Steering control of a personal transporter

The present application is a continuation-in-part of U.S. application Ser. No. 09/325,976, filed Jun. 4, 1999, itself a continuation in part of U.S. application Ser. No. 08/479,901, filed Jun. 7, 1995, now issued as U.S. Pat. No. 5,975,225, which is a continuation in part of U.S. application Ser. No. 08/384,705, filed Feb. 3, 1995, now issued as U.S. Pat. No. 5,971,091, which is a continuation in part of U.S. application Ser. No. 08/250,693, filed May 27, 1994, now issued as U.S. Pat. No. 5,701,965, which in turn is a continuation in part of U.S. application Ser. No. 08/021,789, filed Feb. 24, 1993, now abandoned, all of which applications are hereby incorporated by reference.

FIELD OF THE INVENTION

The present application is directed to modes of powering and controlling a motorized personal transporter.

BACKGROUND OF THE INVENTION

Dynamically stabilized transporters refer to personal vehicles having a control system that actively maintains the stability of the transporter while the transporter is operating. The control system maintains the stability of the transporter by continuously sensing the orientation of the transporter, determining the corrective action to maintain stability, and commanding the wheel motors to make the corrective action. If the transporter loses the ability to maintain stability, such as through the failure of a component, the rider may experience discomfort at the sudden loss of balance. For some dynamically stabilized transporters, such as those described in U.S. Pat. No. 5,701,965, which may include a wheelchair for transporting a disabled individual down a flight of stairs, it is essential, for the safety of the operator, that the vehicle continue to operate indefinitely after detection of a failed component. For other dynamically stabilized transporters, however, the operator may readily be capable of safely dismounting from the transporter in case of component failure. It is desirable that control modes be provided for such vehicles from which the operator is capable of safely dismounting in case of mishap.

SUMMARY OF THE INVENTION

In accordance with preferred embodiments of the present invention, there is provided an intelligent battery pack. The battery pack has a battery container sealed against moisture and a plurality of battery blocks housed within the battery container. Additionally, the battery pack has a plurality of sensors, each of which is for monitoring a characteristic of a distinct battery block. Finally, the battery pack has a processor disposed within the battery container for generating a fault flag for transmission to a circuit external to the battery container on occurrence of a critical fault in at least one of the battery blocks within the battery container.

In accordance with alternate embodiments of the invention, the battery pack may also have an electrical connector in communication with the processor for providing electrical and signal communication between the processor and circuitry exterior to the container. At least one of the plurality of sensors may be a temperature sensor in thermal contact with at least one of the plurality of battery blocks. The battery container may include battery cells additional to the plurality of battery blocks or a second sensor for monitoring a characteristic of the at least one of a battery block, the second sensor also being in signal communication with the connector. The second sensor may be a voltage sensor generating a signal characteristic of the voltage of the battery block.

In accordance with further alternate embodiments of the invention, the processor of the intelligent battery pack of claim 1 may also transmit an identifying characteristic of the battery pack, where the identifying characteristic may be a battery cell type, a number of battery cells, or a serial number.

In accordance with another aspect of the invention, a rider detector is provided for detecting the presence of a rider on a base of a two-wheeled dynamically balanced transporter. The rider detector has a mat covering the base of the transporter, the mat itself having a mat edge attached to the base, a mat wall having a bottom portion and a top portion, the bottom portion attached to the mat edge, and a mat cover having a top surface and a bottom surface, with the mat cover attached to the mat wall and supported above the base. Finally, the rider detector has a switch mounted on the base and positioned below the bottom surface of the mat cover, the switch changing from a first state to a second state when the mat cover is displaced into contact with the switch. Additionally, a rigid plate may be disposed under the bottom surface of the mat cover.

In accordance with yet another aspect of the invention, a statically unstable motorized transporter is provided that has a base for supporting a rider and a pair of laterally disposed wheels for supporting the base above a surface. The transporter has a motorized drive for driving the pair of wheels, a pitch sensor coupled to the base, the sensor generating a signal indicative of a transporter pitch and a controller for commanding the motorized drive based only on the transporter pitch.

In accordance with other aspects of the invention, a steering device is provided for a motorized vehicle having a handlebar. The steering device has a rotation sensor, such as a potentiometer, coupled to the handlebar for generating a steering command upon rotation, a rotatable grip for imparting rotary motion to the rotation sensor, and a torsional spring for restoring the rotatable grip to a neutral position upon release of the grip. Alternatively, the steering device may have a rotation sensor coupled to a structure fixed with respect to the user support for generating a steering command upon sensing rotation, a flexible shaft coupled to the rotation sensor, a thumb button for imparting bending to the flexible shaft in such a manner as to provide rotation measured by the rotation sensor, and a spring member for providing a force countering bending of the flexible shaft.

