JP6617918B2 - Electric tool - Google Patents

Description

  The present invention relates to a power tool.

  2. Description of the Related Art Conventionally, electric tools that rotate or vibrate with a rotational force of a motor (rotational force of a rotor) and perform polishing, cutting, cutting, or the like by the rotation or vibration of the distal tool have been widely used. Such an electric tool includes a speed change dial for setting the rotation speed of the motor (rotation speed of the rotor), and is an electric motor that controls the motor so that the rotation speed of the rotor approaches the rotation speed set by the speed change dial. A tool is known (Patent Document 1).

  In the electric power tool described in Patent Document 1, the number of revolutions at no load is set according to the operation position of the speed change dial. In addition, the speed change dial is configured to be operable between the position where the number of rotations under no load is set to the minimum (minimum position) and the position where the rotation speed is set to the maximum (maximum position). The closer to the position, the larger the rotation speed at no load.

Japanese Patent Laid-Open No. 2014-233793

  In power tools, when there is a load, that is, when work is performed with a tip tool, even if some noise is generated, the number of rotations is increased to perform work efficiently, and when no load is applied, that is, work is performed. In the absence, it is desirable to reduce noise. However, the electric power tool described in Patent Document 1 has a problem that when the operation position is close to the maximum position, the rotational speed of the rotor becomes a relatively large value even when there is no load, and a large noise is generated. .

  Then, this invention aims at providing the electric tool which can reduce the noise at the time of no load.

In order to solve the above problems, the present invention rectifies and smoothes a brushless motor, a power supply connection portion connectable to an external AC power supply, an AC voltage output from the external AC power supply, and adjusts the frequency of the external AC power supply. A conversion circuit unit that converts and outputs a variable DC voltage that fluctuates at twice the frequency, an inverter circuit unit that applies the variable DC voltage output from the conversion circuit unit to the brushless motor, and the rotational speed of the brushless motor Motor control means for performing constant rotation speed control to bring the motor closer to the target rotation speed, and when the brushless motor is in a no-load state, the target rotation speed does not generate a non-energized section in which no current flows through the brushless motor. An electric tool characterized by being set as described above is provided. According to this configuration, noise in a no-load state (no load) can be reduced.

In the above configuration, an operation unit for setting the rotation speed of the brushless motor, and a rotation for controlling the rotation speed of the brushless motor according to the set rotation speed set by the operation unit or the operated amount of the operation unit And when the brushless motor is in a no-load state, the rotational speed control means is configured such that the set rotational speed exceeds a predetermined rotational speed or the manipulated amount exceeds a predetermined amount. It is preferable to limit the upper limit of the rotational speed of the brushless motor so that the non-energized section does not occur regardless of the set rotational speed or the operated amount. According to such a configuration, the upper limit of the rotational speed (actual rotational speed) of the motor can be limited in a no-load state. For this reason, by limiting the upper limit of the rotation speed of the motor to a rotation speed at which no loud noise is generated, noise in a no-load state (no load) can be reduced.

In the above configuration, the rotation speed control means is configured to set the rotation speed or the operation amount when the set rotation speed does not exceed the predetermined rotation speed or when the operated amount does not exceed the predetermined amount. It is preferable to increase the number of rotations of the brushless motor as the value increases.

  According to such a configuration, it is difficult to be affected by noise.

Further, it is preferable that the rotation speed control means controls the rotation speed of the brushless motor according to the set rotation speed or the operated amount when the brushless motor is not in the no-load state.

  According to such a configuration, work efficiency can be improved in a non-load state (when there is a load).

In addition, there is provided no-load determining means for determining whether or not the brushless motor is in a no-load state, and the rotation speed control means is independent of the set rotation speed or the operated amount when in the no-load state. not it is preferable that the brushless motor for controlling the brushless motor so as to rotate below the predetermined speed.

  According to such a configuration, the rotational speed (actual rotational speed) of the rotating shaft can be limited to a predetermined rotational speed or less when there is no load. For this reason, it is possible to reduce noise in a no-load state (no load) by adopting a rotation speed at which no loud noise is generated as the predetermined rotation speed.

Further, the rotation speed control means is configured to perform the predetermined rotation when it is in the no-load state and the set rotation speed exceeds the predetermined rotation speed or when the manipulated amount exceeds the predetermined amount. Preferably, the brushless motor is controlled such that the brushless motor rotates by a number.

According to such a configuration, when there is no load and the set rotational speed exceeds the predetermined rotational speed or the operated amount exceeds the predetermined rotational speed, the rotational speed range is equal to or lower than the predetermined rotational speed. brushless motor at a predetermined rotational speed is a maximum rotation speed to control the brushless motor to rotate. For this reason, when the work is started from the no-load state and becomes a no-load state (loaded state), the brushless motor speed can be increased to the set speed in a short time, improving work efficiency. Can be made.

Also, wireless load determining means is preferably the brushless motor is determined whether or not the wireless load state based on the current flowing through the brushless motor.

  According to such a configuration, it is possible to reliably determine whether or not there is no load with a simple configuration.

The conversion circuit unit preferably includes a rectifier circuit that rectifies the AC voltage and outputs a rectified voltage after rectification , and a smoothing capacitor that smoothes the rectified voltage so that the rectified voltage fluctuates. Moreover, the smooth capacitor induced voltage minimum value of the variation DC voltage or if該被operation amount when the brushless motor is rotated at the predetermined rotational speed than that is exceeded a predetermined amount is generated in the brushless motor follows it and the rectifying voltage smoothing to Turkey as outermost small value if the brushless motor is rotating below the predetermined rotational speed is higher than the induced voltage is preferable.

According to such a configuration, in a state where the rotation speed of the brushless motor is rotating at a predetermined rotation speed or less, or in a state where the operated amount is a predetermined rotation speed or less, a non-energization period does not occur, and the fluctuation range of the rotation speed pulsation is also large. Since it is small, no significant noise is generated. Moreover, if, when the rotational speed of the brushless motor reaches a predetermined rotational speed than the rotational speed pulsation is generated not energized period occurs, but the noise is remarkable, in the unloaded state, of the brushless motor Since the rotational speed is limited to a predetermined rotational speed or less, it is possible to suppress the occurrence of significant noise.

  The capacitance of the smoothing capacitor is preferably 180 μF or less.

  In order to solve the above-mentioned problem, the present invention further includes a motor, an operation unit for setting the rotation number of the motor, and a rotation number of the motor based on the operated amount of the operation unit. And a rotation speed control means for controlling in a range from the first rotation speed to a second rotation speed greater than the first rotation speed, wherein the rotation speed of the motor is determined when the motor is in an unloaded state. As the manipulated amount increases from the first amount to a third amount that is greater than the first amount and less than the second amount, the second rotation number is greater than the first rotation number from the first rotation number. An electric tool characterized by being increased to a third rotational speed smaller than the third rotational speed and being limited to the third rotational speed or less while the manipulated amount increases from the third amount to the second amount. ing.

  According to such a configuration, the rotational speed of the rotating shaft is limited to the third rotational speed or less in the no-load state. For this reason, it is possible to reduce noise in a no-load state (no load) by adopting a rotation speed at which no large noise is generated as the third rotation speed.

  In the above configuration, the rotation speed of the motor is maintained at the third rotation speed while the operated amount increases from the third amount to the second amount in the no-load state. Is preferred.

