Desk-top cutting machine

A desk-top cutting machine including: a base configured to support a workpiece; a cutting part including, a motor configured to rotary drive a cutting tool, a main cover covering an upper portion of the cutting tool, and a protective cover covering a portion of the cutting tool that is not covered by the main cover, the protective cover configured to move in a direction of exposing the cutting tool when the cutting part swings toward a bottom dead point from a top dead point; and a cutting part support mechanism configured to swingably support the cutting part, characterized in that: the motor is configured to be rotated at a first rotational speed slower than a maximum rotational speed thereof when the cutting part is positioned at the top dead point.

TECHNICAL FIELD

The present invention relates to a desk-top cutting machine for cutting a workpiece on a base with a rotational cutting tool.

BACKGROUND ART

In general, such a type of desk-top cutting machine includes a base, a cutting part having an electric motor for rotating a cutting tool such as a circular saw and the like, and a cutting part support mechanism for swingably supporting the cutting part, whereby a workpiece placed on the base is cut as an operator manually operates downwardly the cutting part rotating the cutting tool.

A desk-top cutting machine operated by a battery as well as a commercial power supply has been proposed in recent years, and a demand for power saving is accordingly increasing.

PRIOR ART DOCUMENT

Patent Document

SUMMARY OF INVENTION

Technical Problem

In a related-art desk-top cutting machine, when a trigger switch is turned on, it is common for a cutting tool to be rotatably driven at the maximum speed even before an operator manually manipulates a cutting part having the cutting tool to thereby descend. For this reason, since the cutting tool is driven at the maximum speed before starting the cutting of the material to be cut, power consumption increases and noise generated also tends to increase.

The present invention has been made in view of the above-described situation, and an object of the present invention is to provide a desk-top cutting machine which is capable of reducing noise and reducing power consumption.

Solution to Problem

Advantageous Effects of Invention

According to an aspect of the present invention, there is provided a desk-top cutting machine including: a base configured to support a workpiece; a cutting part including, a motor configured to rotary drive a cutting tool, a main cover covering an upper portion of the cutting tool, and a protective cover covering a portion of the cutting tool that is not covered by the main cover, the protective cover configured to move in a direction of exposing the cutting tool when the cutting part swings toward a bottom dead point from a top dead point; and a cutting part support mechanism configured to swingably support the cutting part, characterized in that: the motor is configured to be rotated at a first rotational speed slower than a maximum rotational speed thereof when the cutting part is positioned at the top dead point.

According to the present invention, it is possible to realize noise reduction and reduction in power consumption while securing a sufficient cutting performance.

DESCRIPTION OF EMBODIMENT

Hereinafter various embodiments of the present invention will be described with reference to the accompanying drawings. In the figures, same reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing, and repetition will be omitted. Also, it will be understood that the embodiment does not intend to limit the invention but exemplify the invention. All of the features and the combinations thereof described in the embodiment are not necessarily essential to the invention.

A desk-top circular saw as a desk-top cutting machine will now be described with reference toFIGS. 1 to 8according to the first embodiment of the present invention. In the descriptions hereinafter, the upper and lower directions and front and rear directions are defined as shown inFIG. 1.

As shown in the figures, the desk-top circular saw includes a base1on which a workpiece40can be placed, a cutting part10having an electric motor21which rotatably drives a circular saw blade20as a cutting tool, and a cutting part support mechanism30that tiltably supports a rotational face (side face) of the circular saw blade20with respect to the upper face of the base1while making the cutting part10swingable in upper and lower directions with respect to the base1and slidably supporting the cutting part10in parallel with the base1.

The base1is configured to be placed on a floor surface, a table surface and the like. A turntable2is embedded in the base1. The turntable2has an upper surface that is substantially flush with an upper face of the base1. The turntable2is rotatably connected to the base1via a rotational shaft that is perpendicular to the upper face thereof. The base1and the turntable2are formed so that the workpiece40may be placed thereon during working.

The structure of the cutting part support mechanism30will be described later. The cutting part support mechanism30is attached to the turntable2. When rotating the turntable2, the cutting part support mechanism30and the cutting part10integrally rotate together with the turntable2(i.e. a direction with respect to the base1is changed).

