Method of controlling a motor

• US 7,791,297 B2
• Filed: 08/30/2007
• Issued: 09/07/2010
• Est. Priority Date: 09/04/2006
• Status: Active Grant

• Current Assignee: Hilti Aktiengesellschaft (Hilti Martin Family Trust)
• Original Assignee: Hilti Aktiengesellschaft (Hilti Martin Family Trust)
• Inventors: Mueller, Thomas, Looser, Markus, Baxivanelis, Konstantin, Stempfhuber, Johannes, Meiendres, Germar
• Primary Examiner(s): Ro; Bentsu
• Assistant Examiner(s): Luo; David S
• Application Number:
  US11/897,387
• Publication Number:
  US 20080054832A1
• Time in Patent Office: 1,104 Days
• Field of Search: 318/434, 361/23, 361/31, 361/33
• US Class Current: 318/434
• CPC Class Codes: H02P 1/04 Means for controlling progress of starting sequence in dependence upon time or upon current, speed, or other motor parameter
• CPC Class Codes: H02P 1/166 Driving load with high inertia
• CPC Class Codes: H02P 29/032 Preventing damage to the motor, e.g. setting individual current limits for different drive conditions

Abstract

A method for controlling a motor (2) which drives a disk-shaped tool (4) of a power tool (1) and to which a motor voltage in the amount of a nominal value is applied in an “on” position of a motor switch (6), includes determination of an actual motor current (IM) applied to the motor (2) and comparing it to a first predetermined threshold (GW1), and automatically triggering of a control process for protecting the motor (2) when an overload condition which is defined in that the first predetermined threshold (GW1) is exceeded beyond a first predetermined limiting time period (grDt1), is met, the control process including reduction of the motor voltage applied to the motor (2) by a magnitude that can be perceived by the user as a choke value.

Claims

1. A method for controlling a motor (2) for driving a disk-shaped tool (4) of a power tool (1) and to which a motor voltage in the amount of a nominal value is applied in an “

on”

position of a motor switch (6), comprising the first step of determining an actual motor current (IM) applied to the motor (2) and comparing it to a first predetermined threshold (GW1); and

a second step of automatically triggering a control process for protecting the motor (2) from overloading when an overload condition, which is defined in that the first predetermined threshold (GW1) is exceeded beyond a first predetermined limiting time period (grDt1), is met, the control process including reducing the motor voltage applied to the motor (2) by a magnitude that can be perceived by a user as a choke value; and

further steps of counting overload events during which the overload conditions are met when they follow one another within a predetermined limiting time period, and turning the motor (2) off after a predetermined quantity of counted overload events.

2. A method according to claim 1, wherein the choke value is at most 75% of the nominal value.

3. A method according to claim 1, comprising the step of increasing the motor voltage relative to the choke value, with the motor voltage reaching the nominal value again, at the earliest, after expiration of a predetermined choking period (DDt).

4. A method according to claim 3, wherein the predetermined choking period (DDt) is at most 1 second.

5. A method according to claim 1, wherein the first limiting time period (grDt1) is at most 1 second.

6. A method according to claim 1, wherein the actual motor current determining step includes comparing the actual motor current (IM) to a second threshold (GW2) that is higher than the first threshold (GW1), and wherein with the second threshold (GW2) being exceeded beyond a second predetermined limiting time period (grDt2) which is less than the first predetermined limiting time period (grDt1), the motor voltage is reduced to the choke value in the second step.

7. A method according to claim 1, wherein output of the motor (2) is reduced by pulse width modulation.