Electric power tool and motor control method thereof

An electric power tool is provided with: a motor; a hydraulic pressure generator driven by the motor and configured to generate a plurality of impacts in one revolution thereof; an impact angle detector configured to detect an impact angle in one impact of the hydraulic pressure generator; an electric current detector configured to detect an electric current applied to the motor; a determination unit configured to determine an impact failure based on the impact angle and the electric current detected by the impact angle detector and the electric current detector; and a rotation controller configured to decrease a rotation speed of the motor when the determination unit determines the impact failure.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an electric power tool in which a hydraulic pressure generator generates a plurality of impacts in one revolution thereof and a motor control method of the electric power tool.

2. Background Art

An electric power impact fastening tool as an electric power tool generally has a mechanism for generating one impact force per one revolution of a hydraulic pressure generator. (Refer to Patent Document 1.) In the electric power tool, a brushless DC motor is directly connected to an oil pulse unit to prevent occurrence of large vibration and reaction. (Refer to Patent Document 2.)

On the other hand, as an impulse wrench which is a hydraulic pressure power tool, there is a tool in which two impact forces per one revolution of a hydraulic pressure generator driven by compressed air (which will be hereinafter also called “two impacts per one revolution”). (Refer to Patent Document 3.) The tool of “two impacts per one revolution” generates a small torque and multiple impacts, thus a screwdriver, etc, is prevented from being away from a screw, etc. (which will be hereinafter called “come out”), at its operation time and an operation efficiency becomes good.

That is, a tool of “two impacts per one revolution” can perform a smooth fastening operation and a usability is good.

A tool adopting the “two impacts per one revolution” as in Patent Document 3 is used for operations in which a rotation speed is small assuming a light load as compared with a tool of “one impact per one revolution”. The reason is that: if the tool of “two impacts per one revolution” and the tool of “one impact per one revolution” have the same impact mechanism in capability, one impact force of the tool of “two impact per one revolution” becomes half as compared with one impact force of the tool of “one impact per one revolution”, and an impact frequency of the tool of “two impact per one revolution” becomes twice of an impact frequency of the tool of “one impact per one revolution”. That is, in the tool of “two impact per one revolution”, an impact failure may occur because the impact frequency becomes high in a high load operation and responsibility of a hydraulic pressure generation mechanism worsens, etc. Here, the impact frequency means a frequency in impulse by oil compression of the hydraulic pressure generator.

SUMMARY OF THE INVENTION

One or more embodiments of the invention provide an electric power tool for suppressing continuation of an impact failure in a type in which a hydraulic pressure generator makes one revolution to produce a plurality of impacts, and a motor control method of the electric power tool.

In accordance with one or more embodiments of the invention, an electric power tool is provided with: a motor; a hydraulic pressure generator driven by the motor and configured to generate a plurality of impacts in one revolution thereof; an impact angle detector configured to detect an impact angle in one impact of the hydraulic pressure generator; an electric current detector configured to detect an electric current applied to the motor; a determination unit configured to determine an impact failure based on the impact angle and the electric current detected by the impact angle detector and the electric current detector; and a rotation controller configured to decrease a rotation speed of the motor when the determination unit determines the impact failure.

Moreover, in accordance with one or more embodiments of the invention, in an electric power tool in which a hydraulic pressure generator driven by a motor generates a plurality of impacts in one revolution thereof, the motor is controlled by: detecting an impact angle in one impact of the hydraulic pressure generator; detecting an electric current applied to the motor; determining an impact failure based on the detected impact angle and the detected electric current; and decreasing a rotation speed of the motor when the impact failure is determined.

In the above electric power tool and its motor control method, an impact failure is determined based on the impact angle in one impact of the hydraulic pressure generator and the applied electric current proportional to the torque of the motor and the rotation speed of the motor is decreased when an impact failure is detected, so that a continuation of impact failure is suppressed. That is, according to the power electric tool and its motor control method of the embodiments of the invention, the impact failure is prevented as described above and thus an operation efficiency becomes good and a smooth fastening operation can be performed and the usability of the power electric tool becomes good.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

First Embodiment

An electric power tool and its motor control method of a first embodiment of the invention is described based on an example of an oil pulse driver of multiple impacts per revolution (in the example, two impacts per revolution) shown inFIG. 1.

