GB2519819A

GB2519819A - Pendulum Bob

Info

Publication number: GB2519819A
Application number: GB1319523.5A
Authority: GB
Inventors: John Crawshaw Taylor; Nigel Harrison; Peter Gerald Harrison
Original assignee: Fromanteel Ltd
Current assignee: Fromanteel Ltd
Priority date: 2013-10-30
Filing date: 2013-11-05
Publication date: 2015-05-06
Anticipated expiration: 2033-11-05
Also published as: GB201319523D0; WO2015063493A2; GB201319187D0; GB2519819B; WO2015063493A3

Abstract

A pendulum bob assembly 2 comprises a mount mountable on a pendulum rod 4 and a bob body 8 movable relative to the mount such that movement of the bob body relative to the mount moves the bob body relative to the pendulum rod and a drive for moving said bob body relative to said mount.

Description

PENDULUM BOB

The present invention relates to a pendulum bob that can be fitted or retro-fitted to most pendulum clocks and which allows the period of the pendulum to be adjusted and thus the clock's timekeeping ability to be improved.

In a pendulum clock, the time base is kept by way of a weight known as a bob attached to a rod, thus forming the pendulum. As is known, the swinging pendulum controls the time of the clock via an escapement. Various factors, such as frictional losses, air resistance, atmospheric changes (e.g. temperature and pressure), accumulations of dust and dirt within the gears, short and long term changes in the oil together with manufacturing imperfections, can cause changes in the amplitude and period of swing of the pendulum. These changes interact with each other cyclically making it exceptionally difficult to achieve accurate time shown on the dial of the pendulum clock Various techniques are known to correct for such changes. The most common technique is to provide a screw thread on the lower end of the rod, onto which is threaded an adjustment nut. The bob rests on top of the nut by gravity. Rotation of the nut raises and lowers the bob, thereby adjusting the period of swing of the pendulum. This technique, however, can only take place intermittently by the owner of the clock who is likely to not know what has caused the error indicated on the clock face, or precisely what the clock error is.

A more recent development, illustrated in US 5268881 involves an electrical motor that moves an eccentrically mounted weight in the bob to adjust the centre of gravity of the pendulum. In this arrangement, the bob itself does not move relative to the rod.

To date, there has not been developed a satisfactory method for accurately and automatically adjusting the period of a pendulum.

From a first aspect the present invention provides a pendulum bob assembly comprising: a mount mountable on a pendulum rod and a bob body movable relative to the mount part such that movement of the bob body relative to the mount part moves the bob body relative to the pendulum rod; and a drive for moving said bob body relative to said mount part.

In accordance with the invention, therefore, a bob body as a whole moves relative to the rod which due to the relatively high weight of the bob body, allows for a much more effective means for adjusting the centre of gravity of the pendulum, and thus the period of swing of the pendulum. The adjustment of the bob itself also obviates the need for an eccentrically mounted weight increasing the outer profile of the bob.

The mount may comprise a hollow body which is able to receive a pendulum rod therein. The lower end of the hollow body is preferably open to allow the rod to extend therethrough to allow for the attachment to the rod of an adjustment nut. Such attachment would occur when the clock is first set. The lower end of the mount may then simply rest on the adjustment nut to locate it relative to the pendulum rod. The weight of the bob maintains the mount part in contact with the adjustment nut. Accordingly, there is no need for an attachment mechanism, eg. a bolt or glue, to be made to the pendulum rod. In other words, an existing pendulum rod does not need to be modified in order to operate with the present invention.

The bob body is preferably slidably received on the mount part. In one embodiment, the bob body comprises a carriage on which the mount is slidably received, or vice versa.

The drive may comprise a drive screw or other drive mechanism arranged, for example, between the carriage and the mount. In one arrangement for example! a drive screw is mounted to the bob body, for example to the carriage, and a drive nut mounted to the mount such that rotation of the drive screw causes relative movement of the mount and the bob body. The drive screw preferably extends parallel to the direction of relative movement of the bob body and mount.

The drive preferably includes a motor, most preferably a stepping motor, to rotate the drive screw or other drive mechanism, preferably via a gear arrangement, for example a worm gear. The motor may be mounted to and is preferably housed within the bob body.

The drive may be electro-magnetic and may comprise one or more solenoids.

The bob body may further comprise a power source for the drive means. For example simple batteries may be provided. This advantageously adds weight to the bob.

The bob body may further comprise means for slidably locating the bob body on the pendulum rod. This may reduce! for example, both lateral and front to back movement of the bob body with respect to the rectangular anti rotation section of a typical pendulum rod.

The locating means may therefore comprise a first component that locates the bob body relative to the pendulum rod in a first direction, whilst allowing the bob to slide relative to the rod. The locating means may also comprise a second component that locates the bob body relative to the pendulum rod in a second direction, for example substantially perpendicular to said first direction, again whilst allowing the bob to slide relative to the rod.

The first and/or second components may have opposed locating surfaces for engaging or positioning close to opposed surfaces of the pendulum rod. They may be adjustable, or rotatable about respective axes, to adjust the position of the locating surfaces relative to the surfaces of the rod thereby allowing a range of rod sizes to be accommodated by the bob.

