Electric assist cart

An electric assist cart includes: a drive wheel provided in a body frame; a control handle used by an operator to input a driving force to the body frame; a torque sensor that detects a driving torque applied to the body frame from the control handle; a controller that computes an assisting force applied to the drive wheel based on the driving torque; an electric motor that applies the assisting force to the drive wheel; a brake that brakes the drive wheel and switches from a braking state to an unbraking state when a predetermined electric current flows; and a brake release switch manipulated by an operator to allow the controller to instruct the predetermined electric current to flow to the brake, wherein the controller maintains the braking state of the brake even when the brake release switch is manipulated without turning on power, and power is then turned on.

RELATED APPLICATIONS

The present application is a National Phase of International Application Number PCT/JP2012/075687, filed Oct. 3, 2012, which claims priority to Japanese Application Number 2011-225975, filed Oct. 13, 2011.

TECHNICAL FIELD

This invention relates to an electric assist cart in which a driving force is assisted by an electric motor.

BACKGROUND ART

In general, when a heavy burden is loaded on a handcart used in a factory or the like, an operator necessarily pushes the handcart with a strong force at the start of delivery. This is a hard work.

As a countermeasure for this problem, JP 2006-290319 A proposes an electric assist hand-push cart in which an operator's force applied to the handcart is detected, and an assistant power corresponding to the human power is applied from an electric motor. In this electric assist hand-push cart, a force applied by an operator in forward and backward movements is assisted depending on the handling of a hand-push frame body from an operator.

In addition, in JP 2002-67970 A, there is disclosed a cargo handling vehicle having an electronic brake capable of switching between a braking state and an unbraking state. In this cargo handling vehicle, the electronic brake can switch between the braking state and the unbraking state using a button switch pressed by an operator.

SUMMARY OF INVENTION

However, in the electronic brake disclosed in JP 2002-67970 A, when a manipulation is performed for switching the electronic brake to the unbraking state without turning on power, and power is then turned on, the electronic brake may simultaneously switch to the unbraking state. If this electronic brake is applied to the cart disclosed in JP 2006-290319 A, for example, when a cart is parked on a sloped road, the cart may slide down as soon as power is turned on.

It is therefore an object of this invention to improve safety of the electric assist cart.

According to one aspect of this invention, an electric assist cart that can travel by applying an assisting force in addition to a driving force applied by an operator, includes: a body frame where a burden can be loaded; a drive wheel provided in the body frame; a handling portion pushed and handled by an operator to input a driving force to the body frame; a torque detection part that is configured to detect a driving torque applied to the body frame by pushing and handling the handling portion; a controller that is configured to compute an assisting force applied to the drive wheel based on the driving torque detected by the torque detection part; an electric motor that is configured to apply the assisting force computed by the controller to the drive wheel; a brake that is configured to brake the drive wheel and switches from a braking state to an unbraking state when a predetermined electric current flows; and a brake release switch manipulated by an operator to allow the controller to instruct the predetermined electric current to flow to the brake. The controller maintains the braking state of the brake even when the brake release switch is manipulated without turning on power, and power is then turned on.

DESCRIPTION OF EMBODIMENTS

First, an electric assist cart100according to an embodiment of the invention will be described with reference toFIGS. 1 to 4.

The electric assist cart100is used to carry a heavy burden, for example, in a factory or the like. The electric assist cart100travels by virtue of an assisting force caused by rotation of an electric motor15described below in addition to a driving force applied from an operator.

The electric assist cart100includes a body frame1, a deck3provided on the body frame1to load a burden, a control handle5as a handling portion by which a driving force can be input from both left and right portions of the body frame1, a pair of drive wheels11provided in both left and right sides of the body frame1with an interval in a travel direction, and a pair of universal wheels12installed in the body frame1in rear of the drive wheels11. The drive wheels11are front wheels of the electric assist cart100, and the universal wheels12are rear wheels of the electric assist cart100.

