Control circuit and control method for a synchronous machine
AssigneeDENTSPLY SIRONA Inc.
InventorsHans-Walter Altendorf, Volker Hill
Life of this patent
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Abstract
The invention relates to a control circuit for a synchronous machine (1) of a dental handpiece, comprising a voltage supply (2) and a clamping circuit (7) connected by switches (6). The invention also relates to a method for determining an angular position of a rotor of a synchronous machine (1), wherein a power supply is switched off for a total period of time (T2), a clamping circuit (7) is connected for a time interval (T1), whereupon an electromotive force is measured, and the angular position is determined from the electromotive force.
Claims6
A control circuit for a synchronous machine of a dental handpiece for controlling a rotary speed of the synchronous machine comprising a power supply having gate driver switches,
- wherein outputs from the gate driver switches are connected via leads to stator windings of a motor having a star point;
- a clamping circuit comprising clamping switches, resistors and a capacitor;
- wherein the capacitor is connected across the resistors and the clamp switches to the stator windings of the motor for a demagnetization of the synchronous machine after closing the clamping switches;
- and
- wherein the capacitor simulates a star point voltage.
A method for determining the angular position of a rotor of a synchronous machine for controlling a rotary speed of the synchronous machine, comprising:
- (a) providing a control circuit for the synchronous machine comprising a power supply having gate driver switches, wherein outputs from the gate driver switches are connected via leads to stator windings of a motor having a star point;
- a clamping circuit comprising clamping switches, resistors and a capacitor;
- wherein the capacitor is connected across the resistors and the clamp to the stator windings of the motor;
- (b) passively simulating a star point voltage by charging the capacitor to an expected value of the star point wherein the capacitor is connected to a preset voltage by a switch;
- (c) interrupting a power supply to the synchronous machine for a total period of time (T2) by opening gate driver switches;
- (d) closing the clamp switches for a total period of time (T1) while the synchronous machine is still rotating;
- (e) opening the clamp switches after the time interval (T1);
- (f) measuring an induced electromagnetic force (EMF) during a time interval (T3), and
- (g) determining the angular position of the rotor from the EMF.
Dependencies are inferred from the claim text.