Portable electric tool

Abstract

[Problem] To provide a portable electric tool configured to issue a notification indicating that there is an increasing risk of a tip tool being damaged. [Solution] This portable electric tool is a belt-type grinding tool 1 that drives an endless grinding belt 48 to perform machining work. The belt-type grinding tool 1 includes: an electric motor 26 for driving the endless grinding belt 48; a power measuring unit (voltage measuring unit 62, current measuring unit 64) for measuring the power consumption of the electric motor 26; and a microcomputer 52. The microcomputer 52 obtains a power consumption amount consumed by the electric motor 26 within a predetermined power integration time (30 seconds) on the basis of the power consumption measured by the power measuring unit, and transmits a predetermined notification signal if the power consumption amount is equal to or greater than a predetermined threshold power amount (3500J). When the notification signal is transmitted, an LED display unit 66 flashes to display a warning.

Description

Portable power tools

[0001] The present invention relates to a portable power tool, and more particularly to a portable power tool that drives an accessory tool to perform a machining operation.

[0002] Portable power tools are known that use an electric motor to drive various cutting tools such as endless grinding belts, drills, and abrasive brushes to perform various machining operations. Portable power tools that are handheld and used by a worker are well known, but tools that can be attached to automated machines such as robots have also been developed (see, for example, Patent Documents 1 to 3).

[0003] When using portable power tools to perform various machining operations such as grinding and drilling, the tool tip driven by an electric motor is usually pressed against the workpiece. For example, in the case of a belt-type grinding tool, grinding is performed by pressing an endless grinding belt, which is rotated by an electric motor, against the workpiece.

[0004] Japanese Patent No. 6516920 Japanese Patent No. 6723833 Japanese Patent Laid-Open No. 2018-111167

[0005] The amount of force used to press a tool bit against a workpiece during a machining operation has an optimal range depending on the tool bit and the type of machining operation. If the pressing force is less than this optimal range, efficient machining becomes difficult. If the pressing force is greater than this optimal range, excessive force or frictional heat may be applied to the tool bit, potentially damaging it. In particular, when a power tool is held and used by a person, it is extremely rare for the person to apply a force large enough to instantly damage the tool bit. However, the tool bit may be damaged if a certain amount of force is continuously applied. For example, in the case of a belt-type grinding tool, if the rotating endless grinding belt is continuously pressed against the workpiece with a force greater than expected, the endless grinding belt may wear rapidly or be rapidly heated by frictional heat, resulting in the endless grinding belt breaking.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a portable power tool that notifies the user that there is an increasing risk of the tool bit being damaged due to continuous load acting on the tool bit.

[0007] That is, the present invention provides a portable power tool that drives a tool tip to perform machining work, comprising: an electric motor for driving the tool tip; a power measurement unit for measuring the power consumption of the electric motor; and a calculation unit that calculates the amount of power consumed by the electric motor within a predetermined power accumulation time based on the power consumption measured by the power measurement unit, and that transmits a predetermined notification signal when the amount of power consumption reaches or exceeds a predetermined threshold power amount.

[0008] In this portable power tool, a notification signal is transmitted when the amount of power consumed by the electric motor within a predetermined power accumulation time exceeds a threshold power amount. When the amount of power consumed by the electric motor increases, it is expected that the load on the tool accessory also increases. Based on the notification signal, the user can be notified that a heavy load is being applied to the tool accessory by, for example, flashing an LED display or sounding a buzzer. Upon receiving this notification, the user can operate the portable power tool to reduce the load on the tool accessory or stop the electric motor to interrupt the machining operation, thereby preventing damage to the tool accessory.

[0009] The calculation unit may measure the power consumption with the power measurement unit at predetermined time intervals and determine the amount of power consumption consumed within the power integration time.

[0010] The predetermined power accumulation time may be set to be between 15 seconds and 75 seconds, and more preferably, to be between 25 seconds and 35 seconds.

[0011] The power consumption control device may further include a storage unit that stores a set value of the power accumulation time and a set value of the threshold power amount, and each of the set values ​​of the power accumulation time and the threshold power amount may be changeable.

[0012] The device may further include a display unit that displays a warning when the notification signal is transmitted.

