Power tools

• US 20040182588A1
• Filed: 02/04/2004
• Published: 09/23/2004
• Est. Priority Date: 02/05/2003
• Status: Active Grant

• Current Assignee: Makita Corporation
• Original Assignee: Makita Corporation
• Inventors: Ishikawa, Goshi, Tokunaga, Manabu
• Granted Patent: US 6,968,908 B2
• Time in Patent Office: Days
• US Class Current: 173/2
• CPC Class Codes: B25B 21/02 with means for imparting impact to screwdriver blade or nut socket
• CPC Class Codes: B25B 23/1453 for impact wrenches or screwdrivers
• CPC Class Codes: B25B 23/1475 for impact wrenches or screwdrivers

Abstract

Power tool (11) may include a motor and oil pulse unit (22) that generates an elevated torque. Oil pulse unit (22) may be coupled to the motor and have output shaft (18). When load acting on output shaft (18) is less than a predetermined value, rotating torque generated by the motor is directly transmitted to output shaft (18). When the load acting on output shaft (22) exceeds the predetermined value, an elevated torque is generated by oil pulse unit (22) and applied to output shaft (18). Output shaft (18) may be connected to load shaft (12). A socket may be attached to the distal end of load shaft (12). Power tool (11) may further include detecting device (20) for detecting change in rotational angle of output shaft (18) and the direction of rotation thereof, and a control device. The detecting device (20) may output signals corresponding to a state of output shaft (18) to the control device. The control device may store the state of output shaft (18) at predetermined interval. Preferably, the control device may further determine a generating time, at which oil pulse unit (22) generates the elevated torque, based upon the state of output shaft (18).

Claims

1. A power tool adapted to tighten a fastener, comprising:

a motor,

means for generating an elevated torque, wherein the elevated torque generating means is coupled to the motor and has output shaft, wherein if a load acting on the output shaft is less than a predetermined value, rotating torque generated by the motor is directly transmitted to the output shaft and if a load acting on the output shaft exceeds the predetermined value, an elevated torque is generated by the elevated torque generating means and applied to the output shaft,

a load shaft connected to the output shaft,

means for detecting change in rotational angle of either the output shaft or the load shaft and the direction of rotation thereof,

a memory for storing a state of either output shaft or the load shaft detected by the detecting means, and

a processor in communication with the motor, the detecting means and the memory, the detecting means communicating signals corresponding to the state of either the output shaft or the load shaft to the processor, wherein the processor stores the state of either the output shaft or the load shaft in the memory at predetermined interval, and wherein the processor determines a generating time, at which the means for generating an elevated torque generates the elevated torque, based upon the state of either the output shaft or the load shaft.

2. A power tool as in claim 1, wherein the means for generating an elevated torque comprises;

an anvil, and

a hammer coupled to the motor, the hammer being adapted to strike the anvil to thereby rotate the anvil and generate the elevated torque.

3. A power tool as in claim 1, wherein the means for generating an elevated torque comprises an oil pulse unit.

4. A power tool as in claim 1,wherein the detecting means comprises:

a plurality of magnets disposed around an outer surface of either the output shaft or the load shaft so that the magnets integrally rotate with the output shaft or the load shaft, each magnet having a South pole and a North pole, wherein the South poles are disposed in an alternating relationship with the North poles,

a first sensor fixedly disposed relative to the magnets, such that the first sensor will not rotate when the output shaft or load shaft rotates, wherein the first sensor latches its output signal to a first level when detecting a North pole magnetic field, and latches its output signal to a second level when detecting a South pole magnetic field, and

a second sensor fixedly disposed relative to the magnets, such that the second sensor will not rotate when the output shaft or load shaft rotates, wherein the second sensor latches its output signal to the first level when detecting the North pole magnetic field, and latches its output signal to the second level when detecting the South pole magnetic field, wherein the output signal of the first sensor and the output signal of the second sensor are shifted by first phase when the output shaft or load shaft rotates in a direction of tightening a fastener, and are shifted by second phase when the output shaft or load shaft rotates in a direction of loosening the fastener.

