Abstract:
A clock comprising concentric rings of slots slits for indicating time by fully illuminating an appropriate one of the slots. Full illumination is propagated from one slot to an adjacent slot by causing all of the slots in a ring of slots to briefly light up sequentially, thus causing a flash of light to propagate around the ring of slots, thus more clearly showing passage of a second, a minute etc as the illumination was switched from the one slot to the adjacent slot.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in International Patent Application No. PCT/GB2006/003938 filed on Oct. 23, 2006 and Great Britain Patent Application No. 0521765.8 filed Oct. 25, 2005. 
     FIELD OF THE INVENTION 
     The present invention relates to clocks and in particular to a novel form of clock. 
     According to a first aspect of the present invention there is provided a clock comprising a static surface with a number of relatively narrow apertures, each corresponding to a representation of an instant of time in a predetermined unit, and a rotatable shutter with a number of relatively narrow apertures, arranged so that light propagating through a selected one of the apertures in the rotatable shutter can also propagate through one of the apertures in the static surface so as to indicate said instant of time; wherein the number of apertures in the rotatable shutter differs from the number of apertures in the surface; and further comprising means for rotating the rotatable shutter from a position in which said one of the apertures in the rotatable shutter is in alignment with one of the apertures in the static surface to a position in which the same one of the apertures in the rotatable shutter is in alignment with an adjacent one of the apertures in the static surface when incrementing the instant of time indicated by one unit. 
     SUMMARY OF THE INVENTION 
     Thus one particular aperture in a rotatable shutter is arranged in alignment with a further aperture in a static shutter surface when displaying a particular unit of time, for example, a particular second, minute, quarter hour, hour, half day, day, week, month, moon phase and &#39;so on. The same aperture in the rotatable shutter is in alignment when the next unit of time, e.g. the next second or the next minute is displayed. 
     The apertures are preferably elongate, e.g. slits, although they could be of other shapes, e.g. circular holes. 
     Since seconds pass quickly, the rotatable shutter behind the static apertures will have to increment forward to the next static aperture with a travel time and pause period in total equating to one second. If for example the clock is controlled by an actual or a virtual seconds&#39; pendulum, the pause to display the actual instant of time may only be the pause at the end of each swing of the pendulum. However, even though the pause is short and may only slightly longer than the transitory indication in other apertures, an observer can easily identify the particular second displayed. 
     It is preferred to index the ‘minutes’ rotatable shutter forward, as is conventional, as the ‘seconds’ shutter completes 60 seconds when indexing forward from indication 59 to 60 or 0 seconds. Similarly the ‘hours’ shutter should move forward to indicate the new hour concurrently with the both the ‘seconds’ shutter and the minutes&#39; shutter index forward from 59 minutes and 59 seconds. This will be discussed again further below. 
     The preferred clock comprises a plurality of concentric rotatable shutters. These shutters may be independently driven, but preferably one of the shutters is driven, e.g. by the escapement, and drives one or more other of the shutters through a suitable mechanism. 
     This has been recognised to be advantageous in its own right and according to another aspect of the present invention therefore there is provided a clock comprising concentric rotatable shutters, means to drive a first said shutter, said first shutter driving at least one further shutter. 
     Since a second is the smallest moment of time normally displayed by a clock it is preferred that the escapement is coupled to, e.g. mounted to, the ‘seconds’ shutter whereby the intermittent rotation of the escapement wheel is transferred to the ‘seconds’ shutter. 
     Preferably means are provided for locking the non-moving shutter(s) during periods of non-movement. For example, a ‘minutes’ ring may be locked in a stationary position to display the current minute whilst the ‘seconds’ ring continues to be driven and displays the appropriate passing seconds. It is advantageous to lock the rotatable shutters behind the static apertures indicating minutes, hours, days, etc to prevent vibration moving the rotating slot out of alignment with the static aperture representing the particular minute, hour, or day etc displayed. 
     Preferably, therefore, the first shutter intermittently drives the at least one further shutter, which is preferably locked in position apart from when it is driven by the first shutter. 
     Preferably therefore, the first shutter is only brought into intermittent driving relationship with a further shutter. For example, the drive may be designed so that as a ‘seconds’ shutter is at its 59 second position, the ‘minutes’ shutter is brought into drive with it. The movement of the ‘seconds’ shutter to the 60 or 0 position also indexes the ‘minutes’ shutter to the next minute position. A similar mechanism could be applied to the ‘hours’ shutter. However, if it were to remain locked in position for throughout a whole hour, as the next hour was approached, an observer might be confused if the clock were to say remain on say the fourth hour right up to the 59 th  minute and the 59 th  second before moving onto the 5 th  hour the next second. To mitigate this problem, it is advantageous to increment the hour shutter forward to display quarter hour intervals. 
     A shutter associated with the day of the week or the date of the month would be expected to change over at the stroke of midnight but preferably remains stationary for 23 hours 59 minutes and 59 seconds, locked into position. 
     In the preferred drive mechanism, the further shutter includes a ring gear that engages a gear wheel directly or indirectly driven by said first shutter. 
     Most preferably the gear wheel is driven by a further gear wheel which engages the first shutter. 
     The first shutter may be provided with teeth over a limited circumferential extent whereby drive is only transmitted to the further shutter(s) over a limited circumferential movement of the first shutter, thereby achieving the intermittent drive discussed above. 
     In a particularly preferred arrangement, the first shutter drives two further shutters, movement of the second further shutter, being controlled by movement of the first further shutter. This allows say both ‘minutes’ and ‘hours’ shutters to be driven off a ‘seconds’ shutter, with movement of the ‘hours’ shutter being controlled by the ‘minutes’ shutter. 
     Preferably therefore, the first further shutter is provided with means for selectively drivingly coupling said first shutter to said second further shutter. Said means may comprise a cam which at an appropriate rotational position engages a cam follower associated with the drive, causing said drive to engage. A person knowledgeable in the art will appreciate that the angular rotation for a seconds ring and a minutes ring is the same whereas the drive mechanism for a quarter hour or day of the week etc requires a different ratio. 
     The accuracy of time keeping of the preferred clock is dependent on the speed at which shutters influencing or determining the indicating of time rotate. In a preferred clock having a given number of apertures in a static surface or an outer face (which is visible to an observer) of the clock, the shutter preferably performs a full rotation in a period of time defined by the number of slots in the static surface or outer face multiplied by the unit of time represented by the slots in the outer face or static surface. For example, in a clock having sixty slots for indicating seconds in a static surface or outer face, a shutter associated with these sixty slots would perform on full rotation in a period defined by the unit of time indicated by the slots, namely seconds, multiplied by the number of slots in the static surface or front face, namely sixty slots. The shutter in question accordingly performs one full rotation once every minute. 
     From another aspect of the present invention there is therefore provided a clock comprising a static surface with a number of relatively narrow apertures each corresponding to a representation of an instant of time in a predetermined unit, and a rotatable shutter with a number of relatively narrow apertures arranged so that light propagating through at least one of the apertures in the shutter can also propagate through one of the apertures in the static surface in a substantially unattenuated manner, wherein the rotatable shutter is arranged to perform one full rotation in a period defined by the number of apertures in the static surface displaying the unit of time multiplied by the unit of time associated with the apertures in the static surface, and wherein the number of apertures in the static surface differs from the number of apertures in the rotatable shutter. 
     The clock is preferably arranged so that, in a process of rotating the rotatable shutter from alignment of an aperture in the rotatable shutter with an aperture in the static surface into alignment of the aperture in the shutter with an adjacent aperture in the static surface, all of the apertures in the static surface are sequentially aligned with a corresponding aperture in the shutter for a period of time. This sequential alignment lasts only for a very short period of time for each aperture, typically shorter than the period of time that is to be displayed divided by the number of apertures in the static surface (e.g. shorter than one sixtieth of a second in the case of a ring of apertures used for indicating seconds, when the ring of apertures comprises sixty apertures) and can be observed as a flash of light racing around the apertures in the static surface, starting from the aperture in the static surface that is in alignment with an aperture in the shutter at the beginning of the rotation of the rotatable shutter. 
     A similar effect can be produced in rings of apertures representing minutes, quarters of an hour, hours, day of the week etc. 
     The apertures in the static surface and the shutter preferably extend in a radial direction and are arranged in a circle. The pitch circle diameter of a circle in which the centre of the apertures in the static surface are arranged is preferably similar or substantially the same as the pitch circle diameter of the circle in which the apertures in the rotatable shutter are arranged, so that light propagating through apertures in the rotatable shutter can propagate through apertures in the static surface in a substantially unattenuated manner. 
     Preferably the width of each aperture, e.g. slit is less than the circumference at the inner edge of the apertures&#39; pitch circle divided by the number of apertures squared. For example the width of each slit in a seconds&#39; ring having 60 slits would be less than the circumference at the slits&#39; inner diameter divided by 3600. This will ensure that each slit is spaced from its neighbour by more than 59 slit widths, thereby enabling the rotatable shutter to be incremented forward by 60 slit widths before the next slit comes into line again. 
     The number of apertures in the static surface is commonly twelve, forty-eight or sixty for representing hours, quarter hours, minutes and seconds, but other numbers of apertures such as seven, thirty one for other indications such as the day of the week or the date of the month etc can be used as necessary. 
