Power tool with torque measuring device

Abstract

Power tool (2) with: a motor (8); a tool unit driven by the motor (8); and a torque determining device (12) for determining a load torque acting on the motor (8) from a workpiece via the tool unit, in which the torque determining means (12) determines the load torque, which reflects at least a drive torque according to a current flowing through the motor (8) and an inertial torque according to a moment of inertia of the motor (8), the power tool (2) is able to selectively switch between an idle mode and a load mode according to the load torque determined by the torque determining means (12), a speed of the motor (8) in the idle mode is lower than a speed of the motor (8) in the load mode, the torque determining means (12) has: a motor model (22) that reflects characteristics of the motor (8) and has an input for the load torque acting on the motor (8) and an output for a state variable related to the motor (8); a comparator (24) for calculating a difference between an actual measured value and the output of the motor model (22) for the state variable related to the motor (8); and an amplifier (26) for amplifying an output of the comparator (24) and outputting the amplified output as a determining value for the load torque acting on the motor (8), and The output of the amplifier (26) is entered into the motor model (22) as the load torque acting on the motor (8).

Description

Technical field

[0001] A technology disclosed in the present application relates to a power tool. Technical background

[0002] Patent document 1 discloses a technology for a power tool in which, based on the current flowing through the motor, a distinction is made between whether the motor is in an idle state or under load, and when it is in the idle state, the motor speed is reduced compared to that in the load state. This technology suppresses the generation of noise or vibration by reducing the motor speed in the idle state compared to the speed in the load state. State of the art patent document

[0003] Patent document 1: US 4,002,959 A

[0004] EP 1 431 006 A2 discloses an operating method and a cooling device for the motor of an electric tool. Summary of the invention

[0005] It is difficult to accurately determine whether a motor is idling or under load based solely on the current flowing through it. For example, even when idling, a large starting current flows through the motor during startup. Using the technology described in patent document 1, the motor is incorrectly determined to be under load in such a case, and its speed is increased accordingly.

[0006] Furthermore, to reduce the motor's speed in the idling state, the current flowing through the motor is limited by phase control or PWM control. Thus, even when the motor's state changes from idling to load, the increase in current flowing through the motor may be small. With the technology described in patent document 1, in such a case, the motor is incorrectly determined to be in the idling state, and there is a risk of the motor stalling while its speed is being reduced.

[0007] Furthermore, immediately after the transition from the no-load state to the load state, the motor is not driven stably at a constant speed, and a transition state exists that indicates unstable behavior. In this transition state, because the influence of an inertial torque corresponding to the motor's moment of inertia is significant, it is difficult to accurately determine the magnitude of a load torque solely based on the current flowing through the motor. If, as in the technology of patent document 1, the determination of whether the motor is in the no-load or load state is based solely on the current flowing through the motor, the point at which the motor speed increases during the switch from the no-load to the load state is delayed.

[0008] For power tools, there is a need for a technology to accurately and quickly determine whether a motor is in an idle or load condition, so that noise or vibration in the idle condition is suppressed, and to improve the response of a motor speed when switching from the idle to the load condition.

[0009] The power tool disclosed in the present application comprises a motor, a tool unit driven by the motor, and a torque determining device for determining a load torque acting on the motor via the tool unit from a workpiece. The torque determining device determines the load torque, which represents or reflects at least a drive torque according to a current flowing through the motor and an inertial torque according to a moment of inertia of the motor. The power tool is capable of selectively switching between an idle mode and a load mode according to the load torque determined by the torque determining device. In the power tool, the motor speed in the idle mode is lower than the motor speed in the load mode.

[0010] In the previously described power tool, the load torque, which corresponds to the drive torque according to the current flowing through the motor and the inertial torque according to the motor's moment of inertia, is determined, and switching between no-load and load modes is performed according to this determined load torque. Using such a configuration allows for accurate and rapid differentiation between no-load and load states of the motor, suppresses noise or vibration during no-load operation, and improves the motor's speed response when switching from no-load to load operation. Brief description of the drawings Fig. 1 is a view that schematically shows a configuration of a reciprocating saw 2; Fig. Figure 2 is a diagram showing a configuration of a monitoring circuit 12 in a block diagram; Fig. Figure 3 is a diagram showing a configuration of the monitoring circuit 12 in conjunction with a motor 8 in a block diagram; Fig. 4 is a diagram that shows a tax system, which is a tax system in Fig. 3 corresponds, shown in a block diagram; Fig. Figure 5 is a diagram showing changes over time of a torque τ acting on the motor 8 and a rotational speed ω of the motor 8 of the reciprocating saw 2; Fig. Figure 6 is a diagram showing a feedback control system for adjusting the speed of the motor 8; Fig. Figure 7 is a flowchart to explain the processing of a control 18; Fig. Figure 8 is a diagram showing an example of a combination of a first specified torque τ1, a second specified torque τ2, a first specified rotational speed ω1 and a second specified rotational speed ω2; Fig. Figure 9 is a diagram showing an example of a setting switch device 14; Fig. 10 is a diagram showing a different configuration of the monitoring circuit 12 in a block diagram; Fig. 11 is a diagram showing a different configuration of the monitoring circuit 12 in a block diagram; Fig. Figure 12 is a diagram showing a different configuration of the monitoring circuit 12 in a block diagram; Fig. Figure 13 is a diagram showing a different configuration of the monitoring circuit 12 in a block diagram. Description of an embodiment

[0011] In an electric tool according to one embodiment, the torque determining means comprises a motor model that represents characteristics of a motor and has an input for a load torque acting on the motor and an output for a state variable related to the motor, a comparator for calculating a difference between an actual measured value and the output of the motor model with respect to the state variable related to the motor, and an amplifier for amplifying an output of the comparator and outputting the amplified output as a determined value for the load torque acting on the motor, and the output of the amplifier is input into the motor model as the load torque acting on the motor.The "state variable related to the motor" is a state variable that relates to the motor's behavior and includes a voltage applied to the motor, a current flowing through the motor, the motor's rotational speed, and the like. In the torque determination method described above, a feedback loop is formed with the motor model, and the actual behavior of the motor can be simulated by the motor model. Thus, a determined value for the load torque acting on the motor can be accurately calculated when the actual measured value of the state variable related to the motor is available. According to the previously described power tool, even if the motor exhibits unstable behavior, the load torque acting on the motor can be accurately determined, and the no-load and load states of the motor can be precisely distinguished by simulating the motor's behavior with the motor model.

