Hybrid human/electric powered vehicle

<u>Technical Field and Background Art</u>

0001The present invention relates to control of an unstable vehicle and, more particularly, to dynamic stabilization of a vehicle propelled at least in part by a user.

0002Propulsion of a person by means of a balancing vehicle entails two components: The first is that of supplying power to effectuate locomotion, while the second is that of maintaining balance. Balance, as used herein, refers to maintaining stability in the fore-aft plane (defined, in turn, by the direction of motion and the vertical). The functions of propulsion and of balance are typically provided either by the user (as in the case of a unicycle, for example) or by a motor in conjunction with a controller (as in the case of the human transporter described in <patcit id="pcit0001" dnum="US5701965A"><text>U. S. Patent 5,701,965</text></patcit>, which is incorporated herein by reference).

0003While specialized skills are typically required for a person to maintain fore-aft balance on an unstable vehicle, only a small portion of the power exerted to achieve locomotion is necessary for the balancing function. Such skills are not trivial and often become diminished with age. Consequently, supplementing the balancing ability of a rider is a desirable aim.

0004<patcit id="pcit0002" dnum="US3869011A"><text>US 3,869,011</text></patcit> describes a stair climbing tracked vehicle with a pair of front tracks, a pair of rear tracks pivoted to the front tracks, and a seat supported on the pivot. The tracks are pivoted with respect to one another to climb up and down stairs.

<u>Summary of the Invention</u>

0005In accordance with preferred embodiments of the invention, a personal transporter is provided that may be propelled by a user according to claim 1. The personal transporter has a platform for supporting the user, and a ground-contacting module that, in turn, has a first ground-contacting element movable about an axis for propelling the platform with respect to an underlying surface. Furthermore, the transporter has a power train for coupling power from the user to the ground-contacting element for impelling the ground-contacting element about its axis and a first sensor for sensing a value of a pitch variable of the personal transporter. A powered actuator provides torque to the ground-contacting element in addition to any torque provided by the user while a controller governs the powered actuator based at least on the value of the pitch variable in such a manner as to maintain stable operation of the personal transporter in an operating position that would be unstable with respect to tipping in the fore-aft plane but for provision of torque to the ground-contacting element.

0006In accordance with another embodiment of the invention, the personal transporter may include a second ground-contacting element and may include a second sensor for sensing the speed of the first ground-contacting element with respect to the underlying surface and a third sensor for sensing the speed of the second ground-contacting element with respect to the underlying surface.

0007In accordance with other embodiments of the invention, the platform may be a seat, the ground-contacting element may be a wheel, and the powered actuator may include a motor. The sensor may include an inclinometer and a gyroscope.

0008In accordance with other aspects of the invention, a method is provided for propelling a personal transporter having a wheel and a power train for conveying power from a user to the wheel. The method has the steps of: <ol id="ol0001" compact="compact"><li>a. sensing a value of a pitch variable of the personal transporter in the fore-aft plane with respect to gravity; and</li><li>b. providing torque to the wheel, based at least on the value of the pitch variable of the personal transporter, in addition to any torque provided by the user, in such a manner as to maintain stable operation of the personal transporter in an operating position that would be unstable with respect to tipping in the fore-aft plane but for provision of torque to the wheel.</li></ol>

0009In accordance with an additional aspect of the invention, a method is provided for propelling a personal transporter having wheels and a power train for conveying power from a user to the wheels. The method has the steps of: <ol id="ol0002" compact="compact"><li>a. sensing a value of a pitch variable of the personal transporter in the fore-aft plane with respect to gravity;</li><li>b. sensing a value of a rate of rotation for each wheel; and</li><li>c. providing torque to the wheels, based at least on the value of the pitch variable of the personal transporter and on the values of the rates of wheel rotation, in addition to any torque provided by the user, in such a manner as to maintain stable linear operation of the personal transporter in an operating position that would be unstable with respect to tipping in the fore-aft plane but for provision of torque to the wheel.</li></ol>

0010In accordance with still other aspects of the invention, sensing the value of the pitch variable may include measuring the pitch and/or the time rate of change of the pitch.