[0013] In one aspect, the tool includes a tool body in which the electric motor is disposed, a drive pulley that is rotationally driven by the electric motor, and an idle pulley that is rotatably attached to the tool body, and the tool tip can be an endless grinding belt that is wound around the drive pulley and the idle pulley.

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A portable power tool according to an embodiment of the present invention will now be described with reference to the accompanying drawings.

[0015] 1 is a perspective view of a belt-type grinding tool (portable power tool) according to an embodiment of the present invention; FIG. 2 is a cross-sectional view of the belt-type grinding tool of FIG. 1; FIG. 3 is a perspective view of the belt-type grinding tool of FIG. 1 with a cover in an open position; and FIG. 4 is a schematic functional block diagram of the belt-type grinding tool of FIG. 1.

[0016] A portable power tool according to one embodiment of the present invention is a handheld belt-type grinding tool 1 that performs grinding work by rotating an endless grinding belt (tip tool). As shown in Figures 1 to 3, the belt-type grinding tool 1 includes a tool body 10, a tension bar 12 that is held on the tool body 10 so as to be movable in the front-rear direction, and a cover 14 attached to the tool body 10. A battery mounting section 16 to which a battery B is detachably attached is provided at the rear end of the tool body 10, and the belt-type grinding tool 1 is powered by the battery B mounted in the battery mounting section 16.

[0017] As shown in FIG. 2 , the tension bar 12 extends along the longitudinal axis L from a front end 18 to a rear end 20, and an idler pulley 22 is rotatably attached to the front end 18. The tool body 10 includes a housing 24, an electric motor 26 housed within the housing 24, and a drive pulley 30 attached to a rotary shaft 28 of the electric motor 26. The housing 24 includes a motor housing 32 that houses the electric motor 26, a grip adapter 34 attached to the motor housing 32, and a grip member 36 attached to the grip adapter 34. The tool body 10 further includes a bracket 38 attached to the motor housing 32 and a bar support member 40 attached to the bracket 38. The bar support member 40 has a bar accommodating hole 42 that receives the rear end 20 of the tension bar 12 and holds the tension bar 12 displaceable in the front-to-rear direction along the longitudinal axis L, and a pulley guard portion 44 that circumferentially covers the drive pulley 30 from an upper position around the rear to a lower position. The pulley guard portion 44 defines a side opening 46 that opens on one side of the drive pulley 30 to expose the drive pulley 30. An endless grinding belt 48 is wound between the idler pulley 22 and the drive pulley 30.

[0018] The cover 14 is attached to the tool body 10 by a mounting screw 50 and is pivotable about the mounting screw 50 between a closed position (FIG. 1) and an open position (FIG. 3). When performing a grinding operation, the cover 14 is in the closed position to hide the drive pulley 30. When replacing the endless abrasive belt 48, the cover 14 is in the open position to expose the drive pulley 30.

[0019] As shown in FIG. 4 , the tool body 10 includes a microcomputer (arithmetic unit) 52, a microcomputer power generation circuit 54, and a motor drive circuit 58. The microcomputer power generation circuit 54 converts the voltage supplied from the battery B into a voltage (e.g., 3.3 V) suitable for the microcomputer 52. A Hall IC 56 is attached to the electric motor 26. The Hall IC 56 is positioned to detect the magnetic field of a magnet that rotates with the electric motor 26 to detect the rotation of the electric motor 26. The microcomputer 52 determines the rotation speed of the electric motor 26 from the output of the Hall IC 56. The microcomputer 52 also includes a memory (storage unit) for storing various setting data related to control. The setting data stored in the memory include a threshold power setting value and a power accumulation time setting value, which will be described later.

[0020] When the start switch 60 located on the side of the housing 24 is turned ON, the motor drive circuit 58 applies the voltage of battery B to the electric motor 26, causing the electric motor 26 to begin operating. This causes the endless grinding belt 48, which is wound around the drive pulley 30 and the idle pulley 22, to rotate. The microcomputer 52 determines the rotational speed of the electric motor 26 based on the output of the Hall IC 56, and controls the amount of current flowing through the electric motor 26 via the motor drive circuit 58 so that the electric motor 26 can maintain a preset constant rotational speed. As a result, even if the pressing force of the endless grinding belt 48 against the workpiece to be ground changes, the endless grinding belt 48 is always driven at a constant speed, making it possible to perform appropriate grinding work.

