POWER SCREWDRIVER

• US 20100116519A1
• Filed: 04/23/2008
• Published: 05/13/2010
• Est. Priority Date: 04/23/2007
• Status: Abandoned Application

• Current Assignee: Loesomat Schraubtechnik NEEF GmbH
• Original Assignee: Loesomat Schraubtechnik NEEF GmbH
• Inventors: Gareis, Marc
• Application Number:
  US12/451,013
• Publication Number:
  US 20100116519A1
• Time in Patent Office: Days
• US Class Current: 173/176
• CPC Class Codes: B25B 23/147 specially adapted for electrically operated wrenches or screwdrivers

Abstract

The invention relates to a power screwdriver (10) comprising a motor (12) as the drive, a desired torque default element (52) and an actual torque determination element (46), a torque gradient determination element (48) and a motor control (40) which controls the motor (12) depending on the torque gradient (dmd_lst/dt). The invention is characterized by a torque threshold determination element (50) which provides a torque threshold value (Md_Lim, Md_Lim1, Md_Lim2) that depends on the torque gradient (dmd_lst/dt) and lies below the desired torque value (Md_Soll). If the actual torque value (md_Ist) exceeds the torque threshold value (Md_Lim, Md_Lim1, Md_Lim2), a motor control (40) presets a speed reduction for the motor (12) or already completely switches off the motor (12). The power screwdriver (10) according to the invention avoids torque overshoots and yet allows the desired torque value (Md_Soll) to be exactly reached in the shortest time possible.

Claims

1. Power screwdriver with an electric motor (12) as the drive, with a desired torque specification element (52) and with an actual torque determination element (46), with a torque gradient determination element (48) and with an electric motor activator (40) which activates the electric motor (12) as a function of the torque gradient (dmd_Ist/dt), wherein a torque threshold definition element (50) is provided, wherein the torque threshold definition element (50) provides a torque threshold value (Md_Lim, Md_Lim1, Md_Lim2) which is dependent on the torque gradient (dmd_Ist/dt) and lies below the desired torque value (Md_Soll), and wherein the electric motor activator (40) specifies a speed reduction for the electric motor (12) or completely switches off the electric motor (12) if the actual torque value (md_Ist) exceeds the torque threshold value (Md_Lim, Md_Lim1, Md_Lim2).

2. Power screwdriver according to claim 1, wherein the electric motor activator (40) specifies the maximum possible speed of the electric motor (12) for the electric motor (12) in the case of an actual torque value (md_Ist) lying below the torque threshold value (Md_Lim, Md_Lim1, Md_Lim2).

3. Power screwdriver according to claim 1, wherein the torque threshold definition element (50) defines the difference (d1, d2) between the desired torque value (Md_Soll) and the torque threshold value (Md_Lim, Md_Lim1, Md_Lim2) as a function of the torque gradient (dmd_Ist/dt).

4. Power screwdriver according to claim 3, wherein the torque threshold definition element (50) defines the difference (d1, d2) as being greater at a higher torque gradient (dmd_Ist/dt) than at a lower torque gradient (dmd_Ist/dt).

5. Power screwdriver according to claim 1, wherein the torque threshold definition element (50) contains a table in which torque gradients (dmd_Ist/dt) and desired torque values (Md_Soll) are filed for defining the torque threshold value (Md_Lim, Md_Lim1, Md_Lim2).

6. Power screwdriver according to claim 1, wherein the torque threshold definition element (50) extrapolates the torque threshold value (Md_Lim, Md_Lim1, Md_Lim2) based on the determined torque gradient (dmd_Ist/dt), the actual torque value (md_Ist) and the desired torque value (Md_Soll).

7. Power screwdriver according to claim 1, wherein a motor current detector (44) is provided that detects the motor current (i_Mot) as a measure of the actual torque value (md_Ist).

8. Power screwdriver according to claim 1, wherein a data carrier (80) is provided in which characteristic values of the screwed connection and/or the power screwdriver (10) are stored and/or which is provided for storing collected data of a screwed connection or characteristic values of the power screwdriver (10).

9. Power screwdriver according to claim 8, wherein the power screwdriver (10) has means (82) for transmitting signals to a data carrier arranged outside the power screwdriver (10).

10. Power screwdriver according to claim 1, wherein a voltage limiter circuit (70) is provided that limits the motor voltage (u_Mot) occurring on the electric motor (12) to a specified limiting voltage (u_Lim) which is set at least to the nominal operating voltage of the electric motor (12).

11. Power screwdriver according to claim 10, wherein the voltage limiter circuit (70) contains a bipolar limiter diode (72).

12. Power screwdriver according to claim 10, wherein the voltage limiter circuit (70) contains a varistor (74).

13. Power screwdriver according to claim 1, wherein a battery (22) is provided for providing the supply voltage (u_Batt).

14. Power screwdriver according to claim 13, wherein the battery (22) is a lithium-based battery (Li ion battery, Li polymer battery).

15. Power screwdriver according to claim 13, wherein a battery voltage drop compensation circuit (60) is provided that compensates for the influence of a falling supply voltage (u_Batt) on the reaching of the set desired torque value (Md_Soll).

16. Power screwdriver according to claim 15, wherein the battery voltage drop compensation circuit (60) increases the set desired torque value (Md_Soll) or reduces the determined actual torque value (md_Ist) if the supply voltage (u_Batt) falls.