JP2013086543A - Power-assisted carriage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance safety of an electric power-assisted carriage having a driving force assisted by an electric motor.SOLUTION: The power-assisted carriage includes: a vehicle body frame 1 on which a load can be placed; drive wheels 11 which are provided in the vehicle body frame 1; an operating handle 5 which is subjected to an operator's pushing operation so that a drive force can be input into the vehicle body frame 1; a torque sensor 6 which detects drive torque, acting on the vehicle body frame 1, by making the operating handle 5 subjected to the pushing operation; an electric motor 15 which imparts an assisting force, corresponding to the drive torque detected by the torque sensor 6, to the drive wheels 11; and a controller 30 which computes the assisting force imparted to the drive wheel 11 and which supplies an electric current, corresponding to the assisting force, to the electric motor 15. The controller 30 stops the supply of the electric current to the electric motor 15 in the case where the torque sensor 6 detects the predetermine drive torque when the power is turned on.

Description

  The present invention relates to an electric assist cart whose driving force is assisted by an electric motor.

  Generally, when a heavy load is placed on a cart used in a factory or the like, an operator needs to push the cart with a large force at the start of transportation, which is a heavy labor.

  As a countermeasure against this, Patent Document 1 proposes an electric assist hand cart that detects the force of an operator pushing the cart and is provided with auxiliary power corresponding to human power by an electric motor. In this electrically assisted hand cart, the pushing force of the worker at the time of forward movement and backward movement is assisted according to the operation of the hand frame by the worker.

JP 2006-290319 A

  However, in the electrically assisted hand cart described in Patent Document 1, when the power is turned on while a force is applied to the hand frame, auxiliary power corresponding to the magnitude of the force applied to the hand frame is driven from the electric motor. It is given to the ring. Therefore, for example, when the worker leans against the hand frame, or when the loaded load is in contact with the hand frame, auxiliary power that is not intended by the worker at the same time as the power is turned on. May occur.

  The present invention has been made in view of the above-described problems, and an object thereof is to improve the safety of an electric assist cart.

  The present invention relates to an electric assist cart capable of traveling with an assist force applied to a driving force applied by an operator, a vehicle body frame on which a load can be placed, a drive wheel provided on the vehicle body frame, a work An operation unit that is pressed by an operator and capable of inputting a driving force to the body frame, a torque detection unit that detects a driving torque that acts on the body frame when the operation unit is pressed, and the torque detection unit An electric motor that applies an assist force according to the drive torque detected by the drive wheel to the drive wheel, and a controller that calculates an assist force applied to the drive wheel and supplies a current corresponding to the assist force to the electric motor And when the torque detector detects a predetermined driving torque when the power is turned on, the controller Characterized by stopping the supply of current to the motor.

  In the present invention, when the torque detector detects a predetermined drive torque when the electric assist cart is turned on, the controller stops supplying current to the electric motor. Therefore, at the same time as the power is turned on, an assist force not intended by the operator is not applied to the drive wheels. Therefore, the safety of the electric assist cart can be improved.

1 is a perspective view of an electric assist cart according to an embodiment of the present invention. It is a side view in FIG. It is a front view in FIG. It is a control block diagram of an electric assist cart. It is a flowchart figure explaining the control at the time of starting in an electric assist cart. It is a flowchart figure explaining the fail safe operation | movement in an electrically assisted cart.

  Embodiments of the present invention will be described below with reference to the drawings.

  First, an electric assist cart 100 according to an embodiment of the present invention will be described with reference to FIGS.

  The electric assist cart 100 is used for transporting heavy objects, for example, in a factory. The electric assist cart 100 travels with the driving force applied by the operator being applied with an assist force due to the rotation of the electric motor 15 described later.

  The electric assist cart 100 includes a vehicle body frame 1, a cargo bed 3 provided on the vehicle body frame 1 on which a load can be placed, and an operation handle 5 as an operation unit capable of inputting driving force from two left and right positions of the vehicle body frame 1. And a pair of drive wheels 11 provided on the left and right sides of the vehicle body frame 1 with a space therebetween, and a pair of universal wheels 12 mounted on the vehicle body frame 1 and provided behind the drive wheels 11. The driving wheel 11 is a front wheel of the electric assist cart 100, and the universal wheel 12 is a rear wheel of the electric assist cart 100.