The base1is provided with a pair of fences3each having a pressing face3athat is substantially perpendicular to its upper face. When cutting the workpiece40having a rectangular cross section as indicated by an imaginary line shown inFIG. 1, since the workpiece40is cut by performing the cutting operation in a state where one side of the workpiece40is abut on the pressing face3aof the fence3, it is possible to perform a safety cutting operation. When rotating the turntable2with respect to the base1, the cutting part10rotates together with the turntable2and accordingly changes its position relative to the fence3, thereby changing the angle between the pressing face3aof the fence3and the rotational face (side face) of the circular saw blade20. Accordingly, the workpiece40abut on the fence3can be cut at various angles.

The cutting part support mechanism30includes a tilt shaft4supported substantially in parallel with the upper face of the turntable2in the vicinity of the end of the rear side (left side inFIG. 1) of the turntable2, a holder5that is tiltably attached to the turntable2through the tilt shaft4(it is possible to adjust its posture from a state of being vertically installed on the upper face of the turntable to a state of being inclined to the left and right so as to form a predetermined angle with respect to the upper face), at least two guide bars7fixedly supported by the holder5in parallel with the upper face of the turntable, a slider8provided slidably with respect to the guide bar7, and a hinge9swingably connecting the cutting part10to the slider8.

In order to fix the holder5at a predetermined inclination angle, a bracket51having a elongated hole51aof a circular arc shape is vertically installed at a rear side of the holder5while being centered on the tilt shaft4from the rear side of the holder5, and a shaft portion52aof the clamp lever52is screwed into the holder5thereby passing through the elongated hole51a. The holder5may be fixed at any inclination angle with respect to the upper face of the turntable due to the clamp lever52being clamping-manipulated. The holder5is fixed at a predetermined inclination angle and the circular saw blade20is accordingly fixed at the same inclination angle, thereby enabling the so-called inclination cutting.

In the cutting part10, a rotational power of the motor21is transmitted to the rotational shaft22to which the circular saw blade20is fixed through a rotational power transmitting mechanism. The cutting part10includes a cutting part case11receiving the motor21and the rotational power transmitting mechanism. Further, a main cover12covering an upper portion of the circular saw blade20is integrally provided to the cutting part case11.

The cutting part case11is provided at the rear end thereof with a connection portion11aconnected to the slider8through the hinge9. The connection portion11ais rotatably mounted to the slider8by means of a hinge pin9aof the hinge9, that is, so as to be swingably movable toward or apart from the base1. The cutting part case11is urged in an upper direction by means of the spring13provided around the hinge pin9a. Accordingly, the cutting part10is position-restricted at a top dead point (as shown inFIGS. 1 and 5) by a stopper (detailed descriptions omitted) provided around the hinge9unless any downward force is applied to an operating handle14provided on an upper portion of the cutting part case11. Here, for the convenience of explanation, a position of the rotational shaft22to which the circular saw blade20is fixed is used as a reference of the position of the cutting part10. That is, the rotational shaft22is positioned at a top dead point unless any downward operational force is applied to the operating handle14. The operating handle14is provided with a trigger switch SW1for controlling rotation or stop of the motor21.

The cutting part case11is provided with a carrying handle15for carrying the circular saw as a whole, separately from the operating handle14. The carrying handle15is provided with a cancel switch SW2. Function of the cancel switch SW2will be described later.

The cutting part10has a protective cover16for covering a portion of the circular saw blade20which is not covered by the main cover12. The protective cover16is supported so as to be rotatable along the inner side of the main cover12. One end of a link17serving as a rotational mechanism of the protective cover16is connected to the protective cover16, and the other end of the link17is connected to a fixing arm18fixed to the slider8. The intermediate portion of the link17is adapted to contact with the roller19rotatably attached to the inner side of the main cover12.

When the rotational shaft22of the cutting part10is in the top dead point, as the operating handle14is pushed down toward the bottom dead point, the protective cover16is rotated, by the link17, counterclockwise as indicated by the arrow L inFIG. 1to expose the circular saw blade20. Accordingly, the circular saw blade is in a state in which the workpiece40can be cut.

