Working machine

Abstract

To provide a working machine capable of suppressing a risk of unstable start-up of a brushless motor.SOLUTION: A control part 41 is configured to be able to control an inverter circuit 42 so as to increase a motor current when a rectified voltage is high and to decrease the motor current when the rectified voltage is low. Specifically, the control part 41 is configured to be able to control the inverter circuit 42 so as to bring the motor current into a large state in a first region including a rising region and a falling region before and after a timing at which the rectified voltage becomes a highest value, and so as to bring the motor current into a small state in a second region including the falling region and the rising region before and after the timing at which the rectified voltage subsequently becomes a lowest value.SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] The present invention relates to a work machine. [Background technology]

[0002] Brushless motors are used as drive sources for work machines (for example, power tools). A sensorless drive system that does not use an element for detecting rotor position information is known as a drive method for brushless motors. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2016 / 067811 [Patent Document 2] Japanese Patent Application Publication No. 2022-135569 Summary of the Invention [Problem to be solved by the invention]

[0004] In the case of work machines powered by AC power, the AC voltage is rectified, for example, using a full-wave rectifier circuit, and the rectified voltage is converted to AC by an inverter circuit and supplied to a brushless motor. A DC link capacitor is installed between the output terminals of the full-wave rectifier circuit to smooth the rectified voltage. During the period corresponding to the valley of the full-wave rectifier circuit's output voltage, current is supplied from the DC link capacitor to the inverter circuit, causing the DC link capacitor voltage to drop (the input voltage to the inverter circuit drops). When the brushless motor's rotation speed is low, such as when starting up, the induced voltage generated by the brushless motor is low, so the DC link capacitor voltage tends to drop significantly. This can cause the rotational position of the brushless motor to be incorrectly estimated, posing a risk of unstable startup of the brushless motor.

[0005] An object of the present invention is to provide a work machine that can reduce the risk of unstable startup of a brushless motor. [Means for solving the problem]

[0006] One aspect of the present invention is a brushless motor having a rotor and a stator having a plurality of windings; an inverter circuit connected to the plurality of windings; a rectification unit configured to rectify an AC voltage and output the rectified AC voltage to the inverter circuit; a capacitor connected in parallel to the inverter circuit on the output side of the rectifier; a control unit that controls the inverter circuit; an operation unit for instructing start and stop of the brushless motor; A work machine equipped with The control unit is configured to be able to control the inverter circuit so that, when the operation unit is operated to start the brushless motor, the current flowing through the brushless motor increases when a rectified voltage, which is the output voltage of the rectifier when an output terminal of the rectifier is assumed to be open, increases, and the current decreases when the rectified voltage decreases. It is characterized by:

[0007] The present invention may be expressed as an "electric working machine," "electric tool," "electrical equipment," etc., and such expressions are also valid aspects of the present invention. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a work machine that can reduce the risk of unstable startup of a brushless motor. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a side cross-sectional view of a work machine 1 according to an embodiment. [Figure 2] 2 is a diagram of the motor 3 in FIG. 1 as viewed from the axial direction with the stator coil omitted. [Figure 3] A diagram of the stator of the motor 3 as seen from the axial direction. [Figure 4] FIG. 2 is a circuit block diagram of the work machine 1. [Figure 5] Schematic diagram showing the definition of the dq coordinate system in vector control. [Figure 6] FIG. 2 is an explanatory diagram of an example of a current vector Idq and its current phase angle β in a dq coordinate system. [Figure 7] (A) is a diagram showing an example of the current vectors Iu, Iv, and Iw of the U, V, and W phases, and the resulting current vector Iuvw. (B) is a diagram showing the current vector Idq (=Iuvw) and its d-component and q-component current vectors Id and Iq. [Figure 8] FIG. 2 is an explanatory diagram of patterns 1 to 6 of on / off combinations of switching elements Q1 to Q6 in vector control and output voltage vectors for each of these. [Figure 9] 10 is an explanatory diagram of patterns 7 and 8 of on / off combinations of switching elements Q1 to Q6 in vector control and output voltage vectors for each of them. FIG. [Figure 10] 1A is an explanatory diagram showing an example of a target voltage vector and a method of combining the target voltage vector in vector control, and FIG. 1B is a timing chart showing the on / off of switching elements Q1 to Q6 for generating the target voltage vector. [Figure 11] FIG. 5 is a functional block diagram of the control unit 41 in FIG. 4, showing the part related to the generation and output of a PWM signal. [Figure 12] 4 is a graph microscopically showing an example of time changes in voltages at various parts, and in the target current and actual current of the q-axis current flowing through the motor 3, in the first control example of the work machine 1; [Figure 13] 6 is a graph microscopically showing an example of time changes in voltages at various parts, and target and actual q-axis currents flowing through the motor 3, in relation to a second control example of the work machine 1; [Figure 14] 4 is a graph showing, in a microscopic manner, an example of time changes in voltages at various parts, and in the target current and actual current of the q-axis current flowing through the motor 3, in relation to a comparative example of the work machine 1; [Figure 15] 4 is a graph showing, macroscopically, an example of the change in the rotation speed of the motor 3 over time when the work machine 1 is performing a lifting operation. [Figure 16]4 is a graph macroscopically showing an example of time changes in the rotation speed of the motor 3, the q-axis current flowing through the motor 3, and the control details of the control unit 41. [Figure 17] 17A is a flowchart of the overall operation of the work machine 1. FIG. 17B is a flowchart of the start-up control (S3) of FIG. [Figure 18] 17A is a flowchart of the normal control (S7) in FIG. 17A. FIG. 17B is a flowchart of the stop control (S9) in FIG. [Figure 19] FIG. 10 is a circuit block diagram of a work machine according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] FIG. 1 is a side cross-sectional view of a work machine 1 according to an embodiment. FIG. 1 defines the mutually orthogonal front-rear and up-down directions of the work machine 1. The work machine 1 is an impact work machine, specifically a hammer drill. The work machine 1 can perform chipping, drilling, and crushing operations on workpieces such as concrete and stone by applying rotational force and impact force to the bit 10. The configuration of the work machine 1, from the rotation of the motor 3 to the rotation and impact of the bit 10, is well known, so only a brief explanation will be given below.