[0012] In a power tool according to one embodiment, the state variable related to the motor is the current flowing through the motor. The motor model further includes an input for the voltage applied to the motor, and an actual measured value of the voltage applied to the motor is input into the motor model. According to this power tool, the load torque acting on the motor can be accurately determined, and the no-load and load states of the motor can be accurately determined based on the actual measured values ​​of the current flowing through the motor and the actual measured values ​​of the voltage applied to the motor, which can be readily detected.

[0013] In one embodiment of a power tool, the torque determination means comprises a first filter for removing at least one high-frequency component and a second filter with the same characteristics as the first filter. The motor is controlled by allowing the current to flow in pulses, and the actual measured value of the current flowing through the motor is input to the comparator via the first filter, while the actual measured value of the voltage applied to the motor is input to the motor model via the second filter. According to this power tool, even when using a motor to which PWM control or phase control is applied, the load torque acting on the motor can be accurately determined, and the no-load and load states of the motor can be accurately distinguished.

[0014] In a power tool according to one embodiment, the state variable related to the motor is the motor speed. The motor model further includes an input for the voltage applied to the motor, and an actual measured value of the voltage applied to the motor is input into the motor model. According to this power tool, the load torque acting on the motor can be accurately determined, and an idle state and a load state of the motor can be accurately distinguished based on the actual measured value of the motor speed and the actual measured value of the voltage applied to the motor, which can be readily detected.

[0015] In a power tool according to one embodiment, the torque determining means determines the load torque acting on the motor by subtracting a product of a moment of inertia and a time derivative of the motor's rotational speed from a product of a torque constant and the current flowing through the motor. According to this power tool, the load torque acting on the motor can be suitably determined using a simple control system, and an idle state and a load state of the motor can be accurately distinguished.

[0016] In a power tool according to one embodiment, the torque determining means determines the load torque acting on the motor by subtracting the product of the moment of inertia and the time derivative of the motor's speed from the product of the torque constant and the current flowing through the motor, and further by subtracting a product of a coefficient of friction and the motor's speed. According to this power tool, the load torque acting on the motor can be accurately determined by a simple control system, and the motor's no-load and load states can be precisely distinguished.

[0017] In a power tool according to one embodiment, the motor speed in no-load mode is adjusted by a feedback control based on the motor speed or an induced voltage so that it is essentially constant. According to this power tool, even if operation in no-load mode is started in a state where a tool unit is held by a workpiece, the duty cycle for the PWM control is automatically extended by the feedback control, and the motor is not stalled.

[0018] In one embodiment of a power tool, operation in idle mode is initiated upon startup. According to this power tool, the generation of noise or vibration during startup can be reliably suppressed.

[0019] In one embodiment of a power tool, the power tool is configured to switch to load mode when the load torque determined by the torque determining means exceeds a first specified torque in the no-load mode. The power tool in one embodiment further comprises a first torque setting means that allows a user to set the first specified torque. The power tool in one embodiment is configured to switch to no-load mode when the load torque determined by the torque determining means falls below a second specified torque in the load mode. The power tool in one embodiment further comprises a second torque setting means that allows a user to set the second specified torque.In one embodiment of the power tool, the power tool further comprises a speed control device that allows a user to adjust the speed in load mode and / or no-load mode. According to these power tools, the operation of the power tool in no-load mode and load mode can be appropriately adjusted by the user according to the specific usage situation.

[0020] In the power tool according to one embodiment, the power tool is designed such that it switches to load mode when the load torque determined by the torque determining means exceeds a first specified torque in the no-load mode, and such that it switches to no-load mode when the load torque determined by the torque determining means falls below a second specified torque in the load mode, and the power tool further comprises a switching means that is capable of switching combinations of at least two or more of the speed in the load mode, the speed in the no-load mode, the first specified torque and the second specified torque in predetermined steps.According to this power tool, a user can select a suitable combination of the speed in load mode, the speed in idle mode, the first specified torque, and the second specified torque, depending on the situation of use.

[0021] In one embodiment of a power tool, the power tool further comprises an operating state switching means capable of switching between an operating state in which switching between no-load mode and load mode is performed, and an operating state in which operation is always performed in load mode. According to this power tool, a user can switch, depending on the situation of use, whether or not switching between no-load mode and load mode is performed.

[0022] In a power tool according to one embodiment, the power tool is configured such that it switches to load mode when the load torque determined by the torque determining means exceeds a first specified torque in the no-load mode, and such that it switches to no-load mode when the load torque determined by the torque determining means falls below a second specified torque in the load mode. The power tool further comprises an operating state switching means capable of switching between an operating state in which switching between no-load mode and load mode is performed, and an operating state in which operation is performed in load mode at all times. The operating state switching means is combined with a means for adjusting at least the speed in load mode and the speed in no-load mode.of the first specified torque or the second specified torque. According to this power tool, configurations of the operating state switching means and the adjusting means can be simplified.

[0023] In one embodiment of a power tool, switching from load mode to idle mode is prevented until a predetermined time has elapsed since a switch from idle mode to load mode. According to this power tool, a condition in which switching between load mode and idle mode occurs frequently can be suppressed, and the operation of the power tool can be stabilized.

[0024] In an electric tool according to one embodiment, the electric tool further comprises a power transmission unit for transmitting power from the motor to a tool unit and a load determination device for determining a load acting on the tool unit from a workpiece, and the load determination device determines the load acting on the tool unit from the workpiece according to the load torque determined by the torque determination device and characteristics of the power transmission unit, and the electric tool is able to selectively switch between no-load mode and load mode according to the load determined by the load determination device instead of the load torque determined by the torque determination device.With this power tool, the idle state and the load state of the motor can also be distinguished precisely and quickly, so that noise or vibration in the idle state can be suppressed and the response of a motor speed when switching from the idle state to the load state can be improved. embodiment

[0025] Fig. Figure 1 shows a reciprocating saw (a saw with a reciprocating saw blade) 2, which is an embodiment of a power tool. The reciprocating saw 2 of this embodiment comprises a saw blade holder 4, a power transmission unit 6, a motor 8, a motor drive circuit 10, a monitoring circuit 12, a setting switch 14, a trigger switch 16, a control unit 18, and a battery 20. The reciprocating saw 2 can be used for woodworking or metalworking.