The body frame1is a frame obtained by combining rectangular pipes. The body frame1includes a planar portion1awhere a burden is loaded using a deck3, a lower projecting portion1bprojecting in the lower side of the planar portion1a, and an erected portion1cerected on the upper portion of the rear end of the planar portion1a.

The deck3is a rimmed flat plate provided to cover the top of the planar portion1aof the body frame1. A burden is directly loaded on the deck3. The deck3may be an unrimmed flat plate. In addition, instead of the deck3, a roller conveyor may be installed on the body frame1, and a burden may be loaded using the roller conveyor.

As illustrated inFIG. 2, a lift unit2is provided between the body frame1and the deck3. The lift unit2lifts or lowers the deck3against the body frame1using an electric lift cylinder2a(refer toFIG. 4). For example, when a heavy burden is loaded on the deck3, and the body frame1sinks to the drive wheel11and the universal wheel12by means of a suspension unit20described below, the lift unit2may lift the deck3to constantly maintain a height of the deck3from the road surface.

The electric lift cylinder2ais electrically connected to a controller30described below and expands or contracts in response to an instruction signal from the controller30. The electric lift cylinder2ais an electric hydraulic linear actuator provided with a hydraulic pump driven by a motor so as to expand or contract by a pressure of the hydraulic fluid discharged from the hydraulic pump.

The control handle5is a reversed U-shaped handle pushed and handled by an operator as illustrated inFIG. 1. Both left and right ends of the control handle5are connected to the erected portion1cof the body frame1. As a result, a driving force input when an operator handles the control handle5is transmitted to the body frame1.

The drive wheel11is a small wheel unturnably provided in a longitudinal direction of the body frame1. A pair of left and right drive wheels11is provided in the vicinity of the front end of the body frame1. The drive wheels11are fixed to the lower projecting portion1bof the body frame1movably upward and downward.

The universal wheel12is a small wheel directed to a movement direction at all times when the cart travels. The universal wheel12turns by a frictional resistance with the road surface to steer the cart toward a movement direction. The universal wheel12is fixed to the lower projecting portion1bof the body frame1movably upward and downward.

The electric assist cart100includes four subsidiary frames4movable upward and downward against the body frame1and a suspension unit20that suspends the driving wheels11and the universal wheels12from the subsidiary frame4.

Four subsidiary frames4are provided for a pair of drive wheels11and a pair of universal wheels12. Two subsidiary frames4are arranged in each of the left and right sides of the body frame1. The drive wheel11or the universal wheel12is rotatably fixed to the lower surface of each subsidiary frame4.

The suspension unit20includes four suspension arms22for supporting the left and right subsidiary frames4of the body frame1movably upward and downward and spring dampers23provided between the body frame1and the left and right subsidiary frames4.

Four suspension arms22are provided for a single subsidiary frame4. Both ends of each suspension arm22are connected to the body frame1and the left and right subsidiary frames4pivotably around a horizontal axis, so that the suspension arm22serves as a parallel link mechanism that supports the subsidiary frame4against the body frame1to allow for parallel displacement.

As a result, even when the subsidiary frame4is lifted or lowered against the body frame1, a posture of the subsidiary frame4does not change, and a positional relationship (alignment) between the drive wheel11and the universal wheel12is maintained constantly. Therefore, even when the subsidiary frame4is lifted or lowered, it is possible to suppress one of the drive wheel11and the universal wheel12from floating from the road surface.

The spring damper23absorbs or dampens vertical vibration in the drive wheel11and the universal wheel12caused by an unprepared road surface or the like and suppresses the vibration from the road surface from being transmitted to the body frame1. The spring damper23has a coil spring23aand a damper23b. The spring damper23expands or contracts as the subsidiary frame4is lifted or lowered.

The coil spring23asupports a load applied to the subsidiary frame4by virtue of its spring force. The coil spring23aexpands or contracts as the subsidiary frame4is lifted or lowered.

A hydraulic fluid filled in the damper23bpasses through a damping valve (not illustrated) as the coil spring23aexpands or contracts, so that the damper23bgenerates a damping force for suppressing vibration of the subsidiary frame4.

