JP2024093736A - Cutting device - Google Patents

Abstract

An electric cutting device capable of stopping a cutting blade at an appropriate position is provided.
[Solution] The cutting device 10 includes a pair of cutting blades 111 that clamp and cut an object to be cut, an electric motor 400 that generates a driving force required for the operation of the cutting blades 111, a control unit 530 that controls the operation of the electric motor 400, and a speed acquisition unit 510 that acquires a speed index that is an index showing the operating speed of the cutting blades 111. The control unit 530 brakes the cutting blades 111 based on the speed index.
[Selected figure] Figure 3

Description

The present invention relates to an electric cutting device.

Electric pruning shears, such as those described in Patent Document 1 below, are known as electric cutting devices. In electric cutting devices, the cutting blades are operated by the driving force of an electric motor instead of by the gripping force of the user, and the material to be cut is cut by clamping it between the pair of cutting blades. The electric pruning shears described above are used to cut tree branches, but cutting devices that cut metals such as rebar are also known.

JP 2021-40594 A

When operating the cutting blades in an electric cutting device, it is preferable to stop the cutting blades at a predetermined target position after cutting is completed. For example, in a cutting device in which a pair of cutting blades operate opposite each other (i.e., the pair of cutting blades operate on an orbit that passes each other in the same plane) rather than pruning shears in which the pair of cutting blades operate, if the timing at which the cutting blades stop is delayed, the cutting blades may collide with each other while maintaining a relatively large relative speed, causing a situation in which part of the cutting blade may be deformed or broken.

However, the operating speed of the cutting blade during cutting is not always constant, but changes depending on the material and shape of the workpiece. For this reason, even if the operation control of the cutting blade is always performed under the same conditions, the cutting blade does not necessarily stop in the same position. In order to prevent the cutting blades from colliding with each other, it is possible to operate the cutting blades at a slow speed, but in that case, problems such as the cutting operation taking too long may occur. Until now, no specific consideration has been given to how to brake the cutting blades in an electric cutting device.

The present invention aims to provide an electric cutting device that can stop the cutting blade at an appropriate position.

The cutting device according to the present invention is an electric cutting device that includes a pair of cutting blades that clamp and cut the workpiece, an electric motor that generates the driving force required for the operation of the cutting blades, a control unit that controls the operation of the electric motor, and a speed acquisition unit that acquires a speed index that is an index showing the operating speed of the cutting blades. The control unit brakes the cutting blades based on the speed index.

The distance the cutting blade travels from the start to the end of braking, i.e., the braking distance, correlates with the operating speed of the cutting blade before braking begins. Therefore, in the cutting device configured as described above, braking of the cutting blade is performed based on a speed index, which is an index that indicates the operating speed of the cutting blade. This makes it possible to stop the cutting blade at an appropriate position even in cases where the braking distance varies depending on the situation.

The present invention provides an electric cutting device that can stop the cutting blade at an appropriate position.

FIG. 1 is a diagram showing the configuration of a cutting device according to a first embodiment. FIG. 2 is a diagram showing a configuration of a guide plate included in the cutting device according to the first embodiment. FIG. 3 is a diagram showing the configuration of a control board included in the cutting device according to the first embodiment. FIG. 4 is a diagram for explaining the operation of the cutting device according to the first embodiment during braking. FIG. 5 is a flowchart showing a flow of processing executed by the control board of the first embodiment. FIG. 6 is a diagram for explaining a method of calculating the braking distance index. FIG. 7 is a diagram for explaining the operation of the cutting blade during braking. FIG. 8 is a flowchart showing the flow of the process executed by the control board. FIG. 9 is a diagram for explaining the process performed during braking. FIG. 10 is a flowchart showing the flow of processing executed by the control board of the second embodiment. FIG. 11 is a diagram for explaining the operation of the cutting blade during braking.

Hereinafter, this embodiment will be described with reference to the attached drawings. To facilitate understanding of the description, the same components in each drawing are denoted by the same reference numerals as much as possible, and duplicate descriptions will be omitted.

A first embodiment will be described. The cutting device 10 according to this embodiment is an electric cutting device configured as a device for cutting rebar at construction sites and the like. The configuration of the cutting device 10 will be described with reference mainly to FIG. 1. The cutting device 10 includes a housing 11, a trigger switch 12, a cutting mechanism 100, a ball screw 200, a reducer 300, an electric motor 400, a control board 500, and a storage battery 600.

The housing 11 is a container that defines the outer shape of the cutting device 10, and is formed, for example, from resin. Inside the housing 11, a ball screw 200, a reducer 300, and the like, which will be described later, are housed. In FIG. 1, the portion of the housing 11 on the front side of the page has been removed, and the internal configuration of the cutting device 10 is shown as a cross-sectional view.