[0026] In the reciprocating saw 2, when a user switches it on and presses the trigger switch 16, the motor 8 is driven by the motor drive circuit 10 using power from the battery 20 to rotate, and the power transmission unit 6 converts the rotary motion of the motor 8 into a reciprocating motion, which moves the saw blade holder 4 back and forth. Consequently, a saw blade attached to the saw blade holder 4 is moved back and forth, cutting a workpiece. Operation of the motor drive circuit 10 is controlled by the controller 18.

[0027] The monitoring circuit 12 determines the torque acting on the motor 8 from a workpiece via the saw blade, the saw blade holder 4, and the power transmission unit 6. The torque acting on the motor 8 is hereinafter referred to as the load torque. Furthermore, the monitoring circuit 12 determines the speed of the motor 8.

[0028] As in Fig. 2 shows an actual measured value V m a voltage applied to motor 8 and an actual measured value i m The current flowing through motor 8 is input into the monitoring circuit 12. The actual measured value V m The voltage applied to motor 8 is detected by a voltage detector (not shown). The actual measured value i m The current flowing through motor 8 is detected by a current detector (not shown). The monitoring circuit 12 outputs a determined value τ. e a torque acting on the motor 8 and a determined value ω e The speed of the motor 8 is transmitted to the control unit 18. The monitoring circuit 12 includes a motor model 22, a comparator 24, and an amplifier 26.

[0029] Motor model 22 models the characteristics of motor 8 as a transfer system with two inputs and two outputs. Motor model 22 uses a voltage V applied to motor 8 and a torque τ acting on motor 8 as inputs, and uses a current i flowing through motor 8 and a rotational speed ω of motor 8 as outputs.

[0030] The characteristics of motor model 22 can be specified based on the input-output characteristics of the actual motor 8. If motor 8 is a DC motor, the characteristics of motor model 22 can be determined, for example, as follows.

[0031] Regarding an electrical system of motor 8, assuming that L is an inductance, i is a current, V is an applied voltage, R is a resistance value, KB is a power generation constant, and ω is a rotational speed, the following relationship applies: Ldidt=V−Ri−KBω

[0032] On the other hand, for a mechanical system of motor 8, assuming that J is a moment of inertia of a rotor, KT is a torque constant, B is a coefficient of friction, and τ is a load torque acting on motor 8, the following relationship applies: Jdωdt=Kti−Bω−τ

[0033] The left-hand side of equation 2 represents an inertial torque corresponding to the motor's moment of inertia. The first term on the right-hand side of equation 2 represents a drive torque corresponding to the current flowing through the motor. The second term on the right-hand side of equation 2 represents a frictional torque.

[0034] Integrating both sides of equation 1 and equation 2 over time yields the following two relationships: i=∫(1LV−RLi−KBLω)dt ω=∫(KTJi−BJω−1Jτ)dt

[0035] By performing a numerical calculation based on Equation 3 and Equation 4, two outputs i and ω can be calculated with respect to two inputs V and τ. As can be seen from the above, if the motor model 22 is configured with the voltage V applied to the motor 8 and the load torque τ acting on the motor 8 as inputs, and the current i flowing through the motor 8 and the rotational speed ω of the motor 8 as outputs, the respective outputs can be obtained by integration without having to differentiate the state variable of the motor 8. By training the motor model 22 such that the output is obtained by integration as described above, the behavior of the motor 8 can be accurately simulated, even if the state variable of the motor 8 changes rapidly.

[0036] As in Fig. Figure 2 shows a current output of motor model 22, that is, a current determination value i.e The current of motor 8 is output to comparator 24. Comparator 24 calculates a difference Δi between the actual current measurement i and the motor 8. m of motor 8 and the current output i e of motor model 22. The calculated difference Δi is amplified with a predetermined gain factor G in the amplifier 26 and then expressed as the determined torque τ. e The signal from motor 8 is fed into a torque input of motor model 22. As previously described, the monitoring circuit 12 forms a feedback loop. The actual voltage measurement V m The voltage applied to motor 8 is fed into a voltage input of motor model 22.

[0037] In the feedback loop described above, by setting the gain factor G in the amplifier 26 as a sufficiently large gain factor, an input torque of the motor model 22, that is, the magnitude of the determined value τ, is achieved. eof the load torque acting on the motor 8, set such that the current determination value i e of motor 8 to the actual current measurement i m of motor 8 converges. Using such a configuration, the load torque τ acting on motor 8 can be e and the rotational speed ω e The current of motor 8 at this time can be calculated using motor model 22, so that the current i m , which flows through motor 8, is realized when the voltage V m is applied to motor 8. The load torque τ e The torque of motor 8, calculated as above, can be considered to be a drive torque according to the current i flowing through the motor. m and represents an inertial torque according to the moment of inertia J of the motor.

[0038] The monitoring circuit 12 outputs the speed output of the motor model 22 as the speed determination value ω. eof motor 8 together with the load torque determination value τ described above e out of.

[0039] A principle for determining the load torque τ and the speed ω of the motor 8 by the monitoring circuit 12 is described with reference to Fig. 3 explained. Fig. 3. The actual motor 8 is expressed by a transfer function M1, and the motor model 22, obtained by virtually running the motor 8 in the monitoring circuit 12, is expressed by a transfer function M2. A relationship between an input τ r (Torque value acting on the actual motor 8) and the output τ e (Torque determination value output by monitoring circuit 12) in a Fig. The tax system shown in point 3 is as follows. τe=GM11+GM2τr

[0040] Therefore, by setting the motor model 22 in the monitoring circuit 12 so that it has characteristics equal to those of the actual motor 8, M1 = M2 = M can be substituted into the equation above, and the following relationship is obtained. τe=GM1+GMτr

[0041] As shown in equation 6, the transfer function from the input τ r to the output τ e in the tax system in Fig. 3 equivalent to a feedback control system in which a forward transfer function is GM and a backward transfer function is 1, as in Fig. As shown in section 4. Therefore, the output τ follows. e the input τ r By adjusting the gain factor G in amplifier 26 so that it is sufficiently large, the output τ converges. e to the input τ r Therefore, the load torque τ acting on motor 8 can rbased on the torque determination value τ output by the monitoring circuit 12 e be determined.