It is noted that a configuration of the suspension unit20is not limited to that described above, but other configurations may be possible if a posture of the subsidiary frame4against the body frame1is maintained.

The electric assist cart100includes: a torque sensor6serving as a pair of torque detection parts for detecting a driving torque applied to each of the left and right portions of the body frame1as the control handle5is pushed and handled; a controller30that computes the assisting force applied to the drive wheel11depending on a driving torque detected by the torque sensor6; a pair of electric motors15for applying an assisting force computed by the controller30to each drive wheel11; a pair of brakes16that brakes rotation of each drive wheel11; and a console29provided with various switches that can be manipulated by an operator.

The torque sensor6is electrically connected to the controller30and outputs an electric signal corresponding to the detected driving torque to the controller30. The torque sensor6includes: a torsion bar (not illustrated) connected between the control handle5and the body frame1and twisted by the driving force input from the handling portion while the driving force is transmitted to the body frame1; and a potentiometer (not illustrated) that outputs an electric signal corresponding to the torsion of the torsion bar. The torque sensor6detects the driving torque based on the torsion of the torsion bar. By changing the torsion bar provided in the torque sensor6, it may also be possible to change a handling sense of an operator depending on a live load of the cart without changing other members.

The electric motor15is electrically connected to the controller30and is rotated depending on the electric signal input from the controller30. As illustrated inFIG. 3, the electric motor15is arranged inside the drive wheel11to apply an assisting force to the driving wheel11. The left and right electric motors15are coaxially provided and arranged in series between a pair of the drive wheels11. The electric motor15has a transmission (not illustrated) that transmits rotation to the drive wheel11by decelerating the rotation.

The brake16is arranged between an output shaft of the electric motor15and the drive wheel11. The brake16has a brake solenoid16a(refer toFIG. 4) that can switch between a braking state and an unbraking state. When the brake16switches to the braking state, the brake16fixes the drive wheel11to a rotation disable state.

The brake solenoid16ais electrically connected to the controller30and switches depending on a predetermined electric current supplied in response to an instruction from the controller30. While no predetermined electric current flows to the brake solenoid16a, the brake16maintains the drive wheel11in the braking state. That is, while no power is applied to the electric assist cart100, the drive wheel11is maintained in the braking state by the brake16.

Meanwhile, when a predetermined electric current flows to the brake solenoid16a, the brake16switches the drive wheel11to the unbraking state. This predetermined electric current has a magnitude of an excitation current capable of switching the brake solenoid16a. In addition, the brake solenoid16afeeds back the magnitude of the applied electric current to the controller30.

The controller30is mounted on the body frame1along with a power supply (not illustrated) or other electronic devices (not illustrated). The controller30performs control of the electric assist cart100and is a microcomputer having a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), and an input/output (I/O) interface. The RAM stores data for the processing of the CPU, and the ROM stores a control program or the like of the CPU in advance. The I/O interface is used to input or output information from/to a connected device. Control of the electric assist cart100is implemented by operating the CPU or the RAM based on the program stored in the ROM.

The controller30is operated based on the power supplied from the power supply. When a voltage of the power supply abruptly decreases, the controller30stops overall control and sets the CPU to a sleep state. Assuming that a battery of 24 V is used as the power supply, the CPU is set to the sleep state, for example, when the voltage drops to, approximately, 18 V. As a result, it is possible to protect the controller30from an abrupt drop of the voltage of the power supply.

The controller30performs control such that the assisting forces for the left and right electric motors15are generated depending on the driving torque detected by the left and right torque sensors6in order to the move the electric assist cart100forward or backward and apply an assisting force in a straight movement, a turning movement, and a curve movement.

The controller30drives the electric motor15on a pulse width modulation (PWM) control basis. The controller30has a pair of electric current detection parts15afor detecting an electric current value flowing through the left and right electric motors15in practice. As a result, it is possible to perform a feedback control for the electric motor15.

