Method of and a device for identifying the position of the rotor of a stepping motor

• US 4,683,428 A
• Filed: 07/17/1985
• Issued: 07/28/1987
• Est. Priority Date: 07/27/1984
• Status: Expired due to Term

• Current Assignee: Asulab SA (The Swatch Group AG)
• Original Assignee: Asulab SA (The Swatch Group AG)
• Inventors: Gete, Henri
• Primary Examiner(s): Karlsen, Ernest F.
• Assistant Examiner(s): Snow, Walter E.
• Application Number:
  US06/755,753
• Time in Patent Office: 741 Days
• Field of Search: 324/207, 324/208, 324/225, 318/696, 368/155, 368/156, 368/157, 368/184, 368/200, 368/202, 368/217, 368/218
• US Class Current: 324/207.25
• CPC Class Codes: G04C 3/143 Means to reduce power consumption by reducing pulse width or amplitude and related problems, e.g. detection of unwanted or missing step
• CPC Class Codes: H02P 6/185 using inductance sensing, e.g. pulse excitation

Abstract

The method according to the invention is applicable to motors comprising a magnetized rotor having two diametrically opposed poles, a stator making up a magnetic circuit having saturable constricted portions and a coil coupled magnetically to the stator. The method consists in applying to the coil an electric pulse, in measuring a control current (I'"'"'₀₁, I'"'"'₀₂) generated within the coil by the electric pulse at the end of a control time interval (t'"'"'_o -t_i) and in comparing the control current with a reference current (I_r), the sign of this comparison being representative of the position of the rotor. In order to take into account the variations in the characteristics of the motor with time, the control time interval (t'"'"'_o -t'"'"'_i) is readjusted periodically by means of first and second electric pulses of a learning signal applied to the coil. The first pulse of this signal generates within the coil a first current (I₁) which reaches the reference current (I_r) after a first time interval (t_a -t_i). The second pulse generates a second current (I₂) which reaches the reference current (I_r) after a second time interval (t_b -t_i). The mean value of the first and second time intervals is then taken as the value of the control time interval (t'"'"'_o -t_i). The device for carrying out this method enables the position of the rotor to be identified under optimal conditions and can be used with advantage in timepieces.

Claims

1. A method of identifying the angular rest position of the rotor of a stepping motor comprising a magnetized rotor having a pair of diametrically opposite poles liable to lie in two rest positions, a stator forming a magnetic circuit having saturable narrow portions and a coil coupled magnetically to the stator for setting up therein a magnetic field, said method comprising:

applying to said coil an electric control pulse;

measuring a control current, generated within the coil by said pulse, at the end of a control time interval counted from the beginning of said pulse;

comparing the control current with a first reference current; and

determining the sign of the comparison between the two currents, this sign being representative of the rest position of the rotor, characterized in that, to determine the control time interval, it further comprises;

applying to the coil a first electric pulse;

measuring a first current in the coil generated by the first electric pulse;

determining a first time interval corresponding to the time needed by the first current to reach a second reference current;

memorizing the first time interval;

applying to the coil a second electric pulse having the same amplitude as the first but of opposite polarity;

measuring a second current in the coil generated by the second electric pulse;

determining a second time interval corresponding to the time needed by the second current to reach the second reference current;

adding the second time interval to the first; and

determining the control time interval as a function of the sum of said first and second intervals.

2. A method as in claim 1, wherein said first and second reference currents are equal.

3. A method as in claim 1 or 2, wherein the control time interval is equal to the mean value of the first and second time intervals.

4. A device for determining the angular position of the rotor of a stepping motor comprising a magnetized rotor having a pair of diametrically opposite poles liable to lie in two rest positions, a stator forming a magnetic circuit having saturable narrow portions and a coil coupled magnetically to the stator for setting up therein a magnetic field, said device comprising:

means for generating an electric control pulse;

means for applying said pulse to the coil of the motor;

means for measuring a control current, generated in the coil by said pulse, at the end of a control time interval counted from the beginning of said pulse;

memory means for storing said control time interval;

means for comparing the control current with a first reference current and for generating a signal representative of the sign of the comparison, said sign indicating the angular position of the rotor, characterized in that it further comprises;

means for generating a first electric pulse;

means for applying said first pulse to the coil of the motor;

means for measuring a first current in the coil, generated by said first pulse;

means for determining a first time interval corresponding to the time needed by the first current to reach a second reference current;

means for generating a second electric pulse having the same amplitude as the first but of opposite polarity;

means for measuring a second current in the coil, generated by said second pulse;

means for determining a second time interval corresponding to the time needed by the second current to reach the second reference current;

means for adding the second time interval to the first; and

means for calculating the mean value of said two time intervals and for transferring said mean value into said memory means, said value being the control time interval.