In accordance with alternate embodiments of the invention, the steering device has lever with a top surface substantially flush with the handlebar, the lever being movable by a palm of a hand of the user about a pivot axis substantially parallel to the underlying surface and substantially parallel to the direction of travel of the vehicle. The steering device also has a restoring member for opposing motion of the lever from a neutral position and a sensor for sensing motion of the lever from the neutral position and for generating in response thereto a steering command.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a side view of a personal vehicle lacking a stable static position, for supporting or conveying a subject who remains in a standing position thereon;

FIG. 2

shows a block diagram of the system architecture of an embodiment of the present invention;

FIG. 3

shows a top view of the power source with the top cover removed;

FIG. 4

is a block diagram of the power drive module of an embodiment of the present invention;

FIG. 5

is an electrical model of a motor;

FIG. 6

a

shows a top view of a rider detector in accordance with an embodiment of the present invention;

FIG. 6

b

shows a cut side view of the embodiment of

FIG. 6

a;

FIG. 7

shows an exploded view of a yaw input device in accordance with an embodiment of the present invention;

FIG. 8

a

is a cross-sectional top view of an elastomer-damped yaw input device, shown in its relaxed position, in accordance with an embodiment of the present invention;

FIG. 8

b

is a cross-sectional top view of the yaw input device of

FIG. 8

a

shown in a deflected position;

FIGS. 8

c

and

8

d

are back and top views, respectively, of the yaw input device of

FIG. 8

a

coupled to a handlebar of a personal transporter in accordance with an embodiment of the present invention;

FIGS. 9

a

and

9

b

depict a palm steering device, in a rest state and activated state, respectively, as implemented in a handlebar of a personal transporter in accordance with an embodiment of the present invention;

FIG. 10

is a logical flow diagram of the control program in accordance with embodiments of the present invention;

FIG. 11

is a flow diagram for traction control in accordance with an embodiment of the present invention; and

FIG. 12

is a flow diagram for deceleration-to-zero in accordance for an embodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

A personal transporter may be said to act as ‘balancing’ if it is capable of operation on one or more wheels but would be unable to stand on the wheels but for operation of a control loop governing operation of the wheels. A balancing personal transporter lacks static stability but is dynamically balanced. The wheels, or other ground-contacting elements, that provide contact between such a personal transporter and the ground or other underlying surface, and minimally support the transporter with respect to tipping during routine operation, are referred to herein as ‘primary ground-contacting elements.’

An embodiment of a balancing personal transporter in accordance with the present invention is depicted in FIG.

1

and designated generally by numeral

10

. In certain applications, operation of personal transporter

10

may not require operation for an extended period of time in case of failure. Fail-operative operation may be desirable, however, for a definite period of time in order to allow the transporter to maintain stability while stopping and permitting a user to alight from the vehicle. While certain balancing personal transporters may not be required to operate indefinitely if a component fails, it may, however, advantageously provide fail-detect redundant architecture wherein the critical components such as gyros, batteries, motor windings, and processors are replicated and run in parallel during operation of the transporter. If a failure occurs in one line of components, the parallel line will still maintain the stability of the transporter for at least a short period of time. In accordance with the present invention and as discussed below, the short period of continued operation is advantageously used to bring the transporter to a stop while maintaining balance and then turn off the wheel motors. The transporter is brought to a stop by commanding the transporter to pitch backward as is done in speed limiting.

User

8

is shown in

FIG. 1

, standing on platform (or ‘base’)

12

of ground-contacting module

26

. Wheels

21

and

22

are shown as coaxial about the Y axis. Steering or other control may be provided by thumb wheels

32

and

34

, or by other user input mechanisms described in detail below. A handlebar

14

may be provided on stalk

16

for gripping by the user.

Referring now to

FIG. 2

, a block diagram is shown of the system architecture of an embodiment of the present invention. A left motor

110

drives a left wheel

20

(shown in

FIG. 1

) and a right motor

120

drives a right wheel

21

. Motors

110

and

120

are preferably DC brushless but may be either AC or DC motors and either brushed or brushless. Each motor is energized by a redundant set of windings

111

,

112

,

121

,

122

. Each winding is capable of energizing the motor in the event the complimentary winding is unable to energize the motor. In the discussion below, each redundant component is distinguished by a two letter group identifying either the left (L) or right (R) side of the transporter and either the A group or B group of redundant components. For example, the left motor winding energized by the A group of components is designated as the LA winding.

Each of motor windings

111

,

112

,

121

,

122

is driven by a motor amplifier

132

,

133

,

142

,

143

. The A-group amplifiers

132

,

133

are supplied by the A-group power supply

131

and the B-group amplifiers

142

,

143

are supplied by the B-group power supply

141

. The electrical connections between the power supplies and amplifiers and between the amplifiers and motor windings are expected to carry large currents up to

20

to

40

Amperes and are identified by thick lines

105

in FIG.

2

.