     In a preferred embodiment, the number of apertures in the static surface differs from the number of apertures in the shutter by one to ensure that only one pair of apertures can align at any one time, with no harmonics also in line. The number of apertures in the shutter is accordingly preferably eleven, thirteen, forty-seven, forty-nine, fifty-nine or sixty-one, six or eight, thirty or thirty two etc. If the apertures in the shutter are one less than those in the static the ring of light will appear to revolve anti clockwise whereas with one more aperture the ring of light will appear to rotate clockwise with a conventional clockwise rotation of the ring. 
     In a preferred clock a light source is arranged behind the shutter. It will, however, be appreciated that arranging of such a light source is in no way limiting and the present invention could, for example, also be practised with no additional light source at all beyond incident and reflected light. 
     The static surface can be an external face of the clock. More preferably, however, the clock is provided with a separate outer face that may overlie the static surface. This front face preferably comprises apertures positioned so as to be aligned with the apertures in the static surface. Light propagating through the apertures in the static surface can therefore also propagate through the apertures in the front face. 
     The apertures in the outer face of the clock preferably accommodate light pipes for conveying light from an aperture in the static surface through the front face. The front face of the light pipe may form a continuous surface with the outer face of the clock, but preferably it protrudes above the adjacent surface. The front face of the light pipe is preferably shaped so as to enable light to be emitted and observed over a wide field of view, so that an observer does not need to be normal to the clock face read the time. The face may have a frosted appearance to improve this further. 
     The static aperture may be narrower than the aperture in the front face of the clock. Typically the static aperture is a rectangular slit whereas the aperture in the surface is preferably aesthetically shaped, for example a lenticular slot. 
     The rotatable shutter is preferably coupled to an escapement. The clock then further preferably comprises a pair of pallets and a pallet carrier for controlling the rotation of the escapement and thus the shutter ring. In a preferred clock therefore the shutter can be permitted to rotate by a given angle once every unit of time. For example, a shutter employed to display seconds can be permitted to rotate by six degrees once every second when the number of apertures in the static surface is sixty, so that one aperture in the rotatable shutter moves from alignment with a aperture in the static surface into alignment with an adjacent aperture in the static surface. The preferred drive mechanism will be described in greater detail later in the description. 
     Whereas the following description of the present invention concentrates on a particular well known clock escapement invented in the early eighteenth century by John Harrison and nicknamed the “grasshopper1” escapement, many of the features explained below equally apply to other escapements and could so be adapted by those skilled in the clockmaking art. 
     Prior art clocks employing pallets and pallet carriers can suffer from the disadvantage that pallets exceeding a certain mass can bounce against their positioning stops, hence coming out of alignment with and so losing contact with the escapement instead of remaining in contact with the escapement for the correct length of time. Great care has to be taken to mitigate this problem, even with small escapement wheels and lightweight pallets, for example by the use of special spring loaded stops and energy absorbent materials. However, in accordance with a further feature of this invention, this problem is overcome by the pallets being positively driven into and out of alignment with the escapement. 
     According to another aspect of the present invention, therefore, there is provided a clock comprising an escapewheel, a pair of pallets and a pallet carrier, wherein the pallets are arranged to be positively driven into and out of alignment with the escapewheel. 
     The preferred clock does therefore not suffer from the disadvantages above, as contrary to known pallet and escapement mechanisms, the movement of the pallets is positively controlled and does not rely on factors that may vary depending on the circumstances of use of the clock. Known clocks, for example rely on the pallets moving or accelerating towards the escapement under the influence of gravity. This acceleration may be dependent on the use or location of the clock and more importantly the condition of the oil and lubrication of the pallet bearings and accordingly the movement of the pallets may be so dependent. The preferred clock does not suffer from such dependency, as the pallets are positively driven and held in the correct alignment at all times. If gravity or springs are used to move the pallets there is an increasing small force trying to remove the pallet from alignment and contact with the escapement tooth as the angle of the pallet changes as the escapement tooth moves under its motive force. The pallets of a preferred clock can thus be held in a desired position, for example in alignment and engagement with the escapement tooth, for a desired period of time and subsequently be positively driven from this position. 
     Suitable means may be provided to urge the escapewheel teeth into contact with the pallets. One preferred mechanism will be described later in the specification. 
     In known clocks the pallet carrier is arranged to undergo an oscillating motion by being directly linked to the pendulum or balance wheel of the clock, thereby controlling the clock. The amplitude of oscillation of the pendulum or balance wheel is maintained by imparting a small impulse each oscillation. Thus the pendulum or balance wheel controls the period of the clock and is kept oscillating by virtue of the driving force of the clock. This has the disadvantage that any variation in the oil in the bearings affects the impulse to the pendulum or balance wheel which in turn affects the timekeeping. In turn any variation of the amplitude also affects the timekeeping. 
     In a clock the subject of a further aspect of the present invention the time base of the clock does not rely on a mechanical pendulum or balance wheel but used an independent time base oscillator. Preferably this consists of either the mains frequency or an electronic oscillator as the time base. This can be used to accurately drive a drive member which may be given the appearance of a pendulum or balance wheel, which is more accurate than using a free pendulum or balance wheel. This provides a mechanical clock with all the advantages of modern timekeeping, but with a mysterious and different clock mechanism that appears to be true mechanical clock. 
     From a further aspect therefore, the invention provides a clock comprising an escapement, a pair of pallets and a pallet carrier, wherein the movement of the pallets is controlled by an independent time base oscillator. 
     A motor for moving the pallets and/or the pallet carrier is further preferably provided. This motor can ensure continued operation of the preferred clock, irrespective of any energy losses caused, for example, by the contact between the pallets and the escapement. 
     According to another aspect of the present invention, therefore, there is provided a clock comprising an escapement, a pallet carrier, a pair of pallets and a motor for driving the escapement and the pallet carrier. 
     The motor is preferably a controllable motor such as a stepping motor. With such a motor not only may the motor run either forwards or backwards but also the speed of operation at any angular sector may be accurately controlled and it may be stopped as desired at an accurate position. Thus if the motor is being driven forward and is slowed as a pallet is about to be released, if the motor is stopped just before the point of release and then driven backwards, the pallet will not release from the escapewheel tooth and will then drive the escapewheel and hence the rotatable shutter backwards. As the positions of the pallets are positively and accurately controlled by the mechanism as the mechanism is driven backwards, the pallets will alternately engage and catch the escapewheel, allowing the clock to run backwards. 
     It will be appreciated by a person skilled in the art that it will be difficult to drive both the pallet carrier and the escapewheel directly and continuously. Whereas a crank drive mechanism could drive the pallet carrier and hence the pallets in such a manner, the escapewheel operates in a series of accelerations and decelerations, stopping momentarily between times. To accommodate these variations from uniform motion, the drive mechanism preferably includes a lost motion mechanism. 
     It will be further appreciated that the driving force on the escapewheel must always provide sufficient torque to keep the escapement wheel tooth in contact with the engaged pallet end as the escapement wheel is accelerated and decelerated. 
     The lost motion mechanism and torque are preferably provided by a low rate spring, such as a flat spiral spring. Typically the spring is pre-wound to the extent necessary to provide the torque. As the escapewheel is driven by the motor, the spring accommodates the different motions of the motor and the wheel. As the escapement wheel accelerates, the spring unwinds, driving the escapewheel. While the escapewheel is decelerating or stationary, however, the spring is wound up once more by the drive motor to provide the necessary torque for the next movement of the escapewheel. In one embodiment, particular clock it was found that sufficient torque could be provided by fifteen turns of a multi-turn flat spiral spring. 
     In this mode, the motor can be rotated at a fixed speed in a continuous manner despite the fact that the escapewheel driven by the motor is intermittently prevented from rotation by the pallets. Energy provided by the motor in periods in which the escapewheel is prevented from rotation is simply stored in the spring and used for rotating the escapewheel in periods in which the escapewheel is free to rotate. 
     This is a novel arrangement in its own right and accordingly in another aspect of the present invention there is provided a clock comprising a continuously rotating motor and a pallet controlled escapement driven by the motor but intermittently prevented from rotating by the pallets, and further comprising an energy storage device arranged between the motor and the escapement for sequentially storing driving energy produced by the motor and releasing said energy to drive the escapement. 
     In a preferred clock, a motor drives the pallet carrier and causes the pallet carrier to undergo an oscillating motion. The frequency of this oscillating motion is preferably determined by the drive speed of the motor, which is controlled by the external time base. It will be appreciated that this frequency at least in part determines the period of contact of the pallets with the escapement and thus the latter&#39;s movement. 
     The accuracy of time keeping can accordingly be adjusted by adjusting the drive speed of the motor as necessary from the external time base. 
     It has been recognised that this arrangement is advantageous in its own right and according to another aspect of the present invention there is provided a clock comprising an escapement, a pallet carrier, a pair of pallets and a motor, said motor driving the pallet carrier in an oscillating motion having a frequency determined by the drive speed of the motor. 
     The drive speed of the motor is in turn determined by an external time base. 
     In a preferred clock, the speed of the clock can freely be chosen within the bounds of the possible drive speeds of the motor and, where present, the limitations of the drive spring torque requirement. This permits precise adjustment of the clock&#39;s time keeping accuracy by controlling the drive speed of the motor. Thus the clock can be automatically controlled, for example, to gain an hour when the clocks go forward, by temporarily running the drive motor at a higher speed for a desired period (say a couple of hours) and likewise to lose an hour by temporarily slowing the drive motor down. 