The trigger switch 12 is a switch that is operated by the user's finger. The user can turn the trigger switch 12 on by placing their finger on the trigger switch 12 and pulling it towards themselves. When the user releases the pressure of their finger, the force of the spring causes the trigger switch 12 to return to its original position and return to the off state. When the trigger switch 12 is switched between the on and off states, a corresponding signal is sent to the control board 500, which will be described later. As will be described later, when the trigger switch 12 is turned on by the user's operation, an operation to cut the rebar is initiated.

The cutting mechanism 100 is the part that cuts the rebar, which is the object to be cut. The cutting mechanism 100 has a pair of blade members 110 and a pair of link members 120.

Each blade member 110 is formed with a cutting blade 111 that clamps and cuts the material to be cut. The blade member 110 is held in a state in which it can rotate freely around an axis 101 fixed to the housing 11. In this embodiment, the blade members 110 are arranged opposite each other so that the ridges of the cutting edges of the cutting blades 111 move along an orbit that passes through approximately the same plane. This makes it possible to switch between an open state in which the cutting blades 111 are separated from each other, and a closed state in which the cutting blades 111 are in contact (or close to each other). In the example of Figure 1, a pair of cutting blades 111 are in the closed state.

The link member 120 is a rod-shaped member, one end of which is connected to the blade member 110 via the shaft 102, and the other end of which is connected to the connecting member 230 (described below) via the shaft 231. The link member 120 and the blade member 110 are connected to each other in a state in which they can rotate freely around the shaft 102. Similarly, the link member 120 and the connecting member 230 are connected to each other in a state in which they can rotate freely around the shaft 231. As described later, the connecting member 230 moves in the left-right direction in FIG. 1 by the driving force of the electric motor 400.

When the connecting member 230 moves leftward from the state shown in FIG. 1, the blade member 110 on the upper side of FIG. 1 rotates counterclockwise, and the blade member 110 on the lower side of FIG. 1 rotates clockwise. As a result, the pair of cutting blades 111 changes from a closed state to an open state. On the other hand, when the connecting member 230 moves rightward in FIG. 1 while the pair of cutting blades 111 are in an open state, the blade member 110 on the upper side of FIG. 1 rotates clockwise, and the blade member 110 on the lower side of FIG. 1 rotates counterclockwise. As a result, the pair of cutting blades 111 return to a closed state. In this way, the pair of blade members 110, the pair of link members 120, and the connecting member 230 as a whole constitute a so-called "toggle link mechanism."

In this embodiment, a pair of guide plates 700 are provided near the blade member 110. The guide plates 700 are plate-shaped members made of metal, and are arranged to sandwich the blade member 110 from both the front and rear sides of the paper surface in FIG. 1. The pair of guide plates 700 have the same shape. As shown in FIG. 2, a recess 710 is formed in each guide plate 700.

For convenience of explanation, the right side in FIG. 1 is also referred to as the "tip side" below, and the left side in FIG. 1 is also referred to as the "rear side" below. The recesses 710 are formed so as to retreat from the tip side to the rear side of the guide plate 700. When the cutting device 10 is viewed from the side as in FIG. 1 and FIG. 2, each recess 710 is formed at a position including the cutting blade 111 in the closed state. In the standby state in which the cutting blade 111 is fully open, each cutting blade 111 is in a state of retreating to the outside of the recess 710, and in the viewpoint of FIG. 2, the entire blade member 110 is hidden by the guide plate 700. The guide plate 700 has both the function of covering and protecting the cutting blade 111 in the standby state and the function of guiding the reinforcing bar, which is the object to be cut, between the pair of cutting blades 111 along the recess 710. The guide plate 700 also has the function of stabilizing the position of the cutting device 10 before and after cutting by clamping the rebar in the recess 710.

The ball screw 200 is a device that converts the rotational motion of the electric motor 400 into the linear motion of the connecting member 230, thereby operating the cutting mechanism 100. The ball screw 200 has a screw shaft 210, a nut 220, and a connecting member 230.

The screw shaft 210 is a rod-shaped member that extends linearly from the rear end to the tip end. A male screw is formed on the outer circumferential surface of the screw shaft 210. When the electric motor 400 is driven, the screw shaft 210 rotates around its central axis.

The nut 220 is a generally cylindrical member arranged to surround the screw shaft 210 from the outer periphery. A female screw is formed on the inner periphery of the nut 220, and is screwed into a male screw formed on the outer periphery of the screw shaft 210. The nut 220 is allowed to move along the longitudinal direction of the screw shaft 210, but is restricted from rotating around the central axis of the screw shaft 210. Therefore, when the screw shaft 210 rotates around its central axis, the nut 220 moves in the left-right direction in FIG. 1 along the central axis.