  The vehicle body frame 1 is a frame in which square pipe materials are combined. The body frame 1 is erected on a flat surface portion 1a on which a load is placed via a loading platform 3, a lower projecting portion 1b projecting at a lower portion of the flat surface portion 1a, and an upper rear end of the flat surface portion 1a. And a standing portion 1c.

  The loading platform 3 is a flat plate with an edge provided so as to cover the upper portion of the plane portion 1 a in the body frame 1. A luggage is placed directly on the loading platform 3. The loading platform 3 may be a flat plate without an edge. Further, instead of the cargo bed 3, a roller conveyor may be installed on the vehicle body frame 1, and the luggage may be placed via the roller conveyor.

  As shown in FIG. 2, an elevating device 2 is provided between the body frame 1 and the loading platform 3. The lifting device 2 lifts and lowers the loading platform 3 with respect to the vehicle body frame 1 by an electric lifting cylinder 2a (see FIG. 4). For example, when a heavy object is placed on the loading platform 3 and the vehicle body frame 1 sinks with respect to the drive wheels 11 and the free wheels 12 by a suspension device 20 described later, the lifting device 2 raises the loading platform 3 and the road surface. It is possible to adjust the height of the loading platform 3 to the constant.

  The electric elevating cylinder 2a is electrically connected to a controller 30 described later, and expands and contracts based on a command signal from the controller 30. The electric elevating cylinder 2a is an electrohydraulic linear actuator that includes a hydraulic pump driven by a motor and expands and contracts by the pressure of hydraulic oil discharged from the hydraulic pump.

  As shown in FIG. 1, the operation handle 5 is an inverted U-shaped handle that is pressed by an operator. The left and right ends of the operation handle 5 are connected to the standing portion 1 c in the vehicle body frame 1. As a result, the driving force input by the operator operating the operation handle 5 is transmitted to the vehicle body frame 1.

  The drive wheel 11 is a small wheel provided so as not to be steered in the front-rear direction of the body frame 1. A pair of drive wheels 11 are provided in the vicinity of the front end of the body frame 1. The drive wheels 11 are fixed to the lower projecting portion 1b of the body frame 1 so as to be movable up and down.

  The universal wheel 12 is a small wheel that always faces in the traveling direction when traveling. The universal wheel 12 is turned by the frictional resistance with the road surface and is steered so as to face the traveling direction. The universal wheel 12 is fixed to the lower projecting portion 1b of the body frame 1 so as to be movable up and down.

  The electric assist cart 100 includes four subframes 4 that can move up and down with respect to the body frame 1 and a suspension device 20 that suspends the drive wheels 11 and the universal wheels 12 via the subframes 4.

  Four subframes 4 are provided corresponding to the respective wheels of the pair of drive wheels 11 and the pair of universal wheels 12. Two subframes 4 are arranged on the left and right sides of the body frame 1. A drive wheel 11 or a universal wheel 12 is rotatably fixed to the lower surface of each subframe 4.

  The suspension device 20 includes four suspension arms 22 that support the left and right subframes 4 on the body frame 1 so that the left and right subframes 4 can move up and down, and a spring damper 23 provided between the body frame 1 and the left and right subframes 4.

  Four suspension arms 22 are provided for each subframe 4. Each suspension arm 22 is connected to the body frame 1 and the left and right subframes 4 so as to be rotatable about a horizontal axis, and the suspension arms 22 are parallel links that support the subframe 4 so that the subframe 4 can move in parallel with the body frame 1. Configure the mechanism.

  Thereby, even if the sub-frame 4 moves up and down with respect to the vehicle body frame 1, the posture of the sub-frame 4 does not change, and the positional relationship (alignment) between the drive wheels 11 and the free wheels 12 is kept constant. Therefore, even if the subframe 4 moves up and down, one of the drive wheel 11 and the free wheel 12 is suppressed from floating from the road surface.

  The spring damper 23 absorbs and reduces the vertical vibrations of the drive wheels 11 and the free wheels 12 due to road surface irregularities and the like, and suppresses vibrations from the road surface being transmitted to the vehicle body frame 1. The spring damper 23 includes a coil spring 23a and a damper 23b, and expands and contracts as the subframe 4 moves up and down.