  According to such a configuration, when there is no load and the operated amount exceeds the second amount, the rotation speed of the rotation shaft is the third rotation speed that is the maximum rotation speed in the rotation speed range equal to or less than the third rotation speed. Maintained at rotational speed. For this reason, when the work is started from the no-load state and the state is not the no-load state (loaded state), the rotational speed of the rotary shaft is set in a short time according to the manipulated variable (from the third rotational speed). Can be increased to a large number of revolutions), and work efficiency can be improved.

  The rotation speed control means may control the rotation speed of the motor according to the set rotation speed set by the operation unit or the operated amount of the operation unit when the motor is in a load state. preferable.

  According to such a configuration, it is possible to improve work efficiency when there is a load.

In order to solve the above-mentioned problem, the present invention further rectifies and smoothes a brushless motor, a power supply connecting portion connectable to an external AC power supply, an AC voltage output from the external AC power supply, and a frequency of the external AC power supply. A converter circuit unit that converts and outputs a variable DC voltage that fluctuates at a frequency twice that of the inverter, and an inverter circuit unit that applies the variable DC voltage output from the converter circuit unit to the brushless motor. When the motor is in a no-load state, the brushless motor is driven at a rotational speed that does not generate a non-energized section in which no current flows through the brushless motor. There is provided an electric tool characterized in that the brushless motor is driven at an increased rotational speed.
In order to solve the above-mentioned problem, the present invention further rectifies and smoothes a brushless motor, a power supply connecting portion connectable to an external AC power supply, an AC voltage output from the external AC power supply, and a frequency of the external AC power supply. A converter circuit unit that converts and outputs a variable DC voltage that fluctuates at a frequency twice that of the inverter, and an inverter circuit unit that applies the variable DC voltage output from the converter circuit unit to the brushless motor. When the motor is in a no-load state, the brushless motor can be driven at a rotation speed that does not generate a non-energized section in which no current flows in the brushless motor. The present invention also provides an electric tool characterized in that the brushless motor can be driven by increasing the rotational speed. According to this configuration, noise in a no-load state (no load) can be reduced. Further, it is possible to efficiently perform work in a loaded state (when loaded).

In the above configuration, an operation unit for setting the rotation speed of the brushless motor is provided, and a current flows through the brushless motor regardless of the set rotation speed set by the operation unit or the operated amount of the operation unit. It is preferable that the upper limit of the rotational speed is limited so that the rotational speed is such that no non-energized section is generated. According to such a configuration, the upper limit of the rotational speed (actual rotational speed) of the motor can be limited in a no-load state. For this reason, by limiting the upper limit of the rotational speed of the motor to a rotational speed at which no loud noise is generated, noise in a no-load state (no load) can be reduced.

In the above configuration, provided is a rotation speed control means for controlling the brushless motor so as to limit the upper limit of the rotation speed of the brushless motor according to the set rotation speed set by the operation section or the operated amount of the operation section. The rotation speed control means is configured to set the rotation speed when the brushless motor is in a no-load state and the set rotation speed exceeds a predetermined rotation speed or when the operated amount exceeds a predetermined amount. as the brushless motor is rotated to limit the upper limit of the rotational speed of the brushless motor, regardless of the number or該被operation amount or the predetermined rotational speed, it is preferable to control the brushless motor.

  According to such a configuration, noise during no load can be reduced.

  According to the electric tool of the present invention, noise during no load can be reduced.

1 is a partial cross-sectional side view showing an entire disc grinder according to an embodiment of the present invention. It is a top view which shows the external appearance of the disc grinder by embodiment of this invention. It is a graph which shows the relationship between the user setting rotation speed of the disc grinder and dial setting state by embodiment of this invention. 1 is a circuit diagram including a block diagram showing an electrical configuration of a disc grinder according to an embodiment of the present invention. It is a graph which shows the relationship between the user setting rotation speed of the disc grinder by embodiment of this invention, the target rotation speed in a no-load state, and the state of dial setting. It is the figure which represented typically the meshing location of the pinion gear tooth | gear and bevel gear tooth | gear of the disc grinder by embodiment of this invention, (a) is the downstream surface of the pinion gear tooth | gear upstream of the bevel gear tooth | gear. The state which is in contact with the surface is shown, and (b) shows the state in which the upstream surface of the teeth of the pinion gear is in contact with the downstream surface of the teeth of the bevel gear. It is a time chart which shows the change of the real rotation speed of the rotating shaft of the disc grinder by embodiment of this invention, a fluctuation | variation DC voltage, a motor current, and a gear collision sound, tentatively setting target rotation speed to 32400 rpm (dial setting " 6)). It is a time chart which shows the change of the real rotation speed of the rotating shaft of the disk grinder by embodiment of this invention, a fluctuation | variation DC voltage, a motor current, and a gear collision sound, The target rotation speed is set to 22680rpm (dial setting "4" )). It is a flowchart which shows the drive control of the motor by the control circuit part of the disc grinder by embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, when a specific numerical value is mentioned, for example, when an angle is referred to as “90 °”, it is not only the case where the numerical value is completely coincident with the numerical value, but also substantially the same as the numerical value. Including cases. In addition, when referring to the positional relationship, for example, when referring to parallel, orthogonal, opposite, etc., not only when it is completely parallel, orthogonal, opposite, etc., but also substantially parallel, substantially orthogonal, substantially opposite, etc. Including some cases.

  FIG. 1 is a partial cross-sectional side view showing an entire disc grinder 1 as an example of an electric power tool according to an embodiment of the present invention. As shown in FIG. 1, the disc grinder 1 includes a housing 2, a motor 3, a power transmission mechanism 4, an output shaft portion 5 that detachably holds a grindstone T (tip tool), an inverter circuit 62, and a control circuit portion. 72 (FIG. 4) and a power cord 8 that can be connected to an AC power source. The disc grinder 1 is a portable electric tool that performs operations such as polishing and grinding using a grindstone T that rotates while being held by the output shaft portion 5. In FIG. 1, “front” indicated by an arrow is defined as a forward direction, “rear” is defined as a rear direction, “up” is defined as an upward direction, and “down” is defined as a downward direction. Further, when the disc grinder 1 is viewed from behind, the left is defined as the left direction and the right is defined as the right direction.

  The housing 2 is an outer part of the disc grinder 1, and includes a motor housing 21, a gear housing 22 provided in front of the motor housing 21, and a rear housing 23 provided in the rear of the motor housing 21. Yes. In the present embodiment, the housing 2 is constituted by three portions arranged in the front-rear direction, but is not limited thereto. For example, the motor housing 21 and the rear housing 23 may be integrally formed, or other divided shapes may be used.

  The motor housing 21 is made of resin or metal, has an outer portion 21 </ b> A and a bearing holder portion 21 </ b> B, and houses the motor 3. As shown in FIG. 2, a drive switch 21 </ b> D is provided on the left side surface of the motor housing 21. FIG. 2 is a plan view showing the external appearance of the disc grinder 1.

  Returning to FIG. 1, the outer portion 21 </ b> A is a portion that is gripped by the user when the disc grinder 1 is used, and has a substantially cylindrical shape that extends in the front-rear direction. The bearing holder portion 21B is provided at a rear end portion inside the outer portion 21A, and a plurality of cylindrical portions extending in the front-rear direction that support the outer ring of the ball bearing 21C and a peripheral surface of the cylindrical portion and the outer portion 21A are connected. It has no support. The plurality of support pillars extend radially outward of the cylindrical portion from the circumferential surface of the cylindrical portion, and are disposed at predetermined intervals in the circumferential direction on the circumferential surface of the cylindrical portion. Further, a gap is formed between two adjacent columns, and the internal space of the motor housing 21 and the internal space of the rear housing 23 communicate with each other through the gap.