Each motor

110

120

has a shaft feedback device (SFD)

113

123

that measures the position or angular velocity of the motor shaft. The SFD is in signal communication with the motor amplifiers driving the motor associated with the SFD. For example, the right SFD

123

associated with the right motor

120

is in signal communication with the RA amplifier

133

and the RB amplifier

143

. The SFD is preferably a Hall sensor that determines the position of the shaft, however the SFD may be selected from a variety of sensors such as encoders, resolvers, and tachometers, all listed without limitation for purposes of example. Certain sensors, such as tachometers, may also be used to measure the shaft velocity. Conversion of a signal representing instantaneous shaft velocity to or from a signal representing position is accomplished by integrating or differentiating the signal, respectively.

The A-group amplifiers

132

,

133

are commanded by the A processor

135

while the B-group amplifiers

142

,

143

are commanded by the B processor

145

. Power is supplied to the A processor from the A power source

131

through the A-group DC-DC converter

136

. Similarly, the B power source

141

supplies power to the B processor

146

through the B-group DC-DC converter

145

. The A-group amplifiers

132

,

133

, A-group converter

136

, and A processor

135

are preferably grouped together into a compartment or tray

130

that is at least partially isolated by a barrier

150

from the B-tray

140

containing the B-group amplifiers, B-group converter, and B processor. Physically separating the A tray

130

and B tray

140

reduces the probability of a common point failure. The barrier

150

acts to delay the propagation of a failure, in one tray to the other tray such that the transporter has sufficient time to put the rider in a safe condition to exit the transporter. Similarly, the A power supply

131

is physically separated from the B power supply

141

. The A power supply

131

and the components in the A tray

130

are capable of driving both motors

110

,

120

for a short period of time, on the order of a few seconds, in the event of a failure in any one of the B-group components. Conversely, the B power supply

141

and the components in the B tray

140

are capable of driving both motors

110

,

120

for a short period of time if an A-group component fails.

Although the processors

135

,

145

are physically isolated from each other, signal communication is maintained between the processors via communication channels

137

,

147

. Communication channels

137

,

147

are preferably electrical conductors but may also be electromagnetic such as optical, infrared, microwave, or radio. The A channel

137

transmits signals from the A processor

135

to the B processor

145

and the B channel

147

transmits signals from the B processor

145

to the A processor

135

. Optical isolators

139

,

149

are incorporated into channels

137

,

147

to prevent over-voltages from propagating from a shorted processor to the other processor.

Each processor receives signals from a plurality of sensors that monitor the state of the transporter and the input commands of the rider. The processor uses the sensor signals to determine and transmit the appropriate command to the motor amplifiers. The information transmitted to the processors by the sensors include the spatial orientation of the transporter provided by an inertial measurement unit (IMU)

181

,

182

, the rider directed turn command provided by a yaw input device (YID)

132

,

142

, and the presence of a rider on the transporter provided by a rider detector (RD)

161

,

162

,

163

,

164

. Other inputs to the processor may include a rider operated pitch trim device (PTD)

148

for adjusting the pitch of the transporter to a more comfortable pitch and a stop button (not shown) for bringing the transporter to a stop quickly. Depending on the importance of the sensor to the operation of the transporter, the sensors may or may not be duplicated for redundancy. For example, the spatial orientation of the transporter is central to the operation of the transporter, as is described below, and therefore an A-group IMU

181

supplies transporter orientation information to the A processor

135

and a B-group INM

182

supplies transporter orientation information to the B-processor

145

. On the other hand, the transporter may still be operated in a safe manner without the PTD

148

so only one such device is typically provided. Similarly, an output device such as a display

138

does not require redundancy. A non-redundant device such as a display

138

or a PTD

148

may be connected to either processor.

In the embodiment depicted in

FIG. 2

, display

138

is controlled by the A processor

136

and the PTD

148

is in direct signal communication with the B processor

145

. The information provided by the PTD

148

is transmitted by the B processor

145

to the A processor

135

via the B channel

147

.

Additionally, each processor

135

,

145

communicates with one of the user interface processors (UIPs)

173

,

174

. Each UIP

173

,

174

receives steering commands from the user through one of the yaw input devices

171

,

172

. A A-group UIP

173

also communicates to the non-redundant UIDs such as the display

138

, brake switch

175

, and pitch trim control

148

. Other user interface devices that are not provided redundantly in the embodiment shown in

FIG. 2

, such as a sound warning device, lights, and an on/off switch, may also be connected to the A-group UIP

173

. The A-group UIP

173

may also pass along information provided by the user interface devices to the B-group UIP

174

.

In accordance with preferred embodiments of the invention, the A-group UIP

173

compares calculations of the A-group processor with calculations of the B-group processor and queries the A-group processor

135

with a ‘watchdog’ calculation to verify operation of the A-group processor. Similarly, the B-group UIP

174

queries the B-group processor

145

to verify normal operation of the B-group processor.

Several components of personal transporter

10

, in accordance with various embodiments of the present invention, are now described.