[0011] The work machine 1 here is AC-powered, and a power cord 15 extends from the lower rear end of the housing 2 (the lower end of the handle portion 2a) for connection to an external AC power source 60 (Fig. 4) such as a commercial power source. The rear portion of the housing 2 is the handle portion 2a, and the handle portion 2a is provided with a trigger switch 16 as an operation portion that allows the user to start and stop the motor 3 (the driving state of the motor 3).

[0012] A motor 3, a motion conversion mechanism 4, a rotation transmission mechanism 5, a cylinder 11, and a retainer sleeve 12 (tool holding portion) are held within the housing 2. The cylinder 11 and the retainer sleeve 12 are rotatable relative to the housing 2 around an axis extending in the front-to-rear direction. A piston 6, a striker 8, and an intermediate element 9 are provided within the cylinder 11 and the retainer sleeve 12 so as to be capable of reciprocating in the front-to-rear direction. A pressure chamber 7 (air chamber) is formed between the piston 6 and the striker 8. A tool bit 10 is detachably held at the front end of the retainer sleeve 12.

[0013] The motor 3 is provided in the lower part of the housing 2. Behind the motor 3 in the housing 2, a control board 40 for controlling the driving of the motor 3 is provided.

[0014] The rotation of the motor 3, whose axis is in the vertical direction, is converted into back-and-forth reciprocating motion of a piston 6 by a motion conversion mechanism 4, such as a crank mechanism. The reciprocating motion of the piston 6 causes the pressure (air pressure) in the pressure chamber 7 to fluctuate (expand / compress), driving the striker 8 to reciprocate back and forth. The striker 8 strikes the intermediate element 9, which in turn strikes the tool bit 10.

[0015] Meanwhile, the rotation of the motor 3, whose axis is in the vertical direction, is converted into the rotation of the cylinder 11 and the retainer sleeve 12, whose axis is in the front-to-rear direction, by the rotation transmission mechanism 5, which includes a pair of bevel gears. The tool bit 10 is rotated together with the retainer sleeve 12.

[0016] The user can use the mode setting dial 13 located on the top of the housing 2 to switch the operating mode of the work machine 1 between a hammer mode (impact mode) in which an impact force is applied to the tip tool 10 without a rotational force, and a hammer drill mode (rotary impact mode) in which both a rotational force and an impact force are applied to the tip tool 10.

[0017] As shown in Figures 2 and 3, the motor 3 is an inner rotor brushless motor that includes a rotor core 3b that is disposed around an output shaft 3a and rotates integrally with the output shaft 3a, multiple rotor magnets 3c (permanent magnets) inserted and held in the rotor core 3b, a stator core 3e that is disposed so as to surround the outer periphery of the rotor core 3b, and multiple stator coils 3h (windings) that are disposed in the stator core 3e. The rotor core 3b and the rotor magnets 3c form the rotor of the motor 3 (hereinafter referred to as the "rotor"). The stator core 3e and the stator coils 3h form the stator of the motor 3. The motor 3 here has a four-pole, six-slot configuration, with four rotor magnets 3c and six stator coils 3h.

[0018] As shown in FIG. 2, the stator core 3e includes a cylindrical (annular) yoke portion 3f and a plurality of salient pole portions (teeth) 3g protruding radially inward from the yoke portion 3f. A stator coil 3h is provided on each salient pole portion 3g. As shown in FIG. 3, the stator coil 3h includes U-phase coils U1 and U2, V-phase coils V1 and V2, and W-phase coils W1 and W2. The stator coils 3h are arranged in the following order around the axis of the motor 3: V-phase coil V2, U-phase coil U1, W-phase coil W2, V-phase coil V1, U-phase coil U2, and W-phase coil W1. The stator coils 3h for each phase are connected to each other in a Y-connection (star connection) or a delta connection (not shown).

[0019] Figure 4 is a circuit block diagram of the work machine 1. The entire unit excluding the AC power supply 60 shown in Figure 4 constitutes the motor drive device of the work machine 1. The work machine 1 has a control unit 41, an inverter circuit 42 as a drive unit, an amplifier circuit 44, a control system power supply circuit 45, a rectifier circuit 61 as a rectifier unit, an AC voltage measurement circuit 63 as an AC voltage detection unit, capacitors C1 and C2, and a diode D5.

[0020] The AC voltage measurement circuit 63 detects the input voltage (hereinafter referred to as "AC voltage") from the AC power supply 60 and transmits it to the control unit 41. The rectifier circuit 61 is a full-wave rectifier circuit formed of a diode bridge in this case, and rectifies the AC voltage supplied from the AC power supply 60 to convert it into DC, which is output to the inverter circuit 42.

[0021] The capacitor C1 is a DC link capacitor, and is connected in parallel to the inverter circuit 42 on the output side of the rectifier circuit 61. The voltage across the capacitor C1, that is, the voltage on the input side of the inverter circuit 42, is the DC link voltage.