  The coil spring 23a supports the load received by the subframe 4 by the spring force, and expands and contracts as the subframe 4 moves up and down.

  As the damper 23b expands and contracts, the hydraulic oil filled therein passes through a damping valve (not shown) and generates a damping force that suppresses vibration of the subframe 4.

  The suspension device 20 is not limited to the above-described configuration, and may have another configuration as long as the posture of the subframe 4 with respect to the vehicle body frame 1 is maintained.

  The electric assist cart 100 is detected by a torque sensor 6 as a pair of torque detectors that detect driving torque acting on each of the left and right portions of the vehicle body frame 1 when the operation handle 5 is pressed, and detected by the torque sensor 6. A pair of electric motors 15 for applying an assist force according to the drive torque applied to each drive wheel 11 and an assist force applied to the drive wheel 11 are calculated and a current corresponding to the assist force is supplied to the electric motor 15. Controller 30, a pair of brakes 16 that brake the rotation of each drive wheel 11, and an operation panel 29 provided with various switches that can be operated by an operator.

  The torque sensor 6 is electrically connected to the controller 30 and outputs a voltage corresponding to the detected magnitude of the drive torque to the controller 30. The torque sensor 6 is connected to the operation handle 5 and the vehicle body frame 1 and is twisted by the driving force input from the operation unit and transmits the driving force to the vehicle body frame 1, and the torsion bar is twisted. And a potentiometer (not shown) that outputs a voltage corresponding to the torsion bar, and detects driving torque based on torsion of the torsion bar. By changing the torsion bar provided in the torque sensor 6, it is also possible to change the operation feeling by the operator according to the loaded load of the carriage without changing other members.

  The electric motor 15 is electrically connected to the controller 30 and rotates according to an electrical signal input from the controller 30. As shown in FIG. 3, the electric motor 15 is disposed inside the drive wheel 11 and applies assist force to the drive wheel 11. The left and right electric motors 15 are provided coaxially with each other, and are arranged in series between the pair of drive wheels 11. The electric motor 15 includes a transmission (not shown) that reduces the rotation and transmits it to the drive wheels 11.

  The brake 16 is disposed between the output shaft of the electric motor 15 and the drive wheel 11. The brake 16 has a brake solenoid 16a (see FIG. 4) capable of switching between a braking state and a non-braking state. The brake 16 fixes the drive wheel 11 so as not to rotate when switched to the braking state.

  The brake solenoid 16 a is electrically connected to the controller 30 and is switched according to the current supplied from the controller 30. In a state where no current flows through the brake solenoid 16a, the brake 16 maintains the drive wheels 11 in a braking state. On the other hand, when a current flows through the brake solenoid 16a, the brake 16 switches the driving wheel 11 to the non-braking state.

  The controller 30 is mounted on the vehicle body frame 1 together with a power supply device (not shown) and other electronic devices (not shown). The controller 30 controls the electric assist cart 100 and includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and an I / O interface (input / output interface). It consists of a microcomputer. The RAM stores data in the processing of the CPU, the ROM stores a control program of the CPU in advance, and the I / O interface is used for input / output of information with the connected device. Control of the electric assist cart 100 is realized by operating a CPU, a RAM, and the like according to a program stored in the ROM.

  The controller 30 operates with power supplied from the power supply device. When the voltage of the power supply device suddenly drops, the controller 30 stops all control and puts the CPU in the sleep state. When the power supply device is a 24V battery, for example, when the voltage drops to about 18V, the CPU is set in the sleep state. Thereby, the controller 30 can be protected from a rapid drop in the voltage of the power supply device.

  The controller 30 performs control to cause the left and right electric motors 15 to generate assist force corresponding to the driving torque detected by the left and right torque sensors 6 to move the electric assist cart 100 forward or backward, as well as go straight, turn, bend Assist force to be applied.

  The controller 30 drives the electric motor 15 by PWM (Pulse Width Modulation) control. The controller 30 has a pair of current detectors 15 a that detect current values actually flowing to the left and right electric motors 15. Thereby, feedback control of the electric motor 15 becomes possible.

