Grinding tools

Abstract

To reduce generation of noise by suppressing unnecessary power consumption.SOLUTION: A control circuit determines in S1 whether a side handle is attached to at least one of right and left handle attachment portions or not, and determines in S2 whether the attached side handle is gripped by an operator or not. When a switch is turned ON in S3 while the side handle is gripped, the control circuit rotates a motor at a predetermined high rotational speed in S4. During a work, the control circuit constantly monitors an ON state of the switch in S5, a mounted state of the side handle in S6, and a griped state of the side handle in S7, and stops the motor S8 if any of requirements is not satisfied. In S9, the control circuit monitors load current into the motor in a state where the side handle is gripped. When the load current does not vary for a predetermined time, the control circuit determines that the side handle is gripped and is in a stationary state, and reduces a rotational speed of the motor to a predetermined low rotational speed in S10.SELECTED DRAWING: Figure 15

Description

Technical Field

[0001] The present disclosure relates to grinding tools such as grinders. Note that "grinding" in the present disclosure is a concept that also includes "polishing".

Background Art

[0002] A grinder, which is an example of a grinding tool, has a spindle protruding downward from the front part of a housing that houses a motor and extends in the front-rear direction, and a tip tool such as a disk-shaped grindstone is attached to the lower end of the spindle. Therefore, it is possible to polish a workpiece with the tip tool that rotates together with the spindle. As disclosed in Patent Document 1, in a grinder, the rear part of a housing that extends in the front-rear direction serves as a main handle, and a side handle (auxiliary handle) can be attached to either the left or right side of the front side surface of the housing. An operator operates the grinder by gripping the rear part of the housing with one hand and the side handle with the other hand. In this grinder, in order to prevent the occurrence of kickback in which the grinder is swung around by the reaction force received by the tip tool from the workpiece, a handle detection mechanism that electrically detects the attachment of the auxiliary handle is provided. When the controller does not obtain a detection signal from the handle detection mechanism, it does not drive the motor even when the switch is turned on.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Some of the grinders mentioned above have motors that continue to rotate at the same speed even when the tool tip is not in contact with the workpiece. In this case, power consumption is wasted, and it also leads to noise generation.

[0005] Therefore, the purpose of this disclosure is to provide a grinding tool that can reduce unnecessary power consumption and also reduce noise generation. [Means for solving the problem]

[0006] To achieve the above objective, this disclosure provides a grinding tool comprising a housing for a motor, A spindle that protrudes from the housing, rotates by motor drive, and has a tip tool that can be attached to the protruding end, A switch that can be turned ON / OFF by external operation, A controller that controls the motor's operation based on the ON / OFF operation of a switch, A handle mounting section is provided in the housing, from which an auxiliary handle can be attached and detached. A handle detection mechanism that electrically detects the mounting status of the auxiliary handle to the handle mounting section, It includes a handle grip detection mechanism that electrically detects the gripping state of an auxiliary handle attached to a handle mounting section, The controller detects the attachment of the auxiliary handle using the handle detection mechanism and the gripping of the auxiliary handle using the handle gripping detection mechanism, and then drives the motor when the switch is turned ON. The handle detection mechanism and the handle grip detection mechanism are formed using a common sensor located on the handle mounting side. Then, when the controller detects that the auxiliary handle has been attached and grasped and the switch is turned ON, it controls the motor's rotation to a predetermined first rotation speed, The motor rotation is controlled to a second rotation speed (including 0) that is lower than the first rotation speed if the load on the cutting tool does not change for a predetermined period of time. [Effects of the Invention]

[0007] According to the present disclosure, while the tip tool is not being used away from the workpiece, the motor is controlled at a low rotational speed including 0. Therefore, it is possible to suppress wasteful power consumption and reduce the generation of noise.

Brief Description of the Drawings

[0008] [Figure 1] It is a perspective view of the grinder. [Figure 2] It is a plan view of the grinder. [Figure 3] It is a left side view of the grinder. [Figure 4] It is a sectional view taken along line A-A of FIG. 2. [Figure 5] It is an enlarged sectional view taken along line B-B of FIG. 2. [Figure 6] It is an enlarged sectional view taken along line C-C of FIG. 2. [Figure 7] It is a sectional view taken along line D-D of FIG. 3. [Figure 8] It is an exploded perspective view of the handle attachment part and the handle attachment / grip detection mechanism as seen from the left side. [Figure 9] It is an exploded perspective view of the handle attachment / grip detection mechanism as seen from the right side. [Figure 10] It is a perspective view of the left half housing. [Figure 11] It is a perspective view from below of the grinder with the outer housing omitted. [Figure 12] It is a bottom view of the grinder with the outer housing omitted. [Figure 13] It is a bottom view of the grinder showing a modified example of the wiring with the outer housing omitted. [Figure 14] It is a functional block diagram of the controller. [Figure 15] It is a flowchart of motor control. [Figure 16] It is a flowchart of a modified example of motor control.