As illustrated inFIG. 4, the controller30has an electric current determination part31that determines a magnitude of the electric current flowing to the electric motor15and a time (continuous time) for flowing the electric current and an electric current control part32that stops or restricts supply of the electric current to the electric motor15based on the determination of the electric current determination part31.

The console29is arranged on the rear face of the erected portion1cof the body frame1as illustrated inFIG. 1. The console29is electrically connected to the controller30. The position of the console29is not particularly limited if the console29is provided in a position where an operator can manipulate and see it. The console29includes: a brake release switch24for switching the brake solenoid16a; a deck up/down switch25for controlling the electric lift cylinder2a; and an indicator27that can display various failure modes.

The brake release switch24is a switch capable of switching the brake solenoid16abased on an operator's manipulation. As an operator manipulates the brake release switch24, the controller30instructs a predetermined electric current to flow to the brake solenoid16a, and the drive wheel11switches to an unbraking state. As a result, the electric assist cart100can travel.

The deck up/down switch25is a switch for operating the electric lift cylinder2abased on an operator's manipulation. As an operator manipulates the deck up/down switch25, the electric lift cylinder2aexpands or contracts. As a result, the deck3is lifted or lowered against the body frame1.

The indicator27indicates a state that a part of the functions stop in order to allow an operator to recognize it for a fail-safe capability in the electric assist cart100. The indicator27includes a first indicator27a, a second indicator27b, and a third indicator27c.

The first indicator27aindicates the most insignificant failure mode. The first indicator27ais turned on when the maximum value of the electric current supplied to the electric motor15is restricted. A state that the first indicator27ais turned on is a first failure mode.

The second indicator27bindicates the less insignificant failure mode than that of the first indicator27a. The second indicator27bis turned on when supply of the electric current to the electric motor15stops, or supply of the electric current to the electric lift cylinder2astops. A state that the second indicator27bis turned on is a second failure mode.

The third indicator27cindicates the most significant failure mode. The third indicator27cis turned on when overall functions of the electric assist cart100stop. That is, while the third indicator27cis turned on, supply of the electric current to the electric motor15and the electric lift cylinder2astops, and supply of the electric current to the brake solenoid16astops in the electric assist cart100. Therefore, the brake16switches to the braking state. A state that the third indicator27cis turned on is a third failure mode.

The first and the second failure modes are set only when the electric assist cart100does not enter any failure mode, and a capacity of the power supply remains such that overall functions of the electric assist cart100can be controlled. The third failure mode is set only when the electric assist cart100does not enter the second failure mode, and a capacity of the power supply remains such that an excitation electric current capable of switching the brake solenoid16acan be generated. In addition, each failure mode is released by cutting off the power of the electric assist cart100once and reactivating it.

Next, a driving operation of the electric assist cart100will be described.

When an operator pushes the control handle5with both hands in parallel, the electric assist cart100moves forward straightly. In this case, the driving force input to the body frame1by pushing the control handle5is approximately equal between the left and right sides of the control handle5. Therefore, the driving torques detected by left and right torque sensors6are also approximately equal to each other.

If the left and right torque sensors6detect an equal driving torque, the controller30instructs that the assisting force is equally applied to the left and right driving wheels11from the left and right electric motors15. As a result, the assisting force is equally applied to the left and right drive wheels11.

Therefore, the electric assist cart100moves forward straightly by virtue of the assisting force of the electric motor15in addition to the driving force applied by an operator.

It is noted that, when the electric assist cart100moves backward straightly, the pushing direction of the control handle5and the rotation direction of the electric motor15are reversed, and other actions are similar to those of the case where the electric assist cart100moves forward straightly.

Meanwhile, when an operator applies the pushing force to the control handle5differently between the left and right sides, the electric assist cart100turns left or right. In this case, the assisting force is differently applied to the left and right drive wheels11from the left and right electric motors15.

Specifically, for example, when the electric assist cart100turns left, the pushing force applied to the control handle5by a right hand of an operator is stronger than the pushing force applied to the control handle5by a left hand of an operator. Therefore, the driving torque detected by the right torque sensor6is higher than the driving torque detected by the left torque sensor6.