<u>Brief Description of the Drawings</u>

0011The foregoing features of the invention will be more readily understood by reference to the following detailed description, taken with reference to the accompanying drawings, in which: <ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Fig. 1</figref> is a front view of a simplified embodiment of the present invention;</li><li><figref idref="f0001">Fig. 2</figref> is a side view of a simplified embodiment of the present invention;</li><li><figref idref="f0002">Fig. 3</figref> is a block diagram showing generally the nature of power and control with the embodiment of <figref idref="f0001">Fig. 1</figref>.</li><li><figref idref="f0003">Fig. 4</figref> illustrates the control strategy for a simplified version of <figref idref="f0001">Fig. 1</figref> to achieve balanced operation using wheel torque;</li><li><figref idref="f0004">Fig. 5</figref> is a block diagram showing communication among the control assemblies used in the embodiment of <figref idref="f0001">Fig. 1</figref>;</li><li><figref idref="f0005">Fig. 6</figref> is a block diagram showing the structure of a generic control assembly of the type used in the embodiment of <figref idref="f0004">Fig. 5</figref>;</li><li><figref idref="f0006">Fig. 7</figref> is a block diagram showing providing detail of the driver interface assembly 503 of the type used in the embodiment of <figref idref="f0004">Fig. 5</figref>; and</li><li><figref idref="f0007">Fig. 8</figref> is a schematic of the wheel motor control during balancing and normal locomotion of the embodiment of <figref idref="f0001">Fig. 1</figref>.</li></ul>

<u>Detailed Description of Specific Embodiments</u>

0012As used in this description and any accompanying claims, the term "wheelie" will refer to a mode of operation of a vehicle otherwise having a normally stable mode of operation in which mode the vehicle contacts the underlying surface at an insufficient number of points to provide stability. Certain wheels of the vehicle and feet of the user are typically suspended above the surface in this mode.

0013Referring first to <figref idref="f0001">Fig. 1</figref>, a wheelchair <b>110</b> is shown employing one embodiment of the present invention. Wheelchair <b>110</b> includes seat <b>101</b> and footrest <b>105</b> to carry user <b>108,</b> driven wheels <b>102</b> that suspend the user above surface <b>111,</b> handrails <b>103</b> to permit the user to propel the chair, motors <b>107</b> to provide assistance to propulsion, and casters <b>104</b> to permit, when deployed, the wheelchair to rest stabily on the surface <b>111</b> at more than two areas of contact. A power train allows power to be delivered, using any mechanical means, from the user's musculature to one or more ground-contacting elements, whether by means of linkages, gears, or in any other way. When the wheelchair is dynamically stabilized in accordance with embodiments of the invention, the casters may be retracted. Wheelchair <b>110</b> is shown by way of example only and without limitation, and it is to be understood that any personal transporter capable of coupling user-derived power in order to contribute to propulsion of the transporter is within the scope of the present invention. <figref idref="f0001">Fig. 2</figref> shows a side view of the embodiment of <figref idref="f0001">Fig. 1</figref>.

0014Also attached to the wheelchair are controller <b>106,</b> sensors <b>112,</b> and input device <b>113.</b> The input device <b>113</b> can include force-sensing mechanisms on handrails <b>103,</b> a joystick, or other input device that allows the user to turn dynamic stabilization and power assistance on and off and to alter the degree of dynamic stabilization and power assistance. A pitch sensor such as an inclinometer or gyroscope provides the inclination of the wheelchair with respect to gravity and/or the time rate of change of the inclination. Other pitch sensors such as accelerometers, pendulous reference sensors, and distance probes may be used, as noted in, but not limited by, <patcit id="pcit0003" dnum="US6332103B"><text>U.S. Patent 6,332,103</text></patcit>, incorporated herein by reference. A wheel rotation sensor such as an encoder attached to a motor or wheelchair wheel provides the rate of rotation of the wheelchair wheel.

0015Controller <b>106</b> accepts inputs of wheelchair inclination and/or rate of change of inclination from the pitch sensor and wheel rotation from the wheel rotation sensors and provides commands altering the torque of the motors 107 driving the wheels 102. As a result, wheelchair <b>110</b> accelerates or decelerates so as to maintain balance on two wheels without canceling lean unless the transporter is stationary.

0016In the block diagram of <figref idref="f0002">Fig. 3</figref>, it can be seen that a control system <b>351</b> is used to control the motor drives <b>311</b> and <b>312</b> of the embodiment of <figref idref="f0001">Fig. 1</figref> to achieve locomotion and balance. Motor drives <b>311</b> and <b>312</b> apply torque to left and right wheels respectively. The control system has data inputs including user interface <b>301,</b> pitch sensor <b>302</b> for sensing fore-aft pitch, and wheel rotation sensors <b>303.</b>