The connecting member 230 is a member attached to the nut 220 and moves along the screw shaft 210 together with the nut 220. The connecting member 230 is attached so as to protrude from the nut 220 toward the tip side. A pair of link members 120 are connected to the portion of the connecting member 230 near the end on the tip side via the shaft 231 described above.

A magnet 241 is attached to the outer periphery of the connecting member 230. A hall sensor 242 is attached to the housing 11 at a position near the connecting member 230. The position at which the hall sensor 242 is attached is a position facing the magnet 241 of the connecting member 230 when the nut 220 moves to the rear end from the state shown in FIG. 1 and the cutting blade 111 is fully opened. When the cutting blade 111 is fully opened, the hall sensor 242 faces the magnet 241, causing a signal to be transmitted from the hall sensor 242, which is then input to the control board 500.

The reducer 300 is a device that reduces the rotation of the output shaft 410 of the electric motor 400 and transmits it to the screw shaft 210 of the ball screw 200.

The electric motor 400 is a rotating electric machine for generating the driving force required for the operation of the cutting blade 111, and is, for example, a brushless DC motor. The electric motor 400 has an output shaft 410. The output shaft 410 is a substantially cylindrical member, and its central axis coincides with the central axis of the screw shaft 210. A portion of the output shaft 410 protrudes toward the reducer 300 and is connected to the reducer 300.

When a current is supplied to the coil of the electric motor 400, the output shaft 410 rotates around its central axis. The rotation of the output shaft 410 is transmitted to the screw shaft 210 via the reducer 300, moving the nut 220 toward the front or rear end. This causes the cutting blade 111 of the cutting mechanism 100 to open and close as described above.

A rotation sensor 420 is provided inside the electric motor 400. The rotation sensor 420 is a sensor that transmits a pulse signal every time the output shaft 410 rotates by a predetermined angle, and is provided on a substrate 430 of the electric motor 400. The pulse signal from the rotation sensor 420 is transmitted to the control substrate 500. The control substrate 500 can grasp the rotation angle of the output shaft 410 after a specific timing by counting the number of pulse signals. The control substrate 500 can also grasp the rotation speed of the output shaft 410 based on the number of pulse signals input per unit time. The rotation sensor 420 may be a different type of sensor from that of this embodiment as long as it can measure the rotation angle and rotation speed of the output shaft 410, and may be a sensor separately provided at a position different from that of the electric motor 400. The rotation sensor 420 corresponds to the "speed sensor" in this embodiment.

The control board 500 is a circuit board provided to control the overall operation of the cutting device 10, including the electric motor 400. The control board 500 includes an inverter circuit for adjusting the current supplied to the electric motor 400, a microcomputer for controlling the switching operation in the inverter circuit, etc.

The storage battery 600 stores the power required to operate the electric motor 400 and the control board 500, and is, for example, a lithium-ion battery. The part of the cutting device 10 in which the storage battery 600 is built can be detached from the housing 11 as a battery pack, and can be charged by connecting to an external charger. Alternatively, the storage battery 600 may be configured to be charged while still attached to the housing 11.

The configuration of the control board 500 will be described with reference to FIG. 3. The control board 500, which includes a microcomputer, has a speed acquisition unit 510, a position acquisition unit 520, and a control unit 530 as elements that represent its functions.

The speed acquisition unit 510 is a part that performs processing to acquire a speed index. The "speed index" is an index that indicates the operating speed when the cutting blade 111 opens and closes. In this embodiment, the speed acquisition unit 510 acquires the speed index based on the rotation speed of the electric motor 400 measured by the rotation sensor 420 (speed sensor). Specifically, the number of pulse signals input from the rotation sensor 420 per unit time is calculated and acquired by the speed acquisition unit 510 as the speed index. The speed index may indirectly indicate the operating speed of the cutting blade 111 as in this embodiment, but may also be the value of the operating speed of the cutting blade 111 itself. For example, when the angle between a pair of cutting blades 111 is θ, the amount of change in θ per unit time may be used as the speed index.

The speed index may be obtained based on the measured value of the rotation sensor 420 as described above, but may also be obtained based on other physical quantities. For example, the speed index may be obtained based on the value of the current supplied from the storage battery 600 to the electric motor 400, or based on the terminal voltage of the storage battery 600. In either case, the correspondence between the target physical quantity and the operating speed of the cutting blade 111 may be determined in advance by an experiment or the like, and a calculation map of the speed index may be created based on the correspondence. The calculation map may be stored, for example, in a storage device (e.g., a ROM) (not shown) provided in the control board 500. The above correspondence may be expressed as a formula rather than a map.

