JP3510494B2 - Electric lawn mower - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric lawn mower, and more particularly, to a control of the number of revolutions of a motor at the time of lapping for polishing a reel blade. It relates to an electric lawn mower. 2. Description of the Related Art Conventionally, when the sharpness of a reel blade has deteriorated due to wear in an electric lawn mower, an abrasive is applied to the reel blade and the position of the fixed blade is adjusted to fix the reel blade to the reel blade. There has been used a method of strengthening the contact with the blade, reversing the rotation direction of the reel blade, and periodically performing lapping for polishing the blade edge of the reel blade with an abrasive and a fixed blade. As this kind of electric lawn mower, there is known one equipped with a drive circuit as described in, for example, Japanese Patent Application Laid-Open No. 5-30832. In this electric lawn mower, a direct current motor is used as a drive source, a lawn mowing is performed by supplying a voltage of 24 V at the time of forward rotation, and a voltage of 12 V is supplied at the time of lapping, whereby the reel blade is rotated at a lower speed than at the time of forward rotation. It is configured to be able to do. However, in this conventional electric lawn mower, when the motor is rotated in the reverse direction for lapping, the load applied to the reel blade with the progress of polishing gradually decreases, and gradually decreases. In this case, since the rotation speed is increased, the abrasive applied to the reel blade is scattered, and there is a problem that lapping efficiency is poor. Accordingly, the present invention provides an electric lawn mower which prevents the abrasive from being scattered by absorbing the fluctuation of load when the reel blade is reversed for lapping and rotating the reel blade at a constant speed to prevent the abrasive from scattering. The purpose is to improve the polishing efficiency of the blade. [0006] The electric lawnmower of the present invention, which has been made to achieve the above object, has a reel blade rotated by an AC motor, and applies an abrasive to the reel blade. When the polishing is performed on the reel blade using the fixed blade, the rotation speed of the reel blade during the reverse rotation is set to be lower than the rotation speed during the normal rotation. In the electric lawn mower, the rotation speed of the motor at the time of reverse rotation is controlled to a low speed by phase control, and the rotation speed of the motor does not fluctuate even when a load fluctuates during the grinding of the reel blade. In this manner, a phase control circuit of a back electromotive force feedback system for feeding back the back electromotive force generated in the AC motor is provided. According to this electric lawn mower, when lapping the reel blade, the degree of contact between the fixed blade and the reel blade is adjusted, an abrasive is applied to the reel blade, and the rotation direction of the motor is reversed. After the switching, the lapping is performed by driving the AC motor at a low speed via the speed switching circuit. In addition, at the time of reverse rotation for lapping, the drive current for the AC motor can be greatly suppressed by the phase control, and the rotational speed at the time of reverse rotation can be greatly reduced as compared with the rotational speed at the time of forward rotation. . And, since the phase control is performed by feeding back the back electromotive force so that the rotation speed of the motor does not fluctuate even if the load fluctuates due to the progress of the lapping, from the beginning to the end of the lapping,
The reverse rotation speed of the motor can be kept almost constant.
As a result, it is possible to prevent the occurrence of a situation in which the number of revolutions of the reel blade increases during the lapping and the abrasive is scattered and the lapping efficiency is reduced, and the reel blade can be efficiently polished. Next, an embodiment of the present invention will be described. As shown in FIG. 1, the electric lawn mower 1 according to the embodiment includes a wheel 3 in the front, a roller 5 in the rear, and a lawn mower body 7 having a reel blade, a fixed blade, and an AC motor. A dust case 9 attached to the rear of the lawn mower body 7, a handle 11 extending rearward and obliquely upward from the lawn mower body 7, and a handle 1
1 and a grip 13 attached to the upper end. As shown in FIG. 2, a reel blade 1 rotatably driven by a belt 17 wound around a pulley 15 attached to a rotating shaft of an AC motor, as shown in FIG.
9 and a fixed blade 2 which is attached below the reel blade 19 so as to be adjustable in height and cooperates with the reel blade 19 to cut grass.
1 is provided. The fixed blade 21 is detachably fixed by a screw 27 to an adjustment plate 25 which is vertically rotated with a screw 23 fixing the rear end side as a fulcrum. The adjusting plate 25 is turned up and down by adjusting the tightening state of the adjusting screw 29 attached to the distal end side.
