Electric work machine

Patent metadata

Field	Value
Publication number	US-2023144684-A1
Application number	US-202217982649-A
Country	US
Kind code	A1
Filing date	Nov 8, 2022
Priority date	Nov 11, 2021
Publication date	May 11, 2023
Grant date	—

Abstract

The electric work machine in one aspect of the present disclosure includes an output shaft, a motor, a current measuring circuit, and a controller. The current measuring circuit measures a current value, the current value corresponding to a magnitude of a drive current flowing through the motor. The controller sets a maximum value and a threshold. The controller calculates the correction value less than or equal to the maximum value so that the drive current decreases, in response to the current value having reached the threshold. The controller subtracts, from the control parameter, the correction value calculated, thereby correcting the control parameter. The controller drives the motor based on the control parameter corrected.

First claim

What is claimed is:

1 . An electric driver drill comprising:
an output shaft configured to be detachably attached to a tool bit; a motor configured to drive the output shaft; a mode selector configured to be manually rotated by a user of the electric driver drill to select a first mode from a clutch mode and a drill mode; a gear selector configured to be manually moved by the user to select a second mode from a high speed mode and a low speed mode; a trigger switch configured to be pulled by the user to drive the motor; a current measuring circuit configured to measure a current value, the current value corresponding to a magnitude of a drive current flowing through the motor; a memory device storing a first map, a second map, and a third map,
the first map associating the clutch mode, the drill mode, the high speed mode, and the low speed mode with a first limit threshold, a second limit threshold, a third limit threshold, and a fourth limit threshold,
the second map associating a first pulled distance of the trigger switch and a second pulled distance of the trigger switch respectively with a first desired rotational speed of the motor and a second desired rotational speed of the motor, and
the third map associating the first desired rotational speed and the second desired rotational speed respectively with a first reference value of a duty ratio of a pulse width modulated signal and a second reference value of the duty ratio of the pulse width modulated signal; and
a control circuit programed to
obtain an actual pulled distance of the trigger switch,
set one of the first limit threshold, the second limit threshold, the third limit threshold, and the fourth limit threshold based on (i) the first mode selected, (ii) the second mode selected, and (iii) the first map,
set a first maximum value and a second maximum value based on (i) the first mode selected and (ii) the second mode selected, the first maximum value corresponding to a maximum limit of a first amount of limitation, the second maximum value corresponding to a maximum limit of a second amount of limitation, the first amount of limitation corresponding to a control variable to reduce a rotational speed of the motor, the second amount of limitation corresponding to a control variable to reduce the duty ratio,
calculate a difference between the current value measured and the one of the first limit threshold, the second limit threshold, the third limit threshold, and the fourth limit threshold set,
integrate a first variation, thereby calculating the first amount of limitation, the first variation being calculated by multiplying the difference by a first gain,
set the first maximum value to the first amount of limitation in response to the first amount of limitation calculated being more than or equal to the first maximum value,
integrate a second variation, thereby calculating the second amount of limitation, the second variation being calculated by multiplying the difference by a second gain,
set the second maximum value to the second amount of limitation in response to the second amount of limitation calculated being more than or equal to the second maximum value,
obtain the first desired rotational speed or the second desired rotational speed based on the actual pulled distance obtained and the second map,
subtract the first amount of limitation from first desired rotational speed or the second desired rotational speed obtained, thereby calculating a third desired rotational speed,
obtain the first reference value or the second reference value based on the third desired rotational speed calculated and the second map,
correct the first reference value or the second reference value based on a speed difference, thereby calculating a set value of the duty ratio, the speed difference corresponding to a difference between the third desired rotational speed an actual rotational speed of the motor,
subtract the second amount of limitation from the set value, thereby calculating an output value of the duty ratio, and
drive the motor based on the pulse width modulated signal having the output value.

2 . An electric work machine, comprising:
an output shaft configured to be attached to or being connected to a tool; a motor configured to drive the output shaft; a current measuring circuit configured to measure a current value, the current value corresponding to a magnitude of a drive current flowing through the motor; and a controller configured to
set a maximum value and a threshold,
calculate the correction value less than or equal to the maximum value so that the drive current decreases, in response to the current value having reached the threshold,
subtract, from the control parameter, the correction value calculated, thereby correcting the control parameter, and
drive the motor based on the control parameter corrected.

3 . The electric work machine according to claim 2 ,
wherein the controller is configured to
calculate a variation based on a first difference and a first gain, and
integrate the variation calculated, thereby calculating the correction value, and
wherein the first difference corresponds to a value obtained by subtracting the threshold from the current value measured by the current measuring circuit.

4 . The electric work machine according to claim 2 ,
wherein the control parameter includes a rotational speed of the motor, a voltage applied to the motor, or a duty ratio of a pulse voltage applied to the motor,

5 . The electric work machine according to claim 2 , further comprising a mode selector configured to be manually operated by a user of the electric work machine to select a first mode or a second mode,
wherein the controller is configured to (i) change the maximum value and (ii) drive the motor based on the first mode or the second mode selected by the user through the mode selector.

6 . The electric work machine according to claim 5 ,
wherein the mode selector is further configured to be manually operated by the user to select a third mode, and wherein the controller is configured to allow the correction value to exceed the maximum value in response to the third mode being selected by the user through the mode selector.

7 . The electric work machine according to claim 5 ,
wherein the first mode is a drill mode to drill a hole in a workpiece, wherein the second mode is a clutch mode to fasten a screw, wherein the controller is configured to set a first value for the first mode, and set a second value distinct from the first value for the second mode, wherein the first value is the maximum value corresponding to the drill mode, and wherein the second value is the maximum value corresponding to the clutch mode.

8 . The electric work machine according to claim 7 ,
wherein the controller is configured to make the first value larger than the second value.

9 . The electric work machine according to claim 7 ,
wherein the controller is configured to set a third value for the first mode, and set a fourth value distinct from the third value for the second mode, wherein the third value is the threshold corresponding to the drill mode, and wherein the fourth value is the threshold corresponding to the clutch mode.

10 . The electric work machine according to claim 9 ,
wherein the controller is configured to make the third value smaller than the fourth value.

11 . The electric work machine according to claim 2 , further comprising:
two or more gears configured to transmit a rotation of the motor to the output shaft at a first deceleration ratio or a second deceleration ratio, the second deceleration ratio being larger than the first

Assignees

• Makita Corp

Inventors

• Kato Itsuku

Classifications

• B25B23/147 Primary

  specially adapted for electrically operated wrenches or screwdrivers · CPC title

• B23B45/02 Primary

  driven by electric power · CPC title

• B25F3/00

  Associations of tools for different working operations with one portable power-drive means; Adapters therefor · CPC title