Modes for Carrying Out the Invention

[0009] In one embodiment of the present disclosure, the second rotational speed may be other than zero. According to this configuration, since the tip tool is rotating even when no work is being performed, the work can be resumed in a short time, and a decrease in work efficiency can be suppressed. In one embodiment of the present disclosure, the handle detection mechanism and the handle gripping detection mechanism may be formed using a common sensor. According to this configuration, the handle detection mechanism and the handle gripping detection mechanism can be formed reasonably with less space, and an increase in cost can be suppressed. In one embodiment of the present disclosure, the load state on the tip tool may be the load current of the motor. According to this configuration, the load state can be easily grasped based on the load current. In one embodiment of the present disclosure, when the controller detects a change in the load state while controlling at a second rotational speed other than zero, the rotation of the motor may be controlled to the first rotational speed. According to this configuration, since the work automatically returns to the first rotational speed in a short time when resumed, even if the rotational speed of the motor is reduced in a no-load state, it does not cause a decrease in work efficiency or usability. In one embodiment of the present disclosure, the handle attachment portion may be provided at a plurality of locations. According to this configuration, the auxiliary handle can be attached by selecting an easy-to-operate position. In one embodiment of the present disclosure, the housing may be provided with a battery mounting portion. According to this configuration, the handling of the power cord is eliminated, and the operability and workability are improved.

Example

[0010] Hereinafter, examples of the present disclosure will be described based on the drawings. FIG. 1 is a perspective view showing a grinder which is an example of a grinding tool. FIG. 2 is a plan view of the grinder. FIG. 3 is a left side view of the grinder. FIG. 4 is a cross-sectional view taken along line A-A of FIG. 2. The housing 2 of the grinder 1 extends in the front-to-back direction. The housing 2 has an inner housing 3, a gear housing 4, and an outer housing 5. The inner housing 3 and outer housing 5 are made of resin, while the gear housing 4 is made of metal. The inner housing 3 is cylindrical and houses the motor 6 (a commutator motor in this case). The motor 6 is held inside the inner housing 3 with its output shaft 7 facing in the front-to-back direction. The gear housing 4 is bolted to the inner housing 3 from the front via a gear housing cover 8. Multiple exhaust ports 9, 9·· are formed on the front of the gear housing 4, communicating with the inside of the inner housing 3. The front of the output shaft 7 protrudes into the gear housing 4 through the gear housing cover 8. The gear housing cover 8 is provided with a bearing 10 that supports the output shaft 7. A fan 11 is fixed to the output shaft 7 behind the gear housing cover 8.

[0011] A bevel gear 12 is provided at the front end of the output shaft 7 within the gear housing 4. A bearing box 13 is assembled to the lower part of the gear housing 4. A spindle 14 is provided in the vertical direction inside the gear housing 4 and the bearing box 13. The spindle 14 has a bevel gear 15 at its upper part. The bevel gear 15 meshes with the bevel gear 12 of the output shaft 7. The spindle 14 is supported by upper and lower bearings 16, 16 held within the gear housing 4 and the bearing box 13. The lower end of the spindle 14 protrudes downward from the bearing box 13. A cutting tool 19 (e.g., a disc-shaped grinding wheel) can be attached to the lower end of the spindle 14 by an inner flange 17 and a lock nut 18. A wheel cover 20 is attached to the bearing box 13 to cover the rear upper and rear sides of the cutting tool 19.

[0012] The outer housing 5 is cylindrical and consists of a pair of left and right split housings 5a and 5b fastened together with screws from the left and right directions. The outer housing 5 has a front main body portion 25 and a rear main grip portion 26. Multiple air intake ports 27, 27... are formed on the left and right sides of the rear of the main body portion 25. The main grip portion 26 has a smaller diameter than the main body portion 25 and extends rearward from a position eccentrically upward from the axis of the main body portion 25, sloping downward. The main grip portion 26 is equipped with a switch 28 and a switch lever 29. The switch lever 29 can swing up and down with its rear end as a pivot point, and the switch 28 is turned ON by an upward pushing operation. A power cord 30 is connected to the rear end of the main grip portion 26. The front of the main body 25 coaxially holds the inner housing 3 via a rubber sleeve 31. A metal fixing ring 32, which is externally mounted on the rubber sleeve 31, is provided on the front side of the main body 25. The outer housing 5 is connected to the fixing ring 32 by a protruding portion 63, which will be described later, being screwed to the fixing ring 32.