(Schematic Configuration of Oil Pulse Driver)

As shown inFIG. 1, an oil pulse driver10includes a battery12as a power supply, a brushless DC motor (which will be hereinafter also simply called motor) as a drive means, a speed reducer16for slowing down a rotation of the motor14, a hydraulic pressure pulse generation mechanism18for receiving output of the speed reducer16and generating a hydraulic pressure pulse, a main shaft20to which a rotation impact force by the hydraulic pressure pulse generation mechanism18is transmitted, and a trigger lever22. A driver bit (not shown) is attached to the main shaft20. The battery12is placed detachably.

(Configuration Concerning Hydraulic Pressure Pulse Generation Mechanism)

The configuration concerning the hydraulic pressure pulse generation mechanism will be discussed based onFIGS. 2 and 3. As shown inFIG. 2, the hydraulic pressure pulse generation mechanism18is provided with a hydraulic pressure generator24in a hydraulic pressure generator case23and the main shaft20is inserted into the hydraulic pressure generator24and the hydraulic pressure generator24can rotate relative to the main shaft20. At both ends of the hydraulic pressure generator24, hydraulic pressure generator plates25A and25B are placed so as to seal oil in a state in which oil is filled to generate a torque in the hydraulic pressure generator24. The hydraulic pressure generator case23and the hydraulic pressure generator24are jointed and rotate in one piece by rotation of the motor14.

As shown inFIG. 3, a hydraulic pressure generator chamber26elliptical in cross section is formed in the hydraulic pressure generator24. A pair of blades29placed through a spring28is inserted into a pair of opposed grooves27of the main shaft20in the hydraulic pressure generator24. The blade29moves while abutting the inner face of the hydraulic pressure generator chamber26by the urging force of the spring28. In the main shaft20, a pair of seal parts20A and20B is projected between the paired blades29. On the inner peripheral surface of the hydraulic pressure generator24, four seal parts24A,24B,24C, and24D are projected at both ends of a short shaft elliptical in cross section and at both ends of a long shaft. As shown inFIG. 4, when the hydraulic pressure generator24makes one revolution relative to the main shaft20, the hydraulic pressure generator chamber26are twice sealed and partitioned in two high pressure chambers H and two low pressure chambers L (seeFIG. 3).

(1) to (5) ofFIG. 4show conditions in which the relative angle between the hydraulic pressure generator24and the main shaft20is from 0 degrees to 180 degrees, and (6) to (11) ofFIG. 4show conditions in which the relative angle between the hydraulic pressure generator24and the main shaft20is from 180 degrees to 380 degrees. In (3) and (4) ofFIG. 4, the first impact is performed on the main shaft by an impulse pulse, and in (8) and (9) ofFIG. 4, the second impact is performed. That is, while the hydraulic pressure generator24makes one revolution relative to the main shaft20, two impacts (two impacts per revolution) are performed. The hydraulic pressure pulse generation mechanism of the embodiment is similar to a conventional known mechanism and therefore will not be discussed in more detail.

(Configuration Concerning Control System of Oil Pulse Driver)

The oil pulse driver includes a battery12, a motor driver13, a motor14, and a CPU30, as shown inFIG. 5. The CPU30of a determination unit and a rotation controller includes nonvolatile memory32, an electric current detection section34, and a voltage control section36, and controls the whole operation of the oil pulse driver10. The memory of record means has a storage area for storing programs for controlling various types of processing and a record area for reading and writing various pieces of data and computation data, etc., is recorded in the record area. The CPU30is connected to the battery12and a voltage is applied to the CPU.

As shown inFIG. 2, an electric current is input to the electric current detection section34from the rotating motor14and a voltage of the battery12is input to the voltage control section36of voltage detection means. The voltage control section36outputs a predetermined drive voltage of the motor14to the motor driver13based on the electric current input to the electric current detection section34(namely, load torque) and the voltage input to the voltage control section36.

