Control method of a direct current electric motor

Patent metadata

Field	Value
Publication number	US-11063537-B2
Application number	US-201916656848-A
Country	US
Kind code	B2
Filing date	Oct 18, 2019
Priority date	Dec 6, 2018
Publication date	Jul 13, 2021
Grant date	Jul 13, 2021

Abstract

The present invention concerns a method of controlling a rotational speed of a rotor (3) of a direct current electric motor (1) comprising an inductor circuit (A, B) for rotating the rotor, which is configured to rotate continuously and is equipped with permanent magnets. The method comprises: measuring the rotational speed of the rotor; determining a time drift in the rotor rotation compared to a reference signal; defining N speed thresholds with at least one being a variable speed threshold depending on the determined time drift, the N speed thresholds defining N+1 rotational speed ranges for the rotor; determining in which one of the N+1 rotational speed ranges the determined rotational speed of the rotor is; and finally selecting an action relative to the control of the inductor circuit, based on the determined rotational speed range, for controlling the rotational speed of the rotor.

First claim

The invention claimed is:

1. A control method of a direct current electric motor ( 1 ) comprising a rotor ( 3 ) and an inductor circuit (A, B) for driving the rotor, which is configured to rotate continuously and is equipped with permanent magnets, the method comprising the following steps:
from a start time point, measuring ( 101 , 111 , 115 ) a time drift (Cv) in the rotor rotation by comparing a detected number of rotation cycles of the rotor with a reference number of nominal rotation cycles for the rotor corresponding to a nominal rotational speed, the nominal rotation cycles being determined by a reference clock signal;
defining ( 121 , 125 , 129 , 131 , 141 ) N speed threshold(s) with N being greater than zero, at least one of the speed threshold(s) being a variable speed threshold (dt_T 1 , dt_T 2 ) depending on the measured time drift in the rotor rotation, the N speed threshold(s) defining N+1 rotational speed ranges for the rotor;

the method further comprising a periodic sequence of the following steps;
measuring ( 105 ) a time parameter (dt_Peak) of the direct current electric motor, the value of which is determined by the rotational speed of the rotor;
adjusting the at least one variable speed threshold in function of the current value of the time drift;
based on the measured time parameter, determining ( 133 , 137 , 141 ) in which one of the N+1 rotational speed ranges the rotational speed of the rotor is; and
selecting ( 135 , 139 , 143 ) an action among a group of different defined actions relative to the control of an electrical current through the inductor circuit, based on the determined rotational speed range in the preceding step, to control the rotational speed of the rotor.

2. The control method according to claim 1 , with N being greater than one; wherein at least one of the N speed thresholds is a fixed threshold.

3. The control method according to claim 1 , wherein the inductor circuit (A, B) comprises a first inductor (A) and a second inductor (B), the rotation of the rotor ( 3 ) inducing a first induced voltage across the first inductor (A) and a second induced voltage across the second inductor (B); and wherein the time parameter is a time difference between two consecutive crossings of the first and second induced voltages.

4. The control method according to claim 1 , wherein the group of different defined actions comprises the following actions: applying one or more energy pulses across at least a portion of the inductor circuit; no drive action; and short-circuiting at least a portion of the inductor circuit.

5. The control method according to claim 4 , wherein the group of different defined actions comprises a first action in which a first voltage pulse, with a first voltage level and a first duration, is applied and a second action in which a second voltage pulse, with a second voltage level and a second duration, is applied; and wherein the second voltage level is lower than the first voltage level.

6. The control method according to claim 5 , wherein the second duration is shorter than the first duration.

7. The control method according to claim 1 , wherein there are a plurality of variable speed thresholds; and wherein, if the time drift in the rotor rotation is determined to correspond to substantially zero or to a given small time advance, the variable speed thresholds are selected such as to allow substantially maintaining the current rotational speed of the rotor.

8. The control method according to claim 7 , wherein, if the time drift in the rotor rotation is determined to correspond to at least a given time advance, the variable speed thresholds are selected such as to allow slowing down the rotational speed of the rotor.

9. The control method according to claim 7 , wherein, if the time drift in the rotor rotation is determined to correspond to at least a given time delay, the variable speed thresholds are selected such as to allow accelerating the rotational speed of the rotor.

10. The control method according to claim 1 , wherein the direct current electric motor ( 1 ) is of the horological type and intended to be incorporated, with its control unit implementing the method, in an electromechanical watch movement.

Assignees

• Swatch Group Res & Dev Ltd

Inventors

• Born Jean-Jacques
• Germiquet Christophe
• Nagy Laurent

Classifications

• G04C3/16 Primary

  incorporating an electro-dynamic continuously rotating motor (G04C3/02 - G04C3/12 take precedence) · CPC title

• H02P6/14 Primary

  Electronic commutators · CPC title

• H02P6/06

  Arrangements for speed regulation of a single motor wherein the motor speed is measured and compared with a given physical value so as to adjust the motor speed · CPC title

• H02K21/24

  with magnets axially facing the armatures, e.g. hub-type cycle dynamos · CPC title

• H02P7/2855 Primary

  whereby the speed is regulated by measuring the motor speed and comparing it with a given physical value · CPC title