[0013] A bearing retaining portion 33 is integrally formed at the rear of the inner housing 3. The output shaft 7, which protrudes rearward from the commutator, is supported by a bearing 34 held in the bearing retaining portion 33. A pair of support protrusions 35, 35 are provided above and below the bearing retaining portion 33. The support protrusions 35, 35 are arranged coaxially in the vertical direction perpendicular to the axis of the output shaft 7. Each support protrusion 35 is fitted with a rubber cap 36. On the inner surfaces of the left and right split housings 5a, 5b, as shown in Figure 10, retaining portions 37, 37 are provided above and below, protruding towards the center in the left-right direction and holding the upper and lower rubber caps 36, 36 in the center. Thus, the inner housing 3 is elastically supported within the outer housing 5 via the front rubber sleeve 31 and the rear rubber caps 36, 36. In this state, a cylindrical space S is formed around the entire circumference between the inner housing 3 and the outer housing 5, as shown in Figure 6.

[0014] The rear end of the output shaft 7 extends rearward through the bearing holder 33. A brake drum 38 is fixed to the rear end of the output shaft 7. As shown in Figure 7, a pair of brake arms 39, 39 are provided on both the left and right sides of the brake drum 38 within the main body 25. The brake arms 39, 39 are supported so as to be able to swing from side to side with their upper ends as a pivot point. The brake arms 39, 39 are biased toward the brake drum 38 by having brake shoes 40, 40 that face the outer circumferential surface of the brake drum 38. The brake arms 39, 39 are linked to the swing of the switch lever 29 by a linkage mechanism 41. At the lower limit position of the switch lever 29, when the switch 28 is in the OFF position, the brake drum 38 is pressed against the brake shoes 40, 40 of the brake arms 39, 39. Therefore, the rotation of the brake drum 38 and the output shaft 7 is restricted. When the switch lever 29 is pushed upward from this position to turn the switch 28 ON, the brake arms 39, 39 expand via the linkage mechanism 41, releasing the pressure on the brake drum 38 by the brake shoes 40, 40. Therefore, the rotation of the brake drum 38 and the output shaft 7 is permitted.

[0015] A controller 42 is located inside the main body 25 behind the brake drum 38. The controller 42 is held vertically in the center in the left-right direction. The controller 42 has a control circuit board 43 inside which a microcontroller, memory, etc., are mounted. An adjustment dial 44 is provided on the upper front side of the control circuit board 43. As shown in Figures 1 to 4, the upper part of the adjustment dial 44 is exposed above the outer housing 5. The rotation speed of the motor 6 can be adjusted by rotating the adjustment dial 44.

[0016] On the front left and right sides of the housing 2, there are handle mounting sections 45 from which a side handle 50 can be attached and detached, and a handle mounting / gripping detection mechanism (hereinafter referred to as the "detection mechanism") 46 that detects the mounting state and gripping state of the side handle 50 to the handle mounting section 45. The details are described below. However, since the handle mounting section 45 and the detection mechanism 46 are symmetrical, the left-side handle mounting section 45 and detection mechanism 46 will be described mainly. Figure 8 is an exploded perspective view of the mounting section and detection mechanism from the left side. Figure 9 is an exploded perspective view of the detection mechanism from the right side. First, as shown in Figure 5, the side handle 50 comprises a grip portion 51 and a bolt 52. The grip portion 51 extends in a straight line and has a flange 53 at its end. The bolt 52 is held at the center of the grip portion 51, with a threaded portion 54 protruding from the center of the flange 53. At the center of the flange 53, a boss portion 55 is formed, covering the periphery except for the tip of the threaded portion 54. A contact plate 56 is fixed around the boss portion 55. The contact plate 56 is disc-shaped, coaxially surrounding the boss portion 55, and its end face is formed at a lower position than the end face of the boss portion 55 (closer to the flange 53), exposing the tip of the boss portion 55.

[0017] Receiving surfaces 60 are formed on the left and right sides of the fixing ring 32. The receiving surfaces 60 are defined in the front-to-back and up-to-down directions and are planes that extend in the up-to-down direction. A handle mounting portion 45 is projected from the center of the receiving surface 60 in the up-to-down direction. The handle mounting portion 45 is cylindrical in shape and protrudes to the left. A first screw hole 61 is formed in the left-to-right direction at the center of the handle mounting portion 45, passing through the fixing ring 32 in the radial direction. The side handle 50 is attached coaxially to the handle mounting portion 45 by screwing the threaded portion 54 of the side handle 50 into the first screw hole 61. As shown in Figure 5, the threaded portion 54 can be screwed in until the end face of the boss portion 55 abuts against the end face of the handle mounting portion 45. On the receiving surface 60, two second screw holes 62, 62, which have a smaller diameter than the first screw hole 61, are formed above and below the first screw hole 61, parallel to the first screw hole 61. Here, a rubber sleeve 31 is positioned inside the metal fixing ring 32, thereby providing insulation between the side handle 50, which is attached to the handle mounting section 45, and the motor 6 and other components inside.