0017A simplified control algorithm for maintaining balance in the embodiment of the invention according to <figref idref="f0001">Fig. 1</figref> when the driven wheels <b>102</b> are active for locomotion is shown in the block diagram of <figref idref="f0003">Fig. 4</figref>. Plant <b>401</b> represents the actuation mechanism for driving a vehicle or transporter with a motor, before the control loop is applied. T identifies the wheel torque. The character θ identifies the fore-aft inclination (the pitch angle of the transporter with respect to gravity, i.e., the vertical), x identifies the fore-aft displacement along the surface relative to the reference point, and the dot over a character denotes a variable differentiated with respect to time. Rate gyros may used to obtain θ̇ directly. The remaining portion of the figure is the control used to maintain balance. Boxes <b>402</b> and <b>403</b> indicate differentiation. To achieve dynamic control for providing dynamic stability of the system, the wheel torque T in this embodiment is set to satisfy the following equation: <maths id="math0001"><math display="block"><mi mathvariant="normal">T</mi><mo mathvariant="normal">=</mo><msub><mi mathvariant="normal">K</mi><mn mathvariant="normal">1</mn></msub><mo>⁢</mo><mfenced><msub><mi mathvariant="normal">θ</mi><mn mathvariant="normal">0</mn></msub><mo mathvariant="normal">-</mo><mi mathvariant="normal">θ</mi></mfenced><mo mathvariant="normal">+</mo><msub><mi mathvariant="normal">K</mi><mn mathvariant="normal">2</mn></msub><mo>⁢</mo><mfenced><msub><mover><mi mathvariant="normal">θ</mi><mo mathvariant="normal">˙</mo></mover><mn mathvariant="normal">0</mn></msub><mo mathvariant="normal">-</mo><mover><mi mathvariant="normal">θ</mi><mo mathvariant="normal">˙</mo></mover></mfenced><mo mathvariant="normal">+</mo><msub><mi mathvariant="normal">K</mi><mn mathvariant="normal">3</mn></msub><mo>⁢</mo><mfenced><msub><mi mathvariant="normal">x</mi><mn mathvariant="normal">0</mn></msub><mo mathvariant="normal">-</mo><mi mathvariant="normal">x</mi></mfenced><mo mathvariant="normal">+</mo><msub><mi mathvariant="normal">K</mi><mn mathvariant="normal">4</mn></msub><mo>⁢</mo><mfenced><mover><mi mathvariant="normal">x</mi><mo mathvariant="normal">˙</mo></mover><mo mathvariant="normal">-</mo><msub><mover><mi mathvariant="normal">x</mi><mo mathvariant="normal">˙</mo></mover><mn mathvariant="normal">0</mn></msub></mfenced><mo mathvariant="normal">,</mo></math><img file="EP1512055B1_D0001.tif" /></maths> where: <ul id="ul0002" list-style="bullet" compact="compact"><li>T denotes a torque applied to a ground-contacting element about its axis of rotation;</li><li>θ is a quantity corresponding to the lean of the entire system about the ground contact, with θ₀ representing the magnitude of a system pitch offset, all as discussed in detail below;</li><li>x identifies the fore-aft displacement along the surface relative to a fiducial reference point, with x₀ representing the magnitude of a specified fiducial reference offset;</li><li>a dot over a character denotes a variable differentiated with respect to time; and</li><li>a subscripted variable denotes a specified offset that may be input into the system as described below; and</li><li>K₁, K₂, K₃, and K₄ are gain coefficients that may be configured, either in design of the system or in real-time, on the basis of a current operating mode and operating conditions as well as preferences of a user. The gain coefficients may be of a positive, negative, or zero magnitude, affecting thereby the mode of operation of the vehicle, as discussed below. The gains K₁, K₂, K₃, and K₄ are dependent upon the physical parameters of the system and other effects such as gravity. The simplified control algorithm of <figref idref="f0003">Fig. 4</figref> may maintain balance and also proximity to the reference point on the surface in the presence of disturbances such as changes to the system's center of mass with respect to the reference point on the surface due to body motion of the subject or contact with other persons or objects.</li></ul>

0018The size of K₃ determines the extent to which the transporter will seek to return to a given location. With a non-zero K₃, the effect of x₀ is to produce a specified offset x₀ from the fiducial reference by which x is measured. When K₃ is zero, the transporter has no bias to return to a given location. The consequence of this is that if the transporter is caused to lean in a forward direction, the transporter will move in a forward direction, thereby maintaining balance. Such a configuration is discussed further below.

0019The term "lean" is often used with respect to a system balanced on a single point of a perfectly rigid member. In that case, the point (or line) of contact between the member and the underlying surface has zero theoretical width. In that case, furthermore, lean may refer to a quantity that expresses the orientation with respect to the vertical (i.e., an imaginary line passing through the center of the earth) of a line from the center of gravity (CG) of the system through the theoretical line of ground contact of the wheel. While recognizing, as discussed above, that an actual ground-contacting member is not perfectly rigid, the term "lean" is used herein in the common sense of a theoretical limit of a rigid ground-contacting member. The term "system" refers to all mass caused to move due to motion of the ground-contacting elements with respect to the surface over which the transporter is moving.

0020"Stability" as used in this description and in any appended claims refers to the mechanical condition of an operating position with respect to which the system will naturally return if the system is perturbed away from the operating position in any respect.