[0042] The monitoring circuit 12 of this embodiment can accurately determine the load torque τ acting on the motor 8 on the basis of the voltage V applied to the motor 8 and the current i flowing through the motor 8, without using a sensor designed to detect torque.

[0043] The monitoring circuit 12 of this embodiment can accurately determine the speed ω of the motor 8 on the basis of the voltage V applied to the motor 8 and the current i flowing through the motor 8, without using a sensor designed to detect a speed.

[0044] The monitoring circuit 12 of this embodiment is designed such that the current output i e of engine model 22 to the current i mThe current flowing through the actual motor 8 is converted by using the feedback loop containing motor model 22, which takes the voltage V applied to motor 8 and the load torque τ acting on motor 8 as inputs and the current i flowing through motor 8 and the speed ω of motor 8 as outputs. With such a configuration, the load torque τ acting on motor 8 and the speed ω of motor 8 can be accurately determined without the need for derivation.

[0045] The control unit 18 switches the operating mode of the reciprocating saw 2 based on the torque determination value τ output by the monitoring circuit 12. e um. As in Fig. As shown in Figure 5, in this embodiment of the reciprocating saw 2, when the push-button switch 16 is activated after being switched on, operation begins in idle mode. In idle mode, the controller 18 adjusts the speed of the motor 8 by means of a PI controller such that the speed ω of the motor 8 becomes a first specified speed ω1. The first specified speed ω1 in idle mode is a speed at which vibration or noise is not disturbing when the motor 8 is rotating in a state where the load torque is not acting. When the torque determination value τ eIf a first specified torque τ1 is exceeded in the no-load mode, the mode switches to the load mode. In the load mode, the controller 18 adjusts the speed of the motor 8 by means of a PI controller so that the speed ω of the motor 8 becomes the second specified speed ω2. The second specified speed ω2 is a speed suitable for machining a workpiece. The second specified speed ω2 is a speed that is greater than the first specified speed ω1. In the load mode, when the torque determination value τ e When the torque falls below a second specified torque τ2, the mode switches to idle mode.

[0046] It should be noted that the speed of motor 8 can be adjusted by feedback control based on the determined value (or the actual measured value) of the speed of motor 8. Alternatively, the adjustment can be made by feedback control based on an induced voltage of motor 8 instead of the speed of motor 8. Such control can be implemented using the feedback loop with a comparator 40, a PI controller 42, and motor 8, as shown, for example, in Fig. Figure 6 shows that, with such a control system, even if the push-button switch 16 is activated in a state where the saw blade is engaged with and held against a workpiece, the duty cycle of the PWM control is automatically extended by the feedback control, and the motor 8 is not blocked. Furthermore, in this embodiment, the load torque, which represents not only the drive torque according to the current flowing through the motor 8 but also the inertial torque according to the moment of inertia of the motor 8, is determined. Thus, even when the motor 8 is in a transitional state, the mode can be quickly switched from no-load mode to load mode.

[0047] With the setting switch 14, the user can set the first specified torque τ1, the second specified torque τ2, the first specified speed ω1 and the second specified speed ω2.

[0048] Fig. Figure 7 is a flowchart to explain the operation of the reciprocating saw 2 of this embodiment. When the reciprocating saw 2 is switched on, the control unit 18 performs the following steps: Fig. 7 shown processing.

[0049] In step S2, settings for the first specified torque τ1, the second specified torque τ2, the first specified speed ω1 and the second specified speed ω2 are each obtained from the setting switching means 14.

[0050] In step S4, the system waits for the push button 16 to be switched on.

[0051] In step S6, the operation of the reciprocating saw 2 is started in idle mode. That is, the motor 8 is driven, and a back-and-forth movement of the saw blade holder 4 is initiated. In idle mode, the speed of the motor 8 is set to the first specified speed ω1.

[0052] In step S8, a counter is cleared.

[0053] In step S10, the settings for the first specified torque τ1, the second specified torque τ2, the first specified speed ω1 and the second specified speed ω2 are each obtained from the setting switching means 14.

[0054] In step S12, the determined value τ is calculated. e The load torque acting on the motor 8 is obtained from the monitoring circuit 12.

[0055] Step S14 determines whether the current operating mode is idle or load mode. If the current operating mode is idle, the routine proceeds to step S16. If the current operating mode is load mode, the routine proceeds to step S26.

[0056] In step S16, it is determined whether the determined value τ eThe first specified torque τ1 is exceeded or not by the load torque acting on motor 8. If the determined value τ e If the load torque does not exceed the first specified torque τ1 (NO), the counter is cleared in step S24, and the routine then returns to step S10. If the determined value τ e If the load torque in step S16 exceeds the first specified torque τ1 (YES), the counter is incremented in step S18, and then the routine proceeds to step S20.

[0057] Step S20 determines whether the counter has reached a first predetermined value. If the counter has not reached the first predetermined value (NO), the routine returns to step S10. If the counter has reached the first predetermined value in step S20 (YES), the operating mode is switched from idle mode to load mode in step S22, and the counter is reset in step S24. The routine then returns to step S10.

[0058] In step S26, it is determined whether the determined value τ e The load torque acting on motor 8 falls below the second specified torque τ2 or not. If the determined value τ e If the load torque is not less than the second specified torque τ2 (NO), the counter is cleared in step S34, and then the routine returns to step S10. If the determined value τ eIf the load torque in step S26 falls below the second specified torque τ2 (YES), the counter is incremented in step S28, and then the routine returns to step S30.

[0059] Step S30 determines whether the counter has reached a second predetermined value. If the counter has not reached the second predetermined value (NO), the routine returns to step S10. If the counter has reached the second predetermined value in step S30 (YES), the operating mode is switched from load mode to idle mode in step S32, the counter is cleared in step S34, and then the routine returns to step S10.