[0018] The front end of the outer housing 5 is provided with a pair of left and right protruding portions 63. The protruding portions 63 extend outward from the front end of the outer housing 5 to the left and right, and then are plate-shaped and protrude forward on the left and right outer sides of the receiving surfaces 60, 60 of the fixing ring 32. The front part of the protruding portion 63 is semicircular in side view. A cylindrical portion 64 is formed in the protruding portion 63 and penetrates it in the left-right direction. The cylindrical portion 64 is located at the center of the semicircle. The left end of the cylindrical portion 64 is fitted with the boss portion 55 of the side handle 50. On the left side of the protruding portion 63, a circular receiving recess 65 is formed concentrically with the cylindrical portion 64 when viewed from the side. Above and below the cylindrical portion 64, small cylindrical portions 66, 66 are formed in the receiving recess 65, which penetrate the protruding portion 63 in the left-right direction. The small cylindrical portions 66, 66 are coaxially located to the left outer side of the second screw holes 62, 62 provided in the receiving surface 60 of the fixing ring 32. Behind the cylindrical portion 64, three ribs 67, 67... are formed on the outer circumference of the receiving recess 65. Each rib 67 is formed in an arc shape, spaced apart in the circumferential direction on a concentric circle centered on the cylindrical portion 64. Notches 68 are formed at two locations, top and bottom, on the front of the protruding portion 63, and at the center in the vertical direction on the rear of the protruding portion 63. Outside the ribs 67, a pull-out hole 69 is formed on the lower rear side of the protruding portion 63, which penetrates in the left-right direction.

[0019] The detection mechanism 46 is provided on the protruding portion 63. The detection mechanism 46 comprises a pressure sensor 70, a pressing rubber 71, a movable plate 72, and an outer cover 73. The pressure sensor 70 is sheet-shaped, and its resistance changes depending on the load in the thickness direction. The pressure sensor 70 has a ring shape when viewed from the side, with a cylindrical portion 64 passing through its center and positioned on the bottom surface of the receiving recess 65. Notches 74, 74 are formed on the upper and lower outer circumference of the pressure sensor 70 to avoid interference with the small cylindrical portions 66, 66. A first wiring 90 is electrically connected to the pressure sensor 70, which is drawn out from inside the outer housing 5 through an outlet hole 69 and out to the left outer side of the protruding portion 63.

[0020] The pressure rubber 71 overlaps the pressure sensor 70 from the left side inside the rib 67. The pressure rubber 71 is disc-shaped and penetrates the cylindrical portion 64. Three protrusions 75, 75... are formed on the outer circumference of the pressure rubber 71, which engage with the notches 68, 68... of the protruding portion 63 from the inside. Semicircular inner relief portions 76, 76 are formed on the upper and lower outer circumferences of the pressure rubber 71 to avoid interference with the small cylindrical portions 66, 66. On the left side of the pressure rubber 71, recesses 77, 77... are formed radially inward from the protrusions 75, 75... The recesses 77, 77... are arranged at equal intervals in the circumferential direction of the pressure rubber 71. On the right side of the pressure rubber 71, convex portions 78, 78... are formed, located on the back side of the recesses 77, 77... The movable plate 72 is positioned inside the rib 67 and to the left outside of the pressure rubber 71. The movable plate 72 is disc-shaped and penetrates the cylindrical portion 64. Semicircular relief portions 79, 79 are formed on the upper and lower outer circumferences of the movable plate 72 to avoid interference with the small cylindrical portions 66, 66. Inner pins 80, 80... and outer pins 81, 81... are provided coaxially on both the left and right sides of the movable plate 72. The inner pins 80 and outer pins 81 are arranged at equal intervals in the circumferential direction. The inner pins 80, 80... are located outside the recesses 77, 77... of the pressure rubber 71, respectively.

[0021] The outer cover 73 has the same shape as the protruding portion 63 when viewed from the side. Locking protrusions 82, 82, corresponding to the notches 68, 68, 63 of the protruding portion 63 are formed on the right side of the front and rear ends of the outer cover 73. A round hole 83 is formed in the front of the outer cover 73, coaxial with the left side of the cylindrical portion 64 of the protruding portion 63. The boss portion 55 of the side handle 50 can pass through the round hole 83. A pair of receiving seats 84, 84 are recessed above and below the round hole 83. Each receiving seat 84 has a through hole 85. Each through hole 85 is coaxially positioned to the left of the small cylindrical portion 66 of the protruding portion 63. The outer cover 73 has three small holes 86, 86, 63, through which the outer pins 81, 81, 63 of the movable plate 72 pass.

