# US 10,312,840 B2 · Control circuit and control method for a synchronous machine

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- Number: US 10,312,840 B2
- Document ID: US10312840B2
- Status: Granted
- Kind: B2
- Application number: 15/118,634
- Filed: 2015-02-16
- Published: 2017-03-09
- Granted: 2019-06-04
- Earliest claimed: 2014-02-14
- Assignees: DENTSPLY SIRONA Inc.
- Applicants: DENTSPLY SIRONA Inc.
- Inventors: Hans-Walter Altendorf; Volker Hill
- Web page: https://patentgrep.com/patent/US10312840B2

## CPC

- H02P 6/182: using back-emf in windings
- H02P: CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS

## 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.

## Claims

### Claim 1

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.

### Claim 2 (depends on 1)

The control circuit according to claim 1, wherein the clamping circuit is clamped to the capacitor of the control circuit.

### Claim 3 (depends on 1)

The control circuit according to claim 1, wherein the control circuit has a preset voltage (11) which is connectable to the capacitor by a switch to pre-charge the capacitor to an expected voltage level of the star point.

### Claim 4

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.

### Claim 5 (depends on 4)

The method according to claim 4, wherein the EMF is measured with high impedance.

### Claim 6 (depends on 4)

The method according to claim 4, wherein the EMF is measured several times per rotation of the rotor.