Power tool

• US 20050057206A1
• Filed: 09/10/2004
• Published: 03/17/2005
• Est. Priority Date: 09/12/2003
• Status: Active Grant

• Current Assignee: Makita Corporation
• Original Assignee: Makita Corporation
• Inventors: Uneyama, Tsunehito
• Granted Patent: US 7,084,779 B2
• Time in Patent Office: Days
• US Class Current: 318/365
• CPC Class Codes: B23D 59/001 Measuring or control devices, e.g. for automatic control of work feed pressure on band saw blade measuring in general G01; controlling in general G05
• CPC Class Codes: B23Q 11/0092 actuating braking or stopping means
• CPC Class Codes: B27B 5/38 Devices for braking the circular saw blade or the saw spindle; Devices for damping vibrations of the circular saw blade, e.g. silencing vibration-damping of sawing machines or devices working with circular saw blades B23D47/005
• CPC Class Codes: B27G 19/02 for circular saws
• CPC Class Codes: F16P 3/147 using electro-magnetic technology, e.g. tags or radar

Abstract

The power tool is equipped with a radar for transmitting radio waves towards an area in a vicinity of a rotating tool and for receiving reflected radio waves reflected from a radio wave reflector existing within the area. From the reflected radio waves received by the radar, a distance between the radio wave reflector and the radar, and a speed of change of that distance are calculated. When the calculated distance and speed fulfill a first criterion, a first brake for applying gentle braking to the rotating tool is activated. When the radio wave reflector further approaches to the rotating tool and the calculated distance and speed fulfill a second criterion, a second brake for applying rapid braking to the rotating tool is activated. Distance in the first criterion and the increase as speed increases, and distance corresponding to a certain speed in the first criterion is longer than distance corresponding to the same speed in the second criterion.

Claims

1. A power tool, comprising:

a radar for transmitting radio waves towards an area in a vicinity of a rotating tool, and for receiving reflected radio waves reflected from a radio wave reflector existing within the area;

a means for calculating, from the reflected radio waves received by the radar, a distance between the radio wave reflector and the rotating tool, and a speed of change of the distance;

a first brake for applying gentle braking to the rotating tool when the calculated distance and speed fulfill a first criterion; and

a second brake for applying rapid braking to the rotating tool when the calculated distance and speed fulfill a second criterion.

2. A power tool as set forth in claim 1, wherein distance in the first criterion and the second criterion increases as speed increases, and distance corresponding to a certain speed in the first criterion is longer than distance corresponding to the same speed in the second criterion.

3. A power tool as set forth in claim 2, further comprising:

a one-way clutch inserted between the rotating tool and a motor for causing the rotating tool to rotate, the one-way clutch causing the rotating tool and the motor to be in a disengaged state in a case where the rotation speed at the motor side is slower than the rotation speed at the rotating tool side,

wherein the first brake applies braking force to a component at the motor side of the one-way clutch, and the second brake applies braking force to a component at the rotating tool side of the one-way clutch.

4. A power tool as set forth in claim 3, wherein the first brake is a regenerative brake for braking an electric motor by causing the electric motor to generate power.

5. A power tool as set forth in claim 4, wherein the frequency of the radio waves utilized by the radar is within the range of 1 G to 30 GHz.

6. A power tool as set forth in claim 2, further comprising:

a clutch inserted between the rotating tool and a motor for causing the rotating tool to rotate, the clutch being capable of switching the rotating tool and the motor between an engaged state and a disengaged state,

wherein the first brake, by switching the clutch to the disengaged state, causes a state where a braking force is applied to the rotating tool by means of friction generated between the rotating tool and work, and the second brake applies braking force to a component at the rotating tool side of the clutch.

7. A power tool as set forth in claim 6, wherein

the frequency of the radio waves utilized by the radar is within the range of 1 G to 30 GHz.

8. A power tool, comprising:

a motor for causing a rotating tool to rotate;

a clutch inserted between the rotating tool and the motor, the clutch being capable of switching the rotating tool and the motor between an engaged state and a disengaged state;

a radar for transmitting radio waves towards an area in a vicinity of the rotating tool and for receiving reflected radio waves reflected from a radio wave reflector existing within the area;

a means for calculating, from the reflected radio waves received by the radar, a distance between the radio wave reflector and the rotating tool, and a speed of change of the distance;

a clutch switching means for switching the clutch to the disengaged state when the calculated distance and speed fulfill a first criterion; and

a brake for applying braking force to the rotating tool when the calculated distance and speed fulfill a second criterion.