  As illustrated in FIG. 4, the controller 30 includes a voltage determination unit 31 that determines the magnitude of the voltage output from the torque sensor 6 and the time (continuous time) during which the voltage is continuously output, and the voltage determination unit 31. And a current control unit 32 capable of stopping the supply of current to the electric motor 15 based on the determination.

  As shown in FIG. 1, the operation panel 29 is disposed on the back surface of the standing portion 1 c in the vehicle body frame 1 and is electrically connected to the controller 30. The operation panel 29 is not limited to this position because it may be provided at a position that can be operated and visually recognized by the operator. The operation panel 29 includes a brake release switch 24 for switching the brake solenoid 16a, a loading platform elevating switch 25 for operating the electric elevating cylinder 2a, and an indicator 27 capable of displaying various fail modes.

  The brake release switch 24 is a switch that can switch the brake solenoid 16a by an operator's operation. When the operator operates the brake release switch 24, a current flows through the brake solenoid 16a, and the driving wheel 11 is switched to the non-braking state. Thereby, the electric assist cart 100 can travel.

  The loading platform raising / lowering switch 25 is a switch for operating the electric lifting cylinder 2a by an operator's operation. When the operator operates the loading platform elevating switch 25, the electric elevating cylinder 2a expands and contracts. Thereby, the loading platform 3 moves up and down with respect to the vehicle body frame 1.

  The indicator 27 indicates a state in which a part of the function is stopped for fail-safe in the electric assist cart 100 so that the operator can visually recognize the state. The indicator 27 includes a first indicator 27a, a second indicator 27b, and a third indicator 27c.

  The first indicator 27a indicates the lightest fail mode. The first indicator 27a lights up when the maximum value of the current supplied to the electric motor 15 is limited. The state in which the first indicator 27a is lit is the first fail mode.

  The second indicator 27b indicates the lightest fail mode next to the first indicator 27a. The second indicator 27b is lit when the supply of current to the electric motor 15 is stopped or when the supply of current to the electric lift cylinder 2a is stopped. The state in which the second indicator 27b is lit is the second fail mode.

  The third indicator 27c indicates the heaviest fail mode. The third indicator 27c is lit when all functions in the electric assist cart 100 are stopped. That is, in the state where the third indicator 27c is lit, in the electric assist cart 100, the supply of current to the electric motor 15 and the electric lift cylinder 2a is stopped and the supply of current to the brake solenoid 16a is stopped. As a result, the brake 16 is switched to the braking state. The state in which the third indicator 27c is lit is the third fail mode.

  The first to third fail modes are set only when one of the fail modes is not entered and the capacity of the power supply device remains to be able to control all functions in the electric assist cart 100. The Each fail mode is canceled by turning off the electric assist cart 100 once and restarting.

  Next, the driving operation in the electric assist cart 100 will be described.

  When the operator pushes the operation handle 5 with both hands in parallel, the electric assist cart 100 moves straight forward. In this case, the driving force input to the vehicle body frame 1 when the operation handle 5 is pressed is substantially the same at the left and right ends of the operation handle 5. Therefore, the drive torques detected by the left and right torque sensors 6 are substantially the same.

  When the left and right torque sensors 6 detect the same drive torque, the controller 30 commands the left and right electric motors 15 to apply the same assist force to the left and right drive wheels 11. Thereby, the same assist force is applied to the left and right drive wheels 11.

  Therefore, the electric assist cart 100 moves straight forward with the assist force of the electric motor 15 applied to the driving force applied by the operator.

  When the electric assist cart 100 is moved straight backward, the direction in which the operation handle 5 is pushed is reversed, and the rotation direction of the electric motor 15 is reversed, and the other actions are the same as in the case of moving straight forward. is there.

  On the other hand, when the left and right forces pushing the operation handle 5 are made different by the operator, the electric assist cart 100 turns left or right. At this time, the assist force applied to the left and right drive wheels 11 differs between the left and right electric motors 15.

  Specifically, for example, when the electric assist cart 100 is turned leftward, the force with which the operator pushes the operation handle 5 with the right hand is larger than the force with which the operation handle 5 is pushed with the left hand. Therefore, the drive torque detected by the right torque sensor 6 is larger than the drive torque detected by the left torque sensor 6.