The position acquisition unit 520 is a part that performs processing to acquire a position index. The "position index" is an index that indicates the current position of the cutting blade 111. In this embodiment, the count value of the pulse signal input from the rotation sensor 420, based on the time when the magnet 241 and the hall sensor 242 face each other, is calculated and acquired by the position acquisition unit 520 as the position index. The position index may indirectly indicate the current position of the cutting blade 111 as in this embodiment, but it may also be the value of the current position of the cutting blade 111 itself. For example, when the angle between the pair of cutting blades 111 is θ, the value of θ may be used as the current position.

To make it possible to obtain the position index, a reset operation may be performed when the cutting device 10 is started, for example. In the reset operation, for example, the electric motor 400 may be driven in a direction in which the pair of cutting blades 111 change from a closed state to an open state, and the electric motor 400 may be stopped when a detection signal is input from the hall sensor 242. If the counting of the pulse signal is started from this point, the position index of the cutting blade 111 thereafter may be accurately obtained.

The control unit 530 is a part that controls the operation of the electric motor 400. The control unit 530 controls the opening and closing operation of the cutting blade 111 by adjusting the magnitude of the current supplied to the electric motor 400, for example by PWM control. The control unit 530 also controls the braking operation of the cutting blade 111 by periodically or continuously shorting some of the multiple coils equipped in the electric motor 400, a so-called "short brake."

The process executed by the control board 500 will be outlined with reference to FIG. 4. When cutting rebar, the pair of cutting blades 111 move from the fully open position to the fully closed position. Finally, the cutting blades 111 are stopped by braking performed by the control unit 530. FIG. 4 shows a schematic diagram of the current position of the cutting blades 111 changing between the "fully open position" on the left and the "fully closed position" on the right. The arrow AR1 shown in FIG. 4 indicates the distance that the cutting blades 111 are predicted to travel in the period until braking is completed if braking is started at the current time.

The position corresponding to the tip of arrow AR1 represents the position where braking is completed and the cutting blade is predicted to stop. This position is also referred to below as the "predicted position." If braking is started at the point shown in FIG. 4(A), the predicted position will be before the fully closed position. If the target position at which the cutting blade 111 should stop is set to the fully closed position, braking should be started at the timing shown in FIG. 4(B) when the current position of the cutting blade 111 has progressed further than FIG. 4(A).

However, the length of arrow AR1, i.e., the braking distance of the cutting blade 111, is not always constant but changes depending on the operating speed of the cutting blade 111. For example, when braking is initiated while the cutting blade 111 is operating at high speed, the braking distance becomes longer. In the example of FIG. 4(C), as a result of the braking distance becoming longer as described above, the cutting blade 111 stops at the target position, the fully closed position, even though braking is initiated at the same timing as in FIG. 4(A).

From the above, it can be seen that it is possible to stop the cutting blade 111 at the target position by repeatedly calculating the predicted position and initiating braking at the timing when the predicted position coincides with the target position. Therefore, the control board 500 according to this embodiment repeatedly calculates the length of the arrow AR1 (the braking distance index, described below) in parallel with causing the cutting blade 111 to perform a cutting operation, and measures the appropriate timing for initiating braking to stop the cutting blade 111 at the target position.

The specific flow of the processing executed by the control board 500 will be described with reference to FIG. 5. The series of processing shown in FIG. 5 is started when the trigger switch 12 is turned on by the user.

In the first step S01 of this process, the cutting operation of the cutting blades 111 is started. After this, the pair of cutting blades 111 move in a direction approaching each other. Immediately after the cutting blades 111 start to move, each cutting blade 111 comes into contact with a reinforcing bar (not shown), and by moving further, plastically deforms the reinforcing bar.

In step S02 following step S01, the speed acquisition unit 510 performs a process of acquiring a speed index. In step S03 following step S02, the control unit 530 performs a process of calculating a braking distance index. The "braking distance index" is an index indicating the distance that the cutting blade 111 is predicted to move from when braking of the cutting blade 111 starts until the cutting blade 111 stops during operation of the cutting blade 111. In this embodiment, the number of pulse signals (count value) predicted to be input from the rotation sensor 420 from when braking starts until the cutting blade 111 stops is used as the braking distance index. The braking distance index may indirectly indicate the braking distance of the cutting blade 111 as in this embodiment, but may also be the value of the braking distance itself. For example, when the angle between the pair of cutting blades 111 is θ, a predicted value of the change in θ during the period from the start to the end of braking may be used as the braking distance index.

As mentioned above, the braking distance of the cutting blade 111 changes depending on the operating speed of the cutting blade 111. Therefore, there is a certain correlation between the speed index and the braking distance index. Therefore, the control unit 530 calculates the braking distance index based on the speed index.