[0060] It should be noted that in the flowchart described above, if the torque determination value τ is in step S 16 eIf the torque specified is not greater than the first specified torque τ1, it may be provided that the counter is decremented in step S24 instead of being cleared. In this case, a minimum value of the counter is set to zero, so that no value less than or equal to the minimum value is used. Similarly, it may be provided that if the torque determination value τ e If the torque in step S26 is not less than the second specified torque τ2, the counter is decremented in step S34 instead of being cleared. In this case, it is also stipulated that a minimum counter value is set to zero, so that a value less than or equal to the minimum value is not used.

[0061] The operation of the reciprocating saw 2 is explained. When the reciprocating saw 2 is switched on and the trigger switch 16 is activated, operation begins in idle mode. The saw blade then begins cutting a workpiece, and when the load torque acting on the motor 8 continuously exceeds the first specified torque τ1 for a predetermined period, the mode switches from idle mode to load mode. Subsequently, when the saw blade has finished cutting the workpiece and the load torque acting on the motor 8 remains continuously below the second specified torque τ2 for a predetermined period, the load mode switches back to idle mode.

[0062] According to the reciprocating saw 2 of this embodiment, the mode is switched between no-load mode and load mode according to the load torque acting on the motor 8. With such a configuration, in the no-load mode, in which the load torque does not act on the motor 8, the speed of the motor 8 is kept low, and the generation of noise or vibration can be suppressed.

[0063] According to the reciprocating saw 2 of this embodiment, if the load torque acting on the motor 8 continuously exceeds the first specified torque τ1 for a predetermined period, the mode switches to the load mode. By using such a configuration, if the load torque acting on the motor 8 fluctuates temporarily, the operating mode is not switched. The operation of the reciprocating saw 2 can thus be stabilized.

[0064] According to the reciprocating saw 2 of this embodiment, if the load torque acting on the motor 8 in load mode remains below the second specified torque τ2 for a predetermined period, the mode switches to the no-load mode. By using such a configuration, if the load torque acting on the motor 8 fluctuates temporarily, the operating mode is not switched. The operation of the reciprocating saw 2 can thus be stabilized.

[0065] It should be noted that a configuration can be used in which switching the operating mode is prevented for a predetermined period immediately after switching from idle mode to load mode or immediately after switching from load mode to idle mode. Using such a configuration can suppress a state in which the operating mode is frequently switched.

[0066] The preceding section described the configuration in which the user of the reciprocating saw 2 can optionally set the first specified torque τ1, the second specified torque τ2, the first specified speed ω1, and the second specified speed ω2 using the second setting switch 14. Alternatively, it may be provided that the first specified torque τ1, the second specified torque τ2, the first specified speed ω1, and the second specified speed ω2 are preset upon delivery of the product, and the user of the reciprocating saw 2 cannot change these settings.

[0067] The settings of the first specified torque τ1, the second specified torque τ2, the first specified speed ω1, and the second specified speed ω2 using the setting switch 14 can be implemented in various ways. For example, a rotary knob with rotation angles corresponding to numerical values ​​can be provided. Alternatively, a push-button switch into which the numerical value is entered can be provided. Alternatively, a rotary knob or a switch allowing stepless selection of the numerical value can be provided for each of the following: the first specified torque τ1, the second specified torque τ2, the first specified speed ω1, and the second specified speed ω2. Alternatively, the numerical values ​​can be set according to the actuation range of the push-button switch 16.

[0068] Alternatively, combinations of the first specified torque τ1, the second specified torque τ2, the first specified speed ω1, and the second specified speed ω2 can be determined in advance upon delivery of the product, allowing the user to select which combination to use. In the case of the Fig. In the example shown in Figure 8, the user selects any one of several machining modes, such as a woodworking mode, a metalworking mode, etc. Values ​​for the first specified torque τ1, the second specified torque τ2, the first specified speed ω1, and the second specified speed ω2 are determined according to the selected machining mode. In the example shown in Fig. In the example shown in Figure 8, the first specified torque τ1 and the second specified torque τ2 are set low, the first specified speed ω1 is set low, and the second specified speed ω2 is set high in the woodworking mode compared to the metalworking mode. When machining metal, it takes longer for the saw blade to penetrate the workpiece if the speed of motor 8 is set too low in the no-load mode. Furthermore, if the speed of motor 8 is set too high in the load mode, the saw blade could bind and stop cutting. Therefore, in the example shown in Figure 8, the following applies: Fig. In the example shown in Figure 8, when the metalworking mode is selected, the speed of motor 8 in the no-load mode (i.e., the first specified speed ω1) is set higher than that in the case where the woodworking mode is selected, and the speed of motor 8 in the load mode (i.e., the second specified speed ω2) is set lower than that for the woodworking mode. Furthermore, when metal is being machined, increasing the speed of motor 8 before the saw blade enters a workpiece causes slippage between the saw blade and the workpiece. Thus, in the Fig. In the example shown in Figure 8, when the metalworking mode is selected, the first specified torque τ1, which becomes a reference for switching from the idle mode to the load mode, is set higher than that for the woodworking mode.

[0069] In the embodiment described above, the configuration in which the speed of motor 8 in load mode is set to the second specified speed ω2 has been explained. However, various types of control for the speed of motor 8 in load mode can be used, differing from this. For example, the speed of motor 8 in load mode can be changed according to the magnitude of the load torque acting on motor 8. Alternatively, the rate of change of the speed of motor 8 in load mode can be changed according to the rate of change of the load torque acting on motor 8. By using such configurations, changes in the speed of motor 8 during switching between the no-load mode and the load mode can be smoothed. Alternatively, the speed of motor 8 in load mode can be increased or decreased according to the actuation extent of the push-button switch 16.

[0070] In the embodiment described above, the configuration is such that when the load torque acting on the motor 8 falls below the second specified torque τ2 in load mode, the mode switches to the idle mode. In contrast, it can be provided that once operation is carried out in load mode, operation continues in load mode without switching the operating mode until the trigger switch 16 is turned off or the reciprocating saw 2 is switched off.

