Systems and methods for detecting anvil position using an inductive sensor

Patent metadata

Field	Value
Publication number	US-12240085-B2
Application number	US-202117339820-A
Country	US
Kind code	B2
Filing date	Jun 4, 2021
Priority date	Jun 4, 2020
Publication date	Mar 4, 2025
Grant date	Mar 4, 2025

Abstract

A power tool including a housing, a brushless direct current (DC) motor, an impact mechanism including a hammer and an anvil, an output drive device, a position sensor, and a controller. The power tool also includes a target positioned on a shaft, a magnetic shield positioned on the shaft between the target and the anvil, and a position sensor. The position sensor includes an inductive sensor, a first transmitting circuit trace, and a first receiving circuit trace. The controller is configured to calculate a drive angle based on the determined position of the anvil, and control the brushless DC motor based on the drive angle of the anvil.

First claim

We claim:

1. A power tool comprising:
a housing;
a brushless direct current (DC) motor within the housing, wherein the brushless DC motor includes a rotor and a stator, wherein the rotor is coupled to a motor shaft to produce a rotational output;
an impact mechanism including:
a hammer coupled to the motor shaft, and
an anvil including anvil lugs configured to receive impacts from the hammer;

an output drive device including a shaft coupled to the anvil and configured to rotate to perform a task;
a target positioned on the shaft;
a magnetic shield positioned on the shaft between the target and the anvil, and configured to magnetically isolate the anvil lugs from the target; and
a position sensor including:
an inductive sensor positioned proximate the target,
a first transmitting circuit trace, and
a first receiving circuit trace, wherein the inductive sensor is configured to inject a signal on the first transmitting circuit trace and detect a first output signal on the first receiving circuit trace to determine a position of the anvil; and

a controller coupled to the position sensor and configured to:
calculate a drive angle of the anvil caused by the impact based on the determined position of the anvil, and
control the brushless DC motor based on the drive angle of the anvil.

2. The power tool of claim 1 , wherein, to calculate the drive angle, the controller is configured to:
determine a first rotational position of the anvil upon a first impact between the hammer and the anvil based on the first output signal,
determine a second rotational position of the anvil upon a second impact between the hammer and the anvil based on the first output signal, and
determine a drive angle experienced by the output drive device based on the first rotational position and the second rotational position.

3. The power tool of claim 2 , wherein, to determine the drive angle experienced by the output drive device based on the first rotational position and the second rotational position, the controller is configured to:
determine a difference between the second rotational position and the first rotational position,
subtract a predetermined angle from the difference between the second rotational position and the first rotational position, and
determine the drive angle experienced by the output drive device based on the difference between the second rotational position and the first rotational position subtracted by the predetermined angle.

4. The power tool of claim 2 , wherein the controller is configured to:
control the brushless DC motor based on the drive angle experienced by the output drive device by adjusting a speed of the brushless DC motor based on the drive angle experienced by the output drive device.

5. The power tool of claim 1 , wherein, to control the brushless DC motor based on the drive angle, the controller is configured to:
determine a rotation count by accumulating a value for each calculated drive angle of the anvil below a drive angle threshold of a plurality of calculated drive angles of the anvil, and
reduce a speed of the brushless DC motor in response to determining that the rotation count is greater than a rotation threshold.

6. The power tool of claim 5 , further comprising:
a transceiver coupled to the controller, wherein the controller is configured to receive, wirelessly from an external device via the transceiver, the rotation threshold.

7. The power tool of claim 1 , wherein, to control the brushless DC motor based on the drive angle, the controller is configured to:
determine whether the drive angle of the anvil is less than a drive angle threshold, and
reduce a speed of the brushless DC motor in response to determining that the drive angle of the anvil is less than the drive angle threshold.

8. The power tool of claim 1 , wherein, to control the brushless DC motor based on the drive angle of the anvil, the controller is configured to:
determine whether the drive angle of the anvil is less than a drive angle threshold,
increment an impact counter for a detected impact in response to determining that the drive angle of the anvil is less than the drive angle threshold,
determine whether the impact counter has reached an impact counter threshold, and
reduce a speed of the brushless DC motor in response to determining that the impact counter has reached the impact counter threshold.

9. The power tool of claim 8 , further comprising: a transceiver coupled to the controller, wherein the controller is configured to receive, wirelessly from an external device via the transceiver, a finishing speed, and
wherein the controller, to reduce the speed of the brushless DC motor in response to determining that the impact counter has reached the impact counter threshold, is configured to reduce the speed of the brushless DC motor from a first speed to the finishing speed.

10. The power tool of claim 1 , wherein the position sensor further comprises:
a second receiving circuit trace, wherein the inductive sensor is configured to
detect a second output signal on the second receiving circuit trace, and
determine the position of the anvil based on the first output signal and the second output signal.

11. The power tool of claim 10 , wherein the target includes:
a first target lug that overlaps the first receiving circuit trace and the second receiving circuit trace circuit during a first portion of a rotation path of the anvil, and
a second lug target that overlaps the first receiving circuit trace and the second receiving circuit trace circuit during a second portion of the rotation path of the anvil.

12. An impact power tool comprising:
a housing;
a brushless direct current (DC) motor within the housing, wherein the brushless DC motor includes a rotor and a stator, wherein the rotor is coupled to a motor shaft to produce a rotational output;
an impact mechanism including:
a hammer connected to the motor shaft, and
an anvil including anvil lugs configured to receive impacts from the hammer;

an output drive device including a shaft coupled to the anvil and configured to rotate to perform a task;
a target positioned on the shaft;
a magnetic shield positioned on the shaft between the target and the anvil, and configured to magnetically isolate the anvil lugs from the target; and
a position sensor including:
an inductive sensor positioned proximate the target,
a first transmitting circuit trace, and
a first receiving circuit trace, wherein the inductive sensor is configured to inject a signal on the first transmitting circuit trace and detect a first output signal on the first receiving circuit trace; and

a controller coupled to the position sensor and configured to:
receive, from the position sensor, a first position signal from the position sensor at a first time,
receive a second position signal from the position sensor at a second time,
calculate a drive angle of the anvil based on the first position signal and the second position signal,
control the brushless DC motor based on the drive angle of the anvil.

13. The impact power tool of claim 12 , wherein the position sensor includes:
a second receiving circuit trace, wherein the inductive sensor is configured to:
detect a second output signal on the second receiving circuit trace, and
determine the position of the anvil based on the first output signal and the second output signal.

14. The impact power tool of claim 12 , wherein, to control the brushless DC motor based on the drive angle of the anvil, the controller is configured to reduce a speed of the brushless DC motor.

Assignees

• Milwaukee Electric Tool Corp

Inventors

• Schneider Jacob P
• Fieldbinder Douglas R
• Merget Maxwell L

Classifications

• H02K7/145

  Hand-held machine tool · CPC title

• H02K11/21

  Devices for sensing speed or position, or actuated thereby (specially adapted for machines having non-mechanical commutating devices H02K29/06, H02K29/14) · CPC title

• H02K11/33

  Drive circuits, e.g. power electronics (H02K11/38 takes precedence) · CPC title

• H02P6/16

  Circuit arrangements for detecting position · CPC title

• B25B21/02

  with means for imparting impact to screwdriver blade or nut socket · CPC title