  The motor 3 includes a rotating shaft 31, a rotor 32, and a stator 33. The rotation shaft 31 extends in the front-rear direction, and is rotatably supported by a ball bearing 21 </ b> C and a ball bearing 22 </ b> A provided at the rear portion of the gear housing 22. A cooling fan 31 </ b> A is provided at the front portion of the rotating shaft 31. A sensor magnet 31B for detecting the rotational position of the rotary shaft 31 (rotor 32) is attached to the rear end of the rotary shaft 31. The sensor magnet 31B is a thin columnar permanent magnet, and is arranged so as to be formed in the order of N pole, S pole, N pole, and S pole at intervals of 90 degrees in the circumferential direction of the rotating shaft 31.

  The cooling fan 31 </ b> A is, for example, a plastic centrifugal fan, and rotates together with the rotating shaft 31 to generate cooling air in the housing 2. The cooling air generated by the rotation of the cooling fan 31A flows into the rear housing 23 from a plurality of air inlets 23a formed in the rear portion of the rear housing 23, and cools the circuits such as the power conversion circuit 61 and the inverter circuit 62. Then, it passes through the gaps between the plurality of pillars of the bearing holder portion 21B and flows into the motor housing 21. The cooling air flowing into the motor housing 21 cools the motor 3 and is then discharged from an exhaust hole (not shown) formed on the side surface of the front end portion of the motor housing 21.

  The rotor 32 is a rotor formed by laminating a large number of thin steel plates on an annular shape in the front-rear direction, and has a plurality of permanent magnets 32A. The rotor 32 is fixed to the rotating shaft 31 and is configured to rotate integrally with the rotating shaft 31. The stator 33 is a stator having a laminated structure of thin annular steel plates, and has a stator winding 33A. The stator winding 33 </ b> A is wound around a tooth (not shown) formed on the inner peripheral portion of the stator 33. The electrical configuration of the motor 3 will be described later.

  As shown in FIG. 2, the drive switch 21 </ b> D is a switch for turning on / off the drive of the motor 3. The drive switch 21D is configured to be slidable between an off position (position shown in FIG. 2) and an on position (position moved backward from the off position by a predetermined distance). The drive switch 21 </ b> D is connected to the control circuit unit 72 (FIG. 4), and outputs a start signal for driving the motor 3 to the control circuit unit 72 when it is in the ON position.

  Returning to FIG. 1, the gear housing 22 is manufactured by, for example, integral molding of a metal such as aluminum, and accommodates the power transmission mechanism 4 and rotatably supports the output shaft portion 5.

  The power transmission mechanism 4 is a mechanism that decelerates the rotation of the rotation shaft 31 and transmits it to the output shaft portion 5, and has a pinion gear 41 and a bevel gear 42 that mesh with each other. The pinion gear 41 is fixed to the front end of the rotating shaft 31 and is configured to rotate coaxially with the rotating shaft 31. The bevel gear 42 is configured to rotate around an axis extending in a direction (vertical direction) substantially orthogonal to the rotation axis of the pinion gear 41.

  The output shaft portion 5 includes a shaft portion 5A, a mounting base 5B that holds the grindstone T in a detachable manner, and a washer nut 5C. The shaft portion 5 </ b> A is a shaft extending in the vertical direction fixed to the bevel gear 42 of the power transmission mechanism 4, and is configured to rotate coaxially with the bevel gear 42. The shaft portion 5A is rotatably supported by the gear housing 22 via a metal 22B at the upper end portion thereof and a ball bearing 22C at a substantially vertical center.

  The mounting base 5B is provided at the lower end portion of the shaft portion 5A, and has a disk portion that is substantially circular in a bottom view and a screw portion that extends downward from the center in the bottom view of the disk portion. Yes. The washer nut 5C is configured to be able to be screwed into the threaded portion of the mounting base 5B. The grindstone T is fixed to the output shaft portion 5 by inserting the threaded portion of the mounting base 5B through a through hole formed in the center of the grindstone T in plan view, and the upper surface of the grindstone T on the bottom surface of the disc portion of the mounting base 5B. In the abutted state, the washer nut 5C is screwed onto the threaded portion of the mounting base 5B. Further, the grindstone T is removed from the output shaft portion 5 by releasing the screwing between the screw portion of the mounting base 5B and the washer nut 5C.

  The grindstone T is, for example, a resinoid flexible toy, flexible toy, resinoid toy, sanding disk, etc. having a substantially circular shape in plan view, and depending on the type of abrasive used, the surface of metal, synthetic resin, marble, concrete, etc. Polishing and curved surface polishing are possible. The outer side in the radial direction of the rear side of the grindstone T is covered with a wheel guard 22D provided at the rear end of the lower end of the gear housing 22 in a state where the grindstone T is fixed to the output shaft portion 5. In addition, in this Embodiment, although the grindstone T was attached to the output shaft part 5, it is not restricted to this. For example, other tip tools such as a bevel wire brush, a non-woven fabric brush, and a diamond wheel can be attached to the output shaft portion 5.

  The rear housing 23 is made of resin and has a substantially cylindrical shape extending in the front-rear direction. Inside the rear housing 23, a substrate housing case 23A, a sensor substrate 23B, a first substrate 6 and a second substrate 7 are arranged. Further, the power cord 8 extends rearward from the rear end portion of the rear housing 23. Further, as shown in FIG. 2, a transmission dial portion 9 is provided on the left side of the power cord 8 at the rear end portion of the rear housing 23.

  Returning to FIG. 1, the substrate housing case 23 </ b> A has a box shape with an open bottom, and houses the sensor substrate 23 </ b> B, the first substrate 6, and the second substrate 7. Each of the sensor substrate 23B, the first substrate 6 and the second substrate 7 is covered with a curable resin in a state of being housed in the substrate housing case 23A.

  The sensor substrate 23B is a semicircular substrate in a rear view, and is provided in the vicinity of the sensor magnet 31B on the rear surface of the front wall of the substrate housing case 23A. Three Hall ICs 23C, 23D, and 23E for detecting the position of the sensor magnet 31B, that is, the rotation position (rotation angle) of the rotation shaft 31 (rotor 32) are mounted on the sensor substrate 23B. The three Hall ICs 23C, 23D, and 23E are arranged at a predetermined angle interval in the circumferential direction (rotation direction) of the rotation shaft 31 in the rear view. In the present embodiment, they are arranged at intervals of 60 °. Further, the three Hall ICs 23C, 23D, and 23E output a high signal or a low signal to the control circuit unit 72 according to the change in the magnetic field of the rotating sensor magnet 31B, that is, according to the rotational position of the rotating shaft 31. .

  The first substrate 6 is a flat circuit board and is disposed substantially parallel to a virtual plane orthogonal to the vertical direction. On the first substrate 6, a power conversion circuit 61 including a rectifier circuit 61A and a smoothing capacitor 61B, and an inverter circuit 62 having six switching elements 62A to 62F are mounted. Each of the six switching elements 62 </ b> A to 62 </ b> F, the rectifier circuit 61 </ b> A, and the smoothing capacitor 61 </ b> B is provided so as to extend downward from the first substrate 6. In the present embodiment, the switching elements 62A to 62F are output transistors such as large capacity FETs (electrolytic effect transistors) or IGBTs (insulated gate bipolar transistors), for example.