The motor21is configured to use both battery power and AC commercial power supply as its power supply. The cutting part10is connected to a power cord45for the commercial power supply. Further, a battery receiving part46shown inFIGS. 3 and 4is arranged to a portion which protrudes from a side of the base1. The battery unit48with a battery47therein is secured by a locking screw49of the battery receiving part46.

In the present embodiment, in order to reduce noise and power consumption, when the rotary shaft22of the cutting portion10is located at the top dead point (when there is no operational force in the direction of pushing down the operating handle14), the motor21is rotated at a lower rotational speed (first rotational speed) than its maximum rotational speed. Further, when the rotational shaft22of the cutting part10is located at a bottom dead point side with respect to a predetermined swing position where the rotational shaft22is be positioned between the top dead point and the bottom dead point, the motor21is rotated at high speed (faster speed than the first rotational speed).

As shown inFIGS. 5 and 6, in order to detect the position of the cutting part10(whether at the top dead point) by detecting the position of the protective cover16, a detection switch SW3(micro switch, etc.) as a detecting unit is attached to an edge portion of the main cover12. The attachment position of the detection switch SW3is a position where an operation unit71(actuator) of the detection switch SW3is pressed by the protective cover16when the rotational shaft22of the cutting part10is positioned at the top dead point as shown inFIG. 5. Meanwhile, the operation unit71of the detection switch SW3is not pressed by the protective cover16when the protective cover16is rotated as shown inFIG. 6as the operating handle14is operated to move downward (i.e., the rotational shaft22of the cutting part10moves below the top dead point). Therefore, the detection switch SW3is turned on when the rotational shaft22of the cutting part10is positioned at the top dead point, and turned off when the operation unit71of the detection switch SW3is not pressed as the protective cover16is rotated.

FIG. 7is a schematic configuration of a control system for controlling the rotational speed of the motor21. The control unit60includes a control circuit61connected to the trigger switch SW1, the cancel switch SW2and the detection switch SW3and receiving power supplied from the battery47, and a drive circuit62controlled by the control circuit61to change the supply voltage to the motor21. The drive circuit62performs, for instance, a pulse width control (PWM) of a motor supply voltage. In the case where the AC commercial power supply is used, although not shown, the AC commercial power supply is stepped-down to a predetermined voltage, and then rectified and smoothed by a rectification smoothing circuit thereby obtaining DC voltage that is used instead of the battery voltage. The cancel switch SW2serves to cancel the low-speed rotation so that the motor21is rotated at the maximum rotation speed even when the rotational shaft22of the cutting part10is positioned at the top dead point. Further, the switch SW2functions as a manually operable cancel unit.

FIG. 8is a flowchart showing an example of operation according to the present embodiment. After the trigger switch SW1is turned on in step S1, it is determined whether the cancel switch SW2is off in step S2, and then the motor21is driven at high speed in step S6in the case where the cancel switch SW2is on (in the case of NO). That is, in the control unit60shown inFIG. 7, the control circuit61controls the drive circuit62so that the full voltage of the battery47is applied to the motor21. At this time, instead of applying the full voltage to the motor21immediately, in order to reduce the noise and prevent swing of the cutting part10during startup of the motor, it is preferable that the drive circuit62is controlled by the control circuit61to perform the pulse width control of the motor supply voltage, thereby gradually increasing the effective voltage of the motor21to gradually increase the rotational speed of the motor21until it reaches the maximum rotational speed.

In step S2, it is determined whether the detection switch SW3is on in a case where the cancel switch SW2is off (in the case of YES). In a case where the detection switch SW3is off (the state where the protective cover16is open) (in the case of NO), it is determined that the trigger switch SW1has been turned on while an operator pushes down the operating handle14toward the workpiece40, thereby proceeding to step S6to operate the motor21at high speed.