And it is in a state of being urged in a direction to be rotated downward by a compression spring 31 mounted so as to surround the adjustment screw 29. As shown in FIG. 3, a motor drive switch 35 is attached to the grip portion 33 at the upper end of the grip 13.
Is attached. By turning on / off the motor drive switch 35, the AC motor is driven to execute lawn mowing. In addition, grip 13
The lock-off lever 37 below the grip portion 33 has a rotation direction of the AC motor in a forward rotation direction (a direction for rotating the reel blade 19 counterclockwise in FIG. 2) and a reverse rotation direction (the reel blade 19 in FIG. 2). To rotate clockwise)
And a forward / reverse switch 39 for switching between the two. Motor drive switch 35 and forward / reverse switch 39
Are configured to switch between driving / stopping the motor and switching between normal rotation and reverse rotation by a slide operation. In addition, near the forward / reverse changeover switch 39, a controller 50 for controlling the rotation speed of the motor at low speed during reverse rotation is provided.
Is provided. Next, a drive circuit including the controller 50 employed in the electric lawn mower 1 of the present embodiment will be described. The drive circuit has a configuration as shown in the circuit diagram of FIG. In the drawing, the motor drive switch 35 is denoted by SW1. A indicates an armature, and F1 and F2 indicate fields, respectively. SW2 and SW3 correspond to the above-described forward / reverse switch 39 and are linked to each other. And
SW2 and SW3 connect the COM terminal and the NC terminal as shown by a solid line when the forward / reverse changeover switch 39 is operated in the forward direction, and a single point in the drawing when the forward / reverse switch 39 is operated in the reverse direction. It is configured to operate simultaneously to connect the COM terminal and the NO terminal like a chain line. In FIG. 4, a portion surrounded by a dotted line is a controller 50. The controller 50 includes resistors R1 to R6, diodes D1 and D2, capacitors C1 and
C2, thyristors Q1, Q2 and potentiometer VR
1 is provided. The resistor R1 is provided to limit the value of the current flowing through the thyristor Q2. Further, the resistor R2 and the capacitor C2 constitute a temporary delay circuit for delaying the phase when the thyristor Q2 is turned on during reverse rotation. The resistors R2 and R5 and the potentiometer VR1 are provided as voltage-dividing resistors that determine the gate voltage of the thyristor Q2. The diode D1, the capacitor C1, and the resistor R4 are provided as a noise removing circuit for stabilizing the switching operation of the thyristor Q2. The resistor R3 is connected to the thyristor Q1.
Is provided for setting the gate voltage. The back electromotive force generated in the armature A is fed back to the cathode of the thyristor Q1 via SW2. Note that a resistor R6 and a diode D2
Is provided for circuit protection of the controller 50, and a resistor R6 having a resistance value of about 10 ohms is used. With the above circuit configuration, the motor drive switch 35 (SW) is operated in a state where the forward / reverse switch 39 (SW2, SW3) is operated to the forward rotation side (the connection state between COM and NC).
When 1) is turned on, the drive current flows between the P1 terminal and the P2 terminal to the armature A without passing through the controller 50, and causes the AC motor to rotate normally. At this time, the present embodiment is designed so that the number of rotations of the motor is about 1800 rpm. On the other hand, a forward / reverse switch 39 (SW2, S
When the motor drive switch 35 (SW1) is turned on in a state in which W3) is operated on the reverse rotation side (the connection state between COM and NO), the drive current passes through the controller 50 and flows only to the armature A in the direction of the arrow shown in the figure. Flow and reverse the AC motor. At this time, the resistor R2 and the capacitor C2
The timing at which the switching thyristor Q2 is turned on by the action of the primary delay circuit constituted by
The time constant of the first-order lag is set such that the phase is further delayed by 以上 or more with respect to the half-wave of the alternating current. As a result, the timing at which the thyristor Q1 is turned on is delayed by the phase control by the primary delay circuit, and the number of rotations of the motor is reduced to about 400 to 5
It is designed to be about 00 rpm. Since the back electromotive force generated when the armature A runs idle is fed back to the cathode terminal of the thyristor Q1, when the load applied to the motor is large, the back electromotive force is small. When the load applied to the motor decreases, the back electromotive force increases, so the timing at which the thyristor Q1 turns on is relatively delayed. As a result, the motor is controlled by the feedback of the back electromotive force so that the motor rotates reversely at a substantially constant rotation speed. According to the present embodiment, if the tip of the reel blade 19 becomes dull due to abrasion as a result of adopting the above configuration, an abrasive is applied to the reel blade 19 with a brush or the like. After the adjustment screw 29 is tightened to increase the contact between the fixed blade 21 and the reel blade 19, the forward / reverse switch 39 is switched to the reverse rotation, and the motor drive switch 35 is turned on. By this operation, the reel blade 19 is reversed at a low speed rotation of about 400 to 500 rpm, and the fixed blade 2 is rotated.