Battery

The transporter power required to drive the motors

110

,

120

and electrical components may be supplied by any known source of electrical power known in the electrical arts. Sources of power may include, for example, both internal and external combustion engines, fuel cells, and rechargeable batteries. In preferred embodiments of the present invention, power supplies

131

,

141

are rechargeable battery packs. Various battery chemistry modalities may be used, as preferred under various conditions, and may include, without limitation, lead-acid, Lithium-ion, Nickel-Cadmium (Ni—Cd), or Nickel-metal hydride (Ni—MH) chemistry. Each power supply

131

,

141

is enclosed in a container that protects the battery packs and associated electronics from the environment.

FIG. 3

shows a top view of one embodiment of the power supply with the top cover removed. A tray

205

that is covered and sealed to protect the contents from the environment encloses the components of power supply

200

. Tray

205

houses a plurality of battery blocks

210

, each of which contains a plurality of battery cells

215

. The number of cells

215

packaged in a block

210

and the total number of blocks in the power supply are determined by the expected power requirements of the transporter. In a preferred embodiment, cells

215

are “sub-C”-size cells and each block

210

contains ten cells

215

. In another embodiments, block

210

may contains other numbers of cells

215

. Cells

215

are preferably connected in series, as are blocks

210

. In other embodiments blocks

210

may be connected in parallel with the cells

215

within each block connected in series, or, alternatively, blocks

210

may be connected in series with the cells

215

within each block

210

connected in parallel, each configuration providing advantages for particular applications.

Electrical current flowing into or out of power supply

200

is conducted through a connector

220

that provides the electrical interface between the power supply

200

and the transporter

10

. In an embodiment shown in

FIG. 3

, connector

220

is located on the top cover (not shown) of power supply

200

but any positioning of connector

220

is within the scope of the present invention. In addition to conducting current into or out of power supply

200

, connector

220

may also include a plurality of signal lines that establish signal communication between the power supply internals and any other transporter processor.

The temperature of each block

210

is monitored by the supply controller

230

through temperature sensors

235

. In addition, supply controller

230

also monitors the voltage of each block

210

. If supply controller

230

detects that the temperature of a block

210

is over a preset temperature limit, the supply controller

230

sends an over-temperature signal to the processor through connector

220

. Similarly, if supply controller

230

detects that the voltage of a block

210

is below a preset voltage limit, the supply controller

230

sends an under-voltage signal to the processor through the connector

220

.

Supply controller

230

preferably contains an ID chip

240

that stores information about the power supply such as battery type, the number of cells in the power supply

210

, and optionally, a date code or serial number code. The ID chip

240

may be of any type of permanent or semi-permanent memory devices known in the electronics art. The information contained in the ID chip

240

may be used by the processor

135

,

145

to set various operating parameters of the transporter. The information may also be used by a charger (not shown) to recharge the power supply.

Power supply

200

may be connected via connector

220

to a charger that is either external to the transporter or contained within the transporter. In one embodiment of the present invention, the charger is located on the transporter and is an AC switch mode charger well known in the power art. In another embodiment, the charger is contained within battery tray

205

. In another embodiment of the present invention, power supply

200

is charged by an auxiliary power unit (APU) such as the one described in copending U.S. patent application Ser. No. 09/517,808 entitled “Auxiliary Power Unit”.

Motor Amplifier & Operating Modes

FIG. 4

shows a block schematic of a power module

300

of one embodiment of the present invention. A balancing processor

310

generates a command signal to motor amplifier

320

that, in turn, applies the appropriate power to motor

330

. Balancing processor

310

receives inputs from the user and system sensors and applies a control law, as discussed in detail below, to maintain balance and to govern motion of the transporter in accordance with user commands. Motor

330

, in turn, rotates a shaft

332

that supplies a torque, &tgr;, at an angular velocity, &ohgr;, to a wheel

20

,

21

(shown in

FIG. 1

) that is attached to shaft

332

. In some embodiments, a transmission, not shown, may be used to scale the wheel speed in relation to the angular velocity of the shaft

332

. In a preferred embodiment of the present invention, motor

330

is a three-coil brushless DC motor. In that embodiment, motor

330

has three sets of stator coils although any number of coils may be used. The stator coils are electrically connected to a power stage

324

by coil leads

337

capable of conducting large currents or high voltages. It is understood that the large currents and high voltages are relative to the currents and voltages normally used in signal processing and cover the range above 1 ampere or 12 volts, respectively.

Motor amplifier

320

itself contains both an amplifier processor

322

and a power amplification stage

324

. Amplifier controller

322

may be configured to control either current or voltage applied to the motor

330

. These control modes may be referred to as current control mode and voltage control mode, respectively. Power stage

324

switches the power source

340

into or out of connection with each coil, with the switching of the power stage

324

controlled by the amplifier controller

322

. An inner loop

326

senses whether the output of power stage

324

is as commanded and feeds back an error signal to amplifier controller

322

at a closed loop bandwidth, preferably on the order of 500 Hz. Additionally, control by amplifier controller

322

is based, in part, on a feedback signal from shaft feedback sensor (SFS)

335

.