In step S3, in the case where the detection switch SW3is on (the state where the protective cover16is closed) (in the case of YES), it is determined that the operating handle14is not depressed and the rotational shaft22is positioned at the top dead point, and thereby the motor21is rotated at low speed in step S4, that is, at the first rotational speed slower than the maximum rotational speed. Accordingly, noise and power consumption can be reduced in standby mode. It is preferable that an effective voltage value of the motor21is gradually increased until reaching the effective voltage value required for the low-speed operation by the pulse width control of the control unit60, thereby gradually increasing the rotational speed of the motor21.

Thereafter, it is determined whether the detection switch SW3is off (the state where the protective cover16is open) in step S5. In the case where the detection switch SW3is on (the case where the protective cover16is closed) (in the case of NO), it is determined that there is no change in the state, and then the determination in Step S5is repeated while continuing the slow speed operation.

In the case where the detection switch SW3is off (the case where the protective cover16is opened) in step S5, the processing proceeds to step S6where the motor21is operated at high speed. That is, the rotational speed is increased to the maximum rotation speed. During the high-speed operation of the motor21, the workpiece40can be cut by depressing the operating handle14downward (by making the cutting part10slide if necessary) until the rotational shaft22of the cutting part10arrives at the bottom dead point.

Thereafter, in step S7, it is determined whether the trigger switch SW1is turned off or not. In the case where the trigger switch SW1is turned on (in the case of NO), the step S7is repeated while the high-speed operation is performed.

In the case where the trigger switch SW1is turned off (in the case of YES) in step S7, the motor stops in step S8.

FIG. 9Ashows an example of the relationship between time and the motor rotation speed (≈effective voltage) from the startup of the motor21to the low-speed operation of the motor21in step S4and further to the high-speed operation of the motor21in step S6. As shown inFIG. 9A, when switching the rotational speed of the motor21from a state of the low-speed operation to a state of the high-speed operation, the control unit60performs a pulse width control of the motor supply voltage by controlling the drive circuit62through the control circuit61. Thereby the switching is performed by gradually increasing the rotational speed of the motor by21. Further, the motor speed is controlled so that a first gradient corresponding to a gradual increase of the rotational speed of the motor21during startup of the motor21is more gradual than a second gradient corresponding to a gradual increase of the rotational speed of the motor21when switching from the low-speed operation to the high-speed operation.

FIG. 9Bshows an explanation view in which a region of high-speed control for performing a high-speed operation and a region of low-speed control for performing a low-speed operation of the motor21are divided, in a case where the rotational shaft22of the cutting part10is lowered from the top dead point toward the bottom dead point with respect to the swing support point (hinge pin9a). In a case of detecting the position of the protective cover16by the arrangement of the detection switch SW3shown inFIGS. 5 and 6, since the protective cover16is opened widely by just pushing down slightly the operating handle14, the region where the low-speed operation is performed is in a very narrow range containing a position of the top dead point. That is, the predetermined swing position of the cutting part10(viewed from the position reference of the rotational shaft22) that switches from the low-speed operation to the high-speed operation is positioned at a top dead point side more sufficiently than the swing position of the cutting part10at which the cutting of the workpiece40is started and which requires the maximum cutting capacity.

According to the first embodiment, it is possible to achieve the following effects.

(1) Since the motor21is in a standby mode of a low-speed rotation when the rotational shaft22of the cutting part10is located at the top dead point, and the motor21is switched to high speed when the press operation of the operating handle14is performed, it is possible to achieve a reduction in noise and achieve power saving without impairing the ability of cutting the workpiece40.

(2) The control unit60is capable of controlling the motor21to gradually increase its rotational speed when starting the motor21, and capable of reducing the noise and preventing the cutting portion10from swinging during startup of the motor.

(3) The control unit60is capable of performing switching operation while gradually increasing the rotational speed of the motor when switching the rotational speed of the motor21from low-speed rotation to high-speed rotation. Accordingly, although the cutting part10intended to swing downward swings upward due to reaction force when the rotational speed of the motor21is suddenly switched, it is possible to prevent such phenomenon by gradually increasing the rotational speed of the motor.