     It has been recognised that the possibility of adjusting the drive speed of a motor driving a clock is of importance for the accuracy of time keeping of the clock. It has further been recognised that a clock that can be driven at various speeds lends itself to various ways of presenting the passage of time in unusual manners. 
     According to another aspect of the present invention therefore there is provided a clock comprising means for running the clock at least first and second, different speeds. 
     A preferred clock could, therefore, be run in two different modes. A first mode using, for example, the first speed can be used for accurate time keeping. In a second mode, however, the clock may be operated at a speed lower than the speed required for accurate time keeping, for example to simulate a slower passage of time. After such a simulation of a slower passage of time, the preferred clock can be operated at a speed faster than the speed required for accurate time keeping (for example in a further, third, mode), so that after a period of time the clock displays the correct time once more. 
     A clock comprising a motor further preferably comprises a microprocessor for selecting a speed of the motor according to pre-programmed instructions. These pre-programmed instructions preferably comprise instructions to operate the motor in a special operations mode, such as that discussed above. 
     Most preferably the microprocessor would be programmed so that any errors deliberately introduced were also deliberately corrected say on every minute or five minutes. 
     The present invention also allows the sound produced by a clock to be controlled. If the pallet mechanism and the escapement were perfectly geared together the clock would operate with little or no traditional “tick tock” sound. This sound is created in known clocks by the escapement wheel being released by one pallet, then accelerating and moving forward until it is caught and brought up short by the second pallet to create a “tick” and then being released by the second pallet and caught again by the first pallet to create a “tack”. The different tick tock sound is created by slight differences in clearance and differences in the angle of contact between the pallet face and the escapewheel tooth, as well as slight differences in the speed that the driving force accelerates the escape wheel before it is caught again by a pallet. For a conventional mechanical clock to keep good time the time interval between each tick or tock should be equal so that the clock is said to be “in beat”. If the time interval is unequal it is usually because the linkage between the pendulum or balance wheel is not set up symmetrically. 
     Viewed from a further aspect, the present invention provides a clock having a pallet controlled escapement wheel comprising means by which the sound caused by the escapement wheel tooth contacting the pallet face can be changed whilst the clock is running. 
     Preferably this is achieved by altering the clearance between the escapement wheel tooth and the pallet face so that the escapement wheel has a slightly longer distance to travel before being caught again by the receiving pallet. 
     In the preferred clock discussed above, a pallet carrier undergoes an oscillating motion, and this oscillating motion at least partially determines the manner in which the pallets of the clock engage the teeth of the escapement wheel. It has been recognised that by altering the clearance between the escapewheel tooth and receiving pallet catching the escapewheel, the amount of noise generated by the contacting of the teeth of the escapement by the pallets can be increased or decreased. 
     According to another aspect of the present invention therefore there is provided a clock comprising an escapement, a pallet carrier and a pair of pallets, the pallet carrier, in use, performing an oscillating movement, wherein the clearance between the pallet and the escapewheel tooth is adjustable whilst the clock is running. 
     When the pallet carrier performs normal timekeeping, contact between the pallets and the escapements is preferably adjusted to the minimum to give a smooth operation of the clock, so that only a minimum amount of noise is generated. When clearance between the pallet carrier and the receiving escapewheel tooth is increased the contact between the pallets and the escapewheel tooth is less smooth and can be somewhat abrupt. This leads to an increase in the noise generated when the pallet contacts the tooth of the escapement. This increase in noise can be used to illustrate the passage of time in an audible manner. 
     In the preferred embodiment of clock, the pallet carrier is driven by a motor. This permits sustained operation of the preferred clock irrespective of, for example, any increased loss in energy that may occur when the pallets contact the escapement with an increased clearance. 
     It is preferred that a length of a linkage between the motor and the pallet carrier can be adjusted to provide variable clearance between the receiving pallet and the escapewheel tooth. It is further preferred that the length can be adjusted using a remote control. Through this remote adjustment feature, the clock can be switched from a quiet operation to a louder operation between alternate pallet operations. 
     Whilst it is possible to link the movement of a pendulum of the clock mechanically to the movement of the escapement, for example, by driving the pendulum from the same motor as the escapement, in a preferred embodiment, the pendulum is driven by a separate motor. This has the advantage of reducing inertia in the system due to the pendulum and also allows for more versatile control of the pendulum movement. From a further aspect, therefore, the present invention provides a clock having an escapement mechanism driven by a first motor and a pendulum driven by a second motor. 
     Preferably the clock comprises a control, for example a microprocessor control, which coordinates the movement of the pendulum in a desired manner with respect to the escapement. For example, the pendulum may be driven in phase with the escapement mechanism, in opposition to or lagging behind it. The amplitude of the pendulum swing may be varied over a number of swings, or its speed within a swing varied. The movement of the pendulum may be symmetrical or asymmetrical and may be central or off centre. 
     In a preferred embodiment, the pendulum is driven by a reciprocating carriage which is suitably driven by the drive motor, for example through a drive belt. Preferably the pendulum is pivotally connected to the carriage through a link arm pivotally mounted to the pendulum arm and the carriage. 
     The motion of the clock and pendulum are controlled electronically in preferred embodiments of the invention which allows the motion of the clock and/or pendulum to be controlled interactively by an observer. For example, the escapement or pendulum mechanisms may be programmed to perform in a certain way upon receiving a suitable signal from the observer. This in itself is a novel arrangement, so from a further aspect, therefore, the present invention provides a clock whose motion is controllable interactively by an observer. 
     Preferably the control system of the clock is configured such as to revert to normal time keeping operation at predetermined intervals so that the primary function of the clock, i.e. accurate time keeping, is maintained. Thus, for example, the clock could be arranged to revert to normal operation every minute, 5 minutes or quarter hour for example. 
     Suitable sensors may be incorporated in or associated with the clock in order to provide the interactivity. For example, tactile sensors could be provided which, once touched, initiate interactivity. Different modes of operation of the clock could be initiated by the sensors being operated in a predetermined sequence, for example. 
     Other sensors could also be provided, for example, visual sensors such as small cameras which can recognise movement of the observer to trigger certain modes of operation of the clock. Similarly an audio sensor such as a microphone could be linked to the control system provide the necessary interactivity. 
     As mentioned above, John Harrison invented the so-called grasshopper escapement. This was a precision clock escapement that did not require lubrication. Because of its action and superficial resemblance to an insect, it was called a “grasshopper escapement”. The inventive feature in Harrison&#39;s escapement was that there were no sliding surfaces between the pallet faces and the escapewheel teeth. The period of the swing of the pendulum controlled the rate of the clock and the torque from the driving weights through the escapewheel gave an impulse to the pendulum on each beat. The escapewheel in Harrison&#39;s domestic precision regulators is one of the smallest gear wheels in the clock train, about 35 mm in diameter and is hidden away unseen inside the movement and inside the clock case. 
     At the time of its invention, Harrison&#39;s grasshopper escapement in his precision regulator clocks domestic made them the most accurate timekeepers anywhere in the World. Further objects of the present invention are to demonstrate the simplicity of the action of the Harrison grasshopper escapement, to make it visible in operation to an observer and to improve on its function. 
     According to a further aspect of the present invention there is provided a clock having an escapement mechanism wherein the escapewheel is arranged radially outside the clock face and extends around at least the majority of the periphery of the clock. 
     Thus the escapewheel, and preferably also the pallet carrier and the pallets, are preferably arranged on the outside of the clock. A clock having these elements arranged on the outside can be more easily observed and the function and operation more easily understood. 
     According to another aspect of the present invention therefore there is provided a clock comprising an escapewheel, a pallet carrier and a pair of pallets, wherein the escapewheel, the pallet carrier and the pallets are arranged on the outside of the clock. 
     One preferred clock comprises the escapewheel as the largest wheel in the clock and preferably extending around the outer periphery of the clock with the pallet carrier and pallets arranged above the escapewheel. A virtual pendulum bob may be arranged to swing just below the escapewheel. 
     Historically, several mechanisms are known in clocks with a single driving mechanism to allow that single mechanism to drive both the timekeeping going train and a strike train. For example, in a spring clock the going train may be driven from the inside of a helically coiled clock spring while the strike train is driven from the outside of the clock spring. In this way the clock keeps running forward whilst the strike train is set off to count out the hour. 
     Fun clocks are also known that are deliberately made to run backwards for use in bars etc but the present invention is the first clock that may be controlled at will to normally run forwards but also to be run backwards. Through the use of the variation of the motor speed the time lost by running backwards may be made up by increasing the average speed in running forwards. This enables a novel striking method to be incorporated. 
     As a further preferred feature of the present invention is that a clock may be provided with two distinct backward motions, a first in which the backward motion engages a strike train to strike as required and a second motion in which the clock solely runs backwards. 
     From a further broad aspect, the invention provides a clock having a striking mechanism which is operative only when the clock is being run backwards. 
     Preferably the strike train is engaged to be operated in the first backward motion condition by a cam mechanism that engages the strike train mechanically when the minute ring indicates 59 minutes and the seconds ring is moving to indicate 59 seconds. At this 30 point the microprocessor stops the motor just before the pendulum has completed its full swing and the pallets have not started to change over, and then runs the clock backwards. With the strike train now engaged the clock strikes for each backward motion of the escapewheel. 