Shaft feedback sensor

335

is also in signal communication with the processor

310

and provides information related to the shaft position or motion to the processor. The shaft feedback sensor

335

may be any sensor known in the sensor art capable of sensing the angular position or velocity of a rotating shaft and includes tachometers, encoders, and resolvers. In a preferred embodiment, a Hall sensor is used to sense the position of the rotating shaft

332

. An advantage of a Hall sensor is the low cost of the sensor. In order to obtain a measure of shaft rotation velocity from a position signal provided by shaft feedback sensor

335

, the position signal is differentiated by differentiator

308

. The outer feedback loop

342

operates at a bandwidth characteristic of the balance control provided by balance processor

310

and may be as low as 20-30 Hz.

While current and voltage may be equivalent in certain applications, voltage control is advantageously applied in embodiments of transporter control where the outer loop bandwidth is more than 3-4 times slower than the inner closed loop bandwidth, for the reasons now discussed with reference to FIG.

5

.

FIG. 5

shows an electrical model

410

of a motor. A motor has a pair of terminals

411

,

412

across which a voltage V is applied. Motor

410

also has a rotating shaft

420

characterized by a shaft velocity, &ohgr;, and a torque, &tgr;. Motor

410

may be modeled by resistor

430

of resistance R carrying a current i in series with an ideal motor

435

having a voltage drop V

emf

. For an ideal motor, V

emf

=k

v

·&ohgr; and &tgr;=k

c

· i where k

v

and k

c

are motor constants. Series resistor

430

models the losses of the motor

410

.

The differences in behavior of transporter

10

(shown in

FIG. 1

) due to voltage control or current control can be seen using the example of a transporter encountering and driving over an obstacle. When a wheel

20

of the transporter encounters an obstacle, the wheel velocity will decrease because the torque applied to the wheel is insufficient to drive the wheel over the obstacle. The drop in wheel velocity will be reflected in a decrease in the back-electromotive-force (“back-emf”) voltage across the ideal motor.

Considering, first, the case of voltage control: If the amplifier is in voltage control mode, the voltage applied to terminals

411

,

412

remains constant and additional current will be drawn through resistance

430

and ideal motor

435

. The additional current through the motor will generate the additional torque to drive the wheel over the obstacle. As the transporter drives over the top of the obstacle, the wheel will accelerate under the additional torque that was generated to drive over the obstacle but is no longer required to drive off the obstacle. As the wheel accelerates, the back-emf across the motor will increase and the current through R will decrease in order to keep the voltage across terminals

411

,

412

constant. The decrease in current reduces the applied torque generated by the ideal motor thereby reducing the acceleration of the wheel. The advantage of voltage control mode is that the ideal motor naturally draws the current required to drive over the obstacle and naturally reduces the current to drive off the obstacle without any change required in the motor command. As long as the power source can supply the required current, the motor essentially acts as its own feedback sensor and the control loop delay for the motor is essentially zero.

Under current control mode, on the other hand, the amplifier will keep the current constant through resistor

430

and ideal motor

435

until the controller sends a new current command during the next processor frame. When the wheel encounters the obstacle, &ohgr; decreases and the back-emf across the ideal motor decreases. However, since the amplifier controller is keeping the current constant, the voltage across terminals

411

,

412

is allowed to drop. Since the current is held constant by the amplifier controller, the torque remains constant. However, the torque is insufficient to drive over the obstacle and the inertia of the moving transporter will cause the transporter to pitch forward. As the transporter begins to pitch forward over the obstacle, the balancing controller will detect the pitching, either through a change in the pitch error or through a change in the velocity, and command an increase in current to the amplifier controller, in accordance with the control algorithm taught in U.S. Pat. No. 5,971,091. The motor amplifier will respond to the increased current command by supplying additional current through R and the ideal motor. The increased current through the ideal motor increases the torque applied to the wheel until it is sufficient to drive the wheel over the obstacle. As the transporter moves over the obstacle, however, the increased torque will accelerate the wheels since the obstacle no longer resists the wheels. The wheel acceleration will cause the wheels to move ahead of the transporter's center of gravity (CG) and cause the transporter to pitch backward. The balancing controller will detect the pitching condition through either a change in pitch error or through a change in the transporter velocity and command a decrease in the current supplied to the ideal motor thereby reducing the torque applied to the wheel.

If the delay caused by the balancing controller is negligible and the accuracy of the velocity information fed back to the balancing controller is extremely high, the rider will not notice a difference whether voltage or current control is used. However, if the controller or shaft sensor selected for the transporter has a limited bandwidth, current control mode will not provide the prompt response that voltage control mode exhibits for small obstacles. In a preferred embodiment of the invention, a low-cost Hall effect sensor is employed to detect shaft rotation. In addition, for reasons described below, limitations on the selection of the gains used in the control law for current control mode result in a softer transporter response relative to voltage control mode.

Rider Detector

Operating modes of the transporter may include modes wherein the rider is supported by the transporter but may also include modes where the rider is not supported by the transporter. For example, it may be advantageous for the rider to be able to ‘drive’ the transporter while walking alongside or behind it.