[0022] The detection mechanism 46 sets the pressure sensor 70, the pressure rubber 71, and the movable plate 72 in order in the receiving recess 65. Then, the outer cover 73 is placed over it from the outermost side, and two screws 87, 87 are driven from the left outer side through the through holes 85, 85 and the small cylindrical parts 66, 66 of the protruding part 63 and screwed into the second screw holes 62, 62 of the receiving surface 60. As a result, the handle mounting part 45 is integrally fixed to the protruding part 63 of the outer housing 5. The pressure sensor 70 is prevented from rotating at the bottom surface of the receiving recess 65 by the engagement of the small cylindrical portion 66 and the notch 74. The pressing rubber 71 is prevented from rotating within the receiving recess 65 by the engagement of the small cylindrical portion 66 and the inner relief portion 76, and by the engagement of the protrusion 75 and the notch 68, causing the protrusion 78 to contact the pressure sensor 70. The movable plate 72 is housed so as to be movable in the left-right direction between the pressing rubber 71 and the outer cover 73. However, with each inner pin 80 in contact with each recess 77 of the pressing rubber 71, the movable plate 72 is biased by the elasticity of the pressing rubber 71 to the outermost position, with each outer pin 81 protruding outward from each small hole 86 of the outer cover 73, as shown in the detection mechanism 46 on the right side of Figure 7.

[0023] The pressure sensor 70 is electrically connected to the control circuit board 43 of the controller 42. As shown in Figures 11 and 12, the left and right pressure sensors 70 are electrically connected to each other by a first wiring 90 consisting of multiple signal lines. A second wiring 91, also consisting of multiple signal lines, is electrically connected to the first wiring 90. The second wiring 91 is connected to the control circuit board 43. The first wiring 90 and the second wiring 91 are routed within the cylindrical space S between the inner housing 3 and the outer housing 5. First, within the cylindrical space S, a pair of parallel first protrusions 92, 92 are provided on the front inner surface of the left half-housing 5a, as shown in Figures 6 and 10. The first protrusions 92, 92 extend circumferentially around the half-housing 5a, with their upper ends behind the pull-out holes 69 of the left overhang 63, and reach the lower end of the half-housing 5a.

[0024] A pair of parallel second protrusions 93, 93 are provided on the inner surface of the split housing 5a. The second protrusions 93, 93 rise circumferentially from near the lower inner surface of the split housing 5a in front of the holding portion 37 of the rubber cap 36, then extend forward along the axial direction, and connect to the upper end of the first protrusions 92, 92 behind the pull-out hole 69 of the left overhang portion 63. Each protrusion 92, 93 is provided with a plurality of projections 94, 94... that protrude toward each other at predetermined intervals in the extension direction, and are located opposite each other. Furthermore, a guide groove 95 is formed on the lower right side of the rear of the rubber sleeve 31, which is initially formed in a sloping manner from the central rear end in the left-right direction toward the front right, and then extends to the right along the circumferential direction.

[0025] Both ends of the first wiring 90 pass through the exit holes 69 of the left and right protruding portions 63, respectively, and are pulled out to the left and right outer sides of the protruding portions 63, and are electrically connected to the pressure sensor 70 in the receiving recess 65. In the cylindrical space S, the middle portion of the first wiring 90 is held on the right side by fitting into the guide groove 95 of the rubber sleeve 31, and on the left side is held between the first protrusions 92, 92 of the split housing 5a. The second wiring 91, which is drawn out from the control circuit board 43, is held between the second protrusions 93, 93 within the cylindrical space S and is routed forward along the second protrusions 93, 93. The second wiring 91 is then connected to the first wiring 90 behind the left-side exit hole 69. However, the wiring configuration is not limited to this. For example, as shown in Figure 13, the first wirings 90, 90 connected to the pressure sensors 70, 70 of the left and right detection mechanisms 46, 46, respectively, may be routed to the rear and connected to the controller 42. In this way, by connecting each detection mechanism 46 to the controller 42 with separate first wirings 90, if one of the wirings 90 is disconnected or otherwise damaged, the controller 42 can determine that both are not equipped with handlebars, even if there is no problem with the other wiring 90. In this case, the right-side split housing 5b may also be provided with a second projection 93, 93 to guide the wiring 90.

[0026] Figure 14 is a functional block diagram of the controller 42. The controller 42 comprises a control circuit 100, a sensor circuit 101, a motor drive circuit 102, and a power supply circuit 103. The control circuit 100 is formed by a microcontroller on the control circuit board 43. The sensor circuit 101 outputs resistance values ​​obtained from the left and right pressure sensors 70, 70 as load detection signals to the control circuit 100. The control circuit 100 controls the drive of the motor 6 via the motor drive circuit 102 based on the load detection signals from the sensor circuit 101 and the ON / OFF signals from the switch 28. The power supply circuit 103 creates operating power from the commercial power supplied from the power cord 30 and supplies it to each circuit. The motor drive control by the control circuit 100 will be explained below based on the flowchart in Figure 15.