[0022] Diode D5 and capacitor C2 are connected in series between the output terminals of the rectifier circuit 61. The voltage at the interconnection point of diode D5 and capacitor C2 is input to the control system power supply circuit 45. Diode D5 is used to prevent backflow and prevents capacitor C2 from discharging when the DC link voltage is lower than the voltage of capacitor C2. Capacitor C2 maintains the input voltage to the control system power supply circuit 45. The control system power supply circuit 45 converts the voltage at the interconnection point of diode D5 and capacitor C2 into a power supply voltage for the control unit 41, etc., and supplies it to the control unit 41, etc.

[0023] The inverter circuit 42 converts the DC voltage output from the rectifier circuit 61 into an AC voltage to be applied to the motor 3, and supplies it to the motor 3 (applying it to the stator coils 3h of the U, V, and W phases). The inverter circuit 42 includes switching elements Q1 to Q6 connected in a three-phase bridge. The switching elements Q1 to Q3 are upper switching elements, and the switching elements Q4 to Q6 are lower switching elements.

[0024] Switching elements Q1 and Q4 are connected to one end of the U-phase coil. Switching element Q1 is a U-phase upper switching element, and switching element Q4 is a U-phase lower switching element. Switching elements Q2 and Q5 are connected to one end of the V-phase coil. Switching element Q2 is a V-phase upper switching element, and switching element Q5 is a V-phase lower switching element. Switching elements Q3 and Q6 are connected to one end of the W-phase coil. Switching element Q3 is a W-phase upper switching element, and switching element Q6 is a W-phase lower switching element.

[0025] The shunt resistors Ru, Rv, and Rw are examples of current detection units, and are provided on the low-potential side of the path of the current (current of each phase) flowing through the stator coil 3h of each of the U, V, and W phases, respectively, and convert the current of each phase into a voltage (detect the current of each phase). The amplifier circuit 44 amplifies the voltage across each of the shunt resistors Ru, Rv, and Rw, and transmits it to the control unit 41 as a current detection signal for each of the U, V, and W phases.

[0026] The control unit 41 includes, for example, a microcontroller and a driver IC, and controls the overall operation of the work machine 1. In response to the operation of the trigger switch 16 by the user, the control unit 41 monitors the AC voltage, the DC link voltage, and the current of each phase, and controls the drive of the motor 3 through control of the inverter circuit 42, that is, control of the on / off of the switching elements Q1 to Q6.

[0027] The control unit 41 detects the rotational position of the rotor (hereinafter referred to as "rotor position") and the angular velocity of the rotor (hereinafter referred to as "rotor angular velocity") without using a sensor, based on the current of each phase. The control unit 41 can determine the rotation speed of the motor 3 (hereinafter referred to as "motor rotation speed") based on the rotor angular velocity. The rotor position corresponds to the rotational position of the motor 3.

[0028] The drive control of the motor 3 by the control unit 41 is, for example, vector control. Vector control is also called space vector pulse width modulation (SVPWM).

[0029] FIG. 5 is a schematic diagram showing the definition of the dq coordinate system in vector control. FIG. 6 is an explanatory diagram of an example of a current vector Idq and its current phase angle β in the dq coordinate system. Note that electrical angles are used to explain vector control. Because motor 3 has a four-pole, six-slot configuration, a mechanical angle of 180 degrees of motor 3 corresponds to an electrical angle of 360 degrees. FIG. 5 shows a schematic diagram in which the configuration of motor 3's 180-degree mechanical angle is expanded to 360 degrees. One rotation of motor 3 in FIG. 5 (a rotation of 360 electrical degrees) corresponds to half a mechanical rotation of motor 3 (a mechanical angle of 180 degrees).

[0030] The torque and rotation speed characteristics of the motor 3 change depending on the direction of the current vector Idq (current phase angle β shown in Figure 6) in a dq coordinate system (Figure 5), where the direction of the magnetic flux created by the rotor magnet 3c is the d-axis and the direction magnetically perpendicular to that is the q-axis. If the current vector Idq can be controlled so that the torque and rotation speed characteristics are appropriate, it will be possible to drive the motor 3 with high efficiency. Vector control is the control of the current vector Idq.

[0031] The current vector Idq in the dq coordinate system refers to a current vector obtained by converting the current vector Iuvw, which is a combination of the current vectors Iu, Iv, and Iw of each phase in a uvw coordinate system shown in FIG. 7A, in which the central axes (u-axis, v-axis, and w-axis) of the stator coils 3h of the U, V, and W phases of the inverter circuit 42 are the three axes, into the dq coordinate system as shown in FIG. 7B. Therefore, to perform vector control, it is necessary to control the currents of the U, V, and W phases. To control the currents of the U, V, and W phases, it is necessary to perform switching control of the inverter circuit 42 (switching elements Q1 to Q6) so that a voltage vector in any direction in the uvw coordinate system can be applied to the motor 3 (stator coil 3h).

[0032] As shown in Figures 8(A) to 8(F) and 9(A) to 9(B), there are eight current conduction patterns for the inverter circuit 42, depending on whether the upper (high-side) or lower (low-side) switching elements of each of the U, V, and W phases are energized. Figures 8(A) and 8(B) also show the voltage components of each phase that form the basis of the final voltage vector. Note that the direction of the voltage vector generated by each current conduction pattern shown in Figures 8(A) to 8(F) and 9(A) to 9(B) is the direction when the stator coil 3h is connected in a Y-connection; the direction of the voltage vector is different when the stator coil 3h is connected in a delta connection (not shown).

[0033] 8(A), switching elements Q1, Q5, and Q6 are on, and the others are off. In this case, when the voltage vectors of each phase are combined, a voltage vector pointing in the positive direction of the U axis (U direction) is obtained.

[0034] 8(B), switching elements Q1, Q2, and Q6 are on, and the others are off. In this case, when the voltage vectors of each phase are combined, a voltage vector pointing in the negative direction of the W axis (W- direction) is obtained.