Figure 6 shows an example of the correspondence between the speed index and the braking distance index. Each plot represents an actual measurement value. As shown in Figure 6, the larger the speed index (i.e., the higher the operating speed of the cutting blade 111 during the cutting operation), the larger the calculated braking distance index tends to be. In the example of Figure 6, in the region where the speed index is less than VD1, the correlation between the speed index and the braking distance index is approximated by a straight line L1. Similarly, in the region where the speed index is equal to or greater than VD1 and less than VD2, the correlation between the speed index and the braking distance index is approximated by a straight line L2, and in the region where the speed index is equal to or greater than VD2, the correlation between the speed index and the braking distance index is approximated by a straight line L3. Each of the approximation lines can be calculated using, for example, the least squares method.

These correspondences between the speed index and the braking distance index are measured and calculated in advance by experiments or the like, and then stored as a map in a storage device (e.g., a ROM) (not shown) provided in the control board 500. The control unit 530 calculates the braking distance index in step S03 based on the correspondences thus stored in advance and the speed index acquired in step S02 of FIG. 5.

In step S04 following step S03, the position acquisition unit 520 performs a process of acquiring a position index. In step S05 following step S04, the control unit 530 performs a process of calculating a predicted position, for example. This predicted position is the position of the tip of the arrow AR1 in FIG. 4, and is the position obtained by adding the travel distance of the cutting blade 111 corresponding to the braking distance index to the current position of the cutting blade 111 corresponding to the position index. Note that in step S05, such a predicted position is calculated as a value converted into an index of the same type as the position index. Specifically, the value obtained by simply adding the braking distance index to the position index is calculated as it is as the predicted position.

In the above, "add" means changing the current position of the cutting blade 111 corresponding to the position indicator by the movement distance of the cutting blade 111 corresponding to the braking distance indicator in the direction in which the cutting blade 111 is moving.

In step S06 following step S05, it is determined whether the predicted position calculated in step S05 is equal to or greater than a preset target position. This target position is the position of the cutting blade 111 to be reached at the end of the cutting operation, expressed as an index of the same type as the position index. The target position is set, for example, to a position where the pair of cutting blades 111 are in a closed state. The "position where the pair of cutting blades 111 are in a closed state" refers, for example, to a position where the pair of cutting blades 111 are in abutting contact with each other, that is, a position where the blades are fully closed. The position of the cutting blade 111 just before being fully closed may be set as the target position. Note that in the above, the predicted position being "equal to or greater than the target position" means that the predicted position coincides with the target position or is calculated as a position further to the fully closed side than the target position.

If the predicted position is less than the target position, starting braking at this point will cause the cutting blade 111 to stop short of the target position, as in the example of FIG. 4(A). Therefore, in this case, the process from step S02 onwards is executed again while the cutting blade 111 continues to operate.

If it is determined that the predicted position is equal to or greater than the target position, it means that it is an appropriate time to start braking. In this case, the process proceeds to step S07, and the control unit 530 starts braking the cutting blade 111. After that, the operating speed of the cutting blade 111 gradually decreases. In many cases, the rebar breaks before the cutting blade 111 reaches the target position.

Figure 7 shows an example of changes in the speed index. Line L11 in Figure 7 is an example of when braking is initiated from a state in which the speed index is relatively large. "PD11" represents the position of the cutting blade 111 at the timing when braking is initiated, i.e., the timing when step S06 in Figure 5 is judged to be Yes. After the timing of PD11, the speed index gradually decreases due to braking, and the cutting blade 111 stops when it reaches the target position, the fully closed position.

Line L12 is an example of a case where braking is started when the speed index is smaller than line L11. "PD12" is the position of the cutting blade 111 at the timing when braking is started in this example. In the example of line L12, the braking distance index is calculated to be a smaller value than in the example of line L11, so the timing of braking start is slightly delayed. However, after the timing of PD12, the speed index gradually decreases as in line L12, and the cutting blade 111 also stops when it reaches the fully closed position. Lines L13 and L14 are similar to the above, and the smaller the speed index before braking, the later the timing of braking start (PD13, PD14), but the cutting blade 111 stops at the target position. This is because in either case, the braking distance index is calculated based on the speed index, and as a result, the timing of braking start is appropriately set.

As described above, the control unit 530 of this embodiment is configured to determine the timing to start braking the cutting blade 111 based on the position index and the braking distance index. Specifically, the control unit 530 determines the timing to start braking the cutting blade 111 as the timing at which the predicted position calculated by adding the moving distance of the cutting blade 111 corresponding to the braking distance index to the current position of the cutting blade 111 corresponding to the position index becomes a predetermined target position. As a result, even if the braking distance varies depending on the material or shape of the rebar, for example, braking can be started at a timing corresponding to the variation, and the cutting blade can always be stopped at an appropriate position. Since the cutting blade can always be stopped at an appropriate position, the risk of collision of the cutting blade can be reduced. As a result, it is possible to drive at high speed, thereby shortening the cutting operation time.

