Method for switching off a power tool

• US 20070068480A1
• Filed: 11/30/2004
• Published: 03/29/2007
• Est. Priority Date: 01/28/2004
• Status: Active Grant

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Wiker, Juergen, Walter, Roland, Heilmann, Andreas, Pauli, Mario, Hahn, Dietmar
• Granted Patent: US 7,372,226 B2
• Time in Patent Office: Days
• US Class Current: 123/198.D
• CPC Class Codes: B23Q 11/0092 actuating braking or stopping means
• CPC Class Codes: B23Q 11/04 Arrangements preventing overload of tools, e.g. restricting load
• CPC Class Codes: H02H 7/0854 responsive to rate of change of current, couple or speed, e.g. anti-kickback protection H02H7/0851 takes precedence

Abstract

The present invention is directed to a method for shutting off a drive motor (12) of a power tool that drives a tool, the drive motor (12) being shut off as a function of a variable threshold value (E₁) if the tool jams.

It is provided that the threshold value (E₁) is determined in at least one predetermined time interval (T₁) as a function of a current load speed (n₁) and a no-load speed (n₀).

Claims

1. A method for shutting off a drive motor (12) of a power tool that drives a tool, the drive motor (12) being shut off as a function of a variable threshold value (E₁) if the tool jams,

wherein

the threshold value (E₁) is determined in at least one predetermined time interval (T₁) as a function of a current load speed (n₁) and a no-load speed (n₀).

2. The method as recited in claim 1,

wherein

the threshold value (E₁) is determined as a function of a speed ratio (n₁/n₀) of the current load speed (n₁) and the no-load speed (n₀).

3. The method as recited in claim 1 or 2

wherein

the threshold value (E₁) is calculated as a product of the speed ratio (n₁/n₀) and a starting value (E₀).

4. The method as recited in claim 1,

wherein

the threshold value (E₁) is calculated as the rate of change of a rotational speed (dn/dt) with respect to time normalized for the no-load speed (n₀).

5. The method as recited in claim 1,

wherein

a current load speed (n₁) is compared with a numerical interval listed in a table—

the numerical interval relating to either a load speed or a no-load speed—

and is assigned to the new threshold value (E₁).

6. The method as recited in claim 5,

wherein,

at low load speeds (n₁), the threshold value (E₁) is lowered as a function of a selectable factor.

7. The method as recited in claim 1,

wherein

the threshold value (E₁) is rounded to a whole number.

8. The method as recited in claim 1,

wherein

the threshold value (E₁) is weighted with a setpoint/actual deviation of a rotational-speed regulator and/or a mechanical time constant of the power tool, and/or operating parameters of the power tools.

9. The method as recited in claim 1,

wherein

rotational speed pulses (J₁, J₂) are counted in two consecutive first and second time intervals (T₁, T₂) and are subsequently used to determine the speeds (n₁ n₂), the rotational speed (n₂) determined in the second time interval (T₂) being subtracted from the rotational speed (n₁) determined in the first time interval (T₁) and, if the difference (n₁−

n₂) is greater than the threshold value (E₁), the drive motor (12) is shut off.

10. A power tool with a tool which is drivable by a drive motor (12), with which means are provided to shut off the drive motor (12) as a function of a variable threshold value (E₁) if the tool is jammed,

wherein

the means include at least one detection unit and/or an arithmetic-logic unit to determine at least one threshold value (E₁) which is a function of at least two variables (n₁, n₀).

11. The power tool as recited in claim 10,

wherein

the means include a microcontroller (16) connected with a rotational-speed detection unit (18) and a rotational-speed regulator, it being possible to determine the threshold value (E₁) in a variable manner based on a rotational-speed signal and/or a rotational-speed change signal from the rotational-speed detection unit (18), and a setpoint/actual deviation of a rotational-speed regulator and/or a mechanical time constant of the power tool.

12. The power tool as recited in claim 10,

wherein

the means include a rotational-speed regulating electronic unit (16) for controlling motor voltage and/or motor current.