(4) As described inFIG. 9A, regarding the first gradient of gradually increasing the motor rotational speed during startup of the motor21and the second gradient of gradually increasing the motor rotational speed when switching from the low-speed the rotation to high-speed rotation, the control unit60may control the speed of the motor so that the first gradient is more gradual than the second gradient. If the second gradient is gradual and the speed is gradually increased, there is a possibility that the rotational speed of the motor cannot reach its maximum rotational speed before start of cutting, and accordingly there is a problem that the cutting quality may deteriorate. However, by making the second gradient relatively steep, it is possible to avoid the problem.

FIG. 10shows a second embodiment of the present invention. The second embodiment is different from the first embodiment in the arrangement of the detection switch SW3. That is, the cutting part support mechanism30has a hinge9swingably connected to the cutting part10, and is provided with the detection switch SW3disposed on the slider8near the hinge9. The position of the connection portion11aof the cutting part case11connected to the slider8via the hinge9is detected by the detection switch SW3. In this case, the detection switch SW3becomes a mechanism for detecting the relative movement of the other member with respect to one member around the hinge9.

InFIG. 10, the rotational shaft22of the cutting part10is positioned at the top dead point, the operation unit71(actuator) of the detection switch SW3is pressed by the edge portion of the connection portion11a, and accordingly, the detection switch SW3is turned on. As the operating handle14is operated toward the bottom dead point, the operation unit71of the detection switch SW3is no longer pressed by the connection portion11aand thereby turned off.

In the case of the second embodiment, since the movement of the connection portion11aaccording to the press operation of the operating handle14is slow compared to the movement of the protective cover16, the division of the regions of the low-speed control and high-speed control becomes possible to be set as inFIG. 9Cin which the region of low-speed control is enlarged compared to that ofFIG. 9B. The region of the low-speed control is from the top dead point of the rotational shaft22of the cutting part10to the predetermined swing position thereof. However, the predetermined swing position is positioned at the top dead point side with respect to the position at which the cutting part10starts cutting of the workpiece40and has the maximum cutting ability. This is necessary in order not to reduce the cutting ability.

FIG. 11shows a third embodiment of the present invention. The detection switch SW3is in the vicinity of the hinge9, while the arrangement of the detection switch SW3is opposite to that of the second embodiment described above. That is, the detection switch SW3is attached to the connection portion11aof the cutting part case11connected to the slider8via the hinge9, and an abutting member72is fixed to the slider8to press the operation portion71of the detection switch SW3.

In the state shown inFIG. 11, the rotational shaft22of the cutting part10is positioned at the top dead point, the operation unit71of the detection switch SW3is pressed by the abutting member72of the slider8side, and the detection switch SW3is turned on accordingly. As the operating handle14is operated toward the bottom dead point, the operation unit71of the detection switch SW3is no longer pressed by the abutting member72and thereby turned off.

Even in the case of the third embodiment, since the movement of the connection portion11aaccording to the press operation of the operating handle14is slow compared to the movement of the protective cover16, the division of the regions of the low-speed control and high-speed control becomes possible to be set as inFIG. 9Cin which the region of low-speed control is enlarged compared to that ofFIG. 9B.

In the second and third embodiments, there is a case where the predetermined swing position of switching from the low-speed control shown inFIG. 9Cto high-speed control is positioned closer to the bottom dead point than in the first embodiment. For that reason, the second gradient is made steeper than the first gradient shown inFIG. 9Aand accordingly the control unit60controls the motor21so that the rotational speed of the motor may reach its maximum rotational speed before start of cutting. Thereby, it is possible to avoid the problem that the motor rotational speed cannot reach its maximum rotational speed before start of cutting operation and the cutting quality deteriorates accordingly. The other effects are the same as in the first embodiment.

In the foregoing, the present invention has been described according to the preferred embodiments. However, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the claimed invention. Hereinafter, modification examples will be described.

In the first embodiment, the control unit60has been described as controlling the rotational speed of the motor, for example, by a pulse width control of the motor supply voltage. However, the configuration of the control unit60is not limited thereto but frequency control and phase control of the motor supply voltage may also be possible.

In each embodiment, the detection switch SW3is assumed as a mechanical micro switch or the like but may be a proximity switch or the like.

