Power Tool with Power Supply Circuit Supplying Different Level DC Voltages to Different Auxiliary Devices

Abstract

An electrically-driven power tool includes a power supply circuit capable of outputting a plurality of DC voltages different in level through conversion of a commercial AC voltage. A lamp and its associated switch are provided. When the switch is turned ON to light the lamp, the DC voltage is applied to the lamp so that voltage gradually increases up to a predetermined level during a predetermined period of time. By doing so, a voltage being applied, for example, to a microcomputer from the power supply circuit is prevented from momentarily lowering at the time when the switch is turned ON.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which:

FIG. 1 is a perspective view showing a miter saw according to one embodiment of the invention;

FIG. 2 is a circuit diagram showing a power supply circuit incorporated in the miter saw shown in FIG. 1;

FIG. 3 is a block diagram of a display control circuit for controlling a display device mounted on the miter saw shown in FIG. 1;

FIG. 4 is a graphical representation showing output current/voltages from a conventional power supply circuit when a lamp is turned on; and

FIG. 5 is a graphical representation showing output current/voltages from the power supply circuit according to the embodiment of the invention.

Claims

1. A power tool comprising: a power supply circuit configured to output a plurality of DC voltages different in level including a first DC voltage and a second DC voltage;a first auxiliary unit supplied with the first DC voltage from the power supply circuit;a second auxiliary unit having a switch and being supplied with a voltage changing up to the second DC voltage during a predetermined period of time, and supplied with the second DC voltage after expiration of the predetermined period of time up to a time when the switch is turned OFF.

2. The power tool according to claim 1, wherein the second DC voltage is greater than the first DC voltage.

3. The power tool according to claim 1, wherein the first auxiliary unit comprises a microcomputer.

4. The power tool according to claim 3, wherein the microcomputer includes a memory and executes a process based on data stored in the memory while updating the data in the memory.

5. The power tool according to claim 1, further comprising a time constant circuit connected to the switch wherein the time constant circuit gradually increases the voltage applied to the second auxiliary unit up to the second DC voltage during the period of time determined by a time constant of the time constant circuit.

6. The power tool according to claim 4, further comprising a movable part, and a detection section that detects a position of the movable part and outputs the data indicative of the position of the movable part.

7. A miter saw comprising: a base on which a workpiece is placed;a turntable rotatable relative to the base;a motor;a cutting portion including a cutting blade driven by the motor;a coupling member that couples the cutting portion to the turntable so that the cutting portion is rotatable together with the turntable, pivotally movable toward and away from the base, and tiltable relative to the base, the workpiece being cut when the cutting portion is moved toward the base;a first detector that detects a position of the turntable relative to the base and outputs a first detection signal indicative of the position of the turntable;a second detector that detects a degree of tilt of the cutting portion relative to the base and outputs a second detection signal indicative of the degree of tilt of the cutting portion;a control section that receives the first and second detection signals and produces display data based on the first and second detection signals;a display device that receives the display data from the control section and displays information about a cutting position and a cutting plane of the workpiece;a power supply circuit configured to output a plurality of DC voltages different in level including a first DC voltage and a second DC voltage, the control unit being supplied with the first DC voltage andan auxiliary unit having a switch and being supplied with a voltage changing up to the second DC voltage during a predetermined period of time, and supplied with the second DC voltage after expiration of the predetermined period of time up to a time when the switch is turned OFF.

8. The miter saw according to claim 7, wherein the second DC voltage is greater than the first DC voltage.

9. The mite saw according to claim 7, wherein the first and second detectors are supplied with the first DC voltage.

10. The miter saw according to claim 9, wherein the control unit includes a memory and executes a process based on data stored in the memory while updating the data in the memory to produce the display data.

11. The miter saw according to claim 7, further comprising a time constant circuit connected to the switch wherein the time constant circuit gradually increases the voltage applied to the auxiliary unit up to the second DC voltage during the period of time determined by a time constant of the time constant circuit.