5. A power tool as in claim 1, wherein the detecting means comprises an encoder.

6. A power tool as in claim 1, wherein the processor further (1) calculates the changes in the rotational angle of either the output shaft or the load shaft in the tightening direction from the determined generating time until a predetermined period has elapsed, and (2) determines whether the fastener has reached a seated position against the workpiece based upon the calculated changes in the rotational angle.

7. A power tool as in claim 6, wherein the processor stops the motor when a predetermined time has elapsed after determining that the fastener has reached the seated position against the workpiece.

8. A power tool as in claim 6, wherein the processor stops the motor after a first predetermined time has elapsed from a time when the processor has determined, for a predetermined number of times, that the fastener has reached the seated position against the workpiece.

9. A power tool as in claim 8, wherein the processor does not determine that the fastener has reached the seated position against the workpiece during a second predetermined time elapsing from a time when the processor determined the fastener to reach the seated position against the workpiece.

10. A power tool as in claim 6, wherein the processor stops the motor after the means for generating an elevated torque has generated the elevated torque for a predetermined number of times from a time when the processor determined the fastener to reach the seated position against the workpiece.

11. A power tool as in claim 1, wherein (1) at the time when change in the rotational angle of either the output shaft or the load shaft has occurred, the processor calculates the changes in the rotational angle of the output shaft or the load shaft in the tightening direction during a first predetermined period extending from a time prior to the change in the rotational angle until the change in the rotational angle occurs, (2) when the calculated changes in the rotational angle is within a first predetermined value, the processor further calculates the absolute value of the changes in the rotational angle of either the output shaft or the load shaft in a period lasting from the change in the rotational angle until a second predetermined period has elapsed, and (3) when the absolute value of the changes in the rotational angle is greater than a second predetermined value, the processor determines that the time of occurrence of the change in the rotational angle is the generating time.

12. A power tool as in claim 1, wherein the processor further (1) calculates the changes in the rotational angle of either the output shaft or the load shaft in the tightening direction from the determined generating time until a third predetermined period has elapsed, and (2) determines that the fastener has reached a seated position against the workpiece when the calculated changes during the third predetermined period is within the third predetermined value.

13. A power tool adapted to tighten a fastener, comprising:

a motor,

means for generating an elevated torque, wherein the elevated torque generating means is coupled to the motor and has output shaft, wherein if a load acting on the output shaft is less than a predetermined value, rotating torque generated by the motor is directly transmitted to the output shaft and if a load acting on the output shaft exceeds the predetermined value, an elevated torque is generated by the elevated torque generating means and applied to the output shaft,

a load shaft connected to the output shaft,

means for detecting change in rotational angle of either the output shaft or the load shaft and the direction of rotation thereof,

a memory storing automatic stopping programs for automatically stopping the motor for each of differing types of workpiece, and

a processor in communication with the motor, the detecting means and the memory, the detecting means communicating signals corresponding to the state of either the output shaft or the load shaft to the processor, wherein the processor (1) determining the type of workpiece based upon the signals from the detecting means, and (2) selecting the automatic stopping program based upon the determined type of workpiece, and (3) stopping the motor in accordance with the selected automatic stopping program.

14. A power tool as in claim 13, wherein the processor (1) calculates a cumulative rotational angle of either the output shaft or the load shaft in the tightening direction within a predetermined period after the fastener has reached the seated position against the workpiece, and (2) determines the type of workpiece based upon the calculated cumulative rotational angle.

15. A power tool as in claim 13, wherein the processor (1) calculates average changes in rotational angle of either the output shaft or the load shaft in the tightening direction per one elevated torque after the fastener has reached the seated position against the workpiece, and (2) determines the type of workpiece based upon the calculated average changes.