[0021] When the electric motor 26 starts to operate, the microcomputer 52 determines the voltage applied to the electric motor 26 from the voltage value measured by the voltage measurement unit 62, and determines the current flowing through the electric motor 26 from the voltage value measured by the current measurement unit 64. The microcomputer 52 calculates the power consumption of the electric motor 26 from the determined voltage and current. In other words, the voltage measurement unit 62 and the current measurement unit 64 constitute a power measurement unit for measuring the power consumption of the electric motor 26. The microcomputer 52 reads the set value of the power accumulation time from the memory and, based on the measured power consumption, continuously calculates the amount of power consumed by the electric motor 26 during the power accumulation time. The power accumulation time is preferably set to a time between 15 and 75 seconds, more preferably between 25 and 35 seconds. In this embodiment, the power accumulation time is set to 30 seconds. Specifically, the microcomputer 52 measures the power consumption every second and integrates the power consumption determined every second for 30 seconds to calculate the amount of power consumed by the electric motor 26 during that time. When 30 seconds or more have passed since the electric motor 26 started to operate, each time a new power consumption is measured, the power consumption measured 30 seconds before is subtracted from the power consumption for the previous 30 seconds and the latest power consumption is added. In this way, the power consumption for the most recent 30 seconds is always calculated. The time interval for measuring power consumption may be less than one second or greater than one second.

[0022] The voltage applied to the electric motor 26 depends on the voltage of battery B, and therefore does not generally fluctuate significantly over a short period of time, such as several tens of seconds. In this embodiment, battery B has a maximum voltage of 18 V, so when battery B is fully charged, a voltage of approximately 18 V is applied to the electric motor 26. However, as the power of battery B is consumed, the voltage of battery B gradually decreases, and therefore the voltage applied to the electric motor 26 also gradually decreases. Meanwhile, the current flowing through the electric motor 26 fluctuates significantly with changes in the load applied to the electric motor 26, i.e., the magnitude of the load applied to the endless grinding belt 48. For example, when no grinding operation is being performed, the load applied to the electric motor 26 is small, and the current flowing through the electric motor 26 is approximately 2 to 3 A. Therefore, assuming that the voltage applied to the electric motor 26 is 18 V, the power consumption of the electric motor 26 is 36 to 54 J / s (W), and the power consumption during the power accumulation time (30 seconds) when no load is applied is 1080 to 1620 J (Ws). When the endless grinding belt 48 is pressed against the workpiece with a moderate force to perform grinding, the load on the electric motor 26 increases slightly, and the current flowing through the electric motor 26 is approximately 4 to 5 A. In this case, the power consumption of the electric motor 26 is 72 to 90 J / s (W), and the power consumption during the power accumulation time (30 seconds) when this state is applied is 2160 to 2700 J (Ws). Because the power consumption of the electric motor 26 is correlated with the load applied to the endless grinding belt 48, the magnitude of the load applied to the endless grinding belt 48 can be estimated by calculating the power consumption of the electric motor 26.