     Away from the 59 th  minute and the 5gth second the clock runs backwards without striking. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred embodiment of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which: 
         FIG. 1  shows a front view of a clock embodying the present invention; 
         FIG. 2  shows the clock of  FIG. 1  with the front face and escapewheel teeth covers removed to show the fixed aperture plates and slits; 
         FIG. 3  shows a view of the clock of  FIG. 1  with the planar plates of fixed slits removed to show the rotating shutter plates and slits; 
         FIG. 4  shows a cross-section along line  4 - 4  shown in  FIG. 1 ; 
         FIG. 5  shows a view corresponding to  FIGS. 2 and 3 , but with hidden features shown; 
         FIG. 5-1  shows a detail of the top right quarter of  FIG. 5 ; (view needs rotating clockwise 90′) 
         FIG. 6  shows a view of the mechanism driving the ‘seconds’ shutter ring shown in  FIG. 3 ; 
         FIG. 7  shows illustrates the mechanisms used for transmitting rotational motion from the ‘seconds’ shutter ring to the ‘minute’ and ‘hours’ shutter rings; 
         FIG. 8  shows a view of the base plate of the clock with all components other than the mechanism for operating the pendulum and the pallet carrier removed; 
         FIG. 9-1  shows the mechanism for operating the pallets in a first position; 
         FIG. 9-2  shows the mechanism for operating the pallets in a second position; 
         FIG. 10-1  shows a mechanism that permits snapping shut of the grasshopper&#39;s lower jaw; 
         FIG. 10-2  shows a mechanism that permits the tail of the grasshopper performing a stinging action; 
         FIG. 11  shows a pendulum drive mechanism; 
         FIG. 12  shows a striking mechanism; 
         FIG. 13  shows the striking mechanism of  FIG. 12  from a different direction; 
         FIG. 14  shows the striking mechanism from a further direction; and 
         FIG. 15  shows a view similar to  FIG. 13  but with certain components removed for clarity. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a front view of a clock embodying the present invention. The main visible components of this clock are the front face A, the virtual pendulum B, the escapewheel C, the pallet carrier D covered by a casing representing the shape of a mythical grasshopper, with the front and hind leg casings covering the front and rear pallets E and F. 
     The preferred clock comprises a number of sub-systems that interact with each other. These sub-systems are:
         a sub-system comprising the front face A of the clock with three rings of radially extending slots and three shutter rings arranged behind this front face A (as shown in  FIGS. 1 and 2 ) the shutter rings comprising radially extending slits;   a sub-system for the rotating shutter rings (as shown in  FIGS. 5 and 6 ); a sub-system for moving the virtual pendulum B and the pallet-carrier D (shown in  FIG. 7 );   a sub-system for moving and guiding the front and rear pallets E and F (shown in  FIG. 8 ) and   a sub-system for moving the jaw and tail of a mythical grasshopper defined by the pallet carrier  30  D and the front and rear pallets E and F.       

     The architecture of these sub-systems will now be described in detail with the sub-systems being presented in isolation from each other. Subsequently the interaction of the sub-systems and the complete working of the clock will be described in detail. 
     The Clock&#39;s Front Face and Shutter Mechanism 
       FIG. 1  shows a front view of a preferred clock  2 . The front face  1  of clock  2  has an undulating surface of concentric wave-like crests and troughs. As can be seen from  FIG. 1 , the front face of clock  2  further comprises three concentric rings  4 ,  6  and  8  of radially extending slots  10 ,  11 ,  12  and  13 . 
     The outer ring of slots  4  comprises sixty equidistantly spaced radially extending lenticular slots  10  for indicating seconds. The ring of slots  6  is arranged to indicate minutes and also comprises sixty equidistantly spaced radially extending lenticular slots  11 . The central ring of slots  8  comprises twelve equidistantly spaced radially extending lenticular slots  12  for indicating hours. Between each adjacent pair of these twelve slots  12  three further, shorter equidistantly spaced radially extending lenticular slots  13  are provided for indicating quarter hours. 
     Each of the slots  10 ,  11 ,  12  and  13  holds a lens  14 , the purpose and geometry of which will be described  20  in more detail below. 
       FIG. 2  shows a front view of the preferred clock  2  of  FIG. 1  with the undulating front face  1  and lenses removed. Radially extending inner and outer static aperture plates  15  and  16  lie behind the front face  1  as can be seen from  FIG. 2 ,  15  with a single ring of apertures for hours and quarter hours,  16  with two rings of apertures for seconds and minutes. The three concentric rings of apertures  17 ,  18  and  19 / 20 , are aligned with the slots  10 ,  11  and  12 / 13  in the front face  1  of the clock. The narrow apertures  17 ,  18  and  19 / 20  otherwise correspond generally in size and number with the lenticular slots  10 ,  11  and  12 / 13 . The static aperture plates  15  and  16  are fixed to the chassis of the clock and so the apertures are fixed in position relative to the slots in front plate. As will be described further below, the apertures from part of a Vernier type shutter system. 
     Arranged behind the static aperture plates  15  and  16  are three concentric, rotatable shutter rings, namely ‘seconds’ shutter ring  24 , ‘minutes’ shutter ring  26  and ‘hours’ shutter ring  28 , as shown in  FIG. 3 . Rings  24  and  26  each comprise sixty-one equidistantly spaced radially extending slits  30 - 0  to  30 - 60  and  32 - 0  to  32 - 60  respectively. Ring  28  comprises forty-nine equidistantly spaced radially extending slits  34 . 34 - 48 . 
     Slits  30 - 0  to  30 - 60  and  32 - 0  to  32 - 60  in the two outer rings  24  and  26  have substantially the same length and width as apertures  17  and  18  in the static aperture plate  16  which also are aligned with lenticular slots  10  and  12  in the front face of the clock. The length and width of the slits  34 - 0  to  34 - 48  provided in the inner ring  28  are substantially the same as the apertures  19  and  20  provided in static aperture plate  15  and align and corresponds to the length of the twelve hour slots  16  in the front face of the clock. 
     The respective slits  30 ,  32  and  34  in the rotatable shutter rings are also formed on the same pitch circle diameters as the apertures  17 ,  18  and  19 / 20  in the static aperture plates  15  and  16  and as the slots  10 ,  11  and  12 / 13  in the front face  1  of the clock. Light passing through one of slits  30 - 0  to  30 - 60 ,  32 - 0  to  32 - 60  or  34 - 0  to  34 - 48  in the rotating shutter can pass through an aperture  17 ,  18  or  19 / 20  in the static aperture plates and a slot  10 ,  11  or  12 / 13  in the front face of the clock in an un-attenuated manner when pairs of apertures and slots are in rotational alignment. 
       FIG. 4  shows a cross-section of clock  2  along line  4 - 4  shown in  FIG. 1 . In  FIG. 4  slots  10  and aperture  17  are mounted in alignment with each other and slit  30 - 0  is rotationally aligned with both. Lens  14  has a planar light entry surface  42  that is arranged parallel and slightly spaced apart from the surfaces of static aperture plate  16 . Lens  14  acts as a light guide by receiving light from a narrow aperture in the static aperture plate and conducting the majority of the light by total internal reflections to be emitted from the wider elliptical plan form in the front face of the clock. The lens  14  is held in slot  10  by carrier plate  39  and has a surface  40  that lies slightly proud of the front face  1  of the clock  2  and has a curved and matt or frosted front surface to enable the light to be observed over a wide angle as well as normal to the face of the clock. 
     Also shown in  FIG. 4  are light sources  44  arranged in a plane parallel to ‘seconds’ shutter ring  24  and on the same pitch circle diameter. In the preferred embodiment shown in  FIG. 1 to 4 , light sources  44  are lines of LEDs mounted on printed circuit board (PCB)  46 . In the preferred embodiment the light entry surface  42  of lens  14  is frosted, so that light from the line of multiple LEDs is diffused upon entry into lens  14 , so that an observer cannot distinguish between the separate light sources  44  after the multiple internal reflections as the light is guided up the lens to the front face. 
     Light sources  44  on PCB  46  are mounted to the chassis of the clock  2  in alignment with the median line of the fixed apertures directly above as well as the median line of lens  14  and slot  10 . As mentioned above, shutter rings  24 ,  26  and  28  are rotatable and it will accordingly be understood that rings  24 ,  26  and  28  will attenuate light emitted by light sources  44  unless a slit  30 - 0  is in alignment with a corresponding aperture  10  and with light sources  44 . When a slit  30  is rotated into alignment with an aperture  17  which is fixed in  35  alignment with a corresponding slot  10 , light from light sources  44  enters the lens  14  through light entry surface  42 , is scattered by the frosting and propagates through lens  14  both directly and by multiple internal reflections to exit lens  14  through top surface  40 . Lens  14  therefore acts as light pipe for channeling  5  light from aperture  17  to light exit surface  40 . 
     Each one of the slots  10 ,  11 ,  12  and  13  and their lenses has associated light sources  44  as shown in  FIG. 4 . 
     Also shown in  FIG. 4  is a guide ring  47  mounted to ‘seconds’ shutter ring  24 . The ring  47  comprises a U-shaped groove  48  for engaging with rollers that are arranged around the circumference of the ring  47  and that guide the rotating motion of ‘seconds’ shutter ring  24 . ‘Minutes’ and ‘hours’ shutter rings  26  and  28  are provided with guide rings similar to guide ring  47  provided on the ‘seconds’ shutter ring  24 . The actual shutter rings  26  and  28  with their multiple slits are comparatively flimsy and flexible, so the guide rings  47  maintain the shutter rings  26  and  28  in better spatial alignment and clearance with respect to the fixed aperture plates. 