[0035] 8(C), switching elements Q2, Q4, and Q6 are on, and the others are off. In this case, when the voltage vectors of each phase are combined, a voltage vector pointing in the positive direction of the V axis (V direction) is obtained.

[0036] 8(D), switching elements Q2, Q3, and Q4 are on, and the others are off. In this case, when the voltage vectors of each phase are combined, a voltage vector pointing in the negative direction of the U axis (U-direction) is obtained.

[0037] 8(E), switching elements Q3, Q4, and Q5 are on, and the others are off. In this case, when the voltage vectors of each phase are combined, a voltage vector pointing in the positive direction of the W axis (W direction) is obtained.

[0038] 8(F), switching elements Q1, Q3, and Q5 are on, and the others are off. In this case, when the voltage vectors of each phase are combined, a voltage vector pointing in the negative direction of the V axis (V- direction) is obtained.

[0039] In this way, in the energization patterns 1 to 6, voltage vectors whose directions change at 60-degree intervals are applied to the motor 3 (stator coil 3h).

[0040] In energization pattern 7 shown in FIG. 9(A), the lower switching elements Q4, Q5, and Q6 are on, and the others are off. In energization pattern 8 shown in FIG. 9(B), the upper switching elements Q1, Q2, and Q3 are on, and the others are off. In energization patterns 7 and 8, a 0 vector is applied to the motor 3 (stator coil 3h). One of energization patterns 7 and 8 corresponds to the first state, and the other corresponds to the second state.

[0041] Hereinafter, the voltage vectors resulting from each of the current conduction patterns 1 to 8 will be referred to as "basis vectors." Since the voltage vector that can be applied by a single current conduction pattern is limited to the direction of the basis vector, to apply a voltage vector in an arbitrary direction, it is necessary to combine and output two or more basis vectors.

[0042] FIG. 10A shows an example of a method for generating a target voltage vector by combining basis vectors. In this example, the target voltage vector can be decomposed into a U-direction basis vector (conduction pattern 1), a W-direction basis vector (conduction pattern 2), and a 0-vector basis vector (conduction patterns 7 and 8). Therefore, the target voltage vector can be output by maintaining the inverter circuit 42's current conduction patterns 1, 2, 7, and 8 for periods (t1, t2, t7, and t8) corresponding to the ratio of the lengths of the respective basis vectors. The 0-vector basis vector is required to adjust the absolute value (length) of the voltage vector.

[0043] FIG. 10(B) is a time chart showing the on / off states of the switching elements Q1 to Q6 for generating the target voltage vector shown in FIG. 10(A).

[0044] In vector control, at the leftmost point in FIG. 10(B) (i.e., at the point of the first energization pattern 7), the currents of the U, V, and W phases are detected to identify the rotor position and rotor angular velocity. Then, a voltage vector to be applied to the motor 3 (stator coil 3h) is set according to the identified rotor position and rotor angular velocity. The voltage vector is set by pulse width modulation (PWM) of the voltages applied to the U, V, and W phases.

[0045] Then, at the point at the right end of Figure 10(B) (i.e., the point at which the second current flow pattern 7 occurs), the currents of the U, V, and W phases are again detected to identify the rotor position and rotor angular velocity, and the voltage vector to be applied to the motor 3 (stator coil 3h) is reset according to the identified rotor position and rotor angular velocity.

[0046] Therefore, the period from the left end of Figure 10(B) to the right end of Figure 10(B) is one period of pulse width modulation (PWM), which is also one period of space vector pulse width modulation (SVPWM). When driving each of the U, V, and W phases with PWM, the target voltage vector shown in Figure 10(A) can be output by setting the duty ratio of each phase (the duty ratio of the PWM signal applied to each control terminal of switching elements Q1 to Q6) so that the time ratio of each current conduction pattern within one PWM period is t1:t2:t7:t8, as shown in Figure 10(B). In this way, SVPWM outputs any target voltage vector.

[0047] The motor drive device of the work machine 1 drives the motor 3 using a sensorless drive system. That is, as described above, the control unit 41 detects the rotor position and rotor angular velocity without a sensor, based on the current of each phase. Here, in the low rotation speed range of the motor 3 (for example, 4,000 rpm or less), the induced voltage generated in the stator coil 3h is low, making it difficult to estimate the rotor position. To address this issue, the control unit 41 superimposes a high-frequency superimposed voltage on the control command voltage in a dq coordinate system in the low rotation speed range, and estimates the rotor position from the current response.

[0048] 11 is a functional block diagram of the control unit 41 in FIG. 4, and is a functional block diagram of a portion related to the output and generation of a PWM signal. The control unit 41 includes a carrier signal generator 50, a control command voltage calculation unit 51, a superimposed voltage calculation unit 52, a reference signal calculation unit 53, a uvw / dq conversion unit 54, a comparator 55, and a PWM signal output unit 56.

[0049] The carrier signal generator 50 generates a PWM carrier signal (e.g., a triangular wave). The control command voltage calculation unit 51 calculates a control command voltage in a dq coordinate system. The target voltage vector shown in FIG. 10(A) is an example of a control command voltage. The superimposed voltage calculation unit 52 calculates a superimposed voltage in the dq coordinate system in accordance with the periodic signal from the carrier signal generator 50. The reference signal calculation unit 53 adds the control command voltage and the superimposed voltage in the dq coordinate system.

[0050] A uvw / dq converter 54 converts the sum of the control command voltage and the superimposed voltage in the dq coordinate system into a uvw coordinate system and outputs a U-phase reference signal, a V-phase reference signal, and a W-phase reference signal. A comparator 55 compares each of the U-phase reference signal, the V-phase reference signal, and the W-phase reference signal with the PWM carrier signal and outputs a U-phase output reference signal, a V-phase output reference signal, and a W-phase output reference signal. A PWM signal output unit 56 outputs (applies) a PWM signal to each control terminal of switching elements Q1 to Q6 based on the U-phase output reference signal, the V-phase output reference signal, and the W-phase output reference signal.