The reason why the motor14is a brushless motor is as follows: The brushless motor has small moment of inertia of a rotor as compared with a brush motor and thus if the hydraulic pressure pulse generation mechanism is applied to the type of two impacts per revolution, a change in the rotation speed of the motor is also small. That is, in the brushless motor, a change in the rotation speed caused by load variation is large output, but if the hydraulic pressure pulse generation mechanism is of the type of two impacts per revolution, load variation is small and thus a change in the rotation speed caused by load variation is also small.

Processing concerning an impact control mode will be discussed based on a flowchart shown inFIG. 6. When the trigger lever22is pulled and a switch (not shown) is turned on, the CPU30loads a program, whereby processing in the oil pulse driver10is executed. The executed processing routine is represented by the flowchart ofFIG. 6and the programs are previously stored in the program area of the memory32(seeFIG. 5). The routine is processing while the motor14(seeFIG. 5) is rotating.

On the other hand, an impact failure can occur when the impact frequency is a given value or more, for example, 50 (times/s) or more. At this time, the angle advanced by one impact becomes small as compared with normal impact. That is, as shown inFIG. 9, when the angle advanced by one normal impact is small, the load on the motor is heavy and at the impact failure time, the load on the motor14is light although the impact angle is small.

Therefore, an impact failure occurs when the advance angle per impact (which will be hereinafter also called impact angle) is small and the consumption electric current is small (namely, the load on the motor14is light). In the embodiment, an impact failure is determined by the impact angle and by whether or not the consumption electric current is equal to or less than a threshold value. When an impact failure occurs, the rotation speed of the motor14increases and the consumption electric current also becomes small and thus the impact failure continues.

At step100shown inFIG. 6, the CPU30detects the rotation speed of the motor14. The rotation speed is computed (synonymous with detected) with time t of pulse-to-pulse width L2. At step102, the CPU30detects the impact angle based on the rotation speed (namely, the rotation speed) detected at step100. The advance angle of the motor14(also containing the impact angle) is computed based on the number of pulses output by one impact shown inFIG. 7Aand is determined. That is, as shown inFIG. 7B, the CPU30subtracts idle running angle θ4of the motor14(this angle is constant) from advance angle θ3of the motor14(this angle varies), thereby computing impact angle θ5of screw advance (this angle varies).

At step104, the CPU30determines whether or not the impact angle detected at step102is equal to or less than a threshold value based on the threshold value read from the memory32, for example, 60 degrees. If the determination at step104is NO, namely, the impact angle is more than the threshold value, the CPU30determines that, for example, a screw, etc., is struck against a material of a light load, and returns to step100. If the determination at step104is YES, namely, the impact angle is equal to or less than the threshold value, the CPU30goes to step106and the electric current detection section34of the CPU30detects consumption electric current Iad of the motor14.

At step108, whether or not the consumption electric current detected at step106is less than a threshold value, for example,16A is determined. If the determination at step108is N, namely, the consumption electric current is equal to or more than the threshold value, the load on the motor14is a predetermined load or more and thus the CPU30determines normal impact and returns to step100. If the determination at step108is Y, namely, the consumption electric current is less than the threshold value, the load on the motor14is less than the predetermined load and thus the CPU30determines an impact failure and the rotation speed of the motor14is decreased in the voltage control section36.

The processing of the routine is repeated while the motor14rotates. The processing flow of the program described above (seeFIG. 6) is an example and can be changed as required without departing from the spirit of the invention. For example, at step102, impact frequency may be detected (also in this case, the impact angle is determined based on the impact frequency) and at step104, whether or not the impact frequency is equal to or more than a predetermined value, for example, 50 (times/s) may be determined. If the impact frequency is equal to or more than the predetermined value, the process goes to step106.