In addition, as a control for stopping the cutting blade 111 at an appropriate position, in addition to performing control for adjusting the braking start timing as in this embodiment, control for adjusting the braking strength can also be performed. However, in the latter control, when a strong braking force is required, it is necessary to increase the braking current flowing through the electric motor 400, which results in the electric motor 400 generating a large amount of heat. At construction sites and the like, the cutting device 10 is often operated continuously. For this reason, when control for adjusting the braking strength is performed as described above, the temperature of the electric motor 400 may rise too much. In particular, since the cutting device 10 is required to have a high cutting speed, excessive heating of the electric motor 400 due to continuous use is not desirable. In contrast, in the cutting device 10 according to this embodiment, the braking start timing is adjusted instead of the braking strength, so that the cutting blade can be stopped at an appropriate position while suppressing heat generation from the electric motor 400.

However, depending on the shape of the rebar, the resistance that the cutting blade 111 receives may become too great before the rebar breaks, causing the operating speed of the cutting blade 111 to slow down too much. If this happens, it may take too long for the rebar to break, or the cutting blade 111 may stop before the rebar breaks.

Therefore, the control board 500 of this embodiment prevents such a situation from occurring by executing the process shown in FIG. 8. The flowchart shown in FIG. 8 shows the flow of the process executed by the control board 500 after the transition to step S07 in FIG. 5 and braking is started.

In the first step S11, similar to step S04 in FIG. 5, the position acquisition unit 520 performs a process of acquiring a position index. In step S12 following step S11, it is determined whether a predetermined period of time has elapsed between the timing at which braking was started in step S07 and the current time. If the predetermined period of time has not yet elapsed, the process of step S12 is executed again and the process waits. If the predetermined time has elapsed, the process proceeds to step S13.

In step S13, the position acquisition unit 520 again acquires a position index. In step S14 following step S13, the control unit 530, for example, calculates a braking speed index. The "braking speed index" is an index that indicates the operating speed of the cutting blade 111 after braking of the cutting blade 111 is started when cutting the rebar. In this embodiment, the amount of change in the position index before and after the above-mentioned "predetermined period" has elapsed is calculated as the braking speed index. In other words, the value obtained by subtracting the position index acquired in step S13 from the position index acquired in step S11 is calculated as the braking speed index.

The braking speed index may be calculated as a value different from the above, so long as it indicates the operating speed of the cutting blade 111 after braking of the cutting blade 111 is initiated. For example, the reciprocal of the length of the period required for the rotation speed of the electric motor 400 to decrease to a predetermined value after braking is initiated may be used as the braking speed index.

In step S15 following step S14, it is determined whether the braking speed index calculated as described above is equal to or greater than a predetermined reference value. If the braking speed index is equal to or greater than the reference value, it is determined that the disconnection operation is being performed normally, and the process shown in FIG. 8 is terminated. If the braking speed index is less than the reference value, the process proceeds to step S16.

The transition to step S16 means that the operating speed of the cutting blade 111 has dropped too much for some reason. Therefore, in step S16, the control unit 530 suspends the braking process. Specifically, it suspends the short brake process described above.

In step S17 following step S16, the control unit 530 drives the electric motor 400 again. Thereafter, the electric motor 400 is operated in a direction in which the cutting blade 111 moves toward the target position while remaining in a normal state in which braking is not performed. By operating the cutting blade 111 again with the driving force of the electric motor 400, the rebar can be immediately cut.

Figure 9 shows an example of the change over time of the position index during a cutting operation. In the example of Figure 9 (A), in the period until time t1 when braking begins, the cutting blade 111 moves from the fully open position to the fully closed position at a generally constant speed. After braking begins at time t1, the cutting blade 111 continues to move toward the fully closed position while slowing down due to braking. Note that in Figure 9 (A), the change in the position index after time t1 is depicted as being linear in a simplified manner, but the actual change will differ from this. The same applies to Figure 9 (B) described below.

Time t2 shown in FIG. 9(A) is the time when a predetermined period has elapsed since time t1. "PDS" in FIG. 9(A) is the "reference value" used in the judgment of step S15 in FIG. 8. In the example of FIG. 9(A), the amount of change PD in the position index (i.e., the braking speed index) during the predetermined period from time t1 to time t2 is greater than the reference value PDS. Therefore, in this case, step S15 in FIG. 8 is judged as Yes, and braking is continued.

