Disc grinder

Abstract

It reduces the risk of personal injury or damage to objects caused by contact with the tip of a tool. [Solution] The disc grinder 1 comprises a grinding disc 2 for processing a workpiece, a motor 9 for rotating the grinding disc 2, a controller 10 for controlling the motor 9, and a current detector 7 for detecting the current value of the motor 9. The controller 10 controls the motor 9 based on the detection result of the current detector 7.

Description

Technical Field

[0005]

[0001] The present invention relates to a portable tool, a disc grinder.

Background Art

[0002] FIG. 7 is a perspective view showing the configuration of a conventional disc grinder 101 disclosed in Non-Patent Document 1. The disc grinder 101 includes a polishing disc 102, a grip 103, and a switch 104. When the switch 104 is turned on, a motor (not shown) rotates the polishing disc 102. By pressing the rotating polishing disc 102 against the workpiece, the workpiece can be grinded or polished.

[0003] When using the disc grinder 101, in order to confirm that the polishing disc 102 is properly attached, it is necessary to perform a test run before the grinding operation. In the test run, the operator drives the motor to rotate the polishing disc 102 while confirming that there are no people or objects in front of the polishing disc 102.

[0004] When performing the grinding operation, the operator checks the positional relationship between the workpiece and the polishing disc 102, and presses the rotating polishing disc 102 against the workpiece with an appropriate pressing pressure arbitrarily.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

[0006] In conventional disc grinders 101, if a person unexpectedly steps in front of the rotating grinding disc 102 during a trial run, the operator must quickly change the orientation of the grinding disc 102 or switch off the disc grinder 101. Similarly, if the grinding disc 102 detaches from the workpiece due to the operator's posture changing or a kickback, the operator must quickly change the orientation of the grinding disc 102 or switch off the disc grinder 101. Thus, conventional disc grinders 101 have the disadvantage of not adequately ensuring safety, as the only way to deal with situations where a person unexpectedly comes into contact with the rotating grinding disc 102 is through the operator's quick reaction.

[0007] This invention has been made in view of the above problems, and aims to reduce the risk of injury to the human body or damage to objects caused by contact with an advanced tool. [Means for solving the problem]

[0008] To solve the above problems, the disc grinder according to the present invention comprises an end tool for processing a workpiece, a motor for rotating the end tool, a controller for controlling the motor, and a current detector for detecting the current value of the motor, wherein the controller controls the motor based on the detection result of the current detector.

[0009] In the disc grinder according to the present invention, when the operating mode of the disc grinder is the trial run mode, it is preferable that the controller stops the motor when the current value exceeds a predetermined threshold.

[0010] In the disc grinder according to the present invention, the threshold value is preferably the current value when the tip tool is rotating freely.

[0011] In the disc grinder according to the present invention, when the operating mode of the disc grinder is the work mode, it is preferable that the controller stops the motor if the current value remains at the current value when the tip tool is spinning freely for a predetermined period of time. [Effects of the Invention]

[0012] According to the present invention, the risk of injury to the human body or damage to objects caused by contact with a rotating tip tool can be reduced. [Brief explanation of the drawing]

[0013] [Figure 1] This is a perspective view showing the configuration of a disc grinder according to one embodiment of the present invention. [Figure 2] This is a schematic diagram showing an example of a circuit configuration for driving a motor. [Figure 3] This is a schematic diagram showing another example of a circuit configuration for driving a motor. [Figure 4] This is a flowchart showing the motor control procedure. [Figure 5] This is an explanatory diagram illustrating an example of an accident involving a disc grinder. [Figure 6] This is an explanatory diagram showing other examples of accidents involving disc grinders. [Figure 7] This is a perspective view showing the configuration of a conventional disc grinder. [Modes for carrying out the invention]

[0014] Embodiments of the present invention will be described below with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described below, and various modifications are possible without departing from its spirit.

[0015] FIG. 1 is a perspective view showing the configuration of a disk grinder 1 according to an embodiment of the present invention. The disk grinder 1 is a hand-held power tool and includes a polishing disk 2, a motor, a main grip 3, a sub-grip 4, a paddle switch 5, and an operation mode changeover switch 6.

[0016] The polishing disk 2 is a tip tool for processing a workpiece and is provided at the tip of the disk grinder 1. The motor for rotating the polishing disk 2 is a rotational power source such as an electric or pneumatic fluid machine and is built into the main body of the disk grinder 1. The operator performs a grinding or polishing operation on the workpiece by pressing the rotating polishing disk 2 against the workpiece.