  The second substrate 7 is a flat circuit board, and is disposed above the first substrate 6 and substantially parallel to the first substrate 6. On the second substrate 7, a control power supply circuit unit 71 and a control circuit unit 72 (FIG. 4) are mounted. The electrical configuration of each circuit mounted on the first substrate 6 and the second substrate 7 will be described later.

  The power cord 8 has a tip connection portion (not shown) and a cable portion 81. The tip connection portion includes a first connection terminal 8A and a second connection terminal 8B (FIG. 4) that can be connected to an AC power supply (for example, the commercial AC power supply P shown in FIG. 4). The cable portion 81 has wiring that connects the first connection terminal 8 </ b> A and the second connection terminal 8 </ b> B and the power supply conversion circuit 61. The first connection terminal 8A and the second connection terminal 8B are examples of the “power supply connection portion” in the present invention. Moreover, the commercial AC power source P is an example of the “external AC power source” in the present invention.

  As shown in FIG. 2, the transmission dial portion 9 is an operation portion that can be manually operated by the user for setting the number of rotations of the rotary shaft 31 (rotor 32), and includes a dial 9 </ b> A and a variable (not shown). A resistor and a voltage dividing resistor (not shown) are included. The transmission dial unit 9 is an example of the “operation unit” in the present invention.

  The dial 9A is a disc-shaped dial that can be manually operated, and is supported by the rear housing 23 so as to be rotatable about an axis extending in the left-right direction. On the peripheral surface of the dial 9A, numbers “1” to “6” are engraved at equal intervals in that order. The dial 9 </ b> A is configured to be able to turn approximately 200 ° clockwise in the left side view from the state in which the stamp “1” is positioned in the 3 o'clock direction in the left side view (the dial setting “1” state). When the dial 9A is rotated from the dial setting “1” state by approximately 40 ° clockwise as viewed from the left side, the dial setting “2” is positioned in the 3 o'clock direction when viewed from the left side view. Become. Similarly, the dial setting is “3” at approximately 80 °, the dial setting is “4” at approximately 120 °, the dial setting is “5” at approximately 160 °, and the dial setting is “6” at approximately 200 °. The rotation angle of the dial 9A from the dial setting “1” is an example of the “operated amount” in the present invention. The rotation angle 0 ° is an example of the “first amount” in the present invention, the rotation angle 200 ° is an example of the “second amount” in the present invention, and the rotation angle 120 ° is the “third amount” in the present invention. It is an example of “amount” and “predetermined amount”.

  The variable resistance provided in the speed change dial portion 9 is configured such that its resistance value changes as the rotation angle (operated amount) of the dial 9A changes based on the dial setting “1”. A voltage dividing resistor is connected in series between a reference voltage VCC (to be described later) and GND (not shown). The reference voltage VCC is divided by a variable resistor and a voltage dividing resistor, and the divided voltage is output to the control circuit unit 72 as a user setting signal indicating a user set rotation speed that is a rotation speed set by the user. The user set rotational speed is an example of the “set rotational speed” in the present invention.

  Here, with reference to FIG. 3, specific numerical values of the user-set rotation speed set by the transmission dial unit 9 will be described. FIG. 3 is a graph showing the relationship between the user-set rotation speed and the dial setting state. Note that a solid line R in FIG. 3 indicates the user-set rotation speed corresponding to the dial setting state.

  As shown in FIG. 3, in the present embodiment, the rotational speed of the rotary shaft 31 can be set within a range of 9156 rpm to 32400 rpm. The user-set rotation speed set by the user increases linearly as the dial 9A rotates from the dial setting “1” state to the “6” state, and the dial 9A is the highest when the dial 9A is in the dial setting “1” state. A small 9156 rpm is set, and a maximum of 32400 rpm is set in the state of the dial setting “6”. In addition to the dial settings “1” and “6”, for example, in the state of the dial setting “4”, the user set rotational speed is set to 22680 rpm. 9156 rpm is an example of the “first rotational speed” in the present invention. Further, 32400 rpm is an example of the “second rotational speed” in the present invention.

  Next, referring to FIG. 4, the electrical configuration of the disc grinder 1, that is, the motor 3, the power conversion circuit 61 and the inverter circuit 62 mounted on the first substrate 6, and the control mounted on the second substrate 7. The power supply circuit unit 71 and the control circuit unit 72 will be described. FIG. 4 is a circuit diagram including a block diagram showing an electrical configuration of the disc grinder 1.

  As shown in FIG. 4, the motor 3 is a three-phase brushless motor, and the rotor 32 includes two sets of permanent magnets 32 </ b> A each having a north pole and a south pole. The stator winding 33 </ b> A of the stator 33 has star-connected three-phase coils U, V, and W, and the coils U, V, and W are each connected to an inverter circuit 62.

  The power supply conversion circuit 61 is a circuit that converts an AC voltage output from the commercial AC power supply P into a changing DC voltage (fluctuating DC voltage) and outputs it, and includes a rectifying circuit 61A and a smoothing capacitor 61B. The rectifier circuit 61A is connected to the first connection terminal 8A and the second connection terminal 8B, and full-wave rectifies the AC voltage output from the commercial AC power supply P, that is, the AC voltage has a full-wave rectification waveform. It is a circuit that converts to a DC voltage and outputs it. The smoothing capacitor 61B is an electrolytic capacitor that smoothes the DC voltage of the full-wave rectified waveform output from the rectifier circuit 61A. Since smoothing capacitor 61B in the present embodiment has a small capacity (about 180 μF), the DC voltage of the full-wave rectified waveform output from rectifier circuit 61A is not completely smoothed and output from power supply converter circuit 61. The applied voltage is a DC voltage that fluctuates at a frequency twice that of the commercial AC power supply P (variable DC voltage). The power conversion circuit 61 is an example of the “conversion circuit unit” in the present invention. The DC voltage having a full-wave rectified waveform output from the rectifier circuit 61A is an example of the “rectified voltage” in the present invention.

  The inverter circuit 62 is a circuit that applies the variable DC voltage output from the power conversion circuit 61 to the motor 3, and is connected between the first connection terminal 8 </ b> A and the second connection terminal 8 </ b> B and the motor 3. The six switching elements 62A to 62F of the inverter circuit 62 are connected in a three-phase bridge format, each gate is connected to the control circuit unit 72, and each drain or each source is a coil U, V, Connected to W. The six switching elements 62 </ b> A to 62 </ b> F perform a switching operation for generating a rotating magnetic field for rotating the rotor 32 in a predetermined rotation direction based on a drive signal (gate signal) output from the control circuit unit 72. The inverter circuit 62 is an example of the “inverter circuit portion” in the present invention.

  The control power supply circuit unit 71 is a circuit unit that generates a reference voltage VCC serving as a power supply for the control circuit unit 72 and other circuits, and an IPD circuit 71A that makes the variable DC voltage output from the power conversion circuit 61 constant. It is configured to include a regulator 71B that converts a voltage that has been made constant by the IPD circuit 71A into a reference voltage VCC (5V in the present embodiment), a surge absorbing capacitor, and the like.

  The control circuit unit 72 shows a correspondence between a drive control program used for drive control of the motor 3, a central processing unit (CPU) that performs calculations based on various data, a drive control program, a user-set rotation speed, and a user-set signal. ROM for storing setting table, various data, various threshold values, RAM for temporarily storing data, time measuring unit for measuring time, and amplifying drive signals to gates of six switching elements 62A to 62F And a signal output unit that outputs the signal, and performs drive control of the motor 3 in accordance with the drive control program.