1 is polished through an abrasive. In the initial stage of the grinding, the contact between the reel blade 19 and the fixed blade 21 is strong, so that the load on the motor is large and the back electromotive force is small. Add a lot. However, as grinding progressed, reel blade 1
If the contact between the fixed blade 9 and the fixed blade 21 becomes loose, the load on the motor becomes small and the back electromotive force becomes large. Therefore, the on-time of the thyristor Q1 becomes relatively short, and the drive current to the motor becomes small. As a result, the reel blade 1 during lapping
The reverse rotation speed of No. 9 is substantially constant from the beginning to the end of the lapping, and the rotational speed does not increase with the progress of the lapping. Therefore, there is no possibility that the abrasive is scattered during the lapping and the polishing efficiency is reduced. Further, even if the adjustment of the rubbing strength between the fixed blade 21 and the reel blade 19 in the lapping is different depending on the operator, the lapping can be stably performed at a rotation speed close to a predetermined rotation speed by the back electromotive force feedback control. Work can be done. The embodiment of the present invention has been described above. However, the present invention is not limited to this embodiment, and it is possible to adopt various forms without departing from the gist of the present invention. Of course. As described above, according to the present invention, during lapping, the number of revolutions can be kept low by phase control, and the number of revolutions at the time of reverse rotation does not fluctuate due to back electromotive force feedback control. From the beginning to the end of the process, the scattering of the abrasive is small, the polishing of the reel blade can be reliably performed, and the polishing efficiency can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view showing an overall configuration of an electric lawn mower according to an embodiment. FIG. 2 is an enlarged sectional view of a main part showing a configuration around a reel blade in the electric lawnmower according to the embodiment. FIG. 3 is an enlarged sectional view of a main part showing a configuration of a grip in the electric lawnmower according to the embodiment. FIG. 4 is a circuit diagram showing a configuration of a motor drive circuit in the electric lawnmower according to the embodiment. [Description of Signs] 1 ... Electric lawn mower, 3 ... Wheel, 5 ... Roller, 7 ... Lawn mower body, 9 ... Dust case,
11 ... handle, 13 ... grip, 15 ...
Pulley, 17 ... belt, 19 ... reel blade, 21
... Fixed blade, 23 ... Screw, 25 ... Adjust plate, 27 ... Screw, 29 ... Adjustment screw, 31
... compression spring, 33 ... grip part, 35 (SW1) ... motor drive switch, 37
..Lock-off lever, 39 (SW2, SW3)
Forward / reverse switch, 50 ... controller, A ...
Armature, C1, C2 ... condenser, D1, D
2 ... Diode, F1, F2 ... Field, R
1 to R6: resistor, Q1, Q2: thyristor,
VR1 ... potentiometer.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-30832 (JP, A) JP-A 64-6829 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) A01D 34/46-34/62 B24B 3 / 00,3 / 55

Claims (1)

(57) [Claim 1] A reel blade which is rotated by an AC motor, and an abrasive is applied to the reel blade and the reel blade is rotated in reverse to polish the reel blade using a fixed blade. When doing
In the electric lawn mower provided with a speed switching circuit for setting the rotation speed of the reel blade at the time of the reverse rotation to a lower speed than the rotation speed at the time of the normal rotation, the rotation speed of the motor at the time of the reverse rotation is provided as the speed switching circuit. A phase control of a back electromotive force feedback system for feeding back a back electromotive force generated in the AC motor so that the speed is reduced by the phase control and the rotation speed of the motor does not fluctuate even if the load fluctuates during the grinding of the reel blade. An electric lawn mower comprising a circuit.