Method for switching off a power tool

• US 7,372,226 B2
• Filed: 11/30/2004
• Issued: 05/13/2008
• Est. Priority Date: 01/28/2004
• Status: Active Grant

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Heilmann, Andreas, Wiker, Juergen, Walter, Roland, Pauli, Mario, Hahn, Dietmar
• Primary Examiner(s): Donovan; Lincoln
• Assistant Examiner(s): Brandt; Michael
• Application Number:
  US10/557,936
• Publication Number:
  US 20070068480A1
• Time in Patent Office: 1,260 Days
• Field of Search: 318/461, 173/181, 173/176, 173/179
• US Class Current: 318/367
• 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

In a method for shutting off a drive motor (12) of a power tool that drives a tool, the drive motor (12) is shut off as a function of a variable threshold value (E₁) if the tool jams. 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), 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), and wherein, at low load speeds (n₁), the threshold value (E₁) is lowered as a function of a selectable factor.

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

5. The method as recited in claim 1, wherein the threshold value (E₁) is rounded to a whole number.

6. 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.

7. 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), 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.

8. A power tool with a tool that is drivable by a drive motor, comprising:

means for shutting off the drive motor (12) as a function of a variable threshold value (E₁) if the tool is jammed, 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), 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), and wherein_at low load speeds(n₁), the threshold value (E₁) is lowered as a function of a selectable factor.

9. A power tool with a tool that is drivable by a drive motor, comprising:

means for shutting off the drive motor (12) as a function of a variable threshold value (E₁) if the tool is jammed, 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), 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 shutoff.