[0023] If the grinding operation is performed by pressing the endless grinding belt 48 against the workpiece with even greater force, the load on the endless grinding belt 48 will increase, and the power consumption of the electric motor 26 will also increase. Numerous experiments and experiences have shown that when performing grinding operations using a standard endless grinding belt 48, the endless grinding belt 48 is likely to break if the amount of power consumed within a certain period of time exceeds a certain level. Specifically, in this embodiment, it has been found that if the power consumption of the electric motor 26 during a 30-second power accumulation period exceeds 3,500 J, and if this state continues, the endless grinding belt 48 will often break. In other words, if the amount of power consumed within 30 seconds exceeds 3,500 J, the risk of the endless grinding belt 48 breaking increases. In this embodiment, the threshold power stored in the memory is set to 3500 J. When the amount of power consumed within a power accumulation time (30 seconds) exceeds the threshold power (3500 J), the microcomputer 52 issues a notification signal to notify the user of the increased risk of breakage. When the notification signal is sent from the microcomputer 52, the LED display unit 66 (display unit) provided on the tool body 10 flashes to display a warning. The flashing LED display unit 66 allows the user of the belt-type grinding tool 1 to easily recognize that excessive load is being applied to the endless grinding belt 48, increasing the risk of the endless grinding belt 48 breaking. This allows the user to take action to prevent the endless grinding belt 48 from breaking, such as by reducing the force pressing against the endless grinding belt 48 or temporarily halting the grinding operation. The warning may be an audible warning, such as a buzzer or voice, instead of or in addition to the visual warning displayed on the LED display unit 66. The power accumulation time can be changed as desired, and the set value of the threshold power amount can also be changed accordingly. In the handheld belt-type grinding tool 1 according to this embodiment, the fluctuations in the load on the endless grinding belt 48 and the electric motor 26 are relatively large. Therefore, if the power accumulation time is set extremely short (for example, less than 15 seconds), the amount of power consumed within the power accumulation time will not be stable, making it difficult to properly notify the user of the risk of breakage of the endless grinding belt 48.Furthermore, if the power accumulation time is set too long (e.g., longer than 75 seconds), the endless grinding belt 48 may break before a notification is sent. Therefore, in this embodiment, the power accumulation time is preferably set between 15 and 75 seconds, and more preferably around 30 seconds. However, depending on the situation, the power accumulation time can be set to less than 15 seconds or more than 75 seconds. Multiple power accumulation times and threshold power amounts can also be set. For example, in addition to the above-mentioned power accumulation time (30 seconds) and threshold power amount (3500 J), a second power accumulation time and threshold power amount can be set to 45 seconds and 4000 J, respectively, and a notification signal can be sent when the power consumption during each power accumulation time exceeds either of the corresponding threshold power amounts. Three or more power accumulation times and threshold power amounts can also be set.

[0024] A predetermined upper limit power value is also stored in the memory of the microcomputer 52. When the power consumption of the electric motor 26 exceeds the upper limit power value (e.g., 180 J / s), the microcomputer 52 transmits a predetermined notification signal, causes the LED display unit 66 to flash to display a warning, and stops the operation of the electric motor 26. In the belt-type grinding tool 1, it is rare for a large force to be applied instantaneously to the endless grinding belt 48, causing the endless grinding belt 48 to break, but if an extremely large force exceeding the upper limit power value is applied to the endless grinding belt 48, the operation of the electric motor 26 is stopped for safety reasons.

[0025] The belt-type grinding tool 1 further includes a setting switch 68 for changing the setting data stored in the memory. Operating the setting switch 68 allows the user to change the settings for the threshold power, power accumulation time, upper limit power value, and other settings. For example, the threshold power is initially set to 3500 J, but can also be set to 3000 J or 2500 J. The setting status can be confirmed by the color and state of an LED display unit 70, which consists of three LEDs located near the battery mounting section 16. The belt-type grinding tool 1 can also be connected to an external device (e.g., a personal computer or a programmable logic controller) for communication, allowing the setting data to be changed from the external device. In this case, the microcomputer 52 may transmit a notification signal to the external device, which may visually or audibly display various statuses of the belt-type grinding tool 1 on the external device or another device connected thereto.

[0026] In the belt-type grinding tool 1, the microcomputer 52 issues a notification signal when the amount of power consumed by the electric motor 26 within a predetermined power accumulation time exceeds a predetermined threshold power amount. Based on this notification signal, the LED display unit 66 flashes to display a warning. This allows the user of the belt-type grinding tool 1 to easily recognize that excessive force is continuously acting on the endless grinding belt 48, increasing the risk of the endless grinding belt 48 breaking. Recognizing the risk of breakage, the user can take action to prevent the endless grinding belt 48 from breaking, such as by reducing the force pressing against the endless grinding belt 48 or by stopping the electric motor 26.

[0027] In the above embodiment, the LED display unit 66 displays a warning only when the endless grinding belt 48 is at high risk of breaking. However, the display format of the LED display unit 66 can be changed depending on the amount of power consumed within the power accumulation time. For example, the LED display unit 66 can be illuminated green when the load is within an appropriate range (e.g., 2160 J or more but less than 2700 J), orange when the load is slightly higher (e.g., 2700 J or more but less than 3500 J), and red when the load is at a high risk of breaking (e.g., 3500 J or more). This allows the operator to constantly check the load condition of the endless grinding belt 48 and thereby continue operating the belt-type grinding tool 1 so as not to deviate from the appropriate load range.