As a result, the controller30instructs that the assisting force applied from the right electric motor15to the drive wheel11is stronger than the assisting force applied from the left electric motor15to the drive wheel11. As a result, the assisting force applied to the right drive wheel11becomes relatively stronger than the assisting force applied to the left drive wheel11.

It is noted that the magnitude of the assisting force can be controlled depending on the pushing force applied by an operator to the control handle5because the left and right torque sensors6can detect the driving torque steplessly.

Next, a control operation for starting the electric assist cart100will be described with reference toFIG. 5.

In steps S101to S103, a start-up routine immediately after power is supplied to the controller30is executed.

In step S101, it is determined whether or not the brake release switch24is manipulated. If it is determined in step S101that the brake release switch24is not manipulated, the process advances to step S102. Otherwise, if it is determined in step S101that the brake release switch24is manipulated, the process advances to step S103.

In step S102, the controller30starts the control operation. As a result, the electric assist cart100can travel by virtue of the driving force of an operator and the assisting force of the electric motor15. As the controller30starts the control operation in step S102, the process returns.

In step S103, the control operation of the controller30stops. As a result, even when the brake release switch24is manipulated, the controller30does not output an instruction for flowing an electric current to the brake solenoid16a. Therefore, the brake16remains in the braking state even when the brake release switch24is manipulated without turning on power, and power is then turned on.

Therefore, the controller30maintains the braking state of the brake16even when power is turned on while the brake release switch24is manipulated. Therefore, the brake16does not switch to the unbraking state as soon as the power of controller30is turned on. Therefore, it is possible to improve safety of the electric assist cart100.

It is noted that a fact that the operation of the controller30stops, and the braking state of the brake16is maintained is notified to an operator by turning on the first to third indicators27a,27b, and27cat the same time. The first to third indicators27a,27b, and27cserve as a notification device. The notification device is not limited to such a configuration, but any other configuration may be employed if a fact that the operation of the controller30stops is notified to an operator in a visual or auditory sense.

As a result, a user can recognize a fact that power is turned on while the brake release switch24is manipulated. The state that the control operation of the controller30stops is released as a user switches to a state that the brake release switch24is not manipulated, and a restart operation is performed.

Next, a fail-safe operation in the electric assist cart100will be described with reference toFIG. 6.

In step S201, it is determined whether or not the brake release switch24is manipulated. If it is determined in step S201that the brake release switch24is manipulated, the process advances to step S202. Meanwhile, if it is determined in step S201that the brake release switch24is not manipulated, the process returns.

In step S202, the electric current values of the left and right brake solenoids16aare read to the controller30.

In steps S203and S204, a part of the functions of the electric assist cart100stops when an electric current excessively flows to the brake solenoid16aover a normal use range.

In step S203, the electric current determination part31determines whether or not an electric current having a magnitude equal to or larger than a first setting value flows to any one of the left and right brake solenoids16a. In this case, the first setting value is set to be larger than the maximum value of the electric current normally supplied to the brake solenoid16a. For example, the first setting value is set to 2.0 [A] when an excitation current flowing to the brake solenoid16ain a normal use is set to 1.5 [A].

If it is determined in step S203that the electric current flowing to the brake solenoid16ais equal to or larger than the first setting value, the process advances to step S204. Meanwhile, if it is determined in step S203that the electric current value flowing to the brake solenoid16ais smaller than the first setting value, the process advances to step S206.

In step S204, the electric current determination part31determines whether or not the electric current equal to or larger than the first setting value determined in step S203continuously flows for a first setting time. In this case, the first setting time is set to a time for which the brake solenoid16acan be protected when the electric current having a magnitude equal to or larger than the first setting time flows. Since the first setting time is a time for which an excessive electric current having a magnitude that does not flow in a normal use flows, the first setting time is set to a very short time. For example, the first setting time is set to 50 [ms].

If it is determined in step S204that the electric current equal to or larger than the first setting value continuously flows for the first setting time, the process advances to step S205, and the mode switches to the third failure mode.