[0071] It may also be provided that the user of the reciprocating saw 2 can optionally select whether to switch between no-load mode and load mode as described above, or whether to operate continuously in load mode. Such switching of the operating state can be carried out using a rotary knob or a slide switch. Furthermore, such a means for switching the operating state can be combined with the setting switch 14 for setting the first specified torque τ1, the second specified torque τ2, the first specified speed ω1, and the second specified speed ω2. In the case described in Fig. The setting switch 14 shown in 9 can be changed to any mode from a first mode (see 9) by means of a slide switch which can be switched in three stages. Fig. 9A) and a second mode (see Fig. 9C), in which a switch is made between idle mode and load mode, and a forced mode (see Fig. 9B), in which operation is carried out in load mode the entire time. The first mode, for example, is the one in Fig. The eight woodworking modes shown are shown, and the second mode is, for example, the one in Fig. 8 Metalworking modes are shown. Using such a configuration simplifies the setting switch 14 and improves the operability of the reciprocating saw 2.

[0072] The determination of the load torque in the monitoring circuit 12 can be carried out by various methods that differ from the one described above. For example, if the motor 8 is a DC motor and the motor drive circuit 10 performs PWM control of the motor 8, as shown in Fig. 10 is shown to indicate that the actual voltage measurement value V m , which is applied to the motor 8, passes through a filter 27 in the monitoring circuit 12, and the actual current measurement i m The current flowing through motor 8 passes through filter 29. Filter 27 and filter 29 are filters that have the same characteristics and remove at least one high-frequency component, and which can be configured, for example, as low-pass or band-pass filters.

[0073] When motor 8 is controlled by PWM control, the actual current measurement i fluctuates. m and the actual voltage measurement V m The current fluctuates rapidly during power-up, but hardly at all during power-off. Therefore, if the duty cycle of the PWM control is short, or if the sampling period of the monitoring circuit 12 is not sufficiently short, the fluctuation of the actual measured current value i can be excessive.m and the actual voltage measurement value V m During power-up, the current cannot be accurately measured, and certain errors for the load torque τ acting on motor 8 and the speed ω of motor 8 become large. However, to shorten the sampling period of the monitoring circuit 12, a high-performance IC chip should be used, which increases the complexity. Thus, filtering the actual current measurement i m and the actual voltage measurement value V m using filter 27 and filter 29, which have the same characteristics as in Fig. As shown in Figure 10, the high-frequency component is removed. Consequently, fluctuations in the actual current measurement i m and the actual voltage measurement value V m off, and the behavior of the motor 8 can be recorded more accurately without shortening the sampling period of the monitoring circuit 12 in this way.

[0074] Alternatively, as in Fig. 11 shows the monitoring circuit 12 designed such that the actual measured value V m the voltage applied to motor 8 and the actual measured value ω m The rotational speed of motor 8 is used as input and the determined value τ e for the load torque acting on the motor 8 and the determined value i e The current flowing through motor 8 is used as the output. In this case, the actual measured value V is used. m The voltage applied to motor 8 is detected by a voltage detector (not shown), and an actual measured value ω is obtained. m The rotational speed of motor 8 is detected by a rotational speed detector (not shown).

[0075] At the in Fig. The monitoring circuit 12 shown in 11 provides a speed output of the motor model 22, that is, the determined value ω. eThe rotational speed of motor 8 is input into a comparator 30. The comparator 30 calculates a difference Δω between the actual measured value ω. m the speed of motor 8 and the speed output ω e of motor model 22. The calculated difference Δω is amplified in an amplifier 32 with a predetermined gain factor H and then used as the determining torque τ. e The torque input of motor 8 is fed into the torque input of motor model 22. As previously described, the monitoring circuit 12 forms a feedback loop. The actual measured value V m The voltage applied to motor 8 is entered into the voltage input of motor model 22.

[0076] In the feedback loop described above, by adjusting the gain factor H in the amplifier 32 so that it is sufficiently large, the input torque of the motor model 22, that is, the magnitude of the torque determination value τ e, which acts on the motor 8, is set so that the speed output of the motor model 22, that is, the speed determination value ω e of motor 8 to the actual speed measurement ω m of motor 8 converges. By using such a configuration, the load torque τ acting on motor 8 can be e and the current flowing through motor 8 i e at this point in time to realize the rotational speed ω m of motor 8, when the voltage V m The value applied to motor 8 can be determined using motor model 22.

[0077] The configuration in which the load torque τ acting on motor 8 was explained in the preceding section. e is determined by integration without derivation, using motor model 22. In contrast, the load torque τ acting on motor 8 can be ealso determined by a differential operation based on equation 2 given above.

[0078] At the in Fig. The monitoring circuit 12 shown here determines the value τ. e of the torque acting on motor 8 using the actual measured value i m of the current flowing through motor 8 and the actual measured value ω m The engine speed 8 is output as input. In this case, the actual measured value i m of the current flowing through motor 8 is detected by a current detector (not shown), and the actual measured value ω m The rotational speed of motor 8 is detected by a rotational speed detector (not shown).

[0079] At the in Fig. In the monitoring circuit 12 shown, a drive torque τ is generated by means of a proportional element 50. Aby multiplying a torque constant KT with the actual measured value i m of the current flowing through motor 8 is calculated. In addition, a frictional torque t is calculated. B by multiplying the coefficient of friction B with the actual measured value ω m The rotational speed of the motor 8 is calculated using a proportional element 52. Furthermore, a time derivative for the actual measured value ω is calculated using a derivative element 54. m The speed of the motor 8 is calculated, the calculated derivative value is smoothed by a low-pass filter 56, and then an inertial torque τ is calculated. C The moment of inertia J of the motor 8 is calculated by multiplying it by a proportional element 58. Comparators 60 and 62 subtract the frictional torque τ. B and the moment of inertia τ C of the drive torque τ A , and the determination value τ e The load torque is calculated.

[0080] It should be noted that in the Fig. In the monitoring circuit 12 shown, if the coefficient of friction B is sufficiently small, the proportional element 52 and the comparator 60 can be omitted. Furthermore, if the time derivative of the actual measured value ω m Since the speed of the motor 8 does not change rapidly, the low-pass filter 56 can also be omitted.