[0051] Figure 12 is a graph showing, in microscopic terms, an example of the time changes in the voltage of each part, and the target current (hereinafter referred to as "q-axis target current") and actual current (hereinafter referred to as "q-axis actual current") of the q-axis current (hereinafter referred to as "q-axis current") flowing through the motor 3, in control example 1 of the work machine 1.

[0052] 12 (and FIGS. 13 and 14 described below), the rectified voltage is a voltage obtained by full-wave rectifying an AC voltage, and is the output voltage of rectifier circuit 61 when it is assumed that the output terminal of rectifier circuit 61 is open. AC voltage measuring circuit 63 shown in FIG. 4 has an internal full-wave rectifier circuit, and converts the voltage after full-wave rectification to an amplitude that can be input to control unit 41, and inputs it to control unit 41. Control unit 41 can detect (estimate) the phase and magnitude of the rectified voltage from the input signal from AC voltage measuring circuit 63.

[0053] In FIG. 12 (and FIG. 13 described later), the estimated current section is a section in which a minute current flows to the motor 3 (stator coil 3h) that is small enough not to accelerate or decelerate the motor 3 (so as not to affect the driving of the motor 3) and that allows the rotor position to be detected, i.e., a section in which the q-axis target current is small. Note that in the estimated current section, the d-axis current flowing through the motor 3 is also small (not shown). The torque current section is a section in which a large current flows to the motor 3 (stator coil 3h) that generates torque to accelerate the motor 3, i.e., a section in which the q-axis target current is large. The torque current section corresponds to a first section including the rising and falling regions before and after the timing when the rectified voltage reaches its maximum value. The estimated current section corresponds to a second section including the rising and falling regions before and after the timing when the rectified voltage reaches its minimum value following the first section. The motor current in the estimated current section is large enough to prevent the voltage of capacitor C1 from falling below a predetermined value (e.g., 30 V).

[0054] The control unit 41 can change the magnitude of the q-axis current (magnitude of the motor current) by changing the time proportion (duty) of the current patterns 1 to 6 shown in Figures 8(A) to (F) in the PWM period, i.e., the time proportion of the current patterns other than the current patterns 7 and 8 shown in Figures 9(A) and (B).

[0055] In control example 1 shown in FIG. 12, the control unit 41 is configured to repeat the following cycle: after the trigger switch 16 is turned on, when the rectified voltage becomes higher than the first threshold value at the time of rising in the rising region (increasing process) of the rectified voltage, the control unit 41 transitions from the estimated current section to the torque current section (increases the q-axis current), and when the rectified voltage becomes lower than the second threshold value at the time of falling in the falling region (decreases process) of the rectified voltage, the control unit 41 transitions from the torque current section to the estimated current section (decreases the q-axis current).

[0056] That is, when the trigger switch 16 is operated to start the motor 3, the control unit 41 is configured to be able to control the inverter circuit 42 so that the current flowing to the motor 3 increases when the rectified voltage increases and decreases when the rectified voltage decreases. The control unit 41 is also configured to be able to control the inverter circuit 42 so that the q-axis current is large around the timing when the rectified voltage reaches its highest value, and so that the q-axis current is small around the subsequent timing when the rectified voltage reaches its lowest value.

[0057] By providing an estimation current section as shown in FIG. 12 , the q-axis current near the valley of the rectified voltage is suppressed. This prevents an excessive drop in the DC link voltage, even when the motor rotation speed is low and the induced voltage generated by the motor 3 is low. This prevents a decrease in the current response to the rotor position estimation voltage applied to the motor 3, i.e., the superimposition of the superimposed voltage. This reduces the risk of the rotor position not being detected correctly and the risk of unstable startup of the motor 3. Specifically, according to the inventor's findings, an excessive drop in the DC link voltage reduces the current response of the U, V, and W phases to the superimposed voltage, making it difficult to detect the rotor position based on the current response of each phase. Because a large current, for example, approximately 100 A, flows in the work machine 1, a large measurement range for current detection is required, and accurate detection is difficult with a small current response. This problem is solved by providing an estimation current section as shown in FIG. 12 .

[0058] In FIG. 12, the reason why the threshold value (second threshold value) at the time of falling is set higher than the threshold value (first threshold value) at the time of rising is as follows.

[0059] For example, when controlling the DC link voltage so that it does not fall below 30 V, the rectified voltage rises during the period from when the q-axis current increases to when the DC link voltage falls. Therefore, by setting the threshold value at the time of rise so that the rectified voltage rises to 30 V or higher before the DC link voltage falls below 30 V, the DC link voltage can be prevented from falling below 30 V even if the threshold value at the time of fall is set to less than 30 V, i.e., even if the q-axis current is increased when the rectified voltage is below 30 V (even when the transition from the estimation current section to the torque current section occurs). Note that setting the threshold value at the time of fall to 30 V reliably prevents the DC link voltage from falling below 30 V.

[0060] On the other hand, during the falling process of the rectified voltage, taking into account the delay in the decrease in the q-axis actual current relative to the decrease in the q-axis target current and the decrease in the DC link voltage in the estimated current section, it is necessary to decrease the q-axis target current (transition from the torque current section to the estimated current section) at a timing when the rectified voltage is higher than 30 V by a certain amount. In other words, the threshold value during the falling process needs to be higher than 30 V by a certain amount. For this reason, the threshold value during the falling process is set higher than the threshold value during the rising process. In other words, the control unit 41 is configured so that the rectified voltage when switching from the first region to the second region is higher than the rectified voltage when switching from the second region to the first region. This achieves a good balance between stabilizing the start of the motor 3 by preventing an excessive decrease in the DC link voltage and improving response by ensuring the length of the torque current section, i.e., accelerating the increase in motor rotation speed when the trigger switch 16 is turned on.

