example, JP2006-340938A). 
     The outer blade cassette  30  shown in  FIGS. 9 and 10  has three laterally elongated outer blades  32 ,  33 ,  34  as arranged in parallel within a blade case  31  in the form of a laterally elongated frame which is open at its upper and lower sides. The rough shaving outer blade  33  is positioned between the border shaving outer blade  32  and the finish shaving outer blade  34 , and these blades  32 ,  33 ,  34  are left exposed from the upper end opening of the blade case  31 . 
     The rough shaving blade  33  and the finish shaving blade  34  each comprise a reticular blade  33   a  or  34   a  made of a thin metal sheet having a multiplicity of perforations and fixed to a laterally elongated frame  33   b  or  34   b  which is open at its upper and lower sides. 
     The border shaving outer blade  32  is made from a metal sheet by bending the sheet to an inverted L shape and having a multiplicity of cutouts in a row and formed at the bent portion to provide a cutting edge. 
     The border shaving outer blade  32  is attached to an auxiliary member  32   a  to be described below. 
     The outer blade cassette  30  is removably provided with a protective cover  20  as shown in  FIG. 4 . 
     With reference to  FIG. 16(   a ), the finish shaving outer blade  34  has a perforation pattern shown and providing a cutting edge.  FIG. 16(   b ) is an enlarged view of one unit of perforation pattern. 
     The rough shaving outer blade  33  has a perforation pattern shown in  FIG. 17(   a ) and providing a cutting edge.  FIG. 17(   b ) is an enlarged view of one unit of perforation pattern. 
     With both the rough shaving outer blade  33  and the finish shaving blade  34 , each unit of perforation pattern has a central perforation  38  or  38   a  and five perforations  39  or  39   a  generally equidistantly arranged around the central perforation. The perforations  38 ,  39  of the finish shaving blade  34  are more rounded than those  38   a,    39   a  of the rough shaving blade  38 . 
     The border shaving outer blade  32  has the same perforation pattern as conventionally. 
     When water is applied to interior of the blade case  31 , the border shaving blade  32  permits smoother passage of water therethrough than the rough shaving blade  33  or the finish shaving blade  34 . 
     The auxiliary member  32   a  is incorporated in the blade case  31  for pushing up the border shaving outer blade  32  to a border shaving level. The border shaving blade  32  is attached to the auxiliary member  32   a.  The auxiliary member  32  is biased by a spring (not shown) toward such a direction as to move the border shaving blade  32  into the blade case  31 . 
     The auxiliary member  32   a  is provided with a border shaving inner blade (not shown) slidable on the inner surface of the border shaving outer blade  32 . This inner blade is coupled by a link  56  to the engaging portion  45   b  on the connector  45  and reciprocatingly slidable. 
     With the border shaving outer blade  32  in its lower end position as shown in  FIG. 2(   a ), the border shaving outer blade  32 , the rough shaving outer blade  33  and the finish shaving outer blade  34  increase in this order in the height of projection from the upper side opening  31   a  of the blade case  31 , and the outer faces of these blades  32 ,  33 ,  34  are positioned generally on a plane F. 
     The head upper case member  5  shown in  FIG. 9  is in the form of a laterally elongated frame which is open at its upper and lower sides. With the border shaving outer blade  32  positioned on the front side, the outer blade cassette  30  is placed into the case member  5  through the upper side opening thereof. In this state, the inner blades  35 ,  35  are slidable in contact with the respective inner surfaces of the rough shaving outer blade  33  and the finish shaving outer blade  34 . 
     A push knob  55  for pushing up the border shaving outer blade  32  is laterally slidably provided on the front wall of the head upper case member  5 . 
     As shown in a phantom line in  FIG. 2(   c ), the outer blade  32  is used as pushed up for border shaving as in the prior art. 
     With the push knob  55  provided on the front wall of the head upper case member  5 , the push knob  55  faces inward when the head  2  is tilted to the pull shaving position as shown in  FIGS. 18 and 19 . This obviates the likelihood that the push knob  55  will be moved inadvertently at a touch during pull shaving. 
     The head upper case member  5  has formed in its rear wall a laterally elongated large washing window  51  occupying at least half the rear wall area and closed with a lid  52 , which is pivoted at opposite ends of its lower portion and biased toward an opening direction by a spring  53 . 
     Disposed above the lid  52  of the case member  5  is a lock knob  54  which is slidable upward or downward. The lid  52  can be locked in a closed position by the lock knob  54  as moved down, or can be unlocked when the knob is moved up. 