  Thereby, the controller 30 commands the assist force applied from the right electric motor 15 to the drive wheels 11 to be larger than the assist force applied from the left electric motor 15 to the drive wheels 11. As a result, the assist force applied to the right drive wheel 11 is greater than the assist force applied to the left drive wheel 11.

  Since the left and right torque sensors 6 can detect the drive torque steplessly, the magnitude of the assist force can be controlled according to the force with which the operator presses the operation handle 5.

  Next, with reference to FIG. 5, the control at the time of starting in the electric assist cart 100 will be described.

  Steps S101 to S107 are executed in a startup routine immediately after the controller 30 is powered on. Specifically, steps S101 to S105 stop supplying the current to the electric motor 15 when the torque sensor 6 detects a predetermined drive torque when the controller 30 is powered on. . The predetermined drive torque at this time is a drive torque having a magnitude detected by the torque sensor 6 when the operation handle 5 is pressed from a neutral position where the operation handle 5 is not operated.

  In step S <b> 101, the voltage output from the left and right torque sensors 6 is read into the controller 30.

  In step S102, the deviation between the output voltage from the torque sensor 6 at the neutral position and the voltage output from the left and right torque sensors 6 is calculated. The output voltage from the torque sensor 6 at the neutral position is set to the middle value of the voltage range that the torque sensor 6 can output.

  Here, since the torque sensor 6 can output a voltage in the range of 0 to 5 [V], the output voltage from the torque sensor 6 at the neutral position is set to 2.5 [V]. Therefore, in step S102, it is calculated how much the voltage output from the left and right torque sensors 6 is different from 2.5 [V] which is the voltage at the neutral position.

  Actually, since the output voltage varies depending on the device, after assembling the electric assist cart 100, the output voltage of the torque sensor 6 when the operation handle 5 is located in the neutral position is measured, and the measured value is obtained. It is set as the output voltage from the torque sensor 6 in the neutral position. Below, the case where the output voltage from the torque sensor 6 in the neutral position is set to 2.5 [V] will be described.

  In step S103, the voltage determination unit 31 determines whether or not the deviation calculated in step S102 is greater than or equal to the first set value. The first set value at this time is set to a voltage having a magnitude that fluctuates due to noise or the like even if the operator does not operate the operation handle 5.

  In other words, the first set value is set to a voltage that can clearly determine that the operation handle 5 has been operated when the voltage output from the torque sensor 6 exceeds the first set value. The first set value is set to 0.3 [V], for example. That is, the voltage determination unit 31 determines that the deviation is greater than or equal to the first set value when the voltage output from the torque sensor 6 exceeds the range of 2.5 [V] ± 0.3 [V]. .

  If it is determined in step S103 that the voltage deviation calculated in step S102 is greater than or equal to the first set value, the process proceeds to step S104.

  In step S104, the voltage determination unit 31 determines whether or not the state where the voltage deviation calculated in step S102 is equal to or greater than the first set value has elapsed for the first set time or more. The first set time at this time is set to 100 [ms], for example.

  If it is determined in step S104 that the voltage deviation is equal to or greater than the first set value, the process proceeds to step S105 to enter the second fail mode. On the other hand, if it is determined in step S104 that the voltage deviation is not less than the first set value, the process returns.

  In step S <b> 105, the current control unit 32 stops supplying current to the left and right electric motors 15 based on the determination by the voltage determination unit 31. At this time, the current control unit 32 is directed to both the left and right electric motors 15 even when only one of the torque sensors 6 continuously outputs a voltage equal to or higher than the first set value for the first set time. Stop the output of current. Thereby, the assist of the driving force by the electric motor 15 in the electric assist cart 100 is stopped.

  Here, in the conventional electric assist cart, for example, when the worker is leaning against the operation handle or when the loaded load is in contact with the operation handle, the operator is turned on at the same time as the power is turned on. There is a possibility that an unintended assist force may be generated.

  On the other hand, in the electric assist cart 100, as described above, when the torque sensor 6 detects a predetermined drive torque when the power is turned on, the controller 30 applies power to the left and right electric motors 15. Stop supplying current. Therefore, at the same time as the power is turned on, an assist force not intended by the operator is not applied to the drive wheels. Therefore, the safety of the electric assist cart 100 can be improved.