[0027] When power is supplied from the power cord 30, the control circuit 100 determines in step 1 (hereinafter simply referred to as "S") whether or not a side handle 50 is attached to at least one of the left and right handle mounting sections 45, 45. This determination is made by checking whether the resistance values ​​of the pressure sensors 70, 70 in the left and right detection mechanisms 46, 46 exceed a predetermined first threshold via the first wiring 90 and the second wiring 91. Specifically, when the threaded portion 54 of the side handle 50 is screwed into either the left or right handle mounting portion 45, 45, the boss portion 55 comes into contact with the handle mounting portion 45. In this state, a gap smaller than the amount of protrusion of the outer pins 81 from the outer cover 73 is formed between the left and right sides of the outer cover 73 and the end faces of the contact plates 56 of the side handle 50. As a result, each outer pin 81 that is in contact with the end faces of the contact plates 56 is pressed, and the movable plate 72 moves inward to the left and right.

[0028] Then, each inner pin 80 of the movable plate 72 presses against each recess 77 of the pressure rubber 71. As a result, each protrusion 78 on the back side of each recess 77 presses against the pressure sensor 70. When the pressure sensor 70 is pressed, the resistance value changes and is input from the sensor circuit 101 to the control circuit 100 as a load detection signal. When the control circuit 100 confirms that the input resistance value exceeds a first threshold, it determines that the side handle 50 has been attached (YES in S1). Therefore, when neither the left nor right handle mounting section 45, 45 has a side handle 50 attached (NO in S1), the resistance values ​​of the pressure sensors 70, 70 do not exceed the first threshold. Consequently, even if the switch lever 29 is pushed in and the switch 28 is turned ON in this state, the control circuit 100 does not drive the motor 6.

[0029] Next, in S2, the control circuit 100 determines whether or not the attached side handle 50 has been grasped by the worker. This determination is made based on whether the resistance value of the pressure sensor 70 exceeds a predetermined second threshold in the detection mechanism 46 to which the side handle 50 is attached. This second threshold is set to a value greater than the first threshold. This is because when the side handle 50 is gripped, the side handle 50 tilts relative to the handle mounting portion 45, increasing the load on the pressure sensor 70 and thus increasing the resistance value, and this increased resistance value is detected. Therefore, if the resistance value of the pressure sensor 70 exceeds the second threshold, the control circuit 100 determines that the side handle 50 is being gripped (YES in S2). On the other hand, if the resistance value of the pressure sensor 70 does not exceed the second threshold, the control circuit 100 determines that the side handle 50 is not being gripped (NO in S2). Consequently, even if the switch lever 29 is pushed in and the switch 28 is turned ON in this state, the control circuit 100 does not drive the motor 6.

[0030] With the attached side handle 50 being held, if the switch lever 29 is pressed in S3 and the switch 28 is turned ON (YES in S3), the control circuit 100 supplies drive power to the motor 6 in S4 to a predetermined high rotational speed (for example, 9000 min⁻¹). -1 The motor 6 is rotated by pressing the switch lever 29. As mentioned above, the braking force on the brake drum 38 is released when the switch lever 29 is pressed, so the output shaft 7 rotates together with the brake drum 38. The rotation of the output shaft 7 is transmitted to the spindle 14 via the bevel gears 12 and 15. As a result, the tip tool 19 rotates. The operator can perform grinding or other operations on the workpiece using the tip tool 19 by gripping the main grip portion 26 with one hand and the grip portion 51 of the side handle 50 with the other hand.

[0031] During operation, the control circuit 100 constantly monitors the ON state of switch 28 in S5, the mounting status of side handle 50 in S6, and the gripping status of side handle 50 in S7. If any of the requirements are not met (NO in any of S5-S7), the motor 6 is stopped in S8. Therefore, if the switch lever 29 is released, the side handle 50 is removed, or the hand is released from the side handle 50, the motor 6 will stop. Then, in S9, the control circuit 100 monitors the load current (torque) to the motor 6 while the side handle 50 is being gripped. If the load current does not fluctuate for a predetermined time (e.g., 2 to 10 seconds) (YES in S9), it is assumed that no work is being performed, i.e., the motor is stationary while gripping the side handle 50, and in S10 the motor 6 is set to a predetermined low rotational speed (e.g., 4000 to 5000 min⁻¹). -1The speed is reduced to ). If the load current fluctuates within a predetermined time during operation (NO in S9), the system returns to S4 and the high rotational speed is maintained. On the other hand, even after the rotation speed has decreased in S10, if the grinder 1 is shaken or its posture is changed while the side handle 50 is held with the switch 28 ON, or if grinding or other work is resumed, the load current of the motor 6 will fluctuate. The control circuit 100, detecting this, determines in S9 that it is not stationary with the side handle 50 held, and returns to S4 to restore the rotation speed of the motor 6 to high.