  In the drive control of the motor 3, the control circuit unit 72 detects the current flowing through the motor 3, that is, the motor current, detects the rotational position and rotational speed (actual rotational speed) of the rotating shaft 31, and detects the user-set rotational speed. . In the present embodiment, the rotational position and the actual rotational speed of the rotating shaft 31 coincide with the rotational position and the actual rotational speed of the rotor 32, respectively.

  The motor current is detected by reading the voltage drop value of the shunt resistor 6A provided between the power conversion circuit 61 and the inverter circuit 62 and calculating from the voltage drop value. The rotation position of the rotary shaft 31 is detected by calculating based on the high signal or low signal output from the three Hall ICs 23C, 23D, and 23E. The actual rotational speed of the rotary shaft 31 is detected by calculating from the detected rotational position of the rotary shaft 31. The user-set rotation speed is detected by reading the value of the user setting signal output from the transmission dial unit 9 and referring to the setting table.

  Further, the control circuit unit 72 forms a drive signal for sequentially switching the switching elements to be conducted among the switching elements 62A to 62F based on the detected rotational position of the rotating shaft 31, and the drive signal is sent from the signal output unit. It amplifies and outputs to each gate of switching element 62A-62F. As a result, a predetermined magnetic coil among the coils U, V, and W of the motor 3 is sequentially energized to generate a rotating magnetic field, and the rotor 32 is rotated in a predetermined rotational direction. In this case, the drive signal for driving (conducting) the switching elements 62D to 62F connected to the negative power supply side line (second connection terminal 8B side line, minus line) of the inverter circuit 62 is a pulse width modulation signal. (PWM signal) is output. The PWM signal is a signal whose duty ratio can be changed.

  Further, the control circuit unit 72 determines the target rotational speed, and controls the motor 3 so that the actual rotational speed of the rotating shaft 31 becomes the target rotational speed, that is, performs constant rotational speed control. More specifically, the target rotational speed is compared with the detected actual rotational speed of the rotating shaft 31, and the duty ratio of the PWM signal output to the switching elements 62D to 62F is changed according to the comparison result, thereby rotating the rotational speed. Feedback control is performed to bring the actual rotational speed of the shaft 31 closer to the target rotational speed. The control circuit unit 72 is an example of the “rotational speed control unit” and the “motor control unit” in the present invention.

  Next, drive control of the motor 3 according to the drive control program by the control circuit unit 72 will be described. In the drive control by the control circuit unit 72, it is possible to reduce noise in a no-load state (a state where no work is performed) and maintain work efficiency in a loaded state.

  Control when the motor 3 is in a no-load state will be described with reference to FIG. FIG. 5 is a graph showing the relationship between the user-set rotation speed and the target rotation speed in the no-load state and the dial setting state. Note that a broken line R in FIG. 5 indicates the user-set rotation speed according to the dial setting state, and a solid line S indicates the target rotation speed according to the dial setting state.

  As shown in FIG. 5, in the no-load state, in view of the fact that significant noise is generated when the actual rotational speed of the rotating shaft 31 exceeds a predetermined rotational speed Nt (22680 rpm in the present embodiment). Thus, when the user set rotational speed set by the transmission dial unit 9 exceeds the predetermined rotational speed Nt, the target rotational speed is set to a value equal to or smaller than the predetermined rotational speed Nt regardless of the user set rotational speed, and the actual rotation shaft 31 is Control is performed so that the rotational speed is equal to or lower than the predetermined rotational speed Nt (restricted to the predetermined rotational speed Nt or lower, that is, the upper limit of the actual rotational speed is limited). This suppresses occurrence of significant noise in the no-load state. In the present embodiment, when the dial setting “4” is exceeded, the user set rotational speed exceeds the predetermined rotational speed Nt. Therefore, the target rotational speed is set to the predetermined rotational speed Nt, and the rotary shaft 31 in the no-load state. The motor 3 is controlled so that the actual number of revolutions becomes a predetermined number of revolutions Nt. In the present embodiment, when the user set rotational speed set by the transmission dial unit 9 in the no-load state exceeds the predetermined rotational speed Nt, the target rotational speed is set to the predetermined rotational speed Nt. The number is not limited to this as long as it is several Nt or less. The predetermined rotation speed Nt is an example of the “third rotation speed” in the present invention.

  On the other hand, in the no-load state, when the user set rotational speed is set to a predetermined rotational speed Nt or less (in the present embodiment, dial setting “4” or less), no significant noise is generated. The motor 3 is controlled so that the rotational speed is set as the target rotational speed and the actual rotational speed of the rotary shaft 31 becomes the target rotational speed, in other words, the set rotational speed set by the user.

  Next, control when the motor 3 is in a loaded state will be described. In a loaded state, in order to prioritize work efficiency over noise reduction, the actual rotational speed of the rotary shaft 31 is not limited, and the actual rotational speed of the rotary shaft 31 is set to the user-set rotational speed set by the user. The motor 3 is controlled. That is, the user set rotational speed shown in FIG. 3 is used as the target rotational speed as it is.

  Here, the relationship between the rotation speed of the rotating shaft 31 and the noise during driving of the motor 3 will be described. In general, noise during driving of the motor of the electric tool increases as the rotational speed of the rotary shaft increases. In particular, as in the case of the disc grinder 1 according to the present embodiment, in a configuration in which an AC voltage output from a commercial AC power source is converted into a variable DC voltage and the variable DC voltage is applied to a motor coil, When the rotation speed exceeds a certain value, noise becomes more prominent. This is because the induced voltage generated in the coil of the motor due to the rotation of the rotating shaft is higher than the minimum value of the fluctuation DC voltage, and the non-energization period in which no current flows in the coil and the energization period in which the current flows in the coil Since the rotation pulsations with a large fluctuation range occur and the gear teeth of the power tool are engaged with each other, the gear teeth that engage with each other repeatedly collide violently and generate a loud collision sound at each collision. is there.

  In the present embodiment, when the actual rotational speed of the rotating shaft 31 exceeds the predetermined rotational speed Nt, a non-energization period occurs and rotational pulsations with a large fluctuation range occur, and the pinion gear 41 and the bevel gear 42 mesh with each other. A loud collision noise is generated at the location. For this reason, the predetermined rotational speed Nt is used as a threshold value for limiting the actual rotational speed of the rotating shaft 31 in the no-load state.

  Here, the collision of the teeth of the pinion gear 41 and the bevel gear 42 when the rotational speed pulsation occurs in the present embodiment will be described with reference to FIG. FIG. 6 is a diagram schematically showing the meshing positions of the teeth of the pinion gear 41 and the teeth of the bevel gear 42 in the present embodiment. FIG. (B) shows a state where the upstream surface 41B of the tooth of the pinion gear 41 is in contact with the downstream surface 42A of the tooth of the bevel gear 42. Note that an arrow C1 shown in FIG. 6 indicates the rotation direction of the pinion gear 41, and an arrow C2 indicates the rotation direction of the bevel gear 42.

  When rotation speed pulsation occurs, the rotation shaft 31 repeats deceleration and acceleration, and the pinion gear 41 fixed to the rotation shaft 31 also repeats deceleration and acceleration. The state where the downstream surface 41A of the tooth of the pinion gear 41 is in contact with the upstream surface 41B of the tooth of the bevel gear 42 (the state shown in FIG. 6A, for example, the actual rotational speed of the rotary shaft 31 is the rotational speed pulsation. When the pinion gear 41 decelerates from the moment when the maximum number of rotations is reached in the fluctuation range, the rotation speed of the pinion gear 41 is substantially reduced with respect to the bevel gear 42 that maintains the same rotation speed as that immediately before the pinion gear 41 decelerates. It will be slower by the amount. This is a configuration in which the bevel gear 42 and the output shaft portion 5 holding the grindstone T rotate together, and since the integral rotating body has a large inertia, it is rotated by the pinion gear 41 for a short time. This is because the bevel gear 42 can maintain the rotational speed even if it is not driven.