     The circumferential width of the apertures in the fixed ‘seconds’ and ‘minutes’ aperture plate  16  is preferably less than one three thousand six hundredth part of the minimum circumference at the base of the slits. For ease of manufacture the apertures are made with parallel sides, rather than tapering with radius. This ensures that there are 59 slit width positions between each pair of adjacent slits. The slits in the shutter rings should preferably have a width the same as or smaller than the aperture width. 
     FIGS.  5  and  5 - 1  illustrate the relative radial positions of ‘seconds’ apertures  17 - 0  to  17 - 59  and slits  30 - 0  to  30 - 60 , ‘minute’ apertures  18 - 0  to  18 - 59   35  and slits  32 - 0  to  32 - 60  and ‘hour’ and ‘quarter hour’ apertures  19 - 0  to  19 - 11  together with the intermediate  20  apertures and slits  34 - 0  to  34 - 48  for the case where the clock  2  indicates 12 o&#39;clock midday or midnight. In this case, the slots  10 ,  11  and  12  that extend vertically on the upper half of the front face of clock  2  will be in fixed alignment with apertures  17 - 0 ,  18 - 0 , and  19 - 0  in static aperture plates  16  and  15  and also exactly in alignment with slits  30 - 0 ,  32 - 0  and  34 - 0  of rotating shutter rings  24 ,  26  and  28  respectively so that the light emitted from the three linear light sources of LEDs  44  passes through the moving slits in the rotating shutter rings, passes unattenuated through the apertures in the static aperture plates, is gathered by the lenses and displayed on the face of the clock  2  as three vertical bars of light representing the time of exactly 12 o&#39;clock. 
     Each ring of slots  4  and  6  in the front face  1  of the clock  2  comprises sixty equidistantly spaced slots  10  and  11  which are in alignment with sixty equidistantly spaced apertures  17  and  18  provided in the static aperture plate  16 . The rotating ‘seconds’ and ‘minutes’ shutter rings  24  and  26  in contrast each comprise sixty-one equidistantly spaced slits. Thus the angular spacing of slits  30 - 0  to  30 - 60  is smaller than the angular spacing of apertures  17 . Equally, the angular spacing of slits  32 - 0  to  32 - 60  is smaller than the angular spacing of apertures  18 . 
     The different number of apertures in the static plate  16  and the slits in shutter rings  24  and  26  together with their chosen width of less than one three  30  thousand six hundredth of the minimum pitch circle circumference form a Vernier arrangement whereby only one slit of the sixty-one slits  30 - 0  to  30 - 60  and  32 - 0  to  32 - 60  in shutter rings  24  and  26  can at any one time be in perfect alignment with an aperture  17  or an aperture  18 . 
     It will be appreciated at exactly 12 o&#39;clock that only light emitted by light sources  44  located behind these particular three vertically extending and aligned slits and apertures can propagate through in an unattenuated manner and be gathered up by the lenses  14  to be displayed on the front face of the clock. Light emitted by light sources located behind all the other slots and lenses in the face can not enter the corresponding apertures in the static aperture plate  16  as the each and every other slit in the rotating shutter plate is out of line and masks the fixed apertures from the light sources. An observer will accordingly only see the vertically extending slots  10 ,  11 , and  12  fully illuminated to display the uniae time of 12 o&#39;clock midnight or midday in the example of FIGS.  5  and  5 - 1 . It can be seen from  FIG. 5-1  that the difference in spacing between fixed apertures  17  and the moving slits  30  increases with increasing distance from slot  30 - 0 . It is important to note that all of slits  30 - 1  to  30 - 60  are located on the counter clockwise side of a corresponding slot  10 . This means that, when ‘seconds’ shutter disc  24  is rotated, by one three thousand six hundredth part of the pitch circle circumference a slit  30 - 1  comes into alignment with the next clockwise adjacent fixed apertures  17 - 1 . Starting from 12 o&#39;clock, when ‘seconds’ shutter ring  24  is rotated, as the misalignment between slit  30 - 1  and the adjacent aperture  17 - 1  for slot  10 - 1  is the smallest, slit  30 - 1  is the first rotating slit to come into perfect rotational alignment with fixed aperture  17 - 1  and slot  10 - 1 . The next slit that comes into rotational alignment with a fixed aperture and associated lens and slot in the clock face is slit  30 - 2  as the rotational misalignment with the adjacent aperture  17 - 2  for slot  10 - 2  is the second smallest. Slit  30 - 60  is maximally misaligned with aperture  17 - 59  and appears to be very close to alignment with the counter-clockwise adjacent aperture  17 - 59 . It will be appreciated that, as ‘seconds’ shutter ring  24  is rotated in the clockwise direction, slit  30 - 60  moves away from this counter-clockwise adjacent slit  17  and towards the clockwise adjacent aperture  17 - 0  and is accordingly the last one of slits  30 - 1  to  30 - 60  to come into alignment with an aperture  17  when ‘seconds’ shutter ring  24  is rotated. 
     Mechanism for Rotating the ‘Seconds’ Shutter Ring 
     In the following description the mechanism for rotating the ‘seconds’ shutter ring  24  will be described. 
       FIG. 6  shows an enlarged view of part of the rectangular section labelled VI in  FIG. 5  but with shutter rings  24 ,  26  and  28  removed to show a detailed view of the mechanism employed to rotate the ‘seconds’ shutter ring  24 . The rotation of the ‘seconds’ ring is directly controlled by the escapement mechanism which consists of an escapewheel  72  mounted on the outside of the seconds ring  24  and two pallets  150 ,  152  mounted on a pallet carrier  114  (see  FIG. 9 ). 
     As the pallets are connected to the virtual pendulum that oscillates, the motion of the ‘seconds’ ring is intermittent and it would be exceedingly complex to drive this intermittent motion directly from the drive motor. This problem is overcome by including some resilience in the drive mechanism in the form of a spiral drive spring that can take up half a turn of so in either direction without a large change in the driving torque of the escapewheel. 
     A motor  60 , preferably a servo motor, is connected to and continuously drives crank  62  via a precision toothed drive belt  64 . Crank  62  comprises a gear ring  62 -A which meshes and drives a gear ring  66 -A provided on the outside of spring device  66 . 
     Spring device  66  comprises a spiral flat coil of spring steel that can be wound up like a clock spring to provide the required torque to urge the escapewheel  72  on the outer periphery of the ‘seconds’ ring  24  against the pallet arms  150 ,  152 . The spiral coil provides a low rate, virtually constant, torque even as the coil winds up or unwinds an extra half turn or so. On its outside the spring  66 -B is wound through the rotation of gear ring  66 -A induced by the crank  62 . An inside end of spring  66 -B is connected to, and drives, a further gear wheel  66 -C. Gear wheel  66 -C is driven by the torque in the spring  66 -B and meshes with and drives gear wheel  68 . The servo motor  60  is accordingly adapted to provide the torque to urge the escapewheel  72  up against the pallet arms  150 ,  152  as they in turn engage and disengage with the corresponding teeth in the escapewheel  72  through a constant force drive spring  66 . The spring also takes up the intermittent stop go motion of the virtual pendulum and the pallet carrier  114  whilst being continuously driven by the drive motor. 
       FIG. 6  shows three of the sixty teeth  74  of the escapewheel  72 , an actuation rod  76  eccentrically mounted on crank  62  and connected to the virtual pendulum B and pallet carrier  114  as will be explained below. Further provided is a precision toothed drive belt (not shown) for accurately positioning the pallet faces to follow precisely the end of the appropriate escapewheel tooth  74  as will be described in more detail below. 
     Mechanism for Rotating the ‘Minute’ Shutter Ring 
       FIG. 7  illustrates a mechanism for transmitting rotational movement from the ‘seconds’ shutter ring  24  on to the ‘minutes’ shutter ring  26 . As can be seen from  FIG. 7 , a short section of six teeth  80  is provided on an outer edge of ‘seconds’ shutter ring  24 —on the inside of the escapewheel  72  respectively. Teeth  80  mesh with a birdcage gear  82  created from six small sealed roller cage bearings when teeth  80  are in an appropriate rotational location as the seconds wheel revolves, typically between the 59 th  and 60 th  or zero second positions. Gear  82  drives gear  84  through one revolution via driving cylinder  86  and precision toothed drive belt  88 . 
     ‘Minutes’ shutter ring  26  comprises a continuous row of teeth  90  along an outer edge thereof. Teeth  90  mesh with gear  84  and it will be appreciated that, every time teeth  80  mesh with gear  82 , gear  84  rotates so as to rotate ‘minutes’ shutter ring  26 . Teeth  80 ,  90 , gears  82  and  84 , drive cylinder  86  and drive belt  88  rotate ‘minutes’ shutter ring  26  by one sixtieth of a revolution every time teeth  80  move past gear  82 . Because of the reduced circumference on the minutes wheel  26  as compared to the larger seconds wheel  24  the pitch of the six teeth  80  correspond to five teeth on  90  and the diameters of birdcage wheels  82  and  84 . 