  In the second fail mode, the second indicator 27b is turned on. Therefore, the operator can be notified that the second fail mode is entered. An operator who knows that the second fail mode has been entered causes the operation handle 5 to be positioned at the neutral position from the state in which the operation handle 5 is pressed, and then restarts the electric assist cart 100 to thereby provide the second fail mode. The mode can be canceled.

  On the other hand, if it is determined in step S103 that the voltage deviation calculated in step S102 is smaller than the first set value, the process proceeds to step S106.

  In step S106, the voltage determination unit 31 determines whether or not a state in which the voltage deviation calculated in step S102 is smaller than the first set value has elapsed for the second set time or more. The second set time at this time is set to 100 [ms], for example.

  If it is determined in step S106 that the voltage deviation is smaller than the first set value, the process proceeds to step S107. On the other hand, if it is determined in step S106 that the voltage deviation is smaller than the first set value, the process returns.

  In step S107, assist control in the electric assist cart 100 is started, and the start-up routine is exited. As a result, the electric assist cart 100 is normally activated and operable.

  Next, with reference to FIG. 6, the fail safe operation in the electric assist cart 100 will be described.

  Steps S <b> 201 to S <b> 206 are to stop a part of the function of the electric assist cart 100 when the left and right torque sensors 6 output a voltage outside the range output during normal use. Specifically, when the torque sensor 6 detects a large driving torque compared to the upper limit value of the range that is normally used or a small driving torque compared to the lower limit value, the current is supplied to the electric motor 15. It will stop.

  In step S <b> 201, the voltage output from the torque sensor 6 is read into the controller 30 in accordance with the detected magnitudes of the left and right drive torques.

  In step S202, the voltage determination unit 31 determines whether or not the voltage output from the torque sensor 6 is greater than or equal to a second set value that is larger than the upper limit value of the voltage when normally used.

  Here, the torque sensor 6 can output a voltage in a range of 0 to 5 [V], but is used in a range of 2.5 [V] to ± 0.6 [V] in a neutral position during normal use. It is done. Therefore, the second set value is set to 4.0 [V], which is larger than 3.1 [V], which is the upper limit value of the voltage when normally used.

  If it is determined in step S202 that the voltage output from the torque sensor 6 is greater than or equal to the second set value, the process proceeds to step S203. On the other hand, when it determines with the voltage output from the torque sensor 6 being smaller than a 2nd setting value in step S202, it transfers to step S204.

  In step S203, it is determined whether or not a voltage equal to or higher than the second set value determined in step S202 is continuously output for the second set time. The second set time at this time is set to a time that does not erroneously determine the noise included in the output voltage from the torque sensor 6. For example, the second set time is set to 250 [ms].

  If it is determined in step S203 that the time during which the voltage equal to or higher than the second set value has been continuously output is equal to or longer than the second set time, the process proceeds to step S206 to enter the second fail mode. On the other hand, when it is determined in step S203 that the time during which the voltage equal to or higher than the second set value is continuously output is less than the second set time, the process proceeds to step S204.

  In step S204, the voltage determination unit 31 determines whether or not the voltage output from the torque sensor 6 is equal to or smaller than a third set value that is smaller than the lower limit value of the voltage when normally used.

  As described above, the torque sensor 6 is used in the range of 2.5 [V] to ± 0.6 [V] at the neutral position during normal use. Therefore, the third set value is set to 1.0 [V], which is smaller than 1.9 [V] which is the lower limit value of the voltage when normally used.

  If it is determined in step S204 that the voltage output from the torque sensor 6 is equal to or lower than the third set value, the process proceeds to step S205. On the other hand, if it is determined in step S204 that the voltage output from the torque sensor 6 is greater than the third set value, the process returns.

  In step S205, it is determined whether or not a voltage equal to or lower than the third set value determined in step S204 is continuously output for the second set time.

  In step S205, when it is determined that the time during which the voltage equal to or lower than the third set value is continuously output is equal to or longer than the second set time, the process proceeds to step S206, and the second fail mode is set. On the other hand, if it is determined in step S205 that the time during which the voltage equal to or higher than the third set value is continuously output is shorter than the second set time, the process returns.