According to the embodiment, an impact failure is determined based on the impact angle of one impact by the hydraulic pressure generator24and the load electric current proportional to the load torque of the motor14and if an impact failure is detected, the rotation speed of the motor14is decreased and thus continuation of impact failure is suppressed. That is, according to the embodiment, impact failure is prevented as described above and thus operation efficiency becomes good and smooth fastening operation can be performed and the usability of the oil pulse driver10becomes good. According to the embodiment, two impacts per revolution is small torque multiple impacts and thus come out is prevented.

For impact at the fastening time of a 90-mm screw, as shown inFIG. 10, the time per impact is short in the hydraulic pressure pulse generation mechanism of the type of two impacts per revolution as compared with the type of one impact per revolution and thus the torque force weakens and striking sense becomes good. Vibration of the oil pulse driver10shown inFIG. 1is small in the hydraulic pressure pulse generation mechanism of the type of two impacts per revolution as compared with the type of one impact per revolution as shown inFIG. 11and thus usability is good. Three kinds of types of one impact per revolution inFIG. 11show examples of oil pulse drivers each having a different hydraulic pressure pulse generation mechanism.

Further, the voltage control section36may cause the motor driver13to output the drive electric current corresponding to the optimum rotation speed of the motor14based on the electric current input to the electric current detection section34and the voltage input to the voltage control section36. In this case, rotation of the motor is not affected by the voltage of the battery12shown inFIG. 1and thus particularly occurrence of an impact failure at the full charging time can be prevented. The optimum rotation speed is the rotation speed where an operation of impact, etc., for example, can be performed most efficiently if the load torque of the motor14changes.

Second Embodiment

An electric power tool and its motor control method of a second embodiment of the invention will be discussed below with a block diagram of an oil pulse driver shown inFIG. 12: Parts identical with those of the first embodiment described above are denoted by the same reference numerals and will not be discussed again or is simplified and differences will be mainly discussed.

A CPU40of a rotation controller includes nonvolatile memory42, an electric current detection section44, and a rotating speed controller46and controls the whole operation of the oil pulse driver10shown inFIG. 1. The memory42of record means has a storage area for storing programs for controlling various types of processing and a record area for reading and writing various pieces of data and the impact angle, the threshold value data of consumption electric current, and the like are recorded in the record area.

As shown inFIG. 12, electric current Iad is input to the electric current detection section44from a rotating motor14and the electric current rotation speed of the motor is input to the rotating speed controller46. The rotating speed controller46of the CPU40determines whether or not an impact failure occurs based on the impact angle and the load electric current of the motor14input to the electric current detection section44. If an impact failure occurs, the rotating speed controller46computes motor output voltage from the electric current rotation speed and outputs the motor output voltage to a motor driver13.

The rotating speed controller46may compute the target rotation speed based on the load electric current of the motor14input to the electric current detection section44and the voltage of a battery12and may compute motor output voltage according to the difference between the computed target rotation speed and the electric current rotation speed and may output the motor output voltage to the motor driver13. In this case, the rotating speed controller46controls so that the rotation speed of the motor14becomes the target rotation speed by PI control (proportional-plus-integral control), for example. That is, the motor drive voltage is not directly computed based on load electric current and the target rotation speed may be once computed based on the load electric current of the motor14and the voltage of the battery and finally the motor output voltage may be computed based on the difference between the numbers of revolutions described above.

The rotation speed of the motor14is detected based on inverse striking voltage of the rotating motor14and rotation sensor (hall sensor, encoder), for example. Other components and functions and effects are the same as those of the first embodiment.

In each embodiment described above, the electric power tool is the oil pulse driver of two impacts per revolution by way of example, but the invention can also be applied to thread fastening power electric tools of an oil pulse driver of three or more impacts per revolution, other impact drivers, etc., for example. The invention can also be applied to a power electric tool using a commercial power supply as a power supply.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

10Oil pulse driver (electric power tool)12Battery14Brushless DC motor (drive means)18Hydraulic pressure pulse generation mechanism20Main shaft24Hydraulic pressure generator28Spring29Blade30,40CPU (a determination unit and a rotation controller)32,42Memory (record means)34,44Electric current detection section (an electric current detector)36Voltage control section (voltage detection means and voltage control means)46Rotating speed controller (voltage detection means and rotation speed control means)