Additionally, it is advantageous for certain safety features of the transporter to be triggered if the rider leaves the transporter while the transporter is in motion.

FIGS. 6

a

and

6

b

show a rider detection mechanism used in an embodiment of the present invention.

FIG. 5

a

shows a top view of the rider detector designated generally by numeral

510

. Transporter

10

incorporating the rider detector includes a base

12

, left wheel fender

512

, right wheel fender

514

, support stem

16

for handlebar

14

(shown in FIG.

1

). Wheel fenders

512

and

514

cover the corresponding wheels. Support stem

16

is attached to the base

12

and provides a sealed conduit for transmission of signals from controls

32

,

34

(shown in

FIG. 1

) that may be located on the handlebar to the control electronics sealed in the base

12

. Wheel fenders

512

,

514

are rigidly attached to the sides of the base.

The top of base

12

provides a substantially flat surface and is sized to comfortably support a rider standing on the base

12

. A mat

521

covers the top of the base

12

and provides additional protection to the base

12

from particles and dust from the environment. In an alternate embodiment, the mat may also cover part of the fenders

512

514

and may be used to cover a charger port (not shown) that provides for external charging of the power supply. Mat

521

may be made of an elastomeric material that provides sufficient traction such that the rider does not slip off the mat

521

under expected operating conditions. A plate

522

is position ed between base

12

and mat

521

. Plate

522

is made of a rigid material and evenl distributes the force acting on the plate

522

from the rider's feet such that at least one rider detection switch

523

is activated when a rider is standing on the mat .

FIG. 6

b

shows a cut side view of rider detector

510

. Switch

523

is made of an elastomeric material that may be fabricated as an integral part of the base cover

524

. Although the fabrication cost may be greater, making the switch

523

integral with the base cover

524

eliminates a possible leak source. Switch

523

has a stem

540

extending below base cover

524

and a top

542

that extends above the base cover

524

. When top

542

is depressed, switch

523

deforms such that a stem

540

is displaced downward toward an electronics board

550

that is sealed within base

520

. A n optical switch is located on the electronics board

550

such that when stem

540

is displaced downward, stem

540

interrupts a light beam

557

generated by a source

555

and the light beam interruption is detected by an optical detector

556

.

The mat edge

525

is preferably attached to the top of the base cover

524

. Mat

521

has a raised portion

527

that is support by a wall

526

connecting the mat edge

525

to the raised portion

527

. The height of the wall

526

is sized such that plate

522

does not exert a force on the switch

523

when there is no weight on the mat

521

. When the rider steps on the raised portion

527

, plate

522

is displaced toward electronics board

550

until stem

540

interrupts light beam

557

. When the rider steps off of the transporter, mat

521

returns to the raised configuration as does switch

523

thereby re-establishing light beam contact between the source

555

and detector

556

.

Steering Device

Referring now to

FIG. 7

, an exploded view is shown of an embodiment of a steering device for a scooter-like vehicle such as the balancing vehicle

10

of

FIG. 1. A

potentiometer

602

, or other sensor of the position of a rotatable shaft

604

, is attached to a housing

606

. The housing may be part of handlebar

14

(shown in FIG.

1

). A rotatable grip

608

is attached to potentiometer shaft

604

and provides a grip for the rider. A torsional spring

610

is connected at one end to the rotatable grip

608

and at the other end to the potentiometer

602

or to housing

606

. As the rider rotates grip

608

, the grip turns shaft

604

. Potentiometer

602

, with voltage suitably applied across it, as known in the art, generates a signal substantially proportional to the rotation of the shaft. If the rider releases the grip, torsional spring

610

rotates grip

608

and the shaft to their respective neutral or zero positions. Return of grip

608

to its neutral position allows the transporter to continue traveling in the same direction as when the grip was released. If the grip was not returned to the neutral position when released, the transporter would continue to turn in the direction of the residual rotation.

The direction of rotation may be used to encourage the rider to lean into the turn. For example, referring further to

FIG. 7

, if the rider's right hand holds grip

608

, a twist in the direction of the rider's fingers corresponds to a right turn. The rotation of the rider's right wrist to the outside of the handlebar encourages the rider to shift weight to the right and into the turn. Shifting weight into the turn improves the transporter's lateral stability.

Referring now to

FIGS. 8

a

-

8

d

, a thumb-activated, elastomer-damped, steering input device is shown and designated generally by numeral

620

. A rotation sensor

622

, which is preferably a potentiometer but may be any rotation sensor, is coupled to a structure fixed, with respect to rotation, to the support of a personal transporter, preferably to handlebar

14

(shown in FIG.

1

). A shaft

624

of the steering device

620

is bent with respect to a pivot point

626

in response to force applied to thumb button

630

by thumb

628

of the user. As shaft

624

is bent, local rotation about pivot

626

is read by rotation sensor

622

, and a signal characteristic of the rotation is transmitted to the transporter controller. Shaft

624

of input device

620

is comprised of elastomeric core

632

surrounded by metal sheath

634

. Elastomeric core

632

may be rubber, for example. Distal end

636

of shaft

624

is captured between limit posts

638

which extend from the handlebar and which limit displacement of shaft

624

when the user rotates the proximal end

640

of the device.