The ocating means described above are advantageous in their own right, so from a further aspect the invention provides an apparatus for locating a pendulum rod slidably received within a pendulum bob, said apparatus comprising: one or more adjustable or rotatable components that define a sliding path for the rod; wherein upon adjustment or rotation of said component(s) with respect to the rod, a width or depth of said sliding path increases or decreases.

One or both of the components may comprise two or more pins or other limbs that define a portion of the sliding path for the rod, adjustment or rotation of the component moving the pins to increase or decrease a width of the sliding path.

The bob body may also accommodate a control for the drive means. The control may comprise a printed circuit board which is mounted to the bob body. This facilitates the mounting of control electronics within the bob. The aforementioned carriage may conveniently be mounted to said printed circuit board.

The printed circuit board may comprise a processor or set of processors for controlling said drive. Routines can be written into the processor(s) that control the drive, for example a or the motor, and other electronic parts accommodated within the bob body.

The bob body may also incorporate one or more sensors operatively connected to the control.

The bob body may also comprise means for transmitting data relating to the movement or position of the bob body relative to the mount. Preferably the transmitting means transmits data wirelessly, for example via an optical or infrared transmission.

According to a further aspect of the invention, there is provided a pendulum bob having means for transmitting electronic data from the bob to an external device.

Preferably, the transmitting means comprises a wireless transmitter, for example an infrared, laser or wi-fi transmitter.

According to a further aspect of the invention, there is provided a pendulum assembly for a clock, comprising a pendulum bob assembly as described hereinabove, a pendulum rod, wherein said movement of said bob body relative to said rod changes a period of swing of the pendulum. Movement of the bob body relative to the rod preferably changes an effective length of the pendulum that, in turn, changes its period of swing.

In any of the aspects or embodiments of the present invention described above, an optional base unit may be provided that records each adjustment or correction movement of the bob body relative to the pendulum rod. The optional base unit may record clock error, for example absolute clock error, in seconds a day. The optional base unit may further record or obtain data including any changes in pendulum amplitude against room temperature and barometric pressure. Software in the optional base unit may analyse cyclic errors introduced by train inequalities through a Fourier Analysis. Relevant data may be transmitted to the base unit by the data transmission means described above. The base station and/or computer may be configured to receive data relating to a distance of the bob to the reflector, preferably the shortest distance.

In any of the aspects or embodiments of the present invention described above, means may be provided for detecting each swing of the pendulum, with any discrepancy in the timing-keeping of the clock train mechanism automatically corrected by raising or lowering of the bob body.

In an embodiment of the present invention, there is provided an apparatus for controlling the period of swing of a pendulum, and comprising: a pendulum bob assembly as described hereinabove; a sensor associated with a pendulum bob of said pendulum for counting the number of swings of said pendulum; a processor for calculating a measured period or frequency of swing of said pendulum, based on said counted number of swings, and a desired period or frequency of swing of said pendulum; and a motor for adjusting the instantaneous period or frequency of swing of said pendulum, based on a comparison of said measured period or frequency of swing and said desired period or frequency of swing.

The motor is arranged and adapted to move a weight connected to said pendulum rod relative thereto.

The apparatus for controlling the period of swing of a pendulum is advantageous in its own right, and so from a further aspect of the present invention there is provided an apparatus for controlling the period of swing of a pendulum, and comprising: a sensor associated with a pendulum bob of said pendulum for counting the number of swings of said pendulum; a processor for calculating a measured period or frequency of swing of said pendulum, based on said counted number of swings, and a desired period or frequency of swing of said pendulum; and a motor for adjusting the instantaneous period or frequency of swing of said pendulum, based on a comparison of said measured period or frequency of swing and said desired period or frequency of swing.

Any one of said sensor, processor and motor may be located on or within said pendulum bob or bob body. This advantageously adds weight to the bob or bob body The sensor may comprise an optical sensor, for example a photodiode. An optical sensor is advantageous because it would not interfere with the swing of the pendulum.

Less preferred embodiments are contemplated in which the sensor comprises reed switch or electromagnetic sensor, but these will likely interfere with the components of the clock.

The sensor is preferably triggered, by the optical transmitter described below or otherwise, from a single point in the pendulum's period of swing, e.g. roughly every two seconds.

The apparatus may further comprise an optical transmitter, for example a collimated light source such as a laser.

The apparatus may further comprise means for reflecting light transmitted by the optical transmitter.

The reflecting means may be a reflector, preferably a prismatic reflector. This sends a strong signal back in the direction of transmission of the light and, for example, does not require precise alignment with respect to the optical transmitter.

The optical transmitter may be located on or within the pendulum bob, and optionally the reflector is stationary with respect to the pendulum bob in use; alternatively, the reflector may be located on or within said pendulum bob, and the optical transmitter may be stationary with respect to the pendulum bob in use.

The reflector may be positioned so as to reflect light originating from the optical transmitter when the pendulum bob is travelling at substantially its maximum speed. This means that the sensor will be triggered at the most accurate timing point. Thus the reflector may be arranged at substantially the bottom of the pendulum swing.

The processor may be configured to measure a time at which the laser spot crosses a leading edge, of the reflector, and a time at which the laser spot crosses a trailing edge of the reflector, or indeed crosses at any two predetermined points spaced apart on the reflector.

The processor may be configured to calculate the time taken for the laser spot to traverse the reflector, or the distance between the predetermined points.

The processor may be configured to calculate the speed of the laser spot, using a known distance of the reflector and the time taken for the laser spot to traverse this distance.

The processor may be configured to calculate a sinusoidal amplitude of said laser spot, based on said measured period or frequency of said pendulum and said calculated speed of said laser spot.

Because the time period of the laser spot is known, its amplitude can be calculated and monitored overtime. Because the amplitude of the laser spot changes with the amplitude of the pendulum, this allows variations in the amplitude to be monitored over time against the other recorded data (e.g. environmental conditions). Such amplitude measurements have not been achievable with conventional arrangements not incorporating an optical transmitter.

The precise angular speed and amplitude of the pendulum (as opposed to the laser spot) can be calculated if the distance between the pendulum and the reflector is known.

In practice, as discussed above the reflector will typically be set up so that it is directly beneath the centre point of the pendulum's swing.

The apparatus may further comprise a time base, for example a quartz oscillator, for calculating the measured and/or the desired period or frequency of swing.

The time base may be located on or within said pendulum bob.

The processor may be configured to calculate the number of swings of the pendulum in a given time period and/or the time taken for a given number of swings of the pendulum to occur.

The measured period or frequency of swing preferably corresponds to the calculated number of swings of the pendulum in a given time period and/or the time taken for a given number of swings of the pendulum to occur.

The processor may be configured to calculate an ideal number of swings of the pendulum in the given time period and/or an ideal time for the given number of swings of the pendulum to occur.

The desired period or frequency of swing preferably corresponds to the ideal number of swings of said pendulum in the given time period and/or the ideal time for the given number of swings of the pendulum to occur.

The processor may be configured to calculate a clock error based on the comparison.

The processor may calculate said desired period or frequency of swing to correct for a or said clock error.

The processor may calculate a distance for the weight to move based on the comparison.

As discussed earlier, the apparatus may further comprise a data transfer device in communication with the processor, wherein said data transfer device is configured to transmit data obtained or used by the processor.

The data transfer device may be located on or within said pendulum bob.

A physical cable connection to the pendulum bob or bob body is not practical so to transmit data to and from the bob optical transmitters are preferred. The preferred data transfer device located on the bob or bob body utilises infra-red light because this provides high transmission rates with modest power consumption. It is also not visible to the human eye and hence is not distracting to the clock owner. This has a further advantage that the base unit or computer can be provided in the trunk of the clock below the pendulum to receive data.

The data may comprise any one or more of time, clock error, pendulum speed, instantaneous period or frequency of swing, desired period or frequency of swing, ideal period or frequency of swing, position of pendulum bob, and amplitude of pendulum bob.

The apparatus may further comprise a computer configured to receive data transmitted by the data transfer device.

The computer may comprise software for analysing the transmitted data and outputting information incorporating the transmitted data on a display device.

The apparatus may further comprise an atmospheric data recording device for recording an environmental condition, for example temperature, pressure or humidity, wherein the software is configured to output information incorporating the environmental condition and the transmitted data on the display device. In addition to displaying the basic recorded data the system could also analyse and filter the data, to enable cyclic clock variations to be observed, potentially identity developing clock faults and to see the influence of environmental factors of clock rate and pendulum amplitude.

As an alternative to providing batteries, as referred to herein, or as a method of re-charging the batteries described hereinabove, the bob or bob body could be fitted with an inductive charging loop to transfer energy wirelessly into the bob or bob body and hence prevent the requirement to periodically replace batteries.

In any of the aspects or embodiments described herein, storage means may be provided in the bob or bob body for storing data at the control of the processor. For example, one hours worth of data can be stored within the storage means incorporating, for example the measured/desired/instantaneous period or frequency of swing of the pendulum for every minute. This can then be transferred at intervals, at the command of the processor, to external storage, e.g. the base station or computer described hereinabove, for example every thirty minutes. The external storage may also be located on a remote server with connection thereto via a local or wide area network, or the internet, Whilst it is possible to supply two flexible power supply wires or a single flexible power supply wire and a return through the pendulum rod if made of metal, any spring or wire will interfere with the operation of the pendulum and is likely to fatigue fracture.

Preferably the bob or bob body contains one or more batteries within it, which should be of sufficient power to give a sufficient life, for example one year of operation. As discussed above, a battery advantageously adds to the overall weight of the bob or bob body. A high energy type cell such as a Lithium battery is most preferable.

In a further aspect of the present invention, there is provided a method for controlling the period of swing of a pendulum, said method comprising: counting the number of swings of a pendulum using a sensor associated with a pendulum bob of said pendulum; calculating a measured period or frequency of swing of said pendulum based on said number of swings of said pendulum; calculating a desired period or frequency of swing of said pendulum; and adjusting the instantaneous period or frequency of swing of said pendulum based on a comparison of said measured period or frequency of swing and said desired period or frequency of swing; wherein said adjusting comprises moving a weight connected to said pendulum rod relative thereto.

To set up the pendulum, the time displayed on the clock dial must be pre-set by turning the hands in the normal way so the correct hour is displayed but the minute hand is set for the next coming absolute time minute and fraction of a minute to be in phase with the second hand. The pendulum is then drawn aside by the usual half amplitude and released at the exact second so the clock starts to tick in phase with absolute time.

The sensing means may then immediately start to count the pendulum swings.

This data is then compared to the time base by the processor as described herein.

Initially, the pendulum may be set up out of time, and the processor may control the motor to bring the time of swing of the pendulum into time. Processors incorporating software involving proportional, differential and integral techniques to avoid over and undershoot are known. As the clock must read absolute time, the control circuit must also hold in memory the absolute error for the clock to gain or lose to correct the indicated time back to absolute time.

Clocks can also be influenced by cyclical errors and specific disturbances such as winding or opening the case door, and the processor, base unit or computer can use the stored data to measure these disturbances and progressively correct for long term drift *rather than attempt to follow every short term fluctuation. As the clock comes to time, the processor can reduce how often the sensing means operates to save battery power.

An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figs. lA-iC illustrate a pendulum bob in accordance with the invention and its attachment to a pendulum rod; Fig. 2 is a perspective view of the interior of the pendulum bob shown in Figs. 1A-1C; Fig. 3 is a perspective view of a printed circuit board received within the bob;; Fig. 4 is a perspective view of an adjustment mechanism of the bob; Fig. 5 shows an exploded view of the adjustment mechanism shown in Figure 4; Figs. 6A-6F illustrate components of a locating mechanism; Figs. 7A-70 illustrate components of the printed circuit board and adjustment mechanism in more detail; and Fig. 8 is a cross-section of the pendulum bob.

With reference to Figures lAto 10, a pendulum bob 2 is shown mounted on a pendulum rod 4. The rod 4 comprises, at its lower end, a rectangular anti-rotation section 4a and a cylindrical, threaded section 4b. The bob 2 rests on a nut 6 that is screwed onto the threaded portion 4b of the bob. The nut 6 can be used, in a conventional manner, to move the bob 1 up and down the rod in order to adjust the period of the pendulum during initial set up to bring the pendulum approximately to time.

As shown in Figures lB and 10, the nut 6 can be unscrewed from the threaded portion 43 of the rod 4 and the bob 2 fitted over the lower end of the rod 2. The nut 4 may then be replaced in order to retain the bob 2 on the pendulum rod 4.

The bob 2 comprises a body memberS and a removable cover 10. As it is desirable to provide a heavy dense pendulum body, the body member 8 may be machined from metal such as brass or cast from metal such as lead or brass or moulded from specially filled dense plastic. Likewise the cosmetic cover member 10 may be formed, for example from a specially filled dense moulded plastics material or a polished cast or pressed metal such as brass The two parts 8, 10 may simply be clipped together! so as to enable an easy method to gain access to change the batteries.

With reference to Figure 2, cover plate 10 has been removed to expose the internal components of the bob 2. There are two main assemblies, namely a printed circuit board 12 (Figure 3) and an adjustment mechanism 14 (Figure 4). The printed circuit board (PCB) 12 is mounted into a recess 16 provided in the body member 8 of the bob 2. The PCB 12 mounts various components of a control for the adjustment mechanism 14, for example, a processor 18, sensor 20 and a data transfer device 22. The PCB 12 also mounts a power supply for the bob 2 in the form of two batteries 25.

The adjustment mechanism 14 is mounted to the PCB 12, such that it too is located within the recess 16 of the bob body memberS.

Figure 5 shows an exploded view of the adjustment mechanism 14. In broad terms the adjustment mechanism 14 comprises a mount 24 which is slidably received on a carriage 26. Both the mount 24 and the carriage 26 may conveniently be moulded from a plastics material, preferably filled with glass fibre to retain long term dimensional stability and stiffness.

The carriage 26 mounts a drive screw 28 which is journaled and domed to reduce friction at its ends 30 in bearings 33 formed in the carriage member 26. A nut 32 is mounted on the screw 28 and is captured in a recess 34 formed in the mount 24 such that it cannot rotate with respect to the mount 24.

A motor 36, for example a stepping motor, is mounted to a side of the carriage 26 by means of fasteners 42 (Figure 4) and is provided with a worm gear 38 which engages with a pinion wheel 40 locked onto the drive screw 28.

The mount 24 is formed with a generally rectangular anti-rotational upper section 24a and a cylindrical lower section 24b. The cylindrical lower section 24b is formed with a bore 44therethrough. The mount 24 is also provided with a lug 46 which projects from its rear surface. This engages in an L-shaped slot 48 provided in the carriage member 26 so as to retain the mount 24 on the carriage 26. A stop may be provided on the rear of the carriage 26 to limit the vertically downward movement of the mount 24 with respect to the carriage 26.

The carriage member 26 is formed with an open lower end 50 through which the cylindrical section 24b of the mount 24 projects.

As can be seen from Figure 2, the pendulum rod 4 is received through the open top of the mount 24 with its threaded portion 4b extending through the cylindrical portion 24b of the mount 24. As can also been seen from Figure 2, the lower edge 52 of the cylindrical portion 24b will rest on the adjustment nut 6 attached to the threaded portion 4b of the pendulum rod 2. The mount 24 therefore does not move vertically relative to the nut 6 and thus does not move vertically relative to the rod 4 itself. The nut 6 may then be used to adjust the effective length of the pendulum rod 4 to bring the clock roughly to time before engaging the automatic control system.

Still referring to Figure 2, in order to locate the bob 2 on the pendulum rod 4 (which may vary in size from clock to clock), an adjustable locating mechanism 60 is also provided. The locating mechanism 60 comprises a first component 62 which is received in a slot 64 formed in the bob member 8. As can be seen most clearly from Figure 60, the first locating component comprises an opposed pair of pins 66 which, as can seen from Figure 6B, engage or lie closely adjacent opposed sides 68 of the pendulum rod 4. The component 62 is provided with a cylindrical spigot 70 on its rear surface which engages in a complementary bore in the bob body member 8 such that the component 62 may rotate about an axis 72.

The locating mechanism 60 also includes a second component 74 having front and rear limbs 76a, 76b which engage or lies closely adjacent to, front and back surfaces 78a, 78b of the pendulum rod 4.

The second component 74 further comprises a pair of mounting pins 80 (Figure 6F) which are received in semi-circular recesses in mounting blocks 82 which are in turn slidably received in recesses 84 of the bob body member 8. The second component is rotatable about the axis defined along the axes of the pins 80. The respective rotational axes of the first and second components 62, 74 are perpendicular to one another.

The first and second components 62, 74 may be made from a low friction material such as PTFE to minimise any frictional forces between them and the pendulum rod 4 as and when the motor 36 drives the drive screw 28 up or down moving the carriage 26 against the mount 24 resting with the lower edge 52 against the nut 6 and the whole bob located at the top and sliding against pins 66 and limbs 76a and 76b.

The front limb 76a of the second component 74 comprises a tab 86 which facilitates rotation of the component 74 about the axis formed between the pins 80.

The mounting blocks 82 are retained in the recesses 84 by screws, bolts or other fasteners 86. The respective components 62, 74 may be rotated by hand so as loosely to engage or lie adjacent the respective surfaces of the pendulum rod 4 and the screws 86 then tightened so as to lock the components 62, 74 in position.

The assembly of the bob 2 and its adjustment on the pendulum rod 4 will now be described.

The pendulum rod 4 is introduced through the top of the bob through location mechanism and the mount 24 such that the threaded section 4b of the rod 4 extends out from the bottom of the bob 2. The adjustment nut 6 is then threaded onto the threaded portion 4b of the rod 4 and the bob 4 then allowed to rest on the adjustment nut 6 via the lower end surface 52 of the mount 24.

The location mechanism 60 is adjusted as necessary as described above to and the cover 10 then placed on the bob 2.

The initial position of the bob 2 relative to the rod 4 may be made by turning the adjustment nut 6 which will either raise or lower the mount 24, and thereby the bob body 8, on the rod 4. Subsequent adjustment, however, can be made by means of the motor 36 receiving appropriate signals from the control. Upon receiving an appropriate control command, the motor 36 rotates in one or other direction, in turn causing the drive screw 28 to rotate in one or other direction. As the drive screw 28 is fixed in the carriage 26. the nut 32 will move up and down the drive screw 28. As discussed above, as the nut 32 is retained fixedly in the mount 24, the carriage 26 will move relative to the mount 24.

Moreover, as the mount 24 rests via its lower end 52 on the adjustment nut 6, it does not move relative to the nut 6 or rod 4. Accordingly, the carriage 26, and thus the bob body 8 to which it is mounted will move up or down relative to the mount 24, and thus relative to -12-the pendulum rod, thereby changing the centre of gravity of the pendulum and thus its period.

As shown in Figures 7A-7C, the PCB 12 comprises limit switches 23 that are positioned to interact with a corresponding protrusion 25 on the mount 24. The limit 6 switches 23 define upper and lower limits of travel of the bob 2 with respect to the mount 24. The limit switches 23 send a signal to the controller 18 that the bob 2 has reached its limit of travel. This, in turn, causes the controller 18 to send a signal to the motor 36 to stop, which avoids damaging the various components connected thereto.

As described above, the control for the adjustment mechanism 14 comprises a processor 18, sensor 20 and data transfer device 22. The control further comprises a storage means 19 and a time base 21 (Figure 3).

The sensor 20 is shown in more detail in Fig. 8, and comprises a collimated light source, in this case a laser 202. A prismatic reflector (not shown) is positioned stationary relative to the clock, for example on the floor or surface below the centre point of the pendulum's swing. As will be appreciated, such a position is preferable because the laser dot passes the reflector, and timing point, at maximum speed.

Light from the laser 202 is reflected by the prismatic reflector and is focussed by a lens 204 onto a photodiode 206, which communicates the signal to the processor 18.

The storage means 19 is configured to accept data from the processor 18, which data can be subsequently transferred via the data transfer device 22 to an external base station (not shown). The data transfer device 22 in this case comprises an infrared transmitter for transmitting signals received from the processor 18 and/or storage means 19.

The base station comprises a receiver positioned such that it can receive signals from the data transfer device 22. The base station further comprises a processor arranged and adapted to analyse this data.

The control for the adjustment mechanism has two modes, manual and automatic.

A switch (not shown) is located on the PCB 12 for switching between the two modes, which is accessible through the bob body member 8.

In operation, the user first switches the control to manual mode, in which mode the laser 202 is configured to flash at a predetermined interval, for example every two seconds.

This produces a visible spot on an opposing surface (e.g. a floor). When the bob is released the location of the spot in each cycle can be monitored and, if positioned correctly, the spot appears static. If the spot moves, this indicates that the bob 2 needs to be moved up or down the rod 4 as appropriate. If the position of the spot advances with each pendulum swing (i.e. moves with the instantaneous direction of swing) then the pendulum is swinging too fast, and the bob must be moved down to correct the speed.

Similarly if the spot retreats with each swing (i.e. moves against the instantaneous direction of swing) the bob should be raised. A user can adjust the position of the pendulum bob 2 manually using the nut 6, until the desired position is reached, This manual' adjustment of the bob position is relatively coarse, and requires the pendulum to be stopped while the adjustment is effected.

When the spot appears static, indicating that the pendulum period is correct, the user then stops the pendulum and switches to automatic mode. In this mode, the processor 18 measures the number of cycles of the time base 21 (in this case a 32768 Hz crystal) that occur in a predetermined number, for example thirty swings of the pendulum.

The laser 202 and processor 18 are configured to measure the point at which the laser spot crosses the reflector at a single point in its period. It will, therefore, be appreciated that thirty swings of the pendulum corresponds to approximately one minute.

The processor 18 then subtracts the measured number of cycles from the ideal number of cycles to obtain a clock error value. That is, the clock error is calculated by measuring the elapsed time between the laser crossing the edge of the reflector at the start of one minute, and the subsequent crossing (roughly) a minute later. In this manner, the clock error is a comparison of a measured time and an ideal time. The bob stores the clock error values sequentially in storage means 19.

To save power, which is especially important when using an integrated power source, the processor iBis configured to switch the laser 202 on shortly before it is expected to cross the reflector, and then off shortly afterwards. This is possible due to any clock error being relatively small over the course of a minute.

The processor 18 periodically calculates a correction value corresponding to an adjustment movement of the bob 2 based on the clock error values and pendulum speed.

This calculation is based on proportional, differential and integral techniques. An integral error is used that is representative of the cumulative clock error, to account for long-term fluctuations, and a proportional error is used that is representative of the instantaneous clock error, to account for shod-term fluctuations.

The processor 18 then calculates the number of stepper motor 36 steps required to move the bob 2 the required adjustment distance, and commands the motor 36 to move accordingly.

A correction may be made at regular intervals, which can be chosen by the user or determined by the control. Typically, the interval will depend on how large the clock error values are. For example, if the clock error is large, a correction can be made once an hour. If the clock error is small, then a correction can be made once a day.

It will be appreciated that the corrections made in automatic mode are relatively fine, and typically are for correcting long-term drift of the period of swing of the pendulum due to, for example, frictional losses, air resistance, atmospheric changes and manufacturing imperfections. To correct for such long-term drift manually is not feasible, since the changes cannot be seen visually.

The processor 18 will periodically send data stored in the storage means 19 to the data transfer device 22, including clock error values, pendulum speed, adjustment/correction values, bob position, bob amplitude, and time. The data transfer device 22 will then periodically transmit this data to the base station where it can be further analysed.

Software is provided on the computer of the base station that can analyse the data and display information on a display device. This can include plots of: clock error against time; clock speed against time; correction values against time; bob amplitude against time.

Atmospheric data recording means can be incorporated into or connected to the base station, and may comprise temperature measuring means, atmospheric pressure measuring means, humidity measuring means. In this case the software provided on the computer of the base station can also display information relating to environmental conditions (e.g. temperature, pressure, humidity/relative humidity, etc.) against time.

In a further mode of operation an amplitude of the laser spot can be monitored by the base station or processor 18. In this mode, the processor 18 is configured to control the laser 202 so that it is switched on shortly before it crosses a front edge of the prismatic reflector, and then off shortly after it crosses a back edge of the reflector. This allows the processor 18 to store data in storage means 19 corresponding to the time taken for the laser dot to cross the reflector. The width of the reflector (i.e. from the front edge to the back edge) is known, meaning that the speed of the laser spot across the reflector can be calculated. As the speed is approximately sinusoidal, this will be an average speed, rather than an instantaneous value. The processor 18 may be configured to carry out this calculation and store the result in storage means 19.

Because the time period of the laser spot is known, its amplitude can be calculated and monitored overtime. Because the amplitude of the laser spot changes with the amplitude of the pendulum, this allows variations in the amplitude to be monitored over time against the other recorded data (e.g. environmental conditions).

In a further mode of operation, the base station and/or processor 18 are configured to receive data relating to a distance of the bob to the reflector, preferably the shortest distance. In practice, the reflector will typically be set up so that it is directly beneath the centre point of the pendulum's swing.

Claims

Claims 1. A pendulum bob assembly comprising: a mount mountable on a pendulum rod and a bob body movable relative to the mount such that movement of the bob body relative to the mount moves the bob body relative to the pendulum rod; and a drive for moving said bob body relative to said mount.
2. The pendulum bob assembly as claimed in claim 1, wherein the mount comprises a hollow body which is able to receive a pendulum rod therein.
3. The pendulum bob assembly as claimed in claim 2, wherein the lower end of the hollow body is open to allow a pendulum rod to extend therethrough to allow for the attachment to the rod of an adjustment nut.
4 The pendulum bob assembly as claimed in claim 3, wherein the lower end of the mount is configured to rest on the adjustment nut to locate it vertically relative to the pendulum rod.
5. The pendulum bob assembly as claimed in any preceding claim, wherein the bob body is slidably received on the mount.
6. The pendulum bob assembly as claimed in any preceding claim, wherein the bob body comprises a carriage on which the mount is slidably received, or the mount comprises a carriage on which the bob body is slidably received
7. The pendulum bob assembly as claimed in claim 6, wherein the drive comprises a drive mechanism arranged between the carriage and the bob body or mount.
8. The pendulum bob assembly as claimed in claim 7, wherein the drive mechanism comprises a drive screw.
9. The pendulum bob assembly as claimed in claim 8, wherein the drive screw is mounted to one of the bob body or mount, for example to the carriage, and a drive nut is mounted to the other of the bob body or mount, wherein rotation of the drive screw causes relative movement between the mount and the bob body.
10. The pendulum bob assembly as claimed in claim 9, wherein the drive screw extends parallel to the direction of relative movement of the bob body and mount.
11. The pendulum bob assembly as claimed in claim 8, 9 or 10, wherein the drive comprises a motor to rotate the screw.
12. The pendulum bob assembly as claimed in claim 11, wherein the motor comprises a stepping motor.
13. The pendulum bob assembly as claimed in claim 11 or 12, wherein the motor rotates the screw via a gear arrangement, for example a worm gear.13. The pendulum bob assembly as claimed in claim 11, 12 or 13, wherein the motor is mounted to the bob body.
14. The pendulum bob assembly as claimed in any preceding claim, wherein the bob body further comprises a power source for the drive means.
15. The pendulum bob assembly as claimed in claim 14, wherein said power source comprises one or more batteries mounted within said bob body.
16. The pendulum bob assembly as claimed in any preceding claim, wherein the bob body further comprises means for slidably locating the bob body on the pendulum rod.
17. The pendulum bob assembly as claimed in claim 16, wherein the locating means comprises a first component that locates the bob body relative to the pendulum rod in a first direction, whilst allowing the bob to slide relative to the rod.
18. The pendulum bob assembly as claimed in claim 17, wherein the locating means further comprises a second component that locates the bob body relative to the pendulum rod in a second direction, whilst allowing the bob to slide relative to the rod.
19. The pendulum bob assembly as claimed in claim 18, wherein said first direction is substantially perpendicular to said second direction.
20. The pendulum bob assembly as claimed in claim 17, 180119, wherein the first and/or second components have opposed locating surfaces for engaging opposed surfaces of the pendulum rod.
21. The pendulum bob assembly as claimed in claim 20, wherein the first and second components are rotatable about respective axes to adjust the position of the locating surfaces relative to the surfaces of the rod.
22. The pendulum bob assembly as claimed in any preceding claim, wherein the bob body accommodates a control for the drive means.
23. The pendulum bob assembly as claimed in claim 22, wherein the control comprises a printed circuit board which is mounted to the bob body.
24. The pendulum bob assembly as claimed in claim 22, wherein a or the carriage on which the bob body or mount is slidably received is mounted to said printed circuit board.
25. The pendulum bob assembly as claimed in claim 23 0124, wherein the printed circuit board comprises a processor or set of processors for controlling said moving means.
26. The pendulum bob assembly as claimed in any preceding claim, wherein the bob body further comprises means for transmitting data relating to the movement or position of the bob body relative to the mount.
27. The pendulum bob assembly as claimed in claim 26, wherein the transmitting means comprises a wireless transmitter, for example an optical or nfra-red transmitter.
28. A pendulum assembly for a clock, and comprising: the pendulum bob assembly of any preceding claim; and a pendulum rod; wherein said movement of said bob body relative to said rod changes a period of swing of the pendulum.
29. An apparatus for locating a pendulum rod slidably received within a pendulum bob, said apparatus comprising: one or more adjustable or rotatable components that define a sliding path for the rod; wherein upon adjustment or rotation of said component(s) with respect to the rod, a width of said sliding path increases or decreases.
30. The apparatus as claimed in claim 29, wherein one or both of said components comprises a pair of protrusions or limbs that define said sliding path for the rod, and upon adjustment or rotation of the component said protrusions or limbs move relative to one another to increase or decrease a width of the sliding path.
31. A pendulum bob having means for transmitting electronic data from the bob to an external device.
32. The pendulum bob as claimed in claim 31, wherein said transmitting means comprises a wireless transmitter, for example an infrared, laser or wi-fi transmitter.
33. An apparatus for controlling the period of swing of a pendulum, and comprising: the pendulum bob assembly as claimed in any of claims 1-27; a sensor associated with a pendulum bob of said pendulum for counting the number of swings of said pendulum; a processor for calculating a measured period or frequency of swing of said pendulum, based on said counted number of swings, and a desired period or frequency of swing of said pendulum; and a motor for adjusting the instantaneous period or frequency of swing of said pendulum, based on a comparison of said measured period or frequency of swing and said desired period or frequency of swing; wherein said motor is arranged and adapted to move a weight connected to said pendulum rod relative thereto.
34. An apparatus for controlling the period of swing of a pendulum, and comprising: a sensor associated with a pendulum bob of said pendulum for counting the number of swings of said pendulum; a processor for calculating a measured period or frequency of swing of said pendulum, based on said counted number of swings, and a desired period or frequency of swing of said pendulum; and a motor for adjusting the instantaneous period or frequency of swing of said pendulum, based on a comparison of said measured period or frequency of swing and said desired period or frequency of swing; wherein said motor is arranged and adapted to move a weight connected to said pendulum rod relative thereto.
35. The apparatus as claimed in claim 33 or 34, wherein any one of said sensor, processor and motor are located on or within said pendulum bob.
36. The apparatus as claimed in claim 33, 34 or 35, wherein said sensor comprises an optical sensor, for example a photodiode.
37. The apparatus as claimed in any of claims 33-36, further comprising an optical transmitter, for example a collimated light source such as a laser.
38. The apparatus as claimed in claim 37, further comprising means for reflecting light transmitted by said optical transmitter.39 The apparatus as claimed in claim 38, wherein said reflecting means is a reflector, preferably a prismatic reflector.40. The apparatus as claimed in claim 39, wherein said optical transmitter is located on or within said pendulum bob, and optionally said reflector is stationary with respect to said pendulum bob in use; or said reflector is located on or within said pendulum bob, and optionally said optical transmitter is stationary with respect to said pendulum bob in use.41. The apparatus as claimed in claim 39 or 40, wherein said reflector is positioned so as to reflect light originating from said optical transmitter when said pendulum bob is travelling at substantially its maximum speed.42. The apparatus as claimed in any of claims 33-41, wherein said processor is configured to measure a time at which the laser spot crosses two or more predetermined points spaced apart on said reflector, for example including a leading edge and a trailing edge.-20 - 43. The apparatus as claimed in any of claims 33-42, wherein said processor is configured to calculate the time taken for the laser spot to traverse the reflector.44. The apparatus as claimed in any of claims 33-43, wherein said processor is configured to calculate the speed of the laser spot, using a known distance of the reflector and the time taken for the laser spot to traverse this distance.45. The apparatus as claimed in claim 44, wherein said processor is configured to calculate a sinusoidal amplitude of said laser spot, based on said measured period or frequency of said pendulum and said calculated speed of said laser spot.46. The apparatus as claimed in any of claims 33-45, further comprising a time base, for example a quartz oscillator, for calculating said measured and/or said desired period or frequency of swing.47. The apparatus as claimed in claim 46, wherein said time base is located on or within said pendulum bob.48. The apparatus as claimed in any of claims 33-47, wherein said processor is configured to calculate the number of swings of said pendulum in a given time period and/or the time taken for a given number of swings of said pendulum to occur.49. The apparatus as claimed in claim 48, wherein said measured period or frequency of swing corresponds to said calculated number of swings of said pendulum in a given time period and/or said time taken for a given number of swings of said pendulum to occur.50. The apparatus as claimed in claim 48 or 49, wherein said processor is configured to calculate an ideal number of swings of said pendulum in said given time period and/or an ideal time for said given number of swings of said pendulum to occur.51. The apparatus as claimed in claim 50, wherein said desired period or frequency of swing corresponds to said ideal number of swings of said pendulum in said given time period and/or said ideal time for said given number of swings of said pendulum to occur. -21 -52. The apparatus as claimed in any of claims 33-51 wherein said processor is configured to calculate a clock error based on said comparison.53. The apparatus as claimed in any of claims 33-52, wherein said processor calculates said desired period or frequency of swing to correct for a or said clock error.54. The apparatus as claimed in any of claims 33-53, wherein said processor calculates a distance for the weight to move based on said comparison.55. The apparatus as claimed in any of claims 33-54, further comprising a data transfer device in communication with said processor, wherein said data transfer device is configured to transmit data obtained or used by said processor.56. The apparatus as claimed in claim 55, wherein said data transfer device is located on or within said pendulum bob.57. The apparatus as claimed in claim 55 or 56, wherein said data comprises any one or more of time, clock error, pendulum speed, instantaneous period or frequency of swing, desired period or frequency of swing, ideal period or frequency of swing, position of pendulum bob, and amplitude of pendulum bob.58. The apparatus as claimed in any of claims 55-57, further comprising a computer configured to receive data transmitted by said data transfer device.59. The apparatus as claimed in claim 58, wherein said computer comprises software for analysing said transmitted data and outputting information incorporating said transmitted data on a display device.60. The apparatus as claimed in claim 59, further comprising an atmospheric data recording device for recording an environmental condition, for example temperature, pressure or humidity, wherein said software is configured to output information incorporating said environmental condition and said transmitted data on said display device.61. A method for controlling the period of swing of a pendulum, said method comprising: -22 -counting the number of swings of a pendulum using a sensor associated with a pendulum bob of said pendulum; calculating a measured period or frequency of swing of said pendulum based on said number of swings of said pendulum; calculating a desired period or frequency of swing of said pendulum; and adjusting the instantaneous period or frequency of swing of said pendulum based on a comparison of said measured period or frequency of swing and said desired period or frequency of swing; wherein said adjusting comprises moving a weight connected to said pendulum rod relative thereto.