JP2010173054A - Power tool and method of controlling rotation of motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control torque-rotation speed characteristics of a motor to achieve an optimum operational efficiency. <P>SOLUTION: Current is inputted from the rotating motor 14 to a current detection section 34. The voltage of a rechargeable battery 12 is inputted to a voltage control section 36. The voltage control section 36 outputs a drive voltage corresponding to the optimum rotational frequency of the motor 14 to a motor driver 13 based on the inputted voltage and the current inputted to the current detection section 34. That is, it corresponds to the optimum rotation speed irrespective of the charged condition or load torque of the rechargeable battery, and therefore an impact screwdriver fastens different types of screws as well most efficiently. Accordingly, the motor is controlled based on a load current proportionally related to the load torque and the voltage of the rechargeable battery 12. Hence the motor drive voltage can be suitably varied depending on the load torque, namely, the optimum rotation speed corresponding to a screw load, and the torque-rotation speed characteristics of the motor in response to the power tool can be controlled to achieve the optimum operational efficiency. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electric power tool used for tightening work (screw tightening work) of screws such as bolts and nuts, for example, and a motor rotation control method, and in particular, controls the rotation of a motor so as to have an optimum rotation speed. The present invention relates to a power tool and a motor rotation control method.

  As an electric tool, for example, an impact driver, there is a tool that does not control the rotational speed of a motor or a tool that controls the rotational speed (see Patent Document 1). As a general method for controlling the rotational speed, there is a rotational speed control system for keeping the target rotational speed constant or a voltage control system for making the target voltage constant. Hereafter, the block diagram of each electric tool mentioned above is each demonstrated based on FIG. 9 (A) thru | or FIG. 9 (C).

  As shown in FIG. 9A, an electric tool that does not control the rotational speed of the motor is disposed between a rechargeable battery 80 that serves as a power source, a motor 82 that operates a hammer (not shown), and the rechargeable battery 80 and motor 84. The motor driver 81 is provided. In the rotation speed control method described above, as shown in FIG. 9B, a CPU 84 and a motor driver 81 are connected, and the CPU 84 includes a memory 86 and a rotation speed control unit 88. Then, the rotational speed of the motor 82 is input to the rotational speed controller 88, and the rotational speed controller 88 controls the input rotational speed to be a target rotational speed preset in the memory 86. That is, the rotation speed control method is a method in which control is performed so that the target rotation speed is always constant. In addition, CPU84 is connected to the rechargeable battery 80 and a voltage is applied. In FIG. 9B, substantially the same parts as those shown in FIG. 9A are denoted by the same reference numerals and description thereof is omitted.

  In the voltage control method described above, as shown in FIG. 9C, the CPU 84 is provided with a voltage control unit 90. Then, the voltage of the rechargeable battery 80 is input to the voltage control unit 90, and the voltage control unit 90 controls the input voltage to be a target voltage preset in the memory 86. In other words, the voltage control method is a method in which control is performed so that the target voltage is always constant. Note that in FIG. 9C, components that are substantially the same as those in the configuration illustrated in FIG. 9B are denoted by the same reference numerals, and description thereof is omitted.

Japanese Utility Model Publication No. 8-141925

  By the way, in the electric tool which is not controlled shown in FIG. 9A, the rotation speed of the motor 82 varies depending on the charge amount of the rechargeable battery 80. For example, when the charge amount decreases, the screw tightening speed decreases. That is, as shown in FIG. 10A, in a state where the remaining charge amount is large (hereinafter referred to as full charge) and a state where the remaining charge amount is small (hereinafter referred to as end-of-discharge period), the rotational speed and load torque are proportional (parallel). ) And increase / decrease, so it is not easy to use. In addition, FIG. 10 is the figure which compared the relationship between rotation speed and load torque in the charge condition of a rechargeable battery. Here, the load torque is a torque received by the striking mechanism composed of a hammer or the like at the time of striking, and varies depending on the type of screw. The load torque is proportional to the load current of the motor, and the rotation speed of the motor is determined by the voltage of the rechargeable battery and the load torque. As indicated by the circles in FIG. 10 (A), the optimum rotational speed only matches one point at a certain load torque at the time of full charge, and the working efficiency is poor. The reason will be described below.