User's rotation of proximal end

640

causes shaft

624

to bend as shown in

FIG. 8

b

. Metal sheath

634

acts as a leaf spring, providing a restoring force that counters user's rotation of the device, and brings the device back to the neutral configuration depicted in

FIG. 8

a

. Elastomeric core

632

acts as a shear spring that opposes rotation of the device by the user and increases the opposition as the deflection increases. Increased opposition arises due to differential sliding between metal sheath

634

and elastomeric core

632

as the long (distal) end

624

is bent. The back view of steering input device

620

shown in

FIG. 8

c

shows potentiometer

622

for generating a signal substantially proportional to rotation of shaft

624

. The top view of steering input device

620

shown in

FIG. 8

d

shows the roughly L-shaped elbow

642

of the proximal end

640

of input device

620

. Dashed outline

644

depicts the steering input device in the deflected condition corresponding to

FIG. 8

b.

A further steering device for the personal transporter

10

of

FIG. 1

is shown in

FIGS. 9

a

and

9

b

, in accordance with another embodiment of the invention. Palm steering device

650

is contained on the surface of handlebar

14

. In the rest state depicted in

FIG. 9

a

, upper surface

652

of lever

652

is substantially parallel to and substantially flush with upper surface

656

of handlebar

14

. Lever

652

is constrained to rotate about pivot

658

which is substantially parallel to the ground and parallel to the forward direction of motion of the transporter. The rider places a palm of a hand over lever

652

and, by pressing one side

660

or the other of lever

652

about pivot

658

, causes generation of a steering signal. The steering signal is generated by a rotation sensor

662

at the pivot

658

or by pressure sensors either side of fulcrum

664

.

Inertial Measurement Unit The inertial measurement unit (IMU) houses the sensors used by the processor to determine the orientation and speed of the transporter. Full redundancy may be accomplished through the use of two IMUs that are preferably physically separated from each other and powered by separate power supplies as shown in FIG.

2

. Spatial constraints may require the redundant IMUs to be housed in the same package while still maintaining independent power supplies and independent signal lines to separate processors.

In an embodiment of the present invention, the A-side and B-side IMUs

181

and

182

(shown in

FIG. 2

) are housed in a single package. Each IMU may be equipped to measure the transporter orientation about three axes (pitch, yaw, and roll), about two axes, or about one axis (pitch). In another embodiment, each of the A-side and B-side IMUs is equipped to measure the transporter orientation about three axes. In another embodiment, a three-axis IMU may be paired with a single axis IMU.

Each IMU includes a sensor

190

(shown in

FIG. 2

) and the supporting electronics for the sensor. The sensor may be any device capable of generating a signal that is indicative of the orientation or the rate of change of orientation of the sensor. The generated signal is preferably nearly proportional to the orientation or rate of change of the orientation of the sensor, but other dependencies are within the scope of the present invention. For example, a sensor may be a liquid level pendulous tilt sensor, a physical gyroscope, a solid-state gyroscope, an accelerometer, or a pair of proximity s sensors arranged in a line and separated by a known distance. In various embodiments of the present invention, a solid-state gyroscope is used with a liquid level tilt sensor. The liquid level tilt sensor may be used to correct for drift in the solid-state gyroscope as described in U.S. application Ser. No. 09/458,148, herein incorporated by reference.

A single axis IMU may consist of a solid-state gyroscope and a tilt sensor with both sensors mounted to provide a signal corresponding to the pitch orientation of the transporter. The 3-axis IMU consists of at least three solid-state gyroscopes and a tilt sensor. The gyroscopes may be mounted to provide signals that correspond to a mixture of any of the rotations about three mutually orthogonal axes. Alternatively, the gyroscopes may also be mounted to avoid saturation of the gyroscope signal. The orientation of the gyroscopes will depend on the space constraints of the IMU housing, the saturation limits of the gyroscopes, and the expected performance requirements of the transporter. In one embodiment of the present invention, the 3-axis IMU consists of four solid-state gyroscopes and a tilt sensor. Use of four gyros enables the IMU to detect a failure in one of the gyros. Although the identity of the failed gyro cannot be determined, the existence of a failure is sufficient to alert the processor to take the appropriate action, as described below, while maintaining rider safety and comfort.

Processor In various embodiments of the present invention, a control program running on a processor determines the dynamic state of the transporter and calculates the appropriate command to send to the motor amplifier controllers based on the dynamic state of the transporter and on any rider commands. In a preferred embodiment, the processor also calculates the appropriate switch commands to the power stage

324

(shown in

FIG. 4

) thereby eliminating the need for a separate amplifier controller. The processor may be a digital signal processor (DSP) optimized for controlling motors. The term ‘processor,’ as used herein, also encompasses within its scope an embodiment in analog circuitry of the functions described. The circuitry and associated electronic components required to support the processor are well known in the electronic control circuit art.