     Three of the six roller bearings of birdcage pinion  82  have a second roller bearing mounted coaxially therewith above the plane of the teeth  80  (in the sense of  FIG. 7 ) forming an equilateral triangle. A ring  83  is provided in the plane of these rollers with a cut out aligned with the teeth  80 . The effect of this is after the shutter ring  24  moves on after engagement of the teeth  80  with the pinion  82 , two of the three roller bearings will engage the ring  83 , thereby preventing further rotation of the pinion  82 , and hence locking pinion  86 , the toothed belt  88  and birdcage wheel  89  and finally wheel  90  on the outside of rotating shutter ring  26 . Thus the slit  34  opposite the aperture  17  is locked in place for the next 59 seconds until the cut out and  35  teeth  80  release the minute ring and index it forward a further 6° before being locked again, indicating the next minute. 
     Mechanism for Rotating the ‘Hours’ Shutter Ring 
     Further referring to  FIG. 7 , a lever  92  is arranged to be pivotable about pivot point  94 . Lever  92  comprises a cam follower  96 . A cam  98  is on the inside of escapewheel  72 . In the preferred embodiment cam  98  is provided in a position diametrically opposite to teeth  80 , rather than in the position shown in  FIG. 7 .  FIG. 7  merely intends to illustrate that cam follower  96  causes lever  92  pivot about pivot point  94  in a clockwise direction when cam follower  96  travels over cam  98 . 
     Lever  92  further comprises drive mechanism  100  at an end thereof. Drive mechanism  100  comprises a gear wheel that can mesh with and is driven by gear wheel  82  and that drives precision toothed drive belt  101 . Drive belt  101  in turn drives gear wheel  102  through gear teeth  103  provided on the ‘hours’ shutter ring  28 . 
     When cam follower  96  is in contact with the larger diameter inner surface of the escapement that does not form cam  98 , drive mechanism  100  does not mesh with gear wheel  82  and no driving force can be transmitted to gear teeth  103  on ‘minutes’ shutter ring  28  in this configuration. 
     When cam follower  96  contacts cam  98 , drive mechanism  100  meshes with gear wheel  82  for a period of time and in this configuration driving force can be transmitted from gear wheel  82  to gear teeth  103 . However, as mentioned above, cam  98  is located in a position diametrically opposite of the teeth  80  and cam  98  is positioned so that gear wheel  82  is not normally driven when driving mechanism  100  meshes with gear wheel  82 . 
     When cam follower  96  contacts cam  98  driving mechanism  100  simply travels into and out of engagement with gear wheel  82  without any driving force being transmitted in a normal operation mode. Accordingly in this normal operation mode, gear teeth  80  can travel past and drive gear wheel  82  without driving force being transmitted to gear teeth  103 . It will be appreciated that the driving of gear wheel  82  by gear teeth  80  once every minute does not cause a driving of gear teeth  103  in a normal mode of operation but that gear teeth  90  on the ‘minutes’ shutter ring  26  are driven once every minute through this driving action. 
     Four equidistantly spaced cams  104  are further provided on a cylindrical surface of the ‘minutes’ shutter ring  26 . These cams  104  are arranged to be contacted by cam follower  106  provided on a locking mechanism  107 . When cam follower  106  is contacted by one of cams  104  the locking mechanism  107  is pushed towards the lower end  108  of lever  92 . When cam follower  96  contacts cam  98  while the locking mechanism  107  is in this configuration, locking mechanism  107  locks onto lower end  108  of lever  92  and holds lever  92  in the position in which driving mechanism  100  engages gear wheel  82 . Driving mechanism  100  accordingly remains in driving contact with gear wheel  82  when cam follower  96  looses contact with cam  98 . When in this configuration gear teeth  80  next drive gear wheel  82 , the driving force provided to gear wheel  82  is transmitted to the driving mechanism  100  and onwardly to gear teeth  103  via drive belt  101  and gear wheel  102 . In this configuration, ‘hours’ shutter ring  28  is accordingly rotated. 
     As ‘minutes’ shutter ring  26  carries four equidistantly spaced cams  104 , around its outer edge it will be appreciated that ‘hours’ shutter ring  28  is rotated 360/48=7.5 degrees once every quarter hour. Gear wheels  82  and  102 , drive mechanism  100 , drive belt  101  and gear teeth  103  are arranged so that one passage of gear teeth  80  past gear wheel  82  causes ‘hours’ shutter ring  28  to be rotated by one forty-eighth of a full rotation, thus moving slot  34 - 0  from alignment with one slot  19 / 20  into alignment with the clockwise adjacent slot  19 / 20 . 
     Mechanism for Operating the Virtual Pendulum and the Pallet Carrier 
       FIG. 8  shows base plate or chassis  110  of clock  2  with all components that do not form part of the mechanism actuating the virtual pendulum  112  and the pallet carrier  114  removed. It will be appreciated that, as clock  2  is solely driven by motor  60 , the virtual pendulum  112  does not fulfil the time keeping function normally associated with a pendulum in a known clock but serves merely to give a visual representation of an actual pendulum. Accurate time keeping of the preferred clock  2  solely depends on the driving speed of motor  60  (as will be explained in more detail below) and pendulum  112  is accordingly provided for cosmetic purposes only. 
     As discussed above in relation to  FIG. 6  rod  76  is eccentrically mounted on crank  62 , so that, when crank  62  is rotated by motor  60 , rod  76  reciprocates continuously left and right. Rod  76  is connected to arm  116  pivotally mounted at its lower end to base plate  110  at pivot point  118 . A further rod  120  connects arm  116  to pendulum  112 . Pendulum  112  is pivotally mounted to base plate  110  at point  122 . Rod  120  comprises an extendible section  124  for adjusting the length of rod  120 . This adjustment is used to endure that in spite of any manufacturing tolerances the swing of the virtual pendulum is symmetrical about the centreline. 
     Rod  126  connects arm  116  to a further arm  128 . Rod  126  also comprises an extendible section  130  for adjusting the length of rod  126  to ensure that in spite of any manufacturing tolerances the movement of the pallet carrier is symmetrical about the centreline. 
     The upper end of arm  128  is fixedly attached to a pallet carrier  114  at point  132 . The combination of pallet carrier  114  and rod  128  is pivotally mounted to base plate  110  at the point  132 . The interconnection of links and pivots ensures that the movement of the virtual pendulum and the pallet carrier are always in phase. 
     Mechanism for Operating the Front and Rear Pallets 
       FIG. 9-1  shows the mechanism for operating a front pallet  150  and a rear pallet  152  which are mounted to the pallet carrier  114 . As previously stated in relation to  FIG. 6 , a cylindrical precision toothed drive belt contact surface on crank  62  drives a precision toothed drive belt, which is indicated by reference numeral  78  in  FIG. 9 . Drive belt  78  in turn drives two cams  154  and  156  which can rotate relative to base plate  110  and are fixedly attached to each other, one behind the other, so as to prevent relative movement between them and the drive mechanism. Cams  154  and  156  perform one full rotation every two seconds. 
     Cam follower  158  is connected to front pallet  150  via L-shaped bracket  160  and rods  162 ,  164  and  166 . The connections between L-shaped bracket  160  and rod  162 , the connection between rod  162  and rod  164  and the connection between rod  164  and rod  166  allow relative rotational movement between L-shaped bracket  160  and rod  162 , between rods  162  and  164  and between rods  164  and  166 . Rod  166  is fixedly attached to front pallet  150  so as to prevent relative movement. The combination of front pallet  150  and rod  166  is pivotally attached to pallet carrier  114  at pivot point  168 . Rod  162  is pivotally attached to pallet carrier  114  at pivot point  170 . Front pallet  150  has a contact surface  172  for contacting the tip of teeth  74  of escapewheel  72 . 
     Cam follower  180  is connected to rear pallet  152  via L-shaped bracket  182  and rods  184 ,  186  and  188 . Pallet  152  is deliberately made L shaped to hide behind the cosmetic rear leg  198 . The connections between L-shaped bracket  182  and rod  184 , the connection between rod  186  and rod  188  and the connection between rod  188  and rear pallet  152  allow rotational movement between L-shaped bracket  182  and rod  184 , between rods  186  and  188  and between rod  188  and rear pallet  152 . Rod  184  is fixedly attached to rod  186  to prevent relative movement between rods  184  and  186 . The combination of rods  184  and  186  is pivotally attached to pallet carrier  114  at pivot point  190 . Rear pallet  152  is pivotally attached to pallet carrier  114  at pivot point  192 . Rear pallet  152  has a contact surface  194  for contacting the tips of the teeth  74  of escapewheel  72 . 
     As already mentioned above, the assembly of pallet carrier  114  and pallets  150  and  152  is in the preferred embodiment presented in the form of a mythical grasshopper. Consistent with this, front pallet  150  is covered with a covering member  196  ( FIG. 2 ) that has the appearance of the front leg of a grasshopper, while rear pallet  152  is covered with covering members  198  ( FIG. 2 ) that have the appearance of a hind leg of a grasshopper. Covering member  198  is pivotally mounted to the pallet carrier  114  in pivot point  132 . 
     Mechanism for Moving Jaw and Tail of the Grasshopper 
     The grasshopper covering the pallet carrier  114  and pallets  150  and  152  is shown in more detail in  FIGS. 10-1  and  10 - 2 .  FIG. 10-1  shows a mechanism that causes the grasshopper&#39;s lower jaw to snap upwardly once every minute, in this embodiment between the 59 th  and 60 th  second of every minute and then slowly open.  FIG. 10-2  shows a mechanism that causes the grasshopper&#39;s tail to perform a stinging action once every quarter hour, in this embodiment between the 59 th  and 60 th  second of each 14 th , 29 th , 44 th  and 59 th  minute and then slowly droop down. 