[0081] The preceding section described a configuration in which the load state and the idle state are determined based on the specified value τ. e The load torque acting on motor 8 can be distinguished, and the operating mode of the reciprocating saw 2 can be switched. Based on a similar idea, it can be provided that the load state and the no-load state are determined based on a defined value F. ea load acting on the saw blade from a workpiece is distinguished and the operating mode of the reciprocating saw 2 is switched.

[0082] When elements such as a spring, an air cylinder, a crank, and the like are included in the power transmission unit 6, the curve of a load F acting from a workpiece onto the saw blade differs considerably from the curve of the load torque τ acting on the motor 8. This is particularly pronounced when an impact force acts on the saw blade. Thus, in the Fig. The monitoring circuit 12 shown in Figure 13 determines the load F acting on the saw blade from a workpiece, instead of determining the load torque τ acting on the motor 8. The control unit 18 then switches according to the determined value F. e the load exerted on the saw blade by a workpiece switches between load mode and idle mode.

[0083] The monitoring circuit 12, which is in Fig. Figure 13 shows the motor model 22, which is obtained by modeling the motor 8, the comparator 24, the amplifier 26, a power transmission unit model 25, which is obtained by modeling the power transmission unit 6, and a current detection unit model 28, which is obtained by modeling a (not shown) current detection unit.

[0084] The power transfer unit model 25 models the characteristics of the power transfer unit 6 as a transfer function with one input and one output. The power transfer unit model 25 uses a load applied to the power transfer unit 6 by the saw blade via the saw blade holder 4 as an input and a load torque acting on the motor 8 from the power transfer unit 6 as an output. The characteristics of the power transfer unit model 25 can be specified based on the input-output characteristics of the actual power transfer unit 6.

[0085] Current detection unit model 28 models the characteristics of the current detection unit as a transfer function with one input and one output. Current detection unit model 28 uses the current flowing through the motor 8 as an input and a current detected by the current detection unit as an output. The characteristics of current detection unit model 28 can be specified based on the input-output characteristics of the actual current detection unit.

[0086] As in Fig. As shown in 13, the current output i e The current of motor model 22 is fed into comparator 24 via current detection unit model 28. In comparator 24, a difference Δi is calculated between the actual current measurement of motor 8, that is, the current i. m , which is detected by the current detection unit, and a current egg ecalculated by the current detection unit model 28. The calculated difference Δi is amplified in the amplifier 26 with the predetermined gain factor G and then used as the determined value F. e the load exerted on the saw blade by a workpiece. Furthermore, the determined value F is also given. e the load acting on the saw blade by the workpiece is determined by the power transmission unit model 25 to the value τ e The load torque acting on motor 8 is converted and fed into the torque input of motor model 22. As previously described, the monitoring circuit 12 forms a feedback loop. It should be noted that the actual measured value V m The voltage applied to motor 8 is entered into the voltage input of motor model 22.

[0087] In the feedback loop described above, the magnitude of the motor model 22 is adjusted by setting the gain factor G in the amplifier 26 so that it is sufficiently large, such that the current output of the motor model 22, that is, the current determination value i e of motor 8 to the actual current measurement i m of motor 8 converges, thereby increasing the magnitude of the determined value F e the load exerted on the saw blade by the workpiece is set. Using such a configuration, the determining value F can be set by motor model 22. e the load exerted by the workpiece on the saw blade to generate the current i m , which flows through motor 8 when the voltage V m The amount applied to motor 8 will be calculated.

[0088] If the monitoring circuit 12 in Fig.When used in 13, the controller 18 uses a first specified load F1 and a second specified load F2 as thresholds to switch the operating mode instead of the first specified torque τ1 and the second specified torque τ2 when switching between the load mode and the idle mode.

[0089] In the previously described embodiment, the reciprocating saw 2 was described as an example of the power tool, but the power tool is not limited to this. The power tool could be a jigsaw, a grinder, or the like. Alternatively, the power tool could be a screwdriver. In the case of the screwdriver, a high load torque acts on the motor when a clutch is engaged and the mode is switched from no-load mode to load mode.

[0090] Representative and non-limiting specified examples of the present invention have been described in detail with reference to the accompanying drawings. This detailed explanation is intended only to clarify those details that will allow those skilled in the art to implement the preferred embodiments of the present invention in practice and is not intended to limit the scope of protection of the present invention. Furthermore, the disclosed additional features and inventions can be used to create a further improved power tool, either separately or in combination with the other features and inventions.

[0091] Furthermore, the combinations of features and processes disclosed in the detailed explanation described above are not essential for the practical application of the present invention in the broadest sense, but were merely described to illustrate a representative specified example of the present invention. Moreover, the various features of the previously described representative specified examples and the various features in the claims need not be combined as in the specified examples described herein or in the order given to create additional and useful embodiments of the present invention.

[0092] All features described in this description and / or the claims are intended to individually and independently limit the specified subject matter described in the disclosure of the original application and the claims, irrespective of the configurations of the features described in the embodiments and / or claims. Furthermore, the descriptions relating to all numerical ranges and groups or aggregations, as well as all intermediate configurations, are intended to limit the specified subject matter described in the original application and the claims.

[0093] The specified examples of the present invention have been explained in detail above; however, they merely represent examples and do not limit the claims. The technology described in the claims includes various variations and modifications of the specified examples given above. The technical elements explained in this description or the accompanying drawings have technical applicability individually or due to various combinations and are not limited to the combinations specified in the originally filed claims. Furthermore, the technology presented in the description or the accompanying drawings can solve several problems simultaneously, and solving one of these problems already leads to technical applicability.