[0017] The main grip 3 is a grip held by the operator's right hand and extends in front of the polishing disk 2 as viewed from the operator. The sub-grip 4 is a grip held by the operator's left hand and extends to the left of the polishing disk 2 as viewed from the operator. That is, the operator uses the disk grinder 1 while holding the main grip 3 and the sub-grip 4 with the right hand and the left hand, respectively.

[0018] When the polishing disk 2 is small (generally less than 100 mm in diameter), the sub-grip 4 may be omitted.

[0019] The paddle switch 5 is provided on the main grip 3 and is pressed when the right hand holds the main grip 3. In the present embodiment, the paddle switch 5 is provided at the lower part of the main grip 3 and is pressed by the index finger of the right hand when the right hand holds the main grip 3.

[0020] The operation mode changeover switch 6 is a switch for switching the operation mode of the disk grinder 1. The operation modes include a test operation mode and a work mode, and the operator can select the test operation mode or the work mode by operating the operation mode changeover switch 6.

[0021] The upper housing of the polishing disc 2 houses a motor for rotating the polishing disc 2, a controller for controlling the motor, and a current detector for detecting the motor's current value. The motor is a rotational power source, either an electric motor or a pneumatic fluid machine. The controller controls the motor based on the detection result of the current detector. The controller may be implemented in hardware using logic circuits, etc., or in software using a CPU (Central Processing Unit).

[0022] Figure 2 is a schematic diagram showing an example of a circuit configuration for driving a motor. In Figure 2, the motor 9 is a universal motor and is powered by a power supply 8. The current detector 7 detects the current flowing from the power supply 8 to the motor 9 and outputs a signal indicating the detection result to the controller 10. The controller 10 controls the motor 9 based on the detection result of the current detector 7.

[0023] As will be described later, the controller 10 stops the motor 9 when predetermined conditions are met. The method for stopping the motor 9 is not particularly limited, but the motor 9 may be stopped using regenerative braking or the like, or the motor 9 may be stopped by providing a switch on the power supply line to the motor 9 and opening the switch.

[0024] Figure 3 is a schematic diagram showing another example of a circuit configuration for driving a motor. In Figure 3, the motor 9 is an inverter-controlled synchronous motor or dielectric motor, and the power supply is controlled by an inverter circuit 11 located between the power supply 8 and the motor 9. The current detector 7 detects the current flowing from the inverter circuit 11 to the motor 9 and outputs a signal indicating the detection result to the controller 10. The controller 10 indirectly controls the motor 9 by controlling the inverter circuit 11 based on the detection result of the current detector 7.

[0025] (Motor control) The motor control is described below. The controller 10 performs two types of control on the motor depending on the operating mode of the disc grinder 1. Specifically, when the operating mode of the disc grinder 1 is the trial run mode, the controller 10 stops the motor when the current value detected by the current detector 7 exceeds a predetermined threshold. Also, when the operating mode of the disc grinder 1 is the work mode, the controller 10 stops the motor when the current value detected by the current detector 7 remains at the current value when the grinding disc 2 is spinning freely for a predetermined period of time.

[0026] Figure 4 is a flowchart showing the motor control procedure.

[0027] In step S1, the operator attaches the polishing disc 2, which is the tip tool, to the disc grinder 1. If the polishing disc 2 is already attached, step S1 is omitted.

[0028] In step S2, the operator connects the disc grinder 1 to the power supply.

[0029] In step S3, the operator operates the operation mode selector switch 6 to select the operation mode of the disc grinder 1.

[0030] If the trial run mode is selected ("1" in step S3), the process proceeds to step S4, and the current detector 7 is activated. The current detector 7 begins monitoring the changes in the current value flowing through the motor.

[0031] Subsequently, in step S5, when the operator grasps the main grip 3 and the paddle switch 5 is turned ON, the motor starts to drive.

[0032] Next, in step S6, the current detector 7 detects the current value when the polishing disc 2 is spinning freely (hereinafter referred to as the free-spinning value). The free-spinning value is stored in a memory (not shown), for example.

[0033] If an object comes into contact with the polishing disc 2 while it is rotating, a load is placed on the polishing disc 2, reducing its recoil electromotive force and increasing the motor current. If the current detected by the current detector 7 exceeds a threshold (YES in step S7), it is determined that an object has come into contact with the polishing disc 2, and the controller 10 stops the motor even if the paddle switch 5 is ON (step S8).

[0034] If the motor is running idle for a predetermined time (3 minutes if a new polishing disc 2 is installed at the start of use, or 1 minute if a polishing disc 2 is already installed at the start of use) (if "YES" is selected in step S9), the operator turns off the paddle switch 5 (step S10) and ends the test run.