In step S205, the electric current control part32stops output of the electric current to the left and right brake solenoids16a. In this case, the electric current control part32stops output of the electric current to both the left and right brake solenoids16aeven when the electric current equal to or larger than the first setting value continuously flows to any one of the brake solenoids16afor the first setting time. As a result, both the left and right brakes16have the braking state.

In the third failure mode, the supply of the electric current to the brake solenoid16astops. Therefore, the brake16switches to the braking state, and the supply of the electric current to the electric motor15and the electric lift cylinder2astops. As a result, it is possible to prevent an operator from moving the electric assist cart100while an excessive electric current flows to the brake solenoid16athat switches the braking state of the brake16. In addition, by turning on the third indicator27c, it is possible to notify an operator of a fact that the electric assist cart100has the third failure mode. Therefore, it is possible to improve safety of the electric assist cart100.

Meanwhile, if it is determined in step S204that the continuous time for which the electric current equal to or larger than the first setting value continuously flows is shorter than the first setting time, the process advances to step S206.

In steps S206and S207, a part of the functions of the electric assist cart100stop when the electric current does not flow to the brake solenoid16aas instructed from the controller30.

In step S206, the electric current determination part31determines whether or not the electric current having a magnitude equal to or smaller than a second setting value flows to any one of the left and right brake solenoids16a. In this case, the second setting value is set to be smaller than the minimum value of the electric current at which the brake solenoid16acan switch the brake16from the unbraking state to the braking state. For example, the second setting value is set to 0.1 [A] when the minimum value of the electric current at which the brake solenoid16acan switch is set to 0.5 [A].

If it is determined in step S206that the electric current value flowing to the brake solenoid16ais equal to or smaller than the second setting value, the process advances to step S207. Meanwhile, if it is determined in step S206that the electric current value flowing to the brake solenoid16ais larger than the second setting value, the process returns.

In step S207, the electric current determination part31determines whether or not the electric current equal to or smaller than the second setting value determined in step S206continuously flows for a second setting time. In this case, the second setting time is set to be longer than the first setting time. For example, the second setting time is set to 1 [s].

If it is determined in step S207that the time for which the electric current equal to or larger than the second setting value continuously flows is equal to or longer than the second setting time, the process advances to step S205, and the mode switches to the third failure mode.

In this manner, when the electric current does not flow to the brake solenoid16aas instructed from the controller30, the supply of power to the left and right brake solenoids16astops, and the third indicator27cis turned on. Therefore, it is possible to prevent a state that the electric current does not flow to the brake solenoid16afrom being continuously maintained and notify an operator of a fact that the electric assist cart100enters the third failure mode. Therefore, it is possible to improve safety of the electric assist cart100.

Meanwhile, if it is determined in step S207that the continuous time for which the electric current equal to or larger than the second setting value continuously flows is shorter than the second setting time, the process returns.

According to the aforementioned embodiment, the following effects can be obtained.

The controller30does not output an instruction for flowing the electric current to the brake solenoid16aeven when the brake release switch24is manipulated without turning on power, and power is then turned on in this state. Therefore, the brake16remains in the braking state. That is, the brake16does not switch to the unbraking state as soon as power is supplied to the controller30. As a result, it is possible to improve safety of the electric assist cart100.

Embodiments of this invention were described above, but the above embodiments are merely examples of applications of this invention, and the technical scope of this invention is not limited to the specific constitutions of the above embodiments.

For example, in the flowchart ofFIG. 6, two different failure states are detected, and the control for determining a corresponding failure mode is executed through a single flow. Instead, a control operation for detecting every single failure state may be executed through an independent flow, and a flow may be further provided for determining the failure mode if there is a failure state in any one of the detection results.

This application claims priority based on Japanese Patent Application No. 2011-225975 filed with the Japan Patent Office on Oct. 13, 2011, the entire contents of which are incorporated into this specification.

The embodiments of this invention in which an exclusive property or privilege is claimed are defined as follows: