GB2035625A

GB2035625A - Electronic timepiece

Info

Publication number: GB2035625A
Application number: GB7940285A
Authority: GB
Original assignee: Seiko Instruments Inc
Current assignee: Seiko Instruments Inc
Priority date: 1978-11-22
Filing date: 1979-11-21
Publication date: 1980-06-18
Also published as: JPS5570773A; GB2035625B; DE2946363A1; FR2442543A1

Abstract

In an electronic timepiece including a stepping motor which is normally driven by a signal consisting of simple pulses P1 of alternating polarity, a series of correction pulses P21-P26 is applied when a pulse of the driving signal is incapable of causing the rotor to rotate by one step as a result of one of a plurality of external conditions, e.g. load or magnetic field, affecting the stepping motor. The series of correction pulses consists of a plurality of pulses of different pulse widths each of which is selected to maximise performance of the stepping motor when affected by a given external condition. Circuitry for detecting failure to step is described - Figure 8 not shown. <IMAGE>

Description

SPECIFICATION Electronic timepiece This invention relates to electronic timepieces.

To improve the efficiency of electro-mechanical conversion in a stepping motor of low power consumption, such as an ultra-miniature stepping motor for an electronic wristwatch, a so-called "correcting drive method" has previously been proposed. The correcting drive method is such that a rotor of the stepping motor is usually driven by a drive signal consisting of normal pulses of relatively narrow pulse width, but if the rotor is not rotated by a complete step by a normal pulse of the drive signal for some reason or other, a correcting pulse with a pulse width which is greater than the pulse width of the normal pulse is applied.The correcting drive method means that it is important not only to detect correctly when a normal pulse of the drive signal will not rotate the rotor by a complete step but also to ensure that the rotor is rotated by a complete step when the correcting pulse is applied and when the electronic timepiece is affected by external conditions, for example, change in battery voltage and/or external magnetic fields. In other words, with the correcting drive method it is important that the rotor is rotated with certainty when affected by all external conditions to which the stepping motor is subjected.

According to the present invention there is provided an electronic timepiece including a stepping motor, means for producing a drive signal consisting of alternate pulses of opposite polarity and means for applying a series of correction pulses when a pulse of the driving signal is incapable of causing the rotor to rotate by one step as a result of one of a plurality of external conditions affecting the stepping motor, the series of correction pulses consisting of a plurality of pulses of different pulse widths each of which is selected to maximise performance of the stepping motor when affected by given external conditions.

The invention is illustrated, merely by way of example, in the accompanying drawings, in which: Figure 1(A) illustrates a stepping motor used in both a conventional timepiece and in an electronic timepiece according to the present invention; Figure 1(B) is a waveform of a drive signal conventionally applied to the stepping motor of Figure 1(A); Figures 2, 3 and 4 illustrate graphically the re lationship between pulse width of a drive signal for the stepping motor of Figure 1 (A) and output torque, DC antimagnetic characteristics and AC antimagnetic characteristics; Figure 5 is a waveform of a drive signal of an electronic timepiece according to the present inven tion; Figure 6 illustrates the operation of the stepping motor of Figure 1 (A) in an electronic timepiece according to the present invention;; Figure 7 is a logic diagram illustrating operation of an electronic timepiece according to the present invention; Figure 8 is a circuit diagram of an electronic timepiece according to the present invention; and Figure 9 is a timing chart illustrating, by means of waveforms the operation of the electronic timepiece of Figure 8.

Figure 1 (A) illustrates a stepping motor used in a conventional electronic timepiece as well as in an electronic timepiece according to the present invention, to drive timekeeping hands. Figure 1 (B) illustrates a drive signal conventionally used to drive the stepping motor of Figure 1 (A). The drive signal of Figure 1 (B) conventionally is applied to a coil 3 of the stepping motor and a stator 1 is magnetised with the result that a rotor 2 rotates through 1 80 C by repulsion and attraction between the magnetic poles induced in the stator and permanent magnetic poles of the rotor for each pulse of the drive signal which consists of alternate pulses of opposite polarity.

Conventionally, the width of each pulse of the drive signal is such as to ensure that the rotor will rotate under all conditions. Thus the pulse width must be sufficiently wide to rotate the rotor when a calender mechanism is driven by the stepping motor, when internal resistance of a battery increases, when there is a reduction in drive voltage, when the battery nears the ends of its useful life, etc. Having the pulse width sufficiently wide to rotate the rotor under all conditions has the disadvantage that the power consumption is unnecessarily high when the load on the rotor is relatively low.

To overcome this disadvantage it has already been suggested that the stepping motor is usually driven by normal pulses having a minimum pulse width P1 but when a detecting circuit detects that a normal pulse is insufficient to cause the rotor to rotate by a complete step, a correction pulse having a pulse width P2, which is greater than the pulse width P1, is applied. This means that it is not essential to ensure that the rotor is rotated at all by normal pulses with the pulse width P1 but it is essential that the rotor is rotated under all conditions by correction pulses with the pulse width P2. However, it has been found that if the stepping motor is subjected to various external conditions, such as those mentioned above, it may not be possible to select the pulse width P2 such as to ensure that the rotor is always rotated by a complete step by the correction pulses.

Figures 2,3 and 4 illustrate graphically there lationship between pulse widths, output torque, DC antimagnetic characteristics and AC antimagnetic characteristics of the stepping motor of Figure 1 (A).

The stepping motor used to produce Figures 2, 3 and 4 has the following characteristics: the resistance of the coil 3 was 2.9K & the coil had 8,300 turns, the rotor 2 had an external diameter of 1.25 mm and an external diameter of 0.3 mm and the gap between the rotor and the stator was 0.275 mm. The battery used to produce the drive signal for the stepping motor had a voltage which varied with its capacity and the battery was, for example, a silver peroxide battery.

Figures 2 (A) and 2 (B) show the relationship between pulse width and output torque at a centre wheel and pinion fixed to the rotor when the voltage of the driving signal is respectively 1.57V and 1.8V. It will be seen that the rotor produces a relatively high output torque when the pulse width is 8.0 msec and the voltage is 1 .57V, but the rotor will not be rotated by a complete step with a pulse with a pulse width of 8.0 msec when the battery voltage is 1 .8V.

Figure 3 (A) and Figure 3 (B) show the relationship between pulse width and DC antimagnetic characteristic when the voltage of the drive signal is 1 .57V and 1 .8V respectively. Figures 4 (A) and 4 (B) show the relationship between pulse width and AC antimagnetic characteristics when the voltage of the drive signal is 1.5V and 1 .8V respectively.

From the six graphs of Figures 2,3 and 4, it will be appreciated that there is no single pulse width which will produce maximum output torque, maximum DC antimagnetic characteristics and maximum AC antimagnetic characteristics when the battery voltage is either 1.57V or 1.8V. Thus, if a correction pulse, with a pulse width P2, which is greater than the pulse width P1, is applied when the stepping motor is subject to an external condition which is such that normal pulses with the pulse width P1 are incapable of causing the rotor to rotate by a single step, there is no unique pulse width P2 which will at one and the same time maximise output torque, DC antimagnetic characteristics and AC antimagnetic characteristics unless the pulse width P2 is made considerably greater than that really necessary.

Since the performance of the stepping motor is a function of magnetic density of the rotor, the coil resistance, number of turns of the coil from the shape of the stator and their effect one performance, even if the stepping motor is manufactured within normal tolerances, is not negligible, to ensure rotation of the rotor by the correction pulses either the manufacturing tolerances must be reduced or the standards of manufacture must be relaxed.

Figure 5 illustrates the drive signal of an electronic timepiece according to the present invention. This drive signal consists of normal pulses each with a pulse width P1 which rotates the rotor normally when the load thereon is relatively small and correction pulses with pulse widths P21 and P26 which are produced when a detecting circuit detects that one of the normal pulses is incapable of causing the rotor to rotate by a complete step.If the stepping motor used in the production of Figures 2 to 4 is driven by a drive signal as illustrated in Figure 5 and the pulse width P21 is 8.0 msec, the pulse width P22 is 7.0 msec, the pulse width P23 is 10.0 msec, the pulse width P24 is 6.5 msec, the pulse width P25 is 12.0 msec and the pulse width P26 is 9.5 msec, the maximum output torque when the voltage is 1 .57V occurs with the correction pulse having a pulse width P21,the maximum DC antimagnetic characteristics when the voltage is 1 .56V occurs with the correction pulse with the pulse width P22, the maximum AC antimagnetic characteristics when the voltage is 1 .57V occurs with the correction pulse with the pulse width P23, the maximum output torque when the voltage is 1 .8V occurs with the correction pulse with the pulse width P24, the maximum DC antimagnetic characteristics when the voltage is 1 .8V occurs with the pulse with the pulse width P25 and the maximum AC antimagnetic characteristics when the voltage is 1 .8V occurs with the pulse with the pulse width P26.

Accordingly, when the normal pulses will not rotate the rotor by a complete step for some reason or other, the rotor can be rotated by one of the correction pulses to obtain the highest performance.

If the rotor is rotated by the first correction pulse with the pulse width P21 the subsequent five correction pulses merely increase the magnetisation of the stator to attract the rotor thereto and thus the rotor will only be advanced by one step by the first correction pulse the other correction pulses having no effect on the stepwise rotation.

The operation of the stepping motor of an electronic timepiece according to the present invention is illustrated in conjunction with Figure 6.

Initially the rotor is in the position shown in Figure 6 (A). When the stator is magnetised by a normal pulse having the pulse width P1 and applied to the coil 3, the rotor 2 rotates normally by one step to the position shown in Figure 6 (B). The correction pulses with the pulse widths P22 to P26 follow the normal pulse when the latter is incapable of causing the rotor to rotate by a complete step and since the correction pulses have the same polarity as the immediately preceding normal pulse they tend to rotate the rotor 2 in the same direction as the normal pulse. If the first correction pulse, with the pulse width P21, is sufficient to cause the rotor to rotate by a complete step, the subsequent correction pulses merely maintain the existing magnetisation of the stator caused by the first correction pulse as shown in Figure 6 (B).Since the magnetic poles generated in the stator by the subsequent correction pulses are opposite to those of the rotor those subsequent correction pulses do not urge the rotor to rotate further but merely attract it to the stator Accordingly, the rotor will remain in the position shown in Figure 6 (B) or in 6 (C) as the subsequent correction pulses are applied and after the first correction pulse with the pulse P21 which caused the rotor to rotate by a complete step has terminated.

Thus an electronic timepiece according to the present invention having a stepping motor with the characteristics illustrated in Figures 2 to 4 and driven by the drive signal of Figure 5, produces an output torque at the centre wheel and pinion of 3.6 g.cm.

has DC antimagnetic characteristics of 36 oersted (2865Alm), has AC antimagnetic characteristics of 15 oersted (1 194A/m) when the battery voltage is 1.5V and produces an output torque at the centre wheel and pinion of 3.2 g.cm., has DC antimagnetic characteristics of 40 oersted (3183 A/m) and AC antimagnetic characteristics of 15 oersted (1194A/m) when the battery voltage is 1 .8V.

Though an electronic timepiece according to the present invention has been described and illustrated above with reference to the effect on the stepping motor of change in battery voltage and DC and AC magnetic fields, the electronic timepiece may be designed to take account of other external conditions such as change of temperature and internal resistance of the battery.

In the electronic timepiece according to the present invention and illustrated above when it is detected that the normal pulse with a pulse width P1 is incapable of causing the rotor to rotate by a complete step a series of pulses of different pulse widths are applied to cause it to rotate, the different pulse widths being so chosen to maximise performance under various external conditions to which the stepping motor is subjected. Thus the rotor of the stepping motor will rotate regardless of the external condition which caused the rotor not to be rotated by the normal pulse. Thus an electronic timepiece of high performance and simple construction is obtained.

Figure 8 illustrates an electronic timepiece according to the present invention, and Figure 9 illustrates the operation thereof. An oscillator circuit 11 produces a time standard signal which is frequency divided by a frequency divider circuit 12. The divider circuit produces output signals which are fed to a pulse generating circuit 13 which produces the normal pulses with the pulse width Pal ,the correction pulses with the pulse width P2, the correction pulses with the pulse widths P22 to P26 and detection pulses D1, D2 for judging or detecting whether or not the rotor has been rotated by a complete step by a normal pulse with the pulse width P1.

A T-type flip-flop circuit 14 determines the direction of current flows in a coil 36 of a stepping motor, for example of the type illustrated in Figure land the output of the flip-flop circuit 14 is inverted by a positive-going normal pulse.

Assuming now that the output signals 0 and Q of the flip-flop circuit 14 become logic "0" and "1" respectively at the appearance of a normal pulse, the outputs of respective AND gates 28, 24 become logic "0". Accordingly, current flows in the direction of arrow A in the coil 36. A R-S flip-flop circuit 15 is set so that the output signals 0 and Q thereof become logic "1" and "0" respectively on receipt of a negative-going pulse from a NAND gate 19 and is reset by the output of a NAND gate 18. The output signals Q and Q of the flip-flop circuit become logic "0" and "1" on receipt of a detection pulse D1, and become logic "1" and "0" on receipt of the next detection pulse D2.

As a result, the output of a NAN D gate 21 becomes logic "0" during the existence of the detection pulse D1. This causes the outputs of the AND gates 28, 24 and an AND gate 23 to be logic "0" so that current flows in the coil 36 in the direction of the arrow A.

The voltage across a resistor 37 is proportional to the current flowing in the coil 36. The voltage across the resistor 37 charges a capacitor 38 through a transmission gate 29, and the output of the capacitor 38 is fed to one terminal of a comparator 17.

The output of a NAND gate 20 becomes logic "0" during the existence of the detection pulse D2, and the outputs of the AND gates 23, 24 and an AND gate 27 become logic "0". Accordingly, current flows in the coil 36 in the direction of an arrow B and the voltage across the resistor 37 again is proportional to the value of the current. The voltage across the resistor 37 is fed to the other terminal of the comparator 17.

The comparator 17 detects whether the rotor has rotated a complete step or not from two voltages applied to the input terminals thereof. In the arrangement illustrated in Figure 8, the rotor is not rotated by a complete step when the voltage generated as a result of the detection pulse D1 is higher than the voltage generated as a result of the detection pulse D2.

A A S-Tflip-flop circuit 16 latches the output of the comparator 17 and output signals 0 and Q of the flip-flop circuit 16 are logic "1" and "0" at the existence of a normal pulse. As a result, the output of an AND gate 22 is the correction pulses P2, P21, P22, P23, P24, P25, P26.

On the other hand where the rotor is rotated by a complete step by a normal pulse the output of the comparator 17 becomes logic "0" so that the output signal Q of the flip-flop circuit 16 is logic "0".

Accordingly the output of the AND gate 22 becomes logic "0" and blocks the correction pulses.

An OR gate 26 passes the correction pulse P2 when the output of the comparator 17 is logic "1", and an inverter normal pulse is produced by the AND gate 19 so that current flows in the coil 36 in the direction of arrow A when the correction pulses are produced.

Claims

1. An electronic timepiece including a stepping motor, means for producing a drive signal consisting of alternate pulses of opposite polarity and means for applying a series of correction pulses when a pulse of the driving signal is incapable of causing the rotor to rotate by one step as a result of one of a plurality of external conditions affecting the stepping motor, the series of correction pulses consisting of a plurality of pulse of different pulse widths each of which is selected to maximise performance of the stepping motor when affected by given external conditions.

2. An electronic timepiece substantially as herein described with reference to the accompanying drawings.

3. An electronic timepiece comprising a stepping motor consists of a stator, a rotor, a coil and the like, driving pulses having the minimum pulse width being applied to the stepping motor when the stepping motor drives normally and supplementary correcting pulses being applied to the stepping motor when the stepping motor doesn't drive normally, wherein said correcting pulses consists of several kinds of a series of pulses so as to correspond to any loads to thereby drive the stepping motor under any conditions of load.