  In step S <b> 206, the current control unit 32 stops supplying current to the left and right electric motors 15 based on the determination by the voltage determination unit 31. At this time, even if the current control unit 32 outputs a voltage not less than the second set value or not more than the third set value from only one torque sensor 6 for the second set time, The output of current to both electric motors 15 is stopped. Thereby, the assist of the driving force by the electric motor 15 in the electric assist cart 100 is stopped.

  As described above, the current control unit 32 has a voltage that is larger than the second set value that is larger than the upper limit value of the voltage that is normally used or a voltage that is smaller than the third set value that is smaller than the lower limit value. When the torque sensor 6 outputs continuously for the second set time, the supply of current to the electric motor 15 is stopped. Thereby, when the voltage of the magnitude | size outside the range output at the time of normal use is output to the left and right torque sensors 6, the application of the assist force in the electric assist cart 100 is stopped. Therefore, the safety of the electric assist cart 100 can be improved.

  At this time, the current control unit 32 gradually reduces the current that can be supplied to the electric motor 15 by so-called slope control, and eventually stops. Thus, it is possible to prevent a large deceleration shock from occurring in the electric assist cart 100 due to a sudden decrease in the assist force.

  According to the above embodiment, the following effects are obtained.

  If the torque sensor 6 detects a predetermined drive torque when the power is turned on, the controller 30 stops supplying current to the left and right electric motors 15. Therefore, at the same time as the power is turned on, an assist force not intended by the operator is not applied to the drive wheels. Therefore, the safety of the electric assist cart 100 can be improved.

  The present invention is not limited to the above-described embodiment, and it is obvious that various modifications can be made within the scope of the technical idea.

DESCRIPTION OF SYMBOLS 100 Electric assist cart 1 Body frame 3 Loading platform 5 Operation handle 6 Torque sensor 11 Driving wheel 12 Free wheel 15 Electric motor 15a Current detection unit 16 Brake 16a Brake solenoid 24 Brake release switch 25 Cargo lift switch 27 Indicator 30 Controller 31 Voltage determination unit 32 Current controller

Claims (6)

An electric assist cart capable of traveling with an assist force applied to a driving force applied by an operator,
A body frame on which luggage can be placed;
Drive wheels provided on the vehicle body frame;
An operation unit that is pressed by an operator and capable of inputting a driving force to the body frame;
A torque detection unit that detects a drive torque that acts on the vehicle body frame when the operation unit is pressed;
An electric motor that applies assist force to the drive wheels according to the drive torque detected by the torque detector;
A controller for calculating an assist force applied to the drive wheel and supplying a current corresponding to the assist force to the electric motor;
The controller is configured to stop supplying current to the electric motor when the torque detection unit detects a predetermined driving torque when the power is turned on.   2. The predetermined driving torque is a driving torque having a magnitude that is detected by the torque detection unit when a pressing operation is performed from a neutral position in which the operation unit is not operated. The electric assist cart described in 1. The torque detector is a torque sensor that outputs a voltage corresponding to the magnitude of the detected drive torque,
The controller is
When the voltage output from the torque sensor is different from the voltage when the operation unit is in the neutral position by more than a first set value for a first set time, the predetermined A voltage determination unit that determines that the drive torque has been detected;
The electric assist cart according to claim 2, further comprising: a current control unit that stops supply of current to the electric motor based on the determination of the voltage determination unit.   The controller supplies current to the electric motor when the torque detector detects a driving torque that is large compared to the upper limit value of the range that is normally used or a driving torque that is small compared to the lower limit value. The electric assist cart according to claim 1, wherein the electric assist cart is stopped. The torque detector is a torque sensor that outputs a voltage corresponding to the magnitude of the detected drive torque,
The controller is
A voltage that is greater than the second set value, which is larger than the upper limit value of the voltage when normally used, or less than the third set value, which is smaller than the lower limit value, is continuously output from the torque sensor for the second set time. A voltage determination unit for determining that
The electric assist cart according to claim 4, further comprising: a current control unit that stops supply of current to the electric motor based on the determination of the voltage determination unit.   The electric assist cart according to claim 5, wherein the current control unit stops the electric current supplied to the electric motor by gradually decreasing the electric current.

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