  When the rotational speed of the pinion gear 41 becomes slower than the rotational speed of the bevel gear 42, the tooth downstream surface 41A of the pinion gear 41 and the tooth upstream surface 42B of the bevel gear 42 are separated from each other, and the tooth upstream surface 41B of the pinion gear 41 is separated. It collides with the downstream surface 42A of the tooth of the bevel gear 42 (the state shown in FIG. 6B). A collision sound is generated at the moment of the collision. The magnitude of the collision sound depends on the degree of deceleration of the pinion gear 41, that is, the deceleration rate (the rate of decrease in the rotation speed, the inclination of the decrease), and the greater the degree of deceleration, the greater the collision sound.

  Further, after the above-described collision, when the pinion gear 41 accelerates from the state where the upstream surface 41B of the teeth of the pinion gear 41 is in contact with the downstream surface 42A of the teeth of the bevel gear 42 (the state shown in FIG. 6B). The rotation speed of the pinion gear 41 is increased by the amount substantially accelerated with respect to the rotation speed of the bevel gear 42, and the upstream surface 41 </ b> B of the tooth of the pinion gear 41 is separated from the downstream surface 42 </ b> A of the tooth of the bevel gear 42. The downstream surface 41A of the tooth collides with the upstream surface 42B of the tooth of the bevel gear 42 (the state shown in FIG. 6A). A collision sound is generated again at the moment of the collision. The magnitude of the collision sound depends on the degree of acceleration of the pinion gear 41 (the rate of increase in rotation speed, the inclination of the increase), and the greater the degree of acceleration, the larger the collision sound. Thereafter, the above-described collision is repeated at high speed.

  Thus, when rotation speed pulsation occurs in the rotating shaft 31, the pinion gear 41 and the bevel gear 42 repeatedly collide at high speed, and a gear collision sound is generated at each collision. Further, the greater the fluctuation range of the rotational speed pulsation (the greater the degree of deceleration and acceleration), the greater the gear collision sound, and the noise during driving of the motor 3 becomes more prominent.

  Here, referring to FIG. 7 and FIG. 8, the two cases of the case where the non-energization period occurs and the case where the non-energization period does not occur in the present embodiment are caused by the fluctuation range of the rotational speed pulsation and the gear collision sound. The relationship with the level of noise to be performed will be described. FIGS. 7 and 8 are time charts showing changes in the actual rotational speed of the rotating shaft 31, the variable DC voltage, the motor current, and the gear collision sound. FIG. 7 temporarily assumes that the target rotational speed is 32400 rpm (no load). FIG. 8 shows a case where the target rotation speed is 22680 rpm (dial setting “4”) in the no-load state. In the case of FIG. 7, the duty ratio of the PWM signal slightly varies around 80% due to the feedback control, and in the case of FIG. 8, the duty ratio slightly varies around 60%. Further, the gear collision sound shown in FIGS. 7 and 8 is merely drawn to show the magnitude, and the generation timing thereof is different from the actual generation timing.

  As shown in FIG. 7, if the target rotational speed is set to 32400 rpm (dial setting “6”) in the no-load state, the variable DC voltage applied to the motor 3 via the inverter circuit 62 is 60V. The induced voltage that periodically fluctuates between (minimum value) and 141V (maximum value) and is generated in the motor 3 is about 100V. That is, the induced voltage is a value between the minimum value and the maximum value of the variable DC voltage (the minimum value is equal to or less than the induced voltage). For this reason, the non-energization period X in which the variable DC voltage is less than the induced voltage and the motor current does not flow and the energization period Y in which the variable DC voltage exceeds the induced voltage and the motor current flows alternately occur. In the non-energization period X, since the motor current does not flow, the rotating shaft 31 decelerates and the rotation speed decreases. On the other hand, in the energizing period Y, the motor current of 10 A at maximum flows, so the rotation shaft 31 accelerates and the rotation speed. Rises. That is, since the fluctuation range of the motor current is as large as 10 A, the degree of acceleration and deceleration of the rotating shaft 31 is increased. A rotational speed pulsation having a width is generated. Thereby, the collision sound between the teeth of the pinion gear 41 and the bevel gear 42 is increased, and a remarkable noise is generated.

  As shown in FIG. 8, when the target rotational speed is 22680 rpm (dial setting “4”) in the no-load state, the variable DC voltage applied to the motor 3 ranges from 100 V (minimum value) to 141 V (maximum). Value) and the induced voltage generated in the motor 3 is about 80V. That is, the induced voltage becomes a value smaller than the minimum value of the varying DC voltage, and the varying DC voltage always exceeds the induced voltage. For this reason, the non-energization period during which no motor current flows does not occur, the motor current fluctuates between 3 to 5 A (fluctuation range 2 A), and the degree of acceleration and deceleration of the rotating shaft 31 is temporarily set in a no-load state. Compared with the case where the rotational speed is 32400 rpm (FIG. 7), it is significantly smaller. As a result, only a rotational speed pulsation that fluctuates between 22000 and 22680 rpm, that is, a rotational speed pulsation with a small fluctuation range of about 680 rpm occurs on the rotating shaft 31. In this case, the collision noise between the teeth of the pinion gear 41 and the bevel gear 42 is small, and no significant noise is generated. Note that the difference between the minimum value of the variable DC voltage in the case of FIG. 7 and the case of FIG. 8 is that the duty ratio in the drive control is different and the current supplied to the motor 3 is different. More specifically, the duty ratio and the motor current are larger in the case of FIG. 7 than in the case of FIG. 8, and the voltage between the terminals of the smoothing capacitor 61B of the power conversion circuit 61 drops in the case of FIG. Because.

  Next, specific processing of drive control of the motor 3 by the control circuit unit 72 will be described with reference to FIG. FIG. 9 is a flowchart showing drive control by the control circuit unit 72.

  When the power cord 8 of the disc grinder 1 is connected to the commercial AC power source P, drive control by the control circuit unit 72 is started, and in S101, it is determined whether or not the drive switch 21D is in the ON position. This determination is made based on whether or not a start signal is output from the drive switch 21D.

  If the drive switch 21D is not in the on position (S101: No), it is determined again in S101 whether the drive switch 21D is in the on position. That is, it waits while repeating the determination of S101 until the drive switch 21D is in the ON position.

  On the other hand, if the drive switch 21D is in the ON position (S101: Yes), it is determined in S102 whether the user set rotational speed is equal to or less than a predetermined rotational speed Nt. The predetermined rotation speed Nt is stored in advance in the control circuit unit 72.

  When the user set rotational speed is equal to or less than the predetermined rotational speed Nt (S102: Yes), the target rotational speed is set as the user set rotational speed in S103, and the driving of the motor 3 is started in S104. For example, if the dial setting is “1” by the user, the user-set rotation speed is 9156 rpm, so the target rotation speed is 9156 rpm, and the motor 3 is controlled so that the rotation shaft 31 rotates at 9156 rpm. (Constant rotation control) starts. When the motor 3 is driven, the rotor 32, the rotation shaft 31 and the pinion gear 41 rotate together, and the rotation of the pinion gear 41 causes the output shaft portion 5 holding the bevel gear 42 and the grindstone T to rotate integrally. It becomes possible.