Referring now to

FIG. 10

, a logical flow diagram is presented of the control program executed by the processor. When the rider activates the transporter, the control program performs an initialization procedure

705

. The initialization procedure performs redundancy checks between the processors, checks for any subsystem faults, and initializes the IMUs. After the subsystems and processors have passed the initialization checks and the IMUs are initialized, the initialization procedure alerts the rider that the transporter is ready for use. The alert may be an audio or visual indicator is such as a tone or a light. In a preferred embodiment, the initialization procedure gives the ready alert to the rider after the 1-axis state estimator has initialized. This allows the rider to begin using the transporter while the 3-axis state estimator is still initializing.

The program next checks for rider commands and transporter state sensor signals in

710

. The rider commands may include rider detection described above, yaw commands, pitch trim commands, emergency brake commands, and mode change commands. The transporter state sensor signals may include sensors for measuring the temperature of the transporter components such as battery or motor temperature or potential sensors for measuring the voltage of the battery pack. The state sensors also include the sensors in the IMUs.

The program in

715

determines the transporter orientation based on the sensor signals from the IMUs. In a preferred embodiment, a 3-axis IMU incorporating four solid state gyros and a two-axis tilt sensor, designated as the A-side IMU, is paired with a 1-axis IMU, designated as the B-side IMU. The program first checks for a gyro failure in the A-side IMU by comparing the combined signals from two subsets of the four gyros. If the program determines that one of the four gyros has failed, the program sets an A-side IMU fault flag that will activate a procedure to bring the transporter to a safe condition as described below. The program also estimates the transporter orientation based on the signals from the B-side IMU. If the A-side IMU is not faulted, the B-side estimate is compared to the A-side estimate. If the B-side estimate differs from the A-side estimate by more than a preset amount, the program sets a B-side IMU fault flag which will also activate the safe condition procedure. If the B-side estimate agrees with the A-side estimate to within the same preset amount, the program disregards the B-side estimate and uses the A-side estimate for further processing with the knowledge that the B-side IMU is available to safely bring the transporter to a stop should the A-side IMU fail.

In another embodiment of the present invention, both the A-side and B-side IMUs are 1-axis state estimators.

The program generates the wheel motor commands in

720

. This portion of the program is also referred to as the balance controller. The balance controller is described in U.S. Pat. No. 5,971,091 and U.S. application Ser. No. 09/458,148, both of which are hereby incorporated by reference.

The wheel motor commands are generated through a control law having the form

Command=K

1

&thgr;+K

2

&thgr;

r

+K

3

x+K

4

x

r

where

&thgr;=transporter pitch error

&thgr;

r

=transporter pitch rate error

x=transporter position error

x

r

=transporter velocity error

The dynamic state variables are in the form of an error term defined as the desired value minus the measured value. For example, &thgr; is the desired transporter pitch minus the measured transporter pitch. The measured transporter pitch and pitch rate are determined from the IMU signals. The measured transporter position and transporter velocity are determined from the shaft feedback sensors. For balanced operation, the desired pitch rate is set to zero. The desired pitch may be adjusted by the rider through a pitch trim control and may also be adjusted by the control program during transporter operation.

The adjustable coefficients, K

1

, K

2

, K

3

, and K

4

, are commonly referred to as gains and together form a set of coefficients that define an operating mode. As the values of the coefficients change, the responsiveness and stability of the transporter changes. The gains are set to a value as specified by the user in selection of a mode of operation of the vehicle. For example, K

3

is normally set to zero to allow the transporter to travel but K

3

can be set to a positive value to enable the transporter to remain balanced at a stationary point.

In one embodiment, K

1

is set to a positive value and K

2

, K

3

, and K

4

are set to zero. In this operating mode, the transporter does not automatically balance but the rider may maintain balance and command fore/aft motion of the transporter by adjusting his/her weight in the fore/aft direction while traveling. Unlike a motorized scooter or motorcycle where the rider maintains lateral stability while commanding fore-aft motion, the transporter of the present invention operating with only a non-zero K

1

requires the rider to maintain balance in the fore-aft direction while simultaneously commanding fore-aft movement. The higher level of skill required to operate the transporter in such a mode may be appealing to some riders for its recreational value.

In another embodiment, K

1

and K

2

are set to positive non-zero values and K

3

and K

4

are set to zero. In this mode, the transporter is capable of maintaining balance and requires a steady-state ‘error’ (or ‘offset’) in pitch in order to maintain a steady-state speed. However, a rider could develop the skill to operate the transporter in a balanced state while avoiding instabilities through proper control of the rider's weight shifting.

In typical operation, only K

3

is set to zero. In this mode, the transporter maintains a small pitch ‘error’ while traveling at a steady speed. The responsiveness of the transporter may be modified by adjusting the values of each of the gains relative to each other. For example, if K