(Explanation of optimum rotation speed)
Here, the optimum rotational speed (this content itself is a new matter) will be described. First, FIG. 11 shows the relationship between the striking angle and the striking frequency when one rotation is changed with different screws (screw tightening torque). From FIG. 11, even if the number of rotations is increased more than necessary in different screws, the advance angle does not increase (that is, the impact force does not increase) and the impact frequency only increases. This means that the number of rotations has an optimum number of rotations according to the screw load. If this optimum number of rotations is set as the target number of rotations, it can be hit efficiently and the hitting frequency can be suppressed. The striking frequency is a frequency when the hammer strikes an anvil (not shown).

  And the figure showing the said load torque at the time of replacing a screw load with the load torque of a motor, and the optimal rotation speed is shown in FIG. The optimum rotational speed shown in FIG. 12 and the optimum rotational speed shown in FIG. 11 are the same, and even a screw having a different load is positioned on a line indicating the optimum rotational speed. That is, when the motor is rotated at the optimum rotational speed, the impact driver performs the screw tightening most efficiently even when the screws are different. Therefore, as shown in FIG. 10 (A), when the optimum rotational speed is deviated, the work efficiency is poor.

  On the other hand, in the rotation speed control method shown in FIG. 9B, the rotation speed becomes substantially constant, and therefore, the rotation speed control method matches only with a certain load torque. That is, the rotational speed greatly deviates from the optimal rotational speed as the distance from the coincident portion increases at full charge. Note that a straight line similar to that at the end of discharge in FIG.

  In the voltage control method shown in FIG. 9C, since the target voltage is controlled to be constant, a straight line corresponding to the motor characteristics of the motor itself is drawn. That is, in the voltage control method, a straight line parallel to the motor characteristics of FIG. 10A is obtained, but, as in the rotation speed control method, it matches the optimum rotation speed only at a certain load torque. Accordingly, the rotational speed deviates from the optimal rotational speed as the distance from the matching portion increases.

  Therefore, an object of the present invention is to provide a power tool and a motor rotation control method for controlling the torque-rotational speed characteristics of a motor so that the working efficiency is improved.

  An electric power tool according to the present invention includes a voltage detection unit that detects a voltage of a power source, a current detection unit that detects a current during rotation of the motor, and an optimum motor that is based on the voltage and current detected by each of the detection units. And a rotation control means for calculating a drive voltage corresponding to the rotation speed and outputting the calculated drive voltage to the motor. Here, the optimum rotational speed is the rotational speed at which work such as striking can be performed most efficiently even when the load torque of the motor changes.

  Further, the motor rotation speed control method according to the present invention detects the voltage of the power supply, detects the current during rotation of the motor, and based on the detected voltage and current, the drive voltage corresponding to the optimum rotation speed of the motor. And the drive voltage of the calculation result is output to the motor.

  In the electric tool and motor rotation control method according to the present invention, for example, regardless of the load torque applied to the motor or the state of charge of the rechargeable battery, it matches the optimum rotation speed, so that the electric tool performs the most efficient work without changing the motor. Do well. That is, according to the electric tool and the motor rotation control method of the present invention, the motor control is performed based on the load current and the voltage of the power source that are proportional to the load torque of the motor. The optimum rotational speed corresponding to the load can be appropriately changed, and the torque-rotational speed characteristic of the motor corresponding to the electric tool can be controlled so as to obtain the best working efficiency.

It is sectional drawing of the electric tool of 1st Example which concerns on this invention. It is a block diagram of the electric tool shown in FIG. It is a flowchart figure regarding the motor drive mode of the electric tool shown in FIG. It is a figure showing the control duty by the rechargeable battery voltage-current at the time of using the motor drive system shown in FIG. It is a figure showing the relationship of the voltage correction-voltage and electric current at the time of 14.4V at the time of using the motor drive system shown in FIG. It is a figure showing the change of the screw fastening speed by the screw fastening number (charge amount) when performing continuous screw fastening from a full charge. It is the figure which compared the relationship between the rotation speed in the motor drive mode shown in FIG. 3, and load torque in the charge condition of the rechargeable battery. It is a block diagram of the electric tool of 2nd Example which concerns on this invention. Each block diagram of the electric tool which concerns on a prior art example, (A) is not controlling, (B) is a rotation speed control system, (C) is a block diagram of a voltage control system. FIGS. 9A and 9B are diagrams illustrating the motor characteristics illustrated in FIG. 9. FIG. 10A is a diagram illustrating the motor characteristics of the rotation speed control method and FIG. It is a figure for demonstrating the optimal rotation speed, and is a figure which shows the relationship between the striking angle of one stroke when a rotation speed is changed in a different screw (screw tightening torque), and a striking frequency. It is a figure for demonstrating the optimal rotation speed, and is a figure showing the load torque and optimal rotation speed at the time of replacing a screw load with the load torque of a motor.