[0028] The portable power tool of the present invention may take a form other than the belt-type grinding tool 1. For example, the portable power tool of the present invention may be a chamfering machine. The chamfering machine chamfers the corner of a workpiece by moving the chamfering machine body along the corner with a rotating cutting tip (tip tool). The load on the cutting tip during chamfering primarily depends on the material of the workpiece and the feed speed of the chamfering machine. As the feed speed increases, the load on the cutting tip increases, and the power consumption of the electric motor also increases. In this chamfering machine, the microcomputer (calculation unit) also issues a notification signal when the amount of power consumed by the electric motor within a specified power accumulation time exceeds a predetermined threshold power amount. This prevents excessive force from acting on the cutting tip, which could cause damage to the cutting tip. The threshold power amount may be adjusted appropriately depending on the material of the workpiece.

[0029] The portable power tool of the present invention may be a drilling machine. A drilling machine rotates a drill or annular cutter (tipped tool) to drill holes in a workpiece. The load on the drill or other tool during drilling primarily depends on the material of the workpiece, the tool diameter, and the feed speed of the drill or other tool. As the feed speed increases, the load on the drill or other tool increases, and the power consumption of the electric motor also increases. In this drilling machine, a microcomputer (calculation unit) also issues a notification signal when the amount of power consumed by the electric motor within a specified power accumulation time exceeds a specified threshold power amount. This prevents the drill or other tool from being damaged by excessive force. The threshold power amount setting may be adjusted as needed depending on the material of the workpiece and the diameter of the drill or other tool being used.

[0030] Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments. For example, the portable power tool of the present invention can be, in addition to the above-mentioned tools, other power tools, such as a polishing tool that rotates a grinding wheel or abrasive brush to polish a workpiece. Furthermore, instead of a handheld power tool that is held by an operator, the portable power tool can be an automatic power tool attached to a robot hand. While the above-mentioned embodiments use a battery as the power source, an external AC power source may also be used. The specific setting values, such as the power accumulation time and threshold power amount, shown in the above-mentioned embodiments are merely examples, and the specific values ​​can be changed as appropriate depending on the supply voltage, the rated output of the electric motor, the nature of the machining operation, the type and performance of the tool tip, and the like.

[0031] 1 Belt-type grinding tool (portable power tool) 10 Tool body 12 Tension bar 14 Cover 16 Battery mounting section 18 Front end section 20 Rear end section 22 Idle pulley 24 Housing 26 Electric motor 28 Rotating shaft 30 Drive pulley 32 Motor housing 34 Grip adapter 36 Grip member 38 Bracket 40 Bar support member 42 Bar accommodating hole 44 Pulley guard section 46 Side opening 48 Endless grinding belt (tip tool) 50 Mounting screw 52 Microcomputer (calculation section) 54 Microcomputer power supply generation circuit 56 Hall IC 58 Motor drive circuit 60 Start switch 62 Voltage measurement section 64 Current measurement section 66 LED display section (display section) 68 Setting switch 70 LED display section B Battery L Longitudinal axis

Claims

1. A portable power tool configured to drive a tool tip to perform machining operations, comprising: an electric motor for driving the tool tip; a power measurement unit that measures the power consumption of the electric motor; and a calculation unit that calculates the amount of power consumption consumed by the electric motor within a specified power accumulation time based on the power consumption measured by the power measurement unit, and that transmits a specified notification signal when the amount of power consumption reaches or exceeds a specified threshold power amount.

2. The portable power tool according to claim 1, wherein the calculation unit is configured to measure the power consumption by the power measurement unit at predetermined time intervals and determine the amount of power consumption consumed within the power integration time.

3. The portable power tool of claim 1, wherein the predetermined power accumulation time is between 15 seconds and 75 seconds.

4. The portable power tool of claim 1, wherein the predetermined power accumulation time is between 25 seconds and 35 seconds.

5. A portable power tool as described in claim 1, further comprising a memory unit that stores a set value of the power accumulation time and a set value of the threshold power amount, and the set values ​​of the power accumulation time and the threshold power amount are changeable.

6. The portable power tool according to claim 1, further comprising a display unit configured to display a warning when the notification signal is transmitted.

7. A portable electric tool as claimed in any one of claims 1 to 6, comprising: a tool body in which the electric motor is disposed; a drive pulley which is rotationally driven by the electric motor; and an idle pulley which is rotatably attached to the tool body; and the tool tip is an endless grinding belt which is looped between the drive pulley and the idle pulley.

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