In contrast, in the example shown in FIG. 9(B), the amount of change PD in the position index during the predetermined period from time t1 to time t2 is smaller than the reference value PDS. Therefore, in this case, the answer to step S15 in FIG. 8 is No, and braking is interrupted.

In this way, when the rebar, which is the object to be cut, is being cut, if the braking speed index, which is an index showing the operating speed of the cutting blade 111 after braking of the cutting blade 111 has begun, is smaller than a predetermined reference value PDS, the control unit 530 is configured to interrupt braking of the cutting blade 111 and continue the cutting operation. This makes it possible to quickly resolve the condition even if, for some reason, the rebar becomes difficult to break during braking.

The second embodiment will be described. Below, differences from the first embodiment will be mainly described, and explanations of points in common with the first embodiment will be omitted as appropriate. This embodiment differs from the first embodiment in the content of the processing executed by the control board 500. The series of processing shown in FIG. 10 is executed by the control board 500 of this embodiment in place of the series of processing shown in FIG. 5.

In the first step S21, the cutting operation of the cutting blades 111 is started, similar to step S01 in FIG. 5. After this, the pair of cutting blades 111 move in a direction approaching each other.

In step S22 following step S21, the position acquisition unit 520 acquires a position index in the same manner as in step S04 in FIG. 5. In step S23 following step S22, it is determined whether the position index acquired in step S22 is a value corresponding to a predetermined braking start position. The "braking start position" is a position that is preset as the position of the cutting blade 111 where braking should start. In this embodiment, the braking start position is set as a fixed position that does not vary depending on the speed of the cutting blade 111. If the current position of the cutting blade 111 has not yet reached the braking start position, the processing from step S22 onwards is executed again while the cutting blade 111 continues to operate. When the current position of the cutting blade 111 reaches the braking start position, the process proceeds from step S23 to step S24. In step S24, the speed acquisition unit 510 acquires a speed index in the same manner as in step S02 in FIG. 5.

In step S25 following step S24, the control unit 530 performs a process of provisionally determining the braking force. In this embodiment, the parameter indicating the braking force is the value of the short brake duty, specifically, a value indicating the proportion of the period during which a part of the coil of the electric motor 400 is short-circuited. The braking force provisionally determined in step S25 may always be the same fixed value, but may also be set each time depending on the value of the speed index obtained in step S24.

In step S26 following step S25, the control unit 530 performs a process of calculating the braking distance index, similar to step S03 in FIG. 5. If the braking force provisionally determined in step S25 is set each time according to the value of the speed index, etc., the method of calculating the braking distance index in step S26 may be changed as appropriate according to the set value of the braking force.

In step S27 following step S26, the control unit 530 performs a process of calculating the predicted position, similar to step S05 in FIG. 5. In this embodiment, the value obtained by adding the braking distance index to the position index corresponding to the braking start position, which is a fixed value, is calculated as the predicted position. The predicted position calculated in this manner differs depending on the operating speed of the cutting blade 111.

In step S28 following step S27, it is determined whether the predicted position calculated in step S27 matches a preset target position. In this embodiment, the value of the position index corresponding to the position where the pair of cutting blades 111 are in contact with each other, i.e., the position where they are fully closed, is set as the target position. When the absolute value of the difference between the predicted position and the target position is small enough to be below a preset threshold value, it is determined that the predicted position matches the target position.

If the predicted position matches the target position, the process proceeds to step S29. In step S29, the value of the braking force provisionally determined in step S25 is determined as the final braking force. In step S31 following step S29, the control unit 530 starts braking the cutting blade 111. The control unit 530 performs a short brake process so that the braking force determined in step S29 is generated. After that, the operating speed of the cutting blade 111 gradually decreases. In many cases, the rebar breaks before the cutting blade 111 reaches the target position.

In step S28, if the predicted position does not match the target position, the process proceeds to step S30. In step S30, a process of adjusting the braking force, which is a provisionally determined value, is performed. For example, if the predicted position is ahead of the target position (i.e., if the cutting blade 111 goes too far in the closing direction), the braking force is adjusted to be stronger than before. Conversely, if the predicted position is before the target position (i.e., if the cutting blade 111 stops before it is completely closed), the braking force is adjusted to be weaker than before. In step S30, the braking force is adjusted so that the position of the cutting blade 111 at the time when braking is completed matches the target position. It is preferable that the correspondence relationship between the difference between the predicted position and the target position and the adjustment amount of the braking force is measured in advance and stored, for example, as a map.

After the processing of step S30 is performed, the processing from step S29 onwards is executed, and the cutting blade 111 is braked. In this embodiment, the braking force is adjusted in step S30 as necessary, so that the cutting blade 111 always stops at the target position.