[0061] In Figure 12, after the motor rotation speed increases and the induced voltage generated by the motor 3 becomes high, the system transitions to normal control, such as constant speed control, in which the q-axis target current is not changed depending on the phase of the AC voltage. Because the DC link voltage does not fall below the induced voltage, once the induced voltage becomes high, control that sets an estimated current interval is no longer necessary.

[0062] FIG. 13 is a graph microscopically showing an example of time changes in the voltage of each part, the q-axis target current, and the q-axis actual current, in relation to the second control example of the work machine 1.

[0063] Control example 2 shown in Fig. 13 is similar to control example 1 shown in Fig. 12 in that the threshold value at the time of rising is set as high as the threshold value at the time of falling, and they are used as common threshold values. Control example 2, like control example 1, can achieve stable startup of motor 3 by suppressing excessive drops in DC link voltage, but compared to control example 1, the torque current section is shorter, resulting in a slower response. Control example 2 is otherwise similar to control example 1.

[0064] 12 and 13, the way in which the q-axis target current is increased when switching from the estimation current section to the torque current section may be changed from a stepwise manner to a sloped manner. In this case, the change in the DC link voltage becomes gentler, and the influence of a sudden change in the DC link voltage on rotor position detection is suppressed.

[0065] 12 and 13, the q-axis target current in each torque current section may be changed so as to slope upward rather than being constant. In this case, the initial value of the q-axis target current in any torque current section may be set to the final value of the q-axis target current in the immediately preceding torque current section.

[0066] FIG. 14 is a graph microscopically illustrating an example of time variations in the voltages of various components, as well as the q-axis target current and the q-axis actual current, for a comparative example of the work machine 1. Unlike the control examples 1 and 2 shown in FIGS. 12 and 13, this comparative example executes normal control, maintaining a constant q-axis current target value regardless of the phase of the AC voltage, immediately after the trigger switch 16 is turned on. Therefore, near the valleys of the rectified voltage, the DC link voltage drops significantly, reducing the current response to the superimposition of the superimposed voltage. This increases the risk of the rotor position not being detected correctly. The fact that the q-axis actual current fluctuates up and down near the valleys of the rectified voltage in FIG. 14 is due to the rotor position not being detected correctly. The control examples 1 and 2 described above effectively solve these issues in the comparative example.

[0067] Fig. 15 is a graph macroscopically showing an example of the change in the rotation speed of the motor 3 over time when the work machine 1 is performing chipping work. Particularly in cases such as chipping, where work involves repeatedly turning the trigger switch 16 on and off to check the operation little by little, the worker may feel uncomfortable if the rise in the motor rotation speed in response to the turning on of the trigger switch 16 is slow. Control Example 1 shown in Fig. 12 improves response by ensuring the length of the torque current section, thereby reducing the sense of discomfort felt when performing work that requires repeatedly turning the trigger switch 16 on and off.

[0068] FIG. 16 is a graph showing, in a macroscopic view, an example of time-dependent changes in the rotation speed of the motor 3, the q-axis current flowing through the motor 3, and the control details of the control unit 41.

[0069] At time t1, trigger switch 16 is turned on while motor 3 is stopped. The period from then until time t2 when the motor rotation speed reaches or exceeds the startup rotation speed threshold is the startup control period. As described above, startup control switches between the estimated current section and the torque current section depending on the phase of the AC voltage.

[0070] When the motor rotation speed reaches or exceeds the startup rotation speed threshold at time t2, the control transitions from startup control to normal control. Normal control is a control (constant speed control) that maintains the motor rotation speed at a target value without changing the q-axis target current according to the phase of the AC voltage.

[0071] When the motor rotation speed reaches the target value for constant speed control at time t3, the acceleration section changes to a constant speed section, and the motor rotation speed is maintained at the target value. Note that in constant speed control, in a no-load state where no external load (hereinafter referred to as "load") is applied to motor 3 or a low-load state where the load is low, the motor rotation speed is maintained at the target value by control (duty control) of inverter circuit 42, but in a high-load state where the motor rotation speed cannot be maintained at the target value even when the duty is maximized, the motor rotation speed decreases as the load increases.

[0072] When trigger switch 16 is turned off at time t4, normal control is switched to stop control, the constant speed section is switched to the inertial section, and the motor rotation speed decreases due to natural deceleration. Stop control is a control that passes a minute current (position estimation current) to motor 3 (stator coil 3h) that is small enough not to accelerate or decelerate motor 3 (to an extent that does not affect the driving of motor 3) and that allows rotor position detection, until the motor rotation speed becomes less than the inertial stop threshold (e.g., 1,000 rpm) due to natural deceleration.

[0073] At time t5, when the trigger switch 16 is turned on while the motor 3 is rotating at a rotation speed less than the start rotation speed threshold, the control shifts from stop control to start control.

[0074] At time t6, when the motor rotation speed becomes equal to or greater than the startup rotation speed threshold, the control shifts from startup control to normal control.

[0075] FIG. 17(A) is a flowchart of the overall operation of the work machine 1.

[0076] When the trigger switch 16 is turned on, the control unit 41 performs start-up control (S3). After the start-up control (S3), the control unit 41 transitions to normal control if the start-up completion flag is 1 ("flag: 1" in S5, S7), and transitions to stop control if the start-up completion flag is 0 ("flag: 0" in S5, S9). After the normal control (S7), the control unit 41 transitions to stop control (S9). After the stop control (S9), the control unit 41 ends the processing if the stop-completion flag is 1 ("flag: 1" in S11), and returns to start-up control if the stop-completion flag is 0 ("flag: 0" in S11, S3).