  Hereinafter, the embodied Example 1 and Example 2 are demonstrated respectively about the form for implementing this invention.

  Hereinafter, the electric tool and motor rotation control method according to the first embodiment of the present invention will be described as an example applied to the impact driver shown in FIG.

(Schematic configuration of impact driver)
As shown in FIG. 1, the impact driver 10 includes a rechargeable battery 12 that is a power source, a motor 14 that is a driving means, a speed reduction mechanism 16 that reduces the rotation of the motor 14, a hammer 18 that slides in response to the output of the speed reduction mechanism 16, An anvil 20 and a trigger lever 22 through which the hammering force of the hammer 18 is transmitted are provided. Note that a driver bit (not shown) is attached to the anvil 20. The rechargeable battery 12 is detachably disposed.

(Configuration of impact driver control system)
As shown in FIG. 2, the impact driver includes a rechargeable battery 12, a motor driver 13, a motor 14, and a CPU 30 that is a rotation control means. The CPU 30 includes a nonvolatile memory 32, a current detection unit 34, and a voltage control unit 36, and controls the overall operation of the impact driver 10. The memory 32 as recording means has a storage area for storing programs for controlling various processes and a recording area for reading and writing various data, and operation data, target voltage data, and the like are recorded in this recording area.

  The target voltage data is voltage value data at the optimum rotational speed shown in FIGS. 11 and 12. Here, the optimum rotational speed is the rotational speed at which work such as striking can be performed most efficiently even when the load torque of the motor 12 changes, and the contents already described in FIGS. 11 and 12 (this content itself) Is a new matter). In addition, CPU30 is connected to the rechargeable battery 12, and a voltage is applied.

  As shown in FIG. 2, a current is input from the rotating motor 14 to the current detector 34, and a voltage of the rechargeable battery 12 is input to the voltage controller 36 that is a voltage detector. The voltage control unit 36 corresponds to the optimum rotational speed (see FIG. 7) of the motor 12 based on the current (that is, load torque) input to the current detection unit 34 and the voltage input to the voltage control unit 36. The drive voltage is output to the motor driver 13. The calculation of the drive voltage will be described later.

(Operation of this embodiment)
Based on the flowchart shown in FIG. 3, the process regarding the motor drive mode which drives a motor by optimal rotation speed is demonstrated. The processing in the impact driver 10 shown in FIG. 1 is executed by the CPU 30 loading a program when the trigger lever 22 is pulled and a switch (not shown) is turned on. The processing routine to be executed is represented by the flowchart of FIG. 3, and these programs are stored in advance in the program area of the memory 32 (see FIG. 2). This routine is a process performed at a timing at a predetermined electrical angle, for example, 0 °, while the motor is rotating.

(Motor drive mode)
In step 100 shown in FIG. 3, the voltage control unit 36 (see FIG. 2) of the CPU 30 detects the voltage Vad of the rechargeable battery 12 and records the detected voltage Vad in the memory 32. In step 102, the current detection unit 34 of the CPU 30 detects the current Iad of the rotating motor 14 and records the detected current Iad in the memory 32. In step 104, the CPU 30 calculates a drive voltage (drive signal) based on the voltage value Vad and the current value Iad read from the memory 32.

  Specifically, the calculation is performed with drive voltage = (Vref−α · Iad) / Vad. Here, Vref is a target voltage, and α is a coefficient determined from experimental values. This coefficient α is calculated based on the experimental data of FIG. 4 and varies depending on other factors such as the motor and the striking mechanism. In addition, FIG. 4 is a figure which shows the experimental value in the voltage of a rechargeable battery in a full charge state (16V), the state at the end of discharge (12V), and the normal state (14.4V) in the middle.

  In step 106, the voltage control unit 36 of the CPU 30 outputs the drive voltage calculated in step 104 to the motor driver 13 and controls the motor 14 so as to have an optimum rotational speed. The processing of this routine is repeated again at a timing at an electrical angle, for example, 0 °, while the motor 14 is rotating.

  Note that the above-described program processing flow (see FIG. 3) is an example, and can be changed as appropriate without departing from the gist of the present invention. For example, the voltage Vad and the current Iad may be detected a plurality of times, and the calculation in step 104 may be performed based on the average. Further, the routine may be started based on any electrical angle such as 60 ° or 180 °.