     Referring now to  FIG. 10-1  a cam  220  is mounted to escapewheel  72  (not shown in  FIG. 10-1 ), so that the cam  220 , in use, rotates together with the escapewheel  72 . A cam follower  222  is pivotally mounted to base plate  110  at pivot point  224 . Cam follower  222  is connected to jaw  226  through rods  228 ,  232  and  234  and through L-shaped bracket  230 . L-shaped bracket  230  is pivotally mounted to pallet carrier  114  at pivot point  236 . Jaw  226  is pivotally mounted to pallet carrier  114  at pivot point  238 . Cam follower  222  is pressed against cam  220  under the influence of gravity acting on the jaw  226  and transmitted to cam follower  222  through rods  228 ,  232  and  234  and L-shaped bracket  20   230 . 
     Cam  220  comprises a single step  240  along its inner circumference, in this embodiment causing the jaw to snap shut between the 59 th  and 60 th  second of every minute and then slowly open. 
     Referring now to  FIG. 10-2 , a cam  250  is provided connected to ‘hours’ shutter ring  28  (not shown  FIG. 10-2 ). A cam follower  252  is pivotally mounted to base plate  110  at point  254  and connected to tail  256  through rods  258 ,  262 ,  264  and  266  and bracket  260 . Bracket  260   30  is pivotally mounted to pallet carrier  114  at point  268 . Rod  264  is pivotally mounted to pallet carrier  114  at point  270 . Tail  256  is pivotally mounted to pallet carrier  114  at pivot point  272 . 
     Cam  250  comprises four slopes  274  equidistantly spaced from each other around the outer circumference of cam  250 , in this embodiment causing the sting to erect between the 59 th  and 60 th  second of each 14 th , 29 th , 44 th  and 59 th  minute and then slowly droop down. 
     Function of the Preferred Clock 
     Having described the structure of a preferred clock and of the preferred sub-systems, the function of this preferred clock will be described in more detail in the following. 
     Referring to  FIG. 6 , servo motor  60  continuously drives crank  62  via drive precision toothed belt  64 . Gear wheel  62 -A of crank  62  meshes with gear wheel  66 -A of spring device  66  and continuously winds up spiral spring  66 -B. Spiral spring  66 -B rotates gear wheel  66 -C, which in turn rotates escapewheel  72  through gear wheel  68  when escapewheel  72  is free to rotate. 
     As can be seen from  FIGS. 5 and 9 , the teeth  74  of escapewheel  72  are contacted by faces  172  and  194  of front pallet  150  and the rear pallet  152  respectively. This contact between front and rear pallets  150  and  152  with teeth  74  of escapewheel  72  can prevent rotation of escapewheel  72 . Spring  66  can accordingly only rotate escapewheel  72  when front and rear pallets  150  and  152  permit such rotation. 
     Referring again to  FIG. 6 , it can be seen that crank  2  is connected to rod  76 . Motor  60  continuously drives crank  62  via precision toothed drive belt  64  and thus a continuous right-left oscillating motion is imparted onto rod  76  by crank  62 . 
     Referring now to  FIG. 8 , it will be appreciated that this oscillating motion is transmitted to arm  116 , causing it to perform a rotationally reciprocating movement about pivot point  118 . This motion is transmitted to arm  128  through rod  126  and causes rod  216  to rotationally oscillate about pivot point  132  together with pallet carrier  114 . 
     The pitch circle diameters of the precision toothed outer surface of crank  62  for contacting drive belt  64  and of the of the precision toothed outer contact surface of motor  60  are such that crank  62  performs normally a nominal full revolution once every two seconds. Thus, it will be appreciated that pallet carrier rocks from the position shown in  FIG. 8  to a position in which the left side (the grasshopper&#39;s head) of pallet carrier  114  is closest to escapewheel  72  and back once every two seconds. 
     It will be appreciated that, as pendulum  112  is also connected to rod  116  through rod  120 , virtual pendulum  112  also performs a full period once every two seconds in synchronism with pallet carrier  114 . 
     Now, it will be recalled that crank  62  drives cams  154  and  156  via drive belt  78 . Cams  62 ,  154  and  156  are arranged so that one revolution of cam  62  results in one revolution of cams  154  and  156 , i.e. one revolution every two seconds. Cams  154  and  156  rotate in the clockwise direction. 
     Cams  154  and  156  are shaped so that they (in combination with the rocking motion of pallet carrier  114 ) contact surfaces  172  and  194  of pallets  150  and  152  alternately align the pallet faces with the tips of teeth  74  of escapewheel  72  which determines the movement of the escape wheel  72 . 
       FIG. 9-1  shows the condition in which the pallet carrier  114  is in its counter clockwise-most rotational position. In this position, the pallet face  172  of front pallet  150  has just become aligned with a tooth  74  of the escapewheel  72 , and has pushed the tooth slightly anticlockwise. The rear pallet  152  is still just in contact with its adjacent tooth  74 . 
     As the, pallet carrier  114  and the cams  154 ,  156  now rotate clockwise, the rear pallet  152  is lifted away from its adjacent tooth  74  by the cam follower  180  rising out of the trough in the rear pallet cam  156 . This movement is quite rapid due to the slope of the trough face. 
     The combined motion of the pallet carrier  114  and the front pallet cam  154  cause the face  172  of the front pallet  150  to circumscribe a circular path along the pitch circle of the escapewheel teeth  74 . The adjacent escapewheel tooth  74  remains in contact with the pallet face  172  throughout this movement by virtue of the biasing action of the spiral spring device  66 . 
     This movement continues until the position shown in  FIG. 9-2  where the pallet  114  is in its clockwise-most position. In this position, the rear pallet  152  once more drops back down into contact with an escapewheel tooth  74 , again moving the tooth  74  slightly in a counter clockwise direction. Counter clockwise rotation of the pallet carrier  114  and rotation of the pallet cams  154 ,  156  then causes the front pallet to be lifted out of contact with its adjacent tooth  74 , the movement of the rear pallet face  194  then being along the circular path defined by the pitch circle of the escapewheel teeth  74 . This allows the escapewheel  72  to rotate under the torque of the spring device  66 . 
     This mechanism therefore allows the intermittent movement of the escapewheel  72 , which in turn drives the rotatable seconds shutter  24  through one sixtieth of a rotation per second. 
     At the positions shown in  FIGS. 9-1  and  9 - 2 , the shutter ring  24  is stationary. In this condition, a slit  30 - 0  of the ‘seconds’ rotating shutter ring  24  is in alignment with the aperture  17 - 1  of the fixed shutter ring  16 , allowing a particular second to be indicated through the aligned slot  10  on the clock face. 
     The escapewheel  72  (and thus the shutter ring  24 ) perform one sixtieth of a rotation per second. During this rotation, slit  30 - 0  on rotatable shutter ring  24  moves from alignment with a aperture  17 - 1  on the static aperture plate  15  into alignment with the immediately adjacent aperture  17 - 2  in the clockwise direction such that the next second is indicated through the appropriate aligned slot  10  in the clock face. Thus the illuminated slot  10  moves around the clock face at the rate of one slot  10  per second. 
     In view of the fact that the shutter rings  24 ,  26  and  28  having e.g. sixty-one equidistantly spaced slits  30 - 0  to  30 - 60 , an interesting visual effect is also achieved. 
     In particular, during each 6° rotation of the shutter ring  24 , the slits  30 - 2 ,  30 - 3 ,  30 - 4  etc will sequentially, and for a very brief period of time only, become aligned with static apertures  17 - 2 ,  17 - 3 ,  17 - 4  and so on. This will cause the effect of a band of light racing around the clock face each second. 
     Rotation of the ‘seconds’ shutter ring  24  causes rotation of the ‘minutes’ ring  26  and ‘hours’ ring  28  by the mechanisms described above, and the movement of slits in the rotating shutter rings into alignment with the apertures in the static aperture plates causes illumination of the particular minute, quarter hour or hour as appropriate, with a racing light band effect similar to that occurring on the second ring occurring. 
     To improve the display of a particular second or minute, it is possible to blank off slits  30 - 1  and  30 - 60  and slits  32 - 1  and  32 - 60  in the rotatable shutter rings  24 ,  26 . In this way, a small movement of the rotatable shutter rings will not illuminate an adjacent slot in the clock face. Moreover, the slits  30 - 0  and  32 - 0  may be made wider than the adjacent slits, for example three times wider, to improve the display. 
     Movement of the Grasshopper&#39;s Jaw and Tail 
     As described above, cams  220  and  250  and cam followers  222  and  252  cause jaws  226  and tail  256  perform a snapping and stinging action. The jaw performs the snapping action once every minute while the tail performs the stinging action once every quarter hour. 
     Special Operation Modes 
     The preferred clock  2  lends itself to a variety of special operation modes, some of which will now be described. 
     It will be appreciated that the time keeping precision of clock  2  depends on the speed of motor  60  being constant. If it is desired to let time appear to pass more slowly the motor  60  can be driven more slowly and if it is desired to let time appear to pass more quickly the motor  60  can be driven more quickly. This can be used to illustrate the passage of time in unusual manners. The average speed of clock  2  can of course be chosen to be the correct speed for accurate time keeping with the clock coming out of phase but always arriving back in phase a predetermined particular time eg on the zero second of every particular minute or say every 5 minutes for more extreme excusions. 