  After starting to drive the motor 3, it is determined in S105 whether or not the drive switch 21D is in the OFF position. When the drive switch 21D is not in the off position (S105: No), it is determined again whether or not the drive switch 21D is in the off position. That is, the driving of the motor 3 is continued while repeating the determination of S105 until the drive switch 21D is turned off.

  When the drive switch 21D is in the off position (S105: Yes), the drive of the motor 3 is stopped, the process returns to S101, and waits again until the drive switch 21D is in the on position.

  Returning to S102, when the user set rotational speed is not equal to or lower than the predetermined rotational speed Nt (S102: No), the target rotational speed is set to the predetermined rotational speed Nt in S107, and the driving of the motor 3 is started in S108. For example, when the dial setting is “6” by the user, the user set rotational speed is 32400 rpm, but the target rotational speed is set to the predetermined rotational speed Nt regardless of this, and the rotary shaft 31 is set to the predetermined rotational speed. Control of the motor 3 (constant rotation control) is started so as to rotate at Nt.

  After starting to drive the motor 3, it is determined in S109 whether or not the drive switch 21D is in the OFF position. If the drive switch 21D is in the off position (S109: Yes), the motor 3 is stopped in S106, the process returns to S101, and waits again until the drive switch 21D is in the on position.

  When the drive switch 21D is not in the OFF position (S109: No), the motor current (I) is detected in S110, and it is determined in S111 whether the motor current (I) is equal to or less than the current threshold It. The determination is for determining whether the motor 3 is in an unloaded state or a loaded state. When the motor current (I) is equal to or less than the current threshold It, it is determined that the motor 3 is in an unloaded state. When the current (I) is not less than or equal to the current threshold It, it is determined that the load is not in a no load state (a load state). In the present embodiment, the current threshold It is, for example, 8 A, but is not limited thereto, and may be a value that can determine whether it is a no-load state or a loaded state. The current threshold It is stored in the control circuit unit 72 in advance. The control circuit unit 72 is an example of the “no load determination unit” in the present invention.

  If the motor current (I) is less than or equal to the current threshold It (S111: Yes), it is determined that there is no load, and the process returns to S109 with the target rotational speed maintained at the predetermined rotational speed Nt. On the other hand, if the motor current (I) is not less than or equal to the current threshold It (S111: No), it is determined that the motor is in a loaded state, the target rotational speed is changed from the predetermined rotational speed Nt to the user set rotational speed, and the process returns to S109.

  That is, in the processes from S109 to S112, unless the drive switch 21D is turned off by the user, the rotation speed 31 is set to rotate at the predetermined rotation speed Nt with the target rotation speed set to the predetermined rotation speed Nt in the no-load state. When the motor 3 is controlled and a load is applied, the motor 3 is controlled so that the rotation shaft 31 rotates at the user set rotation speed with the target rotation speed as the user set rotation speed. For example, if the dial setting is set to “6” by the user, the actual rotational speed of the rotating shaft 31 increases from the vicinity of the predetermined rotational speed Nt to the vicinity of 32400 rpm when the load is changed from the no-load state. On the contrary, when the loaded state is changed to the no-loaded state, the actual rotational speed of the rotating shaft 31 drops from around 32400 rpm to around the predetermined rotational speed Nt. Note that when the power cord 8 and the commercial AC power source P are disconnected, the drive control by the control circuit unit 72 ends.

  As described above, the disc grinder 1 according to the embodiment of the present invention includes the motor 3 having the rotating shaft 31 and the manually operable speed change dial portion 9 for setting the number of rotations of the rotating shaft 31. The control circuit 72 determines whether or not the motor 3 is in a no-load state. If the motor 3 is not in a no-load state, the rotation shaft 31 rotates at a user-set rotation speed set by the transmission dial unit 9. When the motor 3 is controlled and in a no-load state, the motor 3 is controlled so that the rotation shaft 31 rotates at a predetermined rotation speed Nt or less regardless of the user-set rotation speed.

  According to such a configuration, the rotation speed (actual rotation speed) of the rotating shaft 31 can be limited to a predetermined rotation speed Nt or less in a no-load state. For this reason, by adopting the rotational speed at which no loud noise is generated as the predetermined rotational speed Nt, noise in a no-load state (no load) can be reduced.

  In addition, when the control circuit 72 in the present embodiment is in a no-load state and the user-set rotation speed exceeds the predetermined rotation speed Nt, the control circuit section 72 has a maximum rotation speed within a rotation speed range equal to or less than the predetermined rotation speed Nt. The motor 3 is controlled so that the rotating shaft 31 rotates at a certain predetermined rotational speed Nt. For this reason, when the work is started from the no-load state and becomes a no-load state (loaded state), the rotational speed of the rotary shaft can be increased to the set rotational speed in a short time, improving work efficiency. Can be made.

  In the present embodiment, the control circuit unit 72 determines whether or not the motor 3 is in a no-load state based on the motor current. Thereby, it can be judged whether it is a no-load state reliably with a simple structure.

  In addition, the disc grinder 1 according to the present embodiment includes a first connection terminal 8A and a second connection terminal 8B that can be connected to the commercial AC power supply P, and a rectifying and smoothing AC voltage output from the commercial AC power supply P. A power conversion circuit 61 that converts the voltage into voltage and outputs it, and an inverter circuit 62 that applies a variable DC voltage to the motor 3 are provided. The power conversion circuit 61 rectifies the AC voltage and outputs a rectified voltage after rectification. When the rectifying circuit 61A and the rotating shaft 31 rotate at a predetermined rotational speed Nt or more, the minimum value of the variable DC voltage is less than the induced voltage generated in the motor 3 and the rotating shaft 31 rotates at the predetermined rotational speed Nt or less. A smoothing capacitor that smoothes the rectified voltage so that the minimum value is higher than the induced voltage.

  According to such a configuration, in the state where the actual rotation speed of the rotary shaft 31 is rotating at a predetermined rotation speed Nt or less, the non-energization period does not occur and the fluctuation range of the rotation speed pulsation is small. Does not occur. In addition, if the actual rotational speed of the rotating shaft 31 exceeds the predetermined rotational speed Nt, a non-energization period occurs and rotational speed pulsation occurs and noise becomes significant. Since the actual rotational speed of the rotating shaft 31 is limited to a predetermined rotational speed Nt or less, it is possible to suppress the occurrence of significant noise.

  Further, in the disc grinder 1, the rotational speed of the rotary shaft 31 is set from 9156 rpm to 32400 rpm based on the amount of operation of the speed change dial unit 9, that is, the rotation angle based on the dial setting “1” state of the dial 9A. A control circuit unit 72 for controlling in the range is provided, and the actual rotational speed of the rotary shaft 31 increases from 9156 rpm to 32400 rpm as the rotation angle increases from 0 ° to 200 ° when not in a no-load state. In the no-load state, the actual rotational speed of the rotary shaft 31 increases from 9156 rpm to a predetermined rotational speed Nt and increases from 120 ° to 200 ° as the rotational angle increases from 0 ° to 120 °. In the meantime, the rotation speed is limited to a predetermined rotation speed Nt or less. For this reason, in the no-load state, the actual rotational speed of the rotating shaft 31 is limited to a predetermined rotational speed Nt or less. Accordingly, by adopting the rotation speed at which no large noise is generated as the predetermined rotation speed Nt, noise in a no-load state (no load) can be reduced.