[0032] As described above, the grinder 1 of the embodiment includes a housing 2 that houses a motor 6, a spindle 14 that protrudes from the housing 2 and rotates when driven by the motor 6, and to which a tip tool 19 can be attached at the protruding end, a switch 28 that is turned ON / OFF by external operation, and a controller 42 that controls the driving of the motor 6 based on the ON / OFF operation of the switch 28. The grinder 1 also includes a handle mounting section 45 provided on the housing 2 to which a side handle 50 (an example of an auxiliary handle) can be attached and detached, a detection mechanism 46 (an example of a handle detection mechanism) that electrically detects the mounting state of the side handle 50 to the handle mounting section 45, and a detection mechanism 46 (an example of a handle grip detection mechanism) that electrically detects the gripping state of the side handle 50 attached to the handle mounting section 45. Furthermore, the controller 42 drives the motor 6 when the switch 28 is turned ON after detecting the mounting of the side handle 50 by the detection mechanism 46 and the gripping of the side handle 50 by the detection mechanism 46. When the controller 42 detects that the side handle 50 has been attached and gripped, and the switch 28 is turned ON, the controller 42 controls the rotation of the motor 6 to a predetermined high rotation speed (an example of a first rotation speed). However, if the load condition on the tip tool 19 does not change for a predetermined time, the controller 42 controls the rotation of the motor 6 to a predetermined low rotation speed (an example of a second rotation speed) that is lower than the high rotation speed. With this configuration, the motor 6 is controlled at a low rotational speed when the tip tool 19 is not being used for work. Therefore, unnecessary power consumption can be reduced and noise generation can be minimized.

[0033] The second rotational speed is a low rotational speed (an example other than 0). Therefore, since the tip tool 19 rotates even when no work is being performed, work can be resumed in a short time, and a decrease in work efficiency can be suppressed. The handle detection and handle grip detection by the detection mechanism 46 are formed using a common pressure sensor 70 (an example of a sensor). Therefore, the handle detection mechanism and the handle grip detection mechanism can be rationally designed in a space-saving manner, and cost increases can be kept to a minimum. The load condition on the cutting tool 19 is the load current of the motor 6. Therefore, the load condition can be easily determined based on the load current. When the controller 42 detects a change in the load condition while controlling at a low rotational speed other than 0, it controls the rotation of the motor 6 to a high rotational speed. Therefore, since the motor automatically returns to a high rotational speed in a short time once work is resumed, reducing the rotational speed of motor 6 under no-load conditions does not result in a decrease in work efficiency or ease of use. The handle mounting section 45 is provided in two locations (an example of multiple locations). Therefore, the side handle 50 can be attached in a position that is easy to operate.

[0034] The following are examples of changes to this disclosure. In the above embodiment, the motor is controlled to a low rotation speed if a no-load state continues for a predetermined time, but it is also possible to stop the motor without reducing the rotation speed. The control method will be explained below based on the flowchart in Figure 16. Steps S11 to S19 are the same as steps S1 to S9 in the above embodiment. However, if the load current does not fluctuate for a predetermined time in S19 (YES in S19), the control circuit 100 assumes that no work is being performed, i.e., that the motor 6 is stationary with the side handle 50 being held, and stops the motor 6 in S20. Next, in S21, it is determined whether the switch lever 29 has been released and the switch 28 has turned OFF. If the switch 28 is turned OFF, the motor 6 stop control is reset and the process returns to S11. Therefore, if the side handle 50 is attached in S11 and the side handle 50 is gripped in S12, and the switch lever 29 is pressed, and the ON state of the switch 28 is confirmed in S13, the control circuit 100 controls the motor 6 at a high rotational speed in S14. If the OFF state of the switch 28 is not confirmed in S21, the motor 6 stop control is maintained.

[0035] In the above modified example, the controller 42 controls the rotation of the motor 6 to zero when the load on the tip tool 19 does not change for a predetermined time, and then resets the control to zero when the switch 28 is turned OFF. Subsequently, when the side handle 50 is attached and gripped, and the switch 28 is turned ON, the motor 6 is controlled to rotate at a high speed. Therefore, by stopping motor 6 in the no-load state, unnecessary power consumption and noise generation can be reliably eliminated. Also, when switch 28 is turned OFF, the stop state of motor 6 is reset, allowing for automatic return to normal operation.

[0036] The detection mechanism is not limited to the above embodiment which employs a single sheet-shaped pressure sensor. For example, an independent pressure sensor may be provided for each inner pin of the movable plate. In this case, the attachment of the side handle may be determined when the resistance value of some (e.g., two) of the pressure sensors exceeds a first threshold, rather than all of them. Similarly, the gripping of the side handle may be determined when the resistance value of some (e.g., two) of the pressure sensors exceeds a second threshold. The number of inner pins and pressure sensors can be increased or decreased as appropriate. The detection mechanism is not limited to one using a pressure sensor. For example, as disclosed in Patent Document 1 mentioned above, a mechanism using a detection plate whose position changes with the attachment of the side handle and a photointerrupter that detects the position of the detection plate may also be used. Other structures can also be adopted. In the examples above, a single detection mechanism can detect both the attachment and gripping of the side handle. However, the attachment detection mechanism and the gripping detection mechanism for the side handle may be formed separately. In this case, the same mechanism may be used for each detection mechanism, or different mechanisms may be used.