In each embodiment, the circular saw blade has been illustrated as a cutting tool, but the present invention may be applied to high-speed cutting machine using a grindstone as a cutting tool.

The present invention provides illustrative, non-limiting examples as follows:

(1) According to a first aspect, there is provided a desk-top cutting machine including: a base configured to support a workpiece; a cutting part including, a motor configured to rotary drive a cutting tool, a main cover covering an upper portion of the cutting tool, and a protective cover covering a portion of the cutting tool that is not covered by the main cover, the protective cover configured to move in a direction of exposing the cutting tool when the cutting part swings toward a bottom dead point from a top dead point; and a cutting part support mechanism configured to swingably support the cutting part, characterized in that: the motor is configured to be rotated at a first rotational speed slower than a maximum rotational speed thereof when the cutting part is positioned at the top dead point.

(2) According to a second aspect, there is provided the desk-top cutting machine according to the first aspect, wherein the motor is configured to rotate at a rotational speed faster than the first rotational speed, when the cutting part is positioned at the bottom dead point side with respect to a predetermined swing position positioned between the top dead point and the bottom dead point.

(3) According to a third aspect, there is provided the desk-top cutting machine according to the second aspect, further including a detecting unit configured to detect a position of the cutting part, wherein the rotational speed of the motor is configured to be switched based on a detection result of the detecting unit.

(4) According to a fourth aspect, there is provided the desk-top cutting machine according to the third aspect, wherein the detecting unit is configured to detect the position of the cutting part by detecting a position of the protective cover.

(5) According to a fifth aspect, there is provided the desk-top cutting machine according to the third aspect, further including a control unit configured to control the rotational speed of the motor, wherein the detecting unit is configured to input the detection result to the control unit, and wherein the control unit is configured to switch the rotational speed of the motor from the first rotational speed to a rotational speed faster than the first rotational speed, based on the detection result of the detecting unit.

(6) According to a sixth aspect, there is provided the desk-top cutting machine according to the fifth aspect, wherein the control unit is configured to switch the rotational speed of the motor from the first rotational speed to the speed faster than the first rotational speed by gradually increasing the rotational speed of the motor.

(7) According to a seventh aspect, there is provided the desk-top cutting machine according to the fifth or sixth aspect, wherein the control unit is configured to control the motor so as to gradually increase the rotational speed of the motor during starting-up of the motor.

(8) According to an eighth aspect, there is provided the desk-top cutting machine according to the seventh aspect, wherein a first gradient corresponding to a gradual increase of the rotational speed of the motor during startup of the motor is more gradual than a second gradient corresponding to a gradual increase of the rotational speed of the motor when switching from the first rotational speed to the speed faster than the first rotational speed.

(9) According to a ninth aspect, there is provided the desk-top cutting machine according to the second aspect, wherein the predetermined swing position is positioned at the top dead point side with respect to a swing position of the cutting part at which cutting of a workpiece is started and the cutting part has a maximum cutting ability.

(10) According to a tenth aspect, there is provided the desk-top cutting machine according to the first aspect, further including a manually operable cancel unit configured to cancel a rotation control at the first rotational speed such that the motor rotates at a maximum rotational speed even when the cutting part is positioned at the top dead point.

(11) According to an eleventh aspect, there is provided the desk-top cutting machine according to the third aspect, wherein the cutting part support mechanism includes a hinge swingably connected to the cutting part, and wherein the detecting unit is provided adjacent to the hinge.

(12) According to a twelfth aspect, there is provided the desk-top cutting machine according to the first aspect, wherein the base or the cutting part is provided with a battery and power is supplied to the motor from the battery.

It will be appreciated by those skilled in the art that all arbitrary combinations of the above-described constituents, and all conversions of expression, made among methods or systems, are also within the scope of the present invention.

This application claims priority from Japanese Patent Application No. 2012-155178 filed on Jul. 11, 2012, the entire contents of which are incorporated herein by reference.

INDUSTRIAL APPLICABILITY

According to an aspect of the invention, there is provided a desk-top cutting machine which is capable of reducing noise and reducing power consumption.