ELECTRIC TOOL AND CONTROLLING METHOD THEREOF

• US 20110303427A1
• Filed: 01/04/2010
• Published: 12/15/2011
• Est. Priority Date: 01/04/2009
• Status: Active Grant

• Current Assignee: Positec Power Tools Company Limited (Positec Group Limited)
• Original Assignee: Positec Power Tools Company Limited (Positec Group Limited)
• Inventors: Tang, Xiangyang
• Granted Patent: US 9,162,331 B2
• Time in Patent Office: Days
• US Class Current: 173/1
• CPC Class Codes: B23P 19/066 by electrical means
• CPC Class Codes: B25B 23/14 Arrangement of torque limiters or torque indicators in wrenches or screwdrivers couplings for transmitting rotation or clutches F16D; devices for measuring torque per se G01L
• CPC Class Codes: B25B 23/147 specially adapted for electrically operated wrenches or screwdrivers
• CPC Class Codes: G05D 17/02 characterised by the use of electric means
• CPC Class Codes: H02P 29/02 Providing protection against overload without automatic interruption of supply protection against faults of stepper motors H02P8/36
• CPC Class Codes: H02P 3/08 for stopping or slowing a dc motor
• CPC Class Codes: H02P 7/285 controlling armature supply only
• CPC Class Codes: H02P 7/29 using pulse modulation

Abstract

A power tool including a motor for rotatably driving a tool bit at an attained rotational speed, a source for supplying an electric current to the motor, a sensor for measuring the current, and a control device. The control component fulfils the task of detecting a variation of the slope of the current in the course of time, and generates a control signal. The rotational speed of the tool is reduced in response to the control signal. The power tool automatically detects whether the work piece operated by the tool bit reaches a predetermined position by electronic control means. It may make sure that the screw is driven into a piece of wood and does not go beyond the predetermined position once it detects that the work piece reaches the position and carries out a changing action.

Claims

1. A method for controlling an electric tool, the electric tool comprising an electric motor and an output shaft which is driven by the electric motor and configured for outputting a rotary torque to drive a tool bit to work on a work piece;

the method comprising;

measuring a parameter representing the load on the output shaft in dependence on time,

calculating a second or higher derivative of the parameter in dependence on time,

generating a control signal according to the second or higher derivative, and

changing a rotational speed of the electric tool in response to the control signal.

2. The method according to claim 1, wherein the parameter is a current supplied to the electric tool.

3. The method according to claim 1, wherein the parameter is one of a rotational speed of the output shaft, a voltage of the electric motor, the rotational speed of the electric motor, and the efficiency of the electric motor.

4. The method according to claim 1, wherein the electric tool further comprises a housing and a planetary gear mechanism accommodated in the housing, the planetary gear mechanism comprising a planet carrier, a planet wheel arranged on the planet carrier and a gear ring arranged around the planet wheel, the parameter is one of a rotational speed of the planet carrier, the displacement of the gear ring relative to the housing, and a pressure of the gear ring applied to the housing.

5. The method according to claim 2, further comprising presetting a predetermined threshold value before generating the control signal.

6. The method according to claim 5, wherein the control signal is generated only when the function value of the second or higher derivative is greater than or equal to the predetermined threshold value.

7. The method according to claim 6, wherein the function includes a function factor of the product of the second derivative and a first derivative.

8. The method according to claim 7, wherein the control signal is generated only when the absolute value of the product of the second or higher derivative and the first derivative of the current is greater than or equal to the predetermined threshold value.

9. The method according to claim 6, wherein the control signal is generated only when the absolute value of the product of the second or higher derivative and the current is greater than or equal to the predetermined threshold value.

10. The method according to claim 1, wherein the control signal is configured to set the rotational speed of the electric tool at a low-speed level or zero, and the control signal is generated instantly or after the preset delay time.

11. An electric tool, comprising:

an output shaft,

an electric motor configured to drive the output shaft to rotate,

a power supply for supplying power to the electric motor,

a sensor for measuring a parameter representing the load on the output shaft, and

a control component configured to calculate a second or higher derivative of the parameter in dependence on time, and generate a control signal according to the second or higher derivative to change a rotational speed of the electric motor.

12. The electric tool according to claim 11, wherein the parameter is current, the control component is further configured to preset a predetermined threshold value, and the control signal is generated only when the function value of the second or higher derivative is greater than or equal to the predetermined threshold value.

13. The electric tool according to claim 12, wherein the control signal is generated only when the absolute value of the product of the second or higher derivative and the current is greater than or equal to the predetermined threshold value.

14. The electric tool according to claim 12, wherein the control signal is generated only when the absolute value of the product of the second or higher derivative and the first derivative of the current is greater than or equal to the predetermined threshold value.

15. The electric tool according to claim 11, wherein the control signal is configured to set the rotational speed of the electric tool at a low-speed level or zero, and the control signal is generated instantly or after preset delay time.

16. The electric tool according to claim 12, wherein the parameter is one of a rotational speed of the output shaft, a voltage of the electric motor, the rotational speed of the electric motor and the efficiency of the electric motor.

17. The electric tool according to claim 12, further comprising a housing and a planetary gear mechanism accommodated in the housing, the planetary gear mechanism comprising a planet carrier, a planet wheel arranged on the planet carrier and a gear ring arranged around the planet wheel, the parameter is one of a rotational speed of the planet carrier, the displacement of the gear ring relative to the housing, and a pressure of the gear ring applied to the housing.

18. A method for controlling an electric tool, comprising:

measuring a parameter representing the load on the electric tool in dependence on time,

calculating a second or higher derivative of the parameter in dependence on time,

generating a control signal according to the second or higher derivative, and

changing the rotational speed of the electric tool in response to the control signal.

19. An electric tool, comprising:

a sensor for measuring a parameter representing the load on the electric tool, and

a control component configured to calculate a second or higher derivative of the parameter in dependence on time, and to generate a control signal according to the second or higher derivative to change a rotational speed of the electric tool.