[0037] The handle mounting portion is not limited to being indirectly attached to the outer housing via a fixing ring, as in the above embodiment. The handle mounting portion can also be directly attached to the outer housing or gear housing. The auxiliary handle is not limited to the side handle of the above embodiment; the shape of the grip portion, etc., can be changed as appropriate. The auxiliary handle can also employ a connection structure other than screw-in.

[0038] The structure of the inner housing and outer housing is not limited to the above embodiment. For example, the outer housing does not have to be a split structure. The inner housing may also be a split structure. The elastic support of the inner housing by the outer housing is not limited to the above embodiment. For example, the length of the rubber sleeve may be changed, or multiple short rubber rings may be arranged in the axial direction. Elastic support can also be omitted. The grinder may be a DC tool that uses a battery pack mounted on a battery compartment in the housing, rather than an AC tool that uses commercial power. In this case, the need to manage a power cord is eliminated, resulting in improved operability and work efficiency. The motor may be a brushless motor. The grinding tools described herein are not limited to grinders. For example, this disclosure is also applicable to other grinding and polishing tools such as polishers and sanders. Therefore, the handle mounting portion is not limited to a pair of left and right portions. The handle mounting portion may be only on the left or right side, or there may be three or more. [Explanation of Symbols]

[0039] 1. Grinder, 2. Housing, 3. Inner housing, 4. Gear housing, 5. Outer housing, 6. Motor, 7. Output shaft, 14. Spindle, 19. Tip tool, 25. Main body, 26. Main grip, 28. Switch, 29. Switch lever, 42. Controller, 43. Control circuit board, 45. Handle mounting section, 46. Handle mounting / gripping detection mechanism, 50. Side handle, 51. Grip section, 52. Bolt, 54. Net 60...receiving surface, 61...first screw hole, 63...protruding part, 65...receiving recess, 69...pull-out hole, 70...pressure sensor, 71...pressure rubber, 72...movable plate, 73...outer cover, 77...recess, 78...protrusion, 80...inner pin, 81...outer pin, 87...screw, 90...first wiring, 91...second wiring, 92...first protrusion, 93...second protrusion, 95...guide groove, 100...control circuit, 101...sensor circuit, 102...motor drive circuit, 103...power supply circuit.

Claims

1. A housing that houses the motor, A spindle that protrudes from the housing and rotates when driven by the motor, with a tip tool attached to its protruding end, A switch that can be turned ON / OFF by external operation, A controller that controls the drive of the motor based on the ON / OFF operation of the switch, The housing is provided with a handle mounting portion from which an auxiliary handle can be attached and detached, A handle detection mechanism that electrically detects the mounting state of the auxiliary handle to the handle mounting portion, The system includes a handle grip detection mechanism that electrically detects the gripping state of the auxiliary handle attached to the handle mounting portion, The controller is a grinding tool that drives the motor when the switch is turned ON after detecting the attachment of the auxiliary handle by the handle detection mechanism and the gripping of the auxiliary handle by the handle gripping detection mechanism, The handle detection mechanism and the handle grip detection mechanism are formed using a common sensor provided on the handle mounting portion side. When the controller detects that the auxiliary handle has been attached and grasped, and the switch is turned ON, it controls the rotation of the motor to a predetermined first rotation speed, A grinding tool characterized in that, if the load on the tip tool does not change for a predetermined time, the rotation of the motor is controlled to a second rotation speed (including 0) that is lower than the first rotation speed.

2. The grinding tool according to claim 1, characterized in that the second rotational speed is other than 0.

3. The grinding tool according to claim 1 or 2, characterized in that the load condition on the tip tool is the load current of the motor.

4. The grinding tool according to claim 1 or 2, characterized in that when the controller detects a change in the load state while controlling at a second rotational speed other than 0, it controls the rotation of the motor to the first rotational speed.

5. The grinding tool according to claim 1, characterized in that the controller controls the rotation of the motor to zero when the load state on the tip tool does not change for a predetermined time, and then when the switch is turned OFF, it resets the control to set the rotation of the motor to zero, and then when the attachment and gripping of the auxiliary handle is detected and the switch is turned ON, it controls the rotation of the motor to the first rotation speed.

6. The grinding tool according to claim 1 or 2, characterized in that the handle mounting portion is provided in multiple locations.

7. The grinding tool according to claim 1 or 2, characterized in that the housing is provided with a battery mounting portion.

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