  In the present embodiment, as shown in FIG. 5, when correction is performed with voltage and current, that is, when this embodiment is applied, the duty also varies in accordance with variation in load torque, that is, load current. On the other hand, when the correction is performed using only the voltage, the duty remains constant even if the load current varies. Further, as shown in FIG. 6, when the control according to the present embodiment is present, the screw tightening speed is always fast and good regardless of the number of screw tightening compared to the case without the control.

  According to the present embodiment, as shown in FIG. 7, since it matches the optimum rotational speed regardless of the state of charge of the rechargeable battery or the load torque, the motor is not changed (that is, the motor that has already been installed is not changed). ) The impact driver can perform screw tightening most efficiently even when the screws are different, and noise can be suppressed. For example, in the case of a heavy screw with a high load torque, the impact is optimized by reducing the rotational speed.

  That is, according to the present embodiment, since the motor control is performed based on the load current proportional to the load torque of the motor, the motor drive voltage can be appropriately changed to the optimum rotational speed corresponding to the load torque, that is, the screw load, It is possible to control the torque-rotational speed characteristic of the motor corresponding to the electric tool so that the working efficiency becomes the best.

  Hereinafter, an electric power tool and motor rotation control method according to a second embodiment of the present invention will be described with reference to a block diagram of an impact driver shown in FIG. Note that parts substantially the same as those in the first embodiment are denoted by the same reference numerals, description thereof is omitted or simplified, and different parts are mainly described.

  The CPU 40 that is a rotation control means includes a nonvolatile memory 42, a current detection unit 44, and a rotation speed control unit 46, and controls the overall operation of the impact driver 10 shown in FIG. The memory 42 as recording means has a storage area for storing programs for controlling various processes and a recording area for reading and writing various data, and the target rotational speed data and the like are recorded in this recording area. The target rotational speed data is data at the optimal rotational speed shown in FIG.

  As shown in FIG. 8, the current Iad is input from the rotating motor 14 to the current detection unit 44, and the voltage Vad of the rechargeable battery 12 and the current motor rotation number are input to the rotation number control unit 46 as voltage detection means. Is entered. Then, the rotation speed control unit 46 calculates the target rotation speed based on the load current of the motor 14 and the voltage of the rechargeable battery 12 input to the current detection unit 44, and calculates the calculated target rotation speed and the current rotation speed. The motor output voltage is calculated from the difference between the two and output to the motor driver 13. Specifically, the rotational speed control unit 46 performs control so that the rotational speed of the motor 14 becomes the target rotational speed, for example, by PI control (proportional / integral control).

  That is, unlike the first embodiment, this embodiment does not directly calculate the motor drive voltage with the load current, but once calculates the target rotational speed with the motor load current and the rechargeable battery voltage, The motor output voltage is finally calculated based on the difference in number. Therefore, according to the present embodiment, even when the motor characteristics are different from each other, it is possible to more accurately control the rotational speed of the motor 14 so as to become the target rotational speed. The rotation speed of the motor 14 is detected based on, for example, a counter electromotive voltage of a rotating motor or a rotation sensor (Hall sensor, encoder). Other configurations and operational effects are the same as those of the first embodiment.

  In each of the above embodiments, the power tool is an example of an impact driver, but the present invention can also be applied to a power tool such as a drill. The present invention can also be applied to an electric tool that uses a commercial power source as a power source.

10 Impact driver (electric tool)
12 Rechargeable battery (power supply)
14 Motor (drive means)
30, 40 CPU (rotation control means)
32, 42 Memory (Recording means)
34, 44 Current detection unit (current detection means)
36 Voltage control unit (voltage detection means and voltage control means)
46 Rotational speed control unit (voltage detection means and rotational speed control means)

Claims (2)

Voltage detection means for detecting the voltage of the power supply;
Current detection means for detecting current during rotation of the motor;
Rotation control means for calculating a drive voltage corresponding to the optimum rotational speed of the motor based on the voltage and current detected by each of the detection means, and outputting the drive voltage of the calculation result to the motor. A power tool.   The power supply voltage is detected, the current during rotation of the motor is detected, a drive voltage corresponding to the optimum rotational speed of the motor is calculated based on the detected voltage and current, and the drive voltage of the calculation result is supplied to the motor. A method for controlling the rotation of a motor, characterized by comprising:

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