     Each of opposite bracket arms  11  of the handle  1  has a circular recessed portion  12  on the outer side of its upper end and a circular protrusion  13  corresponding to the recessed portion  12  and provided on the inner side of the end. These protrusions  13 ,  13  rotatably fit into the respective circular recessed step portions  24  in opposite ends of the lower case member  21   a.    
     With the bracket arms  11 ,  11  elastically deformed outward, the head  2  can be fitted into the space between the arms  11 . 
     A circular hole  18  is formed in the center of the recessed portion  12  of the bracket arm  11 . A sleeve  7  is inserted through the hole  18  and the hole  25  formed in the recessed step portion  24  of the lower case member  21   a.    
     The sleeve  7  has retainers  71 ,  72  at opposite ends thereof. The retainer  71  is disposed at the outer end and is in the form of a flange. Retainers  72  are disposed at the inner end and project outward from symmetric positions  180  degrees away from each other. 
     The sleeve  7  is fitted in position, with the inner end retainers  72 ,  72  in phase with the cutouts  25   a,    25   a  in the hole  25  of the lower case member  21   a,  and is then rotated, whereby the retainers  72 ,  72  are brought out of phase with the cutouts  25   a,    25   a.  This prevents the sleeve  7  from slipping off, effectively precluding the head  2  from slipping out of the handle  1 . 
     Lock means  6  is provided on both the bracket arm  11  and the head  2  for fixing the tilt angle of the head  2 . Although  FIG. 7  shows lock means  6  provided on each of the bracket arms  11 ,  11 , the lock means may be provided on only one side. 
     With reference to  FIGS. 7 ,  11  and  12 , the lock means  6  comprises a lock plate  65  engageable with the bracket arm  11  by the engagement of engaging means  60  between a projection  66  and a cavity  67  for locking the head  2  at a tilt angle, and an unlocking button  61 . 
     The unlocking button  61  fits into the recessed portion  12  in the bracket arm  11  and comprises a stem  62  projecting from the center of the button and slidably extending through the sleeve  7  into the small compartment  27  of the head  2 . 
     The stem  62  comprises two stem pieces  63 ,  63  arranged in parallel at such a distance as to permit the stem to fit into the sleeve  7  tightly. Each of the stem pieces  63  has an outwardly hooked free end  64 , which is engageable with the end face of the sleeve  7  for preventing the stem  62  from slipping off. Despite the presence of the hooked ends  64 , the stem pieces  63  are elastically deformable, reducing the spacing between the stem pieces  63  and enabling the stem  62  to extend through the sleeve  7 . 
     The stem  62  has an effective length, which is greater than the stroke length required for disengaging the engaging means  60 . 
     The lock plate  65  of the embodiment has a lock pin  66   a  serving as the projection  66  of the engaging means  60 . The bracket arm  11  has a lock bore  67   a  serving as the cavity  67  of the engaging means  60 . 
     With reference to  FIG. 7 , the bracket arm  11  has in its recessed portion  12  three lock bores  67   a  as a group, and two groups of bores  67   a  are provided symmetrically in respective positions which are apart by 180 degrees. 
     The three lock bores  67   a  of each group as spaced apart correspond to the respective three tilted positions of the head  2  already mentioned. 
     With reference to  FIG. 11 , the lock plate  65  is accommodated in the small compartment  27  of the head  3 . Two lock pins  66   a  are slidably inserted in the respective two guide bores  26  formed in the end plate  23  of the head  2 . 
     The lock plate  65  is biased toward the unlocking button  61  by a spring  68 , pushing the stem  62  of the button  61  outward at all times. 
     When the head  2  is locked at a specified angle, the lock pins  66   a  extend through the guide holes  26  and are fitted in the corresponding lock bores  67   a  in the bracket arm  11 . 
     When the unlocking button  61  is pressed against the spring  68  as seen in  FIG. 12 , the stem  62  on the button  61  pushes the lock plate  65  inward, moving the lock pins  66   a  out of the lock bores  67   a  of the bracket arm  11  to release the head  2  from the tilted position. 
     In this state, the head  2  is rotatable (tiltable) about the sleeve  7  of the head  2 . The head  2  is tilted and locked reliably at the next tilted position where the lock pins  66   a  engage in the corresponding lock bores  67   a.    
     The unlocking button  61  directly presses the lock plate  65  so as to apply a pressure directly with its stem  62  without any loss. 
     When the free end of the stem  62  of the unlocking button  61  is adapted to prevent slipping off, the button can be always biased toward the direction of slipping off by the spring  68  through the lock plate  65 , whereby the button  61  can be tensioned by the spring at all times and thereby prevented from backlashing. 
     Apparently the present invention can be modified or altered by one skilled in the art without departing from the spirit of the invention. Such modifications are included within the scope of the invention as defined in the appended claims.