     In a further special operations made clock  2  can be made to run backwards. To achieve this motor  60  is run in the counter-clockwise direction. It will be appreciated that this reversal in the running direction of motor  60  causes a change in the movement pattern of pallets  150  and  152 . When motor  60  is operated in reverse pallets  150  and  152  approach the tips of teeth  74  of escapewheel  72  and, aided by the rocking motion of pallet carrier  114 , push against teeth  74  so as to rotate escapewheel  72  in the counter-clockwise direction. Accordingly, the clock  2  runs ‘backwards’. It will be appreciated that the counter-clockwise rotation of escapewheel  72  still requires the continuous drive of the motor  60  to be taken up as intermittent motion of the escapewheel so that the spring  66  performs the same function as when the clock runs forwards. 
     Switching of the clock from the normal running/operation mode in which it correctly displays time to the “backwards” running mode can be achieved without causing any signs other than reversal of time display if the running direction of motor  60  is reversed when crank  62  is in the position shown in  FIG. 8  or rotated by 180 degrees from that position. When crank  62  is in either of these two positions both pendulum  112  and pallet carrier  114  are at one of the extreme points of their motion and their movement is accordingly restricted to a movement back towards the centres of their swings, irrespective of the direction of movement of motor  60 . 
     It has previously been mentioned that rod  126  (shown in  FIG. 8 ) comprises an element  130  for 20 adjusting its length. In a normal operation mode the length of rod  126  and element  130  is chosen so that contact between contact faces  172  and  194  of pallets  150  and  152  is made in an accurate fashion so that noise is minimised. If the length of rod  126  and element  130  is  25  chosen so that the amplitude of the rocking motion of pallet carrier  114  is larger to one side than to the other then the noise made by clock  2  changes. In particular, contact between the contact face  172  to  194  of the pallet  150  or  152  located on the side of the 30 pallet carrier  114  that has the larger amplitude of motion an a tooth  74  of escapewheel  72  will be more abrupt, and accordingly louder, than contact between the other contact face  172  or  194  and a tooth  74 . The noise pattern produced by clock  2  can accordingly be adjusted. 
     The clock  2  can further be designed so that the band of light running around the rings of slots  4 ,  6  and  8  run in the counter-clockwise direction. To achieve this effect, the number of slits provided in ‘seconds’, ‘minutes’ and ‘hours’ shutter rings  24 ,  26  and  28  needs to be one less than the number of apertures provided in static aperture plates  15  and  16  respectively, so that the angular spacing between the slits in the shutter rings  24 ,  26  and  28  is larger than the angular spacing between the corresponding apertures in the static aperture plates  15  and  16 . Applied to a configuration in which sixty slots slits are provided in static aperture plate  16  for each the display of seconds and for the display of minutes, providing, for example, fifty-nine equiangularly spaced slits in ‘second’ and ‘minutes’ shutter rings  24  and  26  permits generating a backwardly running band of light. Providing forty-seven equiangularly spaced slits in ‘hours’ shutter ring  28  allows achieving the same effect for the display of hours and quarter hours if the static aperture plate  15  used in the above discussed embodiment is also employed. 
     Although the present invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that many changes in form and detail may be made, and in particular other types of escapement, pendulum or balance wheel could be used without departing from the scope of the invention as set forth in the accompanying claims. 
     For example, in another embodiment the pendulum  112  may be driven separately from the escapement. Referring to  FIG. 11 , the pendulum  112  is driven by a motor  300  which drives a pulley  302  through a gearbox not shown. A drive belt  304  passes around the pulley and an idler pulley  306 . A guide rail  308  is mounted below the drive belt and supports a carriage  310  for reciprocating movement along the guide rail. The carriage  310  is attached to the guide belt  304  by a fixing block  312 . The pendulum arm  314  is attached to the carriage by a link arm  316  which is pivoted to the carriage by pivot  318  and to the pendulum  314  by pivot  320 . Sensors (not shown) linked to the motor control are provided to prevent the pendulum from moving too far in either direction. 
     This drive arrangement had advantages over the arrangement described above in that it allows both the speed and the amplitude of the pendulum swing to be controlled. Moreover, the effects of inertia on the drive mechanism are minimised. 
     The pendulum drive motor is controlled by the control system of the clock which means that the control system may drive the pendulum in a perfectly conventional manner, i.e. with a constant amplitude and sinusoidal speed, this being synchronised with the escapement by the control system. However, it does allow for the pendulum to be moved in other ways. For example, the amplitude of swing may be varied over the number of swings, for example decreasing to zero and then increasing again, the speed of the swing could be increased in every oscillation, for example, thus moving more slowly towards the centre of the swing and faster towards the outer part of the swing. The pendulum could be stopped at any point in the swing and started again after a given delay, for example half a cycle. Moreover, the position of the swing may be changed so that swing is off centre. The swing may be in time with the rest of the clock motion in opposition or lagging  30  behind it by a desired amount. The pendulum could even move in a completely random manner. 
     A strike mechanism may be incorporated into the clock. An embodiment of such a strike mechanism is described in  FIGS. 12 and 13 . 
     In this embodiment, a further drive belt  400  is taken from the main drive motor  60 . The drive belt engages a pulley  402  which is rotatably mounted on a strike shaft  404 . The pulley  402  freewheels on the strike shaft  404  except when it is selectively engaged to the strike shaft by an engagement mechanism  406 . The engagement mechanism  406  comprises a roller  408  mounted on the end of a lever arm  410  which engages with a cam  412  which is provided facing inwardly on the minutes ring. The cam engages with the wheel  408  only over a relatively short period of time, for example for 2 to 3 minutes on the hour every hour. When the cam  412  engages the wheel  408 , it pivots the lever arm  410  in the direction of arrow A which in turn pivots a rocker arm  414 , which is attached to rotate with the strike shaft  404 , in the direction of arrow B. The rocker arm  414  has a drive pin  416  at one end which, when the rocker arm is so pivoted, will engage with a drive slot  418  provided the pulley  402  such that the pulley will then drive the strike shaft  404  and the strike shaft  404  and pulley  402  will rotate together. 
     The strike shaft  404  passes through a body plate  420  of the clock and is provided with a pulley  422  over which is engaged a chain  424 . A striking plate  426  is arranged below the chain  422 . A sprag clutch  428  is provided between the strike shaft  404  and the pulley  422  such that the latter only turns when the strike shaft  404  rotates backwardly. 
     The strike shaft  404  is provided with a lug  430  which operates a striking mechanism  432 . The striking mechanism  432  comprises a striking arm  434  with a striking head  436  which strikes against a strike block  438 . The strike arm  434  is pivotably mounted about a pivot  440  at one end and is operated through a lifting arm  442 . The lifting arm  442  is mounted to move upwardly and downwardly and has a pin not shown which engages the underside of the strike arm  434  to lift the strike arm  434 . The upper end of the lifting arm  442  is provided with a pivotally mounted pawl  444  for engagement with the lug  430 . When the strike shaft  404  rotates anti-clockwise in the sense of  FIG. 15 , the pawl  444  is simply pushed out of the way by the lug  430  and the lifting arm  442  does not move. However, when the strike shaft rotates clockwise in the sense of  FIG. 15 , the pawl  444  is engaged by the lug  430 , lifting the lifting arm  442  until such time as the lug  430  moves out of engagement with the pawl  444  which will cause the lifting arm  442  and thus the striking arm  434  to drop, thereby dropping the striking head  436  against the strike block  438 . 
     In operation, therefore, when the clock is to strike, at the hour or whenever required, the engagement mechanism  406  engages the pulley  402  with the strike shaft  404  so that the strike shaft  404  rotates. While the clock is being driven in its normal, forward state, although the strike shaft  404  rotates, that movement is not transmitted either to the striking arm  434  (as the lug  430  does not catch on the pawl  444 ) or the chain pulley  422  due to the sprag clutch not engaging. However, when the clock reaches the hour the drive motor  60  begins to run backwardly which then causes the sprag clutch to engage thereby rotating the chain pulley  422  such that the chain  424  rotates and rattles against the rattle plate  426 . The lug  430  also engages the pawl  444  as described above which will cause the striking head  436  to lift and drop as described above. The number of strikes can be controlled by running the drive backwards and forwards. For example, on reaching the hour, the drive may reverse for a predetermined period, for example 1 second, then drive forward for a further time, for example 1 second, then reverse again, repeating this for the number of times required. During each second of reverse drive the chain  424  rattles and the clock strike. 
     While in the embodiment of the invention described above the seconds dial is shown as having sixty seconds, and the pendulum typically swings once per second, the person skilled in the art will recognise that these are not essential features of the invention. For example in a larger clock, where the mass and inertia of the pendulum may be substantial, the pendulum may swing more slowly with swings of 2 or more seconds. This can be accommodated with different effects. For example with each 2 second swing of the pendulum, a seconds ring with 60 divisions can give 2 revolutions of flashing lights before pausing at a 2 second division at the end of the pendulum swing and then racing round twice more before pausing again at then other end of the pendulum swing. It is equally possible to slow the lights down so they only perform a single, half speed revolution within a two second pendulum swing. 
     Similarly half second, rather than second divisions on the dial would produce a more pleasing effect with a pendulum or balance wheel beating in half seconds. Only the method of producing narrow enough apertures in the dial and the accuracy of the mechanism would limit such an arrangement, particularly if individual lights are not used but mirrors, light pipes or reflected light. 
     While the present invention has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this invention may be made without departing from the spirit and scope of the present invention.