[0077] FIG. 17(B) is a flowchart of the start-up control (S3) of FIG. 17(A).

[0078] When the trigger switch 16 is on (ON in S21), the control unit 41 detects the phase and magnitude of the AC voltage (S23). Based on the phase and magnitude of the AC voltage, the control unit 41 determines whether it is a torque current section or an estimated current section, and sets a target current (S25). The control unit 41 applies a voltage vector corresponding to the target current to the motor 3 (S27), detects the current of each phase (S29), and estimates (detects) the rotor position and motor rotation speed (S31).

[0079] If the motor rotation speed is equal to or greater than the startup rotation speed threshold ("Above startup rotation speed threshold" in S33), the control unit 41 sets the startup completion flag to 1 (S35) and ends the startup control. If the motor rotation speed is less than the startup rotation speed threshold ("Below startup rotation speed threshold" in S33), the control unit 41 returns to S21. If the trigger switch 16 is turned off (OFF in S21), the control unit 41 sets the startup completion flag to 0 (S37) and ends the startup control.

[0080] FIG. 18(A) is a flowchart of the normal control (S7) in FIG. 17(A).

[0081] When the trigger switch 16 is on (ON in S41), the control unit 41 sets a target current for constant speed control (S43), applies a voltage vector corresponding to the target current to the motor 3 (S45), detects the current of each phase (S47), and estimates (detects) the rotor position and the motor rotation speed (S49). When the trigger switch 16 is turned off (OFF in S41), the control unit 41 ends normal control.

[0082] FIG. 18B is a flowchart of the stop control (S9) in FIG. 17A.

[0083] The control unit 41 sets a target current for position estimation (S51), applies a voltage vector corresponding to the target current to the motor 3 (S53), detects the current of each phase (S55), and estimates (detects) the rotor position and motor rotation speed (S57).

[0084] If the motor rotation speed is less than the inertial stop threshold ("less than inertial stop threshold" in S59), the control unit 41 sets the stop completion flag to 1 (S61) and ends the stop control. If the motor rotation speed is equal to or greater than the inertial stop threshold ("equal to or greater than inertial stop threshold" in S59), the control unit 41 returns to S51 if the trigger switch 16 is off (OFF in S63), and if the trigger switch 16 is on (ON in S63), the control unit 41 sets the stop completion flag to 0 (S65) and ends the stop control.

[0085] This embodiment has the following advantages.

[0086] (1) When the trigger switch 16 is operated to start the motor 3 while the motor rotation speed is below the startup rotation speed threshold, the control unit 41 is configured to control the inverter circuit 42 so that the motor current increases when the rectified voltage increases and decreases when the rectified voltage decreases. Specifically, the control unit 41 is configured to control the inverter circuit 42 so that the motor current is large in a first region including the rising and falling regions around the timing when the rectified voltage reaches its maximum value, and the motor current is small in a second region including the rising and falling regions around the timing when the rectified voltage reaches its minimum value. This suppresses the motor current around the timing when the rectified voltage reaches its minimum value, preventing the DC link voltage from dropping excessively (for example, below 30 V) even when the motor rotation speed is low and the induced voltage generated by the motor 3 is low. This prevents the current response to the rotor position estimation voltage applied to the motor 3 from becoming small, thereby reducing the risk of the rotor position not being detected correctly and the risk of unstable startup of the motor 3.

[0087] (2) As described above, the configuration prevents the DC link voltage from dropping excessively, so the capacitance of the capacitor C1 (DC link capacitor) can be reduced, and the work machine 1 or the motor drive device can be made smaller.

[0088] (3) The control unit 41 controls the motor current while measuring the phase of the rectified voltage (the phase of the AC voltage). This prevents an excessive decrease in the DC link voltage due to a delay in controlling the motor current, compared to a configuration in which the motor current is controlled based on the magnitude of the DC link voltage, for example.

[0089] (4) As in control example 1 shown in FIG. 12, if the threshold value at the time of rising (first threshold value) is set lower than the threshold value at the time of falling (second threshold value), the response can be improved, i.e., the motor rotation speed can be increased more quickly in response to the ON operation of the trigger switch 16, resulting in a better working feel, compared to when the threshold value at the time of rising is set as high as the threshold value at the time of falling.

[0090] (5) When the operation of the trigger switch 16 is released, the control unit 41 is configured to execute control to decelerate the rotation of the motor 3 while flowing a position estimation current to the motor 3. This makes it possible to estimate the rotor position even in the inertia section where the motor rotation speed decreases due to natural deceleration, and improves response when the trigger switch 16 is turned on in the inertia section.

[0091] Although the present invention has been described above using the embodiments as examples, the present invention is not limited to the embodiments. Various modifications can be made to the details specifically described in the embodiments within the scope of the claims.

[0092] In the embodiment, the voltage at the interconnection point of the diode D5 and capacitor C2, which are connected in series between the output terminals of the rectifier circuit 61, is input to the control-system power supply circuit 45. However, since this configuration suppresses excessive drops in the DC link voltage as described above, as shown in Fig. 19, the diode D5 and capacitor C2 may be omitted from the circuit of Fig. 4, and the DC link voltage may be input directly to the control-system power supply circuit 45 (the output voltage of the rectifier circuit 61 is input to the control-system power supply circuit without passing through a diode). In this case, it is possible to reduce the number of components and make the device smaller.

[0093] The number of rotor poles and stator slots of the motor 3, i.e., the number of rotor magnets 3c and the number of stator coils 3h, are arbitrary. For example, the motor 3 may have a two-pole, three-slot configuration. The shunt resistors Ru, Rv, and Rw may be provided on the high-potential side of the current path of each phase.