[0035] Thus, when the disc grinder 1 is in trial operation mode, the controller 10 stops the motor when the current value detected by the current detector 7 exceeds a predetermined threshold. As a result, as shown in Figure 5, if a person or other object unexpectedly steps in front of the grinding disc 2 and the rotating grinding disc 2 comes into contact with the person or object, or if a kickback phenomenon occurs due to the grinding disc 2 getting stuck, the rotation of the grinding disc 2 will stop automatically, thereby reducing the risk of injury to people or damage to objects due to contact with the grinding disc 2.

[0036] Note that the threshold value may be the idle value. As a result, if an object makes even slight contact with the rotating polishing disc 2, the current value detected by the current detector 7 will exceed the threshold value (YES in step S7), and the controller 10 will stop the motor (step S8).

[0037] Returning to Figure 4, if the work mode is selected as the operating mode of the disc grinder 1 (2 in step S3), the process proceeds to step S11, and the current detector 7 is activated. The current detector 7 begins monitoring the changes in the current value flowing through the motor.

[0038] Subsequently, in step S12, when the operator grasps the main grip 3 and the paddle switch 5 is turned ON, the motor starts to drive.

[0039] Next, in step S13, the current detector 7 detects the idle value. The idle value is stored in a memory (not shown), for example.

[0040] Subsequently, if the current value detected by the current detector 7 remains at the idle value for a predetermined period of time (NO in step S14 and YES in step S16), it is determined that the operator has not been making contact with the workpiece with the polishing disc 2, and the controller 10 stops the motor even if the paddle switch 5 is ON (step S17).

[0041] On the other hand, if the current value detected by the current detector 7 exceeds a threshold (YES in step S14), it is considered that the operator has made contact with the workpiece with the polishing disc 2, and the controller 10 does not stop the motor. The threshold may be the idle value. Subsequently, when the operator removes the polishing disc 2 from the workpiece, the current value drops to the idle value (YES in step S15), and if this condition continues for a predetermined time (YES in step S16), the controller 10 stops the motor even if the paddle switch 5 is ON (step S17).

[0042] The "predetermined time" in step S16 corresponds to the "predetermined time" described in the claims, which in this embodiment is 1.5 seconds. However, the present invention is not limited thereto, and the specific value of the predetermined time can be set to the maximum amount of time during which the operator keeps the polishing disc 2 away from the workpiece without stopping its rotation, for example, when continuously polishing separated parts of the workpiece or intermittently polishing the same part.

[0043] Thus, when the disc grinder 1 is in work mode, the controller 10 stops the motor if the current value detected by the current detector 7 remains at the idle value for a predetermined period of time. This reduces the risk of accidents such as the rotating grinding disc 2 coming into contact with a person if the disc grinder 1 unexpectedly moves away from the workpiece due to a change in the operator's posture, as shown in Figure 6.

[0044] (Additional notes) The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Forms obtained by appropriately combining the technical means disclosed in the embodiments are also included in the technical scope of the present invention.

[0045] The disc grinder 1 according to the above embodiment is equipped with a grinding disc 2 as an end tool for cutting or polishing a workpiece, but the end tool is not limited to this. For example, the disc grinder 1 may be equipped with an industrial grinding wheel for cutting a workpiece as an end tool.

[0046] Furthermore, in the above embodiment, the idle value is detected in step S6 shown in Figure 4, but the idle value may be set in advance. Methods for setting the idle value include setting it according to the respective sizes of the polishing disc 2 and the motor 9, or setting the idle value as the difference (e.g., ±5%) in the change in the motor current value after driving the motor 9 at room temperature in an unloaded state and then performing aging for a predetermined time (e.g., 30 minutes).

[0047] Furthermore, in general, electric motors tend to increase in current when a load is applied. Therefore, in the above embodiment, in the trial operation mode, if the current value of motor 9 increases and exceeds a threshold, motor 9 is stopped. [Explanation of Symbols]

[0048] 1. Angle grinder 2 polishing discs 3 Main Grip 4 Sub-grips 5 Paddle Switches 6. Operation mode selector switch 7 Current detector 8 Power supply 9 Motors 10 Controllers 11. Inverter Circuit

Claims

1. Advanced tools for machining workpieces, A motor for rotating the aforementioned tip tool, A controller for controlling the motor, A current detector for detecting the current value of the motor, Equipped with, The disc grinder is characterized in that the controller controls the motor based on the detection result of the current detector.

2. If the operating mode of the disc grinder is in trial mode, The disc grinder according to claim 1, characterized in that the controller stops the motor when the current value exceeds a predetermined threshold.

3. The disc grinder according to claim 2, wherein the threshold value is the current value when the tip tool is idling.

4. When the operating mode of the disc grinder is set to work mode, The disc grinder according to claim 1, characterized in that the controller stops the motor when the current value is the same as the current value when the tip tool is spinning freely for a predetermined period of time.

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