Figure 11 shows an example of the relationship between the position index (horizontal axis) and the speed index (vertical axis) when braking is performed. Line L21 is an example of the case where braking is initiated from a state where the speed index is relatively large. Line L22 is an example of the case where braking is initiated from a state where the speed index is smaller than line L21. Line L23 is an example of the case where braking is initiated from a state where the speed index is even smaller than line L22.

In both examples, braking begins when the current position of the cutting blade 111 reaches the braking start position. However, the braking force is adjusted as described above according to the speed index. The smaller the speed index immediately before braking begins, the smaller the braking force is set to, and therefore the smaller the slope in the graph of FIG. 11 becomes. As a result of adjusting the braking force, in both examples, the cutting blade 111 stops when the position index reaches a value corresponding to the target position (in this example, the fully closed position).

In this way, the control unit 530 according to this embodiment determines the braking force required to brake the cutting blade 111 based on the speed index. Specifically, the braking force of the cutting blade 111 is determined so that a predicted position calculated by adding the travel distance of the cutting blade 111 corresponding to the braking distance index to a predetermined braking start position becomes a predetermined target position. This makes it possible to stop the cutting blade 111 at the target position regardless of the operating speed of the cutting blade 111.

The present embodiment has been described above with reference to specific examples. However, the present disclosure is not limited to these specific examples. Design modifications to these specific examples made by a person skilled in the art are also included within the scope of the present disclosure as long as they have the features of the present disclosure. The elements of each of the above-mentioned specific examples, as well as their arrangement, conditions, shape, etc., are not limited to those exemplified and can be modified as appropriate. The elements of each of the above-mentioned specific examples can be combined in different ways as appropriate, as long as no technical contradictions arise.

10: Cutting device 111: Cutting blade 400: Electric motor 420: Rotation sensor 510: Speed acquisition unit 520: Position acquisition unit 530: Control unit

Claims (12)

An electrically operated cutting device,
A pair of cutting blades that sandwich and cut the object to be cut;
an electric motor that generates a driving force necessary for the operation of the cutting blade;
A control unit that controls the operation of the electric motor;
A speed acquisition unit that acquires a speed index, which is an index indicating the operating speed of the cutting blade,
The control unit is
A cutting device that performs braking of the cutting blade based on the speed indication. The control unit is
The cutting device of claim 1 , further comprising a step of determining when to initiate braking of the cutting blade based on the speed indicator. A position acquisition unit that acquires a position index, which is an index indicating a current position of the cutting blade,
The control unit is
Calculating a braking distance index based on the speed index, the braking distance index being an index indicating a distance traveled by the cutting blade from when braking of the cutting blade is started until when the cutting blade is stopped during operation of the cutting blade;
The cutting device of claim 2 , further comprising a step of determining a timing for initiating braking of the cutting blade based on the position index and the braking distance index. The control unit is
4. The cutting device according to claim 3, wherein the timing for starting braking of the cutting blade is determined so that a predicted position calculated by adding a moving distance of the cutting blade corresponding to the braking distance indicator to a current position of the cutting blade corresponding to the position indicator becomes a predetermined target position. The cutting device according to claim 4, wherein the target position is a position where the pair of cutting blades are in a closed state. The control unit is
The cutting device of claim 1 , further comprising a step of determining a braking force required for braking the cutting blade based on the speed index. A position acquisition unit that acquires a position index, which is an index indicating a current position of the cutting blade,
The control unit is
Calculating a braking distance index based on the speed index, the braking distance index being an index indicating a distance traveled by the cutting blade from when braking of the cutting blade is started until when the cutting blade is stopped during operation of the cutting blade;
The cutting device of claim 6 , further comprising: determining the braking force based on the position indicator and the braking distance indicator. The control unit is
The cutting device according to claim 7, wherein the braking force of the cutting blade is determined so that a predicted position calculated by adding a moving distance of the cutting blade corresponding to the braking distance index to a predetermined braking start position becomes a predetermined target position. The cutting device according to claim 8, wherein the target position is a position where the pair of cutting blades are in a closed state in contact with each other. A speed sensor is further provided to detect a rotation speed of the electric motor.
The cutting device according to claim 2 , wherein the speed acquisition unit acquires the speed index based on the rotation speed. A speed sensor is further provided to detect a rotation speed of the electric motor.
The cutting device according to claim 6 , wherein the speed acquisition unit acquires the speed index based on the rotation speed. When the object to be cut is being cut,
When a braking speed index, which is an index indicating the operating speed of the cutting blade after braking of the cutting blade is started, is smaller than a predetermined reference value,
The cutting device according to claim 1 , wherein the control unit interrupts braking of the cutting blade and continues the cutting operation.