[0094] The current, voltage, rotation speed, etc., given as specific numerical values ​​in the embodiments do not limit the scope of the invention in any way, and can be changed as desired to suit the required specifications.

[0095] The working machine of the present invention may be any other type of drilling machine having a drilling tip tool, such as a drill, hammer, or earth auger. The working machine of the present invention may also be a cutting machine, such as a portable circular saw, a bench circular saw, a rotary band saw, a jigsaw, a saber saw (reciprocating saw), or a brush cutter; a grinding machine having a grinding tip tool, such as a grinder; a polishing machine having a polishing tip tool, such as a sander or polisher; a cutting machine having a cutting tip tool, such as a plane, trimmer, or router; a fastening machine having a fastening tip tool, such as an impact driver, impact wrench, driver drill, shear wrench, riveter, or rebar tying machine; a crimping machine having a crimping tip tool, such as a crimping machine; a bending machine having a bending tip tool, such as a rebar bender; or a driving machine having a driving tip tool, such as a nail gun or tacker. [Explanation of symbols]

[0096] 1...Work machine (hammer drill), 2...Housing, 3...Motor (brushless motor), 3a...Output shaft, 3b...Rotor core, 3c...Rotor magnet, 3e...Stator core, 3h...Stator coil, 3f...Yoke portion, 3g...Salient pole portion (teeth portion), 4...Motion conversion mechanism, 5...Rotation transmission mechanism, 6...Piston, 7...Pressure chamber (air chamber), 8...Striker, 9...Intermediate element, 10...Tip tool, 11...Cylinder, 12...Retainer sleeve (tool holding portion), 13...Mode setting dial, 15...Power cord, 16 ...Trigger switch, 41...Control unit (microcomputer), 42...Inverter circuit (drive circuit), 44...Amplification circuit, 45...Control system power supply circuit, 50...Carrier signal generator, 51...Control command voltage calculation unit, 52...Superimposed voltage calculation unit, 53...Reference signal calculation unit, 54...UVW / DQ conversion unit, 55...Comparator, 56...PWM signal output unit, 60...AC power supply, 61...Diode bridge (full-wave rectifier circuit), 63...AC voltage measurement circuit, Q1 to Q6...Switching elements, Ru, Rv, Rw...Shunt resistors (current detection unit).

Claims

1. a brushless motor having a rotor and a stator having a plurality of windings; an inverter circuit connected to the plurality of windings; a rectification unit configured to rectify an AC voltage and output the rectified AC voltage to the inverter circuit; a capacitor connected in parallel to the inverter circuit on the output side of the rectifier; a control unit that controls the inverter circuit; an operation unit for instructing start and stop of the brushless motor; A work machine equipped with the control unit is configured to be able to control the inverter circuit so that, when the operation unit is operated to start the brushless motor, the current flowing through the brushless motor increases when a rectified voltage that is an output voltage of the rectifier increases, and the current decreases when the rectified voltage decreases. A work machine characterized by:

2. The work machine according to claim 1, the control unit is configured to be able to control the inverter circuit so as to increase the current in a rising region of the rectified voltage and decrease the current in a falling region of the rectified voltage. A work machine characterized by:

3. The work machine according to claim 2, the control unit is configured to be able to control the inverter circuit to increase the current when the rectified voltage becomes higher than a first threshold in the rising region, and to decrease the current when the rectified voltage becomes lower than a second threshold in the falling region. A work machine characterized by:

4. The work machine according to claim 3, The first threshold is lower than the second threshold. A work machine characterized by:

5. The work machine according to claim 1, The control unit is configured to be able to control the inverter circuit so that the current is large around the timing when the rectified voltage reaches its highest value, and the current is small around the timing when the rectified voltage subsequently reaches its lowest value. A work machine characterized by:

6. The work machine according to claim 5, The control unit is configured to be able to control the inverter circuit so that the current is large in a first region including a rising region and a falling region before and after the timing when the rectified voltage reaches its maximum value, and the current is small in a subsequent second region including a falling region and a rising region before and after the timing when the rectified voltage reaches its minimum value. A work machine characterized by:

7. The work machine according to claim 6, the rectified voltage when switching from the first region to the second region is higher than the rectified voltage when switching from the second region to the first region; A work machine characterized by:

8. The work machine according to claim 6 or 7, the current in the second region is large enough to allow the control unit to estimate the position of the brushless motor based on the current; A work machine characterized by:

9. The work machine according to claim 8, The current in the second region is such that the voltage of the capacitor does not fall below 30V. A work machine characterized by:

10. A work machine according to any one of claims 1 to 7, the control unit is configured to control the inverter circuit so that the brushless motor rotates at a constant speed in a no-load state in which no external load is applied to the brushless motor after the brushless motor is started. A work machine characterized by:

11. A work machine according to any one of claims 1 to 7, the control unit is configured to execute control to decelerate rotation of the brushless motor while causing a position estimation current to flow through the brushless motor when the operation of the operation unit is released. A work machine characterized by:

12. A work machine according to any one of claims 1 to 7, the control unit is configured to execute vector control to set a voltage vector, which is a combination of output voltages of the phases of the inverter circuit, in accordance with a position of the rotor. A work machine characterized by:

13. A work machine according to any one of claims 1 to 7, an AC voltage detection unit that detects the AC voltage input to the rectifier unit, the control unit is configured to detect the rectified voltage based on a detection result of the AC voltage detection unit. A work machine characterized by:

14. A work machine according to any one of claims 1 to 7, a control system power supply circuit to which the output voltage of the rectifier is input without passing through a diode; A work machine characterized by:

Images