  Further, in the present embodiment, the actual rotational speed of the rotary shaft 31 is from 120 ° to 200 ° with respect to the dial 9A in the dial setting “1” state in the no-load state. While increasing, the rotation speed is maintained at a predetermined rotational speed Nt. For this reason, when there is no load and the rotation angle exceeds 120 °, the actual rotation speed of the rotary shaft 31 is the predetermined rotation speed Nt that is the maximum rotation speed in the rotation speed range equal to or less than the predetermined rotation speed Nt. Maintained. As a result, when the operation is started from the no-load state and the state is not the no-load state (loaded state), the actual number of rotations of the rotating shaft 31 is determined according to the rotation angle (predetermined) in a short time. The rotation speed can be increased to a rotation speed greater than the rotation speed Nt), and the working efficiency can be improved.

  The power tool according to the present invention is not limited to the above-described embodiment, and various modifications are possible within the scope of the gist of the invention described in the claims. For example, in the above-described embodiment, the disk grinder 1 has been described as an example. However, the present invention is not limited to this, and can be applied to a multi-cutter, a saver saw, a sander, a polisher, and the like.

  Further, in the present embodiment, the user set rotational speed is set by the rotation angle (operated amount) from the dial setting “1” state of the dial 9 </ b> A of the transmission dial unit 9, but is not limited thereto. For example, a push button type switch may be provided instead of the speed change dial unit 9, and the user set rotation speed may be set by the number of times the push button type switch is pressed. In this case, the operated amount is the number of times the push button is pressed. Furthermore, it is good also as a structure which replaces with the speed-change dial part 9, and provides a liquid crystal touch panel and sets a user setting rotation speed by the frequency | count of a touch. In this case, the operated amount is the number of touches.

  Moreover, in this Embodiment, although the motor 3 was a brushless motor, a motor with a brush may be sufficient. In this case, no significant noise is generated due to the collision noise between the teeth of the pinion gear 41 and the bevel gear 42 described above, but by performing control to limit the actual rotational speed of the rotating shaft 31 in the above-described no-load state, Noise in a no-load state can be reduced.

DESCRIPTION OF SYMBOLS 1 ... Disc grinder 2 ... Housing 3 ... Motor 4 ... Power transmission mechanism 5 ... Output shaft part 6 ... 1st board | substrate 7 ... 2nd board | substrate 8 ... Power cord 8A ... 1st connection terminal 8B ... 2nd connection terminal 9 ... Shift dial 9A ... Dial 21 ... Motor housing 22 ... Gear housing 23 ... Rear housing 31 ... Rotating shaft 32 ... Rotor 41 ... Pinion gear 42 ... Bevel gear 61 ... Power conversion circuit 61A ... Rectifier circuit 61B ... Smoothing capacitor 62 ... Inverter circuit 71 ... Control Power supply circuit unit 72 ... Control circuit unit It ... Current threshold value Nt ... Predetermined rotation speed P ... Commercial AC power supply T ... Grinding wheel VCC ... Reference voltage

Claims (13)

A brushless motor,
A power connection that can be connected to an external AC power source;
A conversion circuit unit that rectifies and smoothes an AC voltage output from the external AC power supply, converts the voltage to a variable DC voltage that fluctuates at a frequency twice that of the external AC power supply, and outputs the changed DC voltage;
An inverter circuit for applying the variable DC voltage output from the conversion circuit to the brushless motor;
Motor control means for performing constant rotational speed control for bringing the rotational speed of the brushless motor close to the target rotational speed,
An electric tool characterized in that, when the brushless motor is in a no-load state, the target rotational speed is set so that a non-energized section where no current flows through the brushless motor does not occur. The conversion circuit section
A rectifier circuit that rectifies the AC voltage output from the external AC power supply and outputs a rectified voltage after rectification;
The power tool according to claim 1, further comprising a smoothing capacitor that smoothes the rectified voltage so as to fluctuate. An operation unit for setting the rotation speed of the brushless motor;
A rotation speed control means for controlling the rotation speed of the brushless motor according to the set rotation speed set by the operation section or the operated amount of the operation section;
In a case where the brushless motor is in a no-load state, the rotation speed control means performs the setting rotation speed or the rotation speed when the set rotation speed exceeds a predetermined rotation speed or when the operated amount exceeds a predetermined amount. The electric tool according to claim 2, wherein the upper limit of the rotation speed of the brushless motor is limited so that the non-energized section does not occur regardless of the operated amount.   When the set rotational speed does not exceed the predetermined rotational speed or when the operated amount does not exceed the predetermined amount, the rotational speed control means increases the set rotational speed or the operated amount. The electric tool according to claim 3, wherein the rotational speed of the brushless motor is increased.   The rotation speed control means controls the rotation speed of the brushless motor according to the set rotation speed or the operated amount when the brushless motor is not in the no-load state. The electric tool described. Comprising no-load determining means for determining whether or not the brushless motor is in a no-load state;
The rotation speed control means controls the brushless motor so that the brushless motor rotates at the predetermined rotation speed or less regardless of the set rotation speed or the operated amount in the no-load state. The power tool according to any one of claims 3 to 5.   The rotational speed control means is in the no-load state, and when the set rotational speed exceeds the predetermined rotational speed or when the manipulated amount exceeds the predetermined rotational speed, The power tool according to claim 6, wherein the brushless motor is controlled so that the brushless motor rotates.   The electric tool according to claim 6, wherein the no-load determining means determines whether or not the brushless motor is in the no-load state based on a current flowing through the brushless motor.   The smoothing capacitor is configured such that when the brushless motor rotates at a speed exceeding the predetermined rotation number or when the manipulated amount exceeds the predetermined amount, the minimum value of the variable DC voltage is equal to or less than an induced voltage generated in the brushless motor; 5. The electric tool according to claim 3, wherein, when the brushless motor rotates at the predetermined rotation speed or less, the rectified voltage is smoothed so that the minimum value is higher than the induced voltage. 6. .   The electric tool according to claim 2 or 9, wherein a capacity of the smoothing capacitor is 180 µF or less. A brushless motor,
A power connection that can be connected to an external AC power source;
A conversion circuit unit that rectifies and smoothes an AC voltage output from the external AC power supply, converts the voltage to a variable DC voltage that fluctuates at a frequency twice that of the external AC power supply, and outputs the changed DC voltage;
An inverter circuit unit that applies the variable DC voltage output by the conversion circuit unit to the brushless motor,
The brushless motor is unloaded condition a is to drive the said brushless motor at a rotational speed unpowered interval no current flows in the brushless motor does not occur when Rutotomoni, wireless load the brushless motor is in loaded conditions A power tool configured to drive the brushless motor by increasing the number of rotations more than the state. An operation unit for setting the rotation speed of the brushless motor;
Regardless of the set rotational speed set by the operating unit or the operated amount of the operating unit, the upper limit of the rotational speed is limited so that the non-energized section where no current flows through the brushless motor does not occur. The power tool according to claim 11 , wherein the power tool is configured. A rotation speed control means for controlling the brushless motor so as to limit the upper limit of the rotation speed of the brushless motor according to the set rotation speed set by the operation section or the operated amount of the operation section;
When the brushless motor is in a no-load state and the set rotational speed exceeds a predetermined rotational speed, or when the manipulated amount exceeds a predetermined amount, the rotational speed control means or claim 12 in which the brushless motor or at the predetermined rotational speed so as to limit the upper limit of the rotational speed of the brushless motor regardless to said operation amount so as to rotate, and controlling the brushless motor The electric tool as described in.

Images