Claims

[1] Power tool (2) with: an engine (8); a tool unit driven by the motor (8); and a torque determining means (12) for determining a load torque acting on the motor (8) from a workpiece via the tool unit, wherein the torque determining means (12) determines the load torque which reflects at least a drive torque according to a current flowing through the motor (8) and an inertia torque according to an inertia moment of the motor (8), the power tool (2) is capable of selectively switching between an idle mode and a load mode according to the load torque determined by the torque determining means (12), a speed of the engine (8) in the idle mode is lower than a speed of the engine (8) in the load mode, the torque determining means (12) comprises: a motor model (22) reflecting characteristics of the motor (8) and having an input for the load torque acting on the motor (8) and an output for a state variable related to the motor (8); a comparator (24) for calculating a difference between an actual measured value and the output of the engine model (22) for the state variable related to the engine (8); and an amplifier (26) for amplifying an output of the comparator (24) and outputting the amplified output as a determination value for the load torque acting on the motor (8), and the output of the amplifier (26) is input into the motor model (22) as the load torque acting on the motor (8). [2] Power tool according to claim 1, wherein the state variable related to the motor (8) is the current flowing through the motor (8), the motor model (22) further comprises an input for a voltage applied to the motor (8) and an actual measured value of the voltage applied to the motor (8) is entered into the motor model (22). [3] Power tool according to claim 2, wherein the torque determining means (12) comprises: a first filter (29) for removing at least one high-frequency component; and a second filter (27) having the same characteristics as those of the first filter, the motor (8) is controlled by allowing the current to flow in pulsed fashion, the actual measured value of the current flowing through the motor (8) is input into the comparator (24) via the first filter (29) and the actual measured value of the voltage applied to the motor (8) is input into the motor model (22) via the second filter (27). [4] Power tool according to claim 1, wherein the state variable related to the motor (8) is the speed of the motor (8), the motor model (22) further comprises an input for a voltage applied to the motor (8) and an actual measured value of the voltage applied to the motor (8) is entered into the motor model (22). [5] Power tool (2) with: an engine (8); a tool unit driven by the motor (8); and a torque determining means (12) for determining a load torque acting on the motor (8) from a workpiece via the tool unit, wherein the torque determining means (12) determines the load torque which reflects at least a drive torque according to a current flowing through the motor (8) and an inertia torque according to an inertia moment of the motor (8), the power tool (2) is capable of selectively switching between an idle mode and a load mode according to the load torque determined by the torque determining means (12), a speed of the engine (8) in the idle mode is lower than a speed of the engine (8) in the load mode and the torque determining means (12) determines the load torque acting on the motor (8) by subtracting a product of the moment of inertia and a time derivative of the speed of the motor (8) from a product of a torque constant and the current flowing through the motor (8). [6] Power tool according to claim 5, wherein the torque determining means (12) determines the load torque acting on the motor (8) by subtracting the product of the moment of inertia and the time derivative of the speed of the motor (8) from the product of the torque constant and the current flowing through the motor (8) and further by subtracting a product of a friction coefficient and the speed of the motor (8). [7] Power tool (2) with: an engine (8); a tool unit driven by the motor (8); and a torque determining means (12) for determining a load torque acting on the motor (8) from a workpiece via the tool unit, wherein the torque determining means (12) determines the load torque which reflects at least a drive torque according to a current flowing through the motor (8) and an inertia torque according to an inertia moment of the motor (8), the power tool (2) is capable of selectively switching between an idle mode and a load mode according to the load torque determined by the torque determining means (12), a speed of the engine (8) in the idle mode is lower than a speed of the engine (8) in the load mode and the speed of the motor (8) in the idle mode is adjusted to be substantially constant by feedback control based on the speed of the motor (8) or an induced voltage. [8] Power tool (2) with: an engine (8); a tool unit driven by the motor (8); a torque determining means (12) for determining a load torque acting on the motor (8) from a workpiece via the tool unit; a power transmission unit (6) for transmitting power from the motor (8) to the tool unit; and a load determining means for determining a load acting on the tool unit from a workpiece, wherein the torque determining means (12) determines the load torque which reflects at least a drive torque according to a current flowing through the motor (8) and an inertia torque according to an inertia moment of the motor (8), the power tool (2) is capable of selectively switching between an idle mode and a load mode according to the load torque determined by the torque determining means (12), a speed of the engine (8) in the idle mode is lower than a speed of the engine (8) in the load mode, the load determining means determines the load acting on the tool unit from the workpiece in accordance with the load torque determined by the torque determining means (12) and characteristics of the power transmission unit, and the power tool (2) is capable of selectively switching between the idle mode and the load mode according to the load determined by the load determining means instead of the load torque determined by the torque determining means (12). [9] Power tool according to one of claims 1 to 8, wherein when the power tool (2) is started, operation in the idle mode is started. [10] Power tool according to one of claims 1 to 9, which is designed to be switched to the load mode when the load torque determined by the torque determining means (12) in the no-load mode exceeds a first specified torque. [11] The power tool of claim 10, further comprising a first torque setting means (14) enabling a user to set the first specified torque. [12] Power tool according to one of claims 1 to 11, which is designed such that it is switched to the idle mode when the load torque determined by the torque determining means (12) in the load mode falls below a second specified torque. [13] The power tool of claim 12, further comprising a second torque setting means (14) enabling a user to set the second specified torque. [14] A power tool according to any one of claims 1 to 13, further comprising a speed setting means (14) enabling a user to set the speed in the load mode and / or the idle mode. [15] The power tool according to any one of claims 1 to 9, which is configured to be switched to the load mode when the load torque determined by the torque determining means (12) in the idle mode exceeds a first specified torque, and which is configured to be switched to the idle mode when the torque determined by the torque determining means (12) in the load mode falls below a second specified torque, further comprising switching means (14) capable of switching, in predetermined stages, combinations of at least two or more of the rotational speed in the load mode, the rotational speed in the idle mode, the first specified torque, and the second specified torque. [16] A power tool according to any one of claims 1 to 15, further comprising an operation state switching means (14) capable of switching between an operation state in which switching is performed between the idle mode and the load mode and an operation state in which operation in the load mode is performed at all times. [17] Power tool according to one of claims 1 to 9, which is designed such that it is switched to the load mode when the load torque determined by the torque determining means (12) in the no-load mode exceeds a first specified torque, and which is designed such that it is switched to the no-load mode when the load torque determined by the torque determining means (12) in the load mode falls below a second specified torque, further comprising an operating state switching means (14) capable of switching between an operating state in which switching is performed between the idle mode and the load mode and an operating state in which operation in the load mode is performed at all times, wherein the operating state switching means (14) is formed together with a means for setting at least the rotational speed in the load mode, the rotational speed in the idle mode, the first specified torque or the second specified torque. [18] A power tool according to any one of claims 1 to 17, wherein switching from the load mode to the idle mode is prevented until a predetermined time has elapsed since switching from the idle mode to the load mode.

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