0021The gains K₁, K₂, K₃, and K₄ are dependent upon the physical parameters of the system and other effects such as gravity. The control algorithm of <figref idref="f0003">Fig. 4</figref> maintains balance in the presence of disturbances such as changes to the system's center of mass with respect to the reference point on the surface due to body motion of the subject or contact with other persons or objects.

0022In order to accommodate two wheels instead of the one-wheel system illustrated in <figref idref="f0003">Fig. 4</figref>, the torque desired from the left motor and the torque desired from the right motor can be calculated separately in the general manner described below with reference to <figref idref="f0007">Fig. 8</figref>. Additionally, tracking both the left wheel motion and the right wheel motion permits adjustments to be made to prevent unwanted turning of the device and to account for performance variations between the two drive motors or uneven underlying surfaces.

0023With respect to forward and reverse motion, leaning forward or backward from the inclination associated with a stationary wheelie would lead to motor assistance for movement as a wheelie in the forward or backward direction in an attempt to compensate for an inclination change detected by the pitch sensor (measuring θ). A manual interface such as joystick or force sensing hand rim may be used in certain embodiments to adjust desired wheel velocity or the desired pitch.

0024It can be seen that the approach of adjusting motor torques permits fore-aft stability to be achieved without the necessity of additional stabilizing wheels or struts (although such aids to stability may be provided). In other words, stability is achieved dynamically, by motion of the components of the device (in this case constituting the entire device) relative to the ground.

0025<figref idref="f0004">Fig. 5</figref> is a block diagram showing communication among the control assemblies used in a device such as that depicted in <figref idref="f0001">Fig. 1</figref>. The device may be powered, for example, by battery stack <b>501.</b> Bus <b>509</b> provides communications (here implemented serially) among and power to the various assemblies (<b>507a</b> and <b>507b</b>). Overall system control of the device is provided by central microcontroller board <b>502.</b> Inputs, derived from sources such as the joystick and pitch sensor, to the central microcontroller board <b>502</b> that establishes the basis for system control are provided by the driver interface assembly <b>503,</b> which is described below in connection with <figref idref="f0006">Fig. 7</figref>.

0026The general structure of the left and right wheel control assemblies, identified in <figref idref="f0004">Fig. 5</figref>, used for the wheelchair attitude, is shown in <figref idref="f0005">Fig. 6</figref>. A motor <b>601</b> receives 3-phase power from power converter <b>602.</b> An output from Hall effect sensor <b>612</b> provides information signals to the power converter <b>602</b> to control the phase of power to the motor. Information signals relating to the shaft rotation of the motor <b>601</b> or of the position of mechanical systems powered by the motor <b>601</b> may be provided by one or more of potentiometer <b>604,</b> tachometer <b>611,</b> or incremental encoder <b>613.</b> (Alternatively, the Hall effect sensor <b>612</b> may itself be utilized.) These signals are fed to peripheral microcontroller board <b>603.</b> Additionally, temperature outputs associated with power converter <b>602</b> and motor <b>601</b> provide input signals to the peripheral microcontroller board <b>603.</b> The peripheral microcontroller board <b>603</b> is in turn in communication with the central microcontroller board <b>502</b> over bus <b>509.</b>

0027<figref idref="f0006">Fig. 7</figref> is a block diagram providing detail of the driver interface assembly <b>503</b> of <figref idref="f0004">Fig. 5</figref>. A peripheral microcomputer board <b>701</b> receives input from joystick <b>702</b> as well as from pitch sensor <b>703.</b> The pitch sensor provides information signals as to pitch and/or pitch rate. Other inputs <b>704</b> may also be desirably provided as an input to the peripheral microcontroller board <b>701.</b> Such other inputs may include signals gated by switches (knobs and buttons) for determining the mode of operation (such as lean mode or balance mode, in the case of a cluster-wheeled transporter, as described in <patcit id="pcit0004" dnum="US5701965A"><text>U.S. Patent 5,701,965</text></patcit>). The peripheral microcontroller board <b>701</b> has inputs for receiving signals from the battery stack <b>501</b> as to battery voltage, battery current, and battery temperature. The peripheral microcontroller board <b>701</b> is in communication over bus <b>509</b> with central microcontroller board <b>502.</b>

0028<figref idref="f0007">Fig. 8</figref> shows the control arrangement for the motors of the right and left wheels (corresponding to items <b>107</b> of <figref idref="f0001">Fig. 1</figref>). The arrangement has inputs of rθ̇_wl (linear velocity of the left wheel relative to the world coordinate system) and rθ̇_wr (liner velocity of the right wheel). Inputs θ, θ̇, and error signals x (described below), subject to gains K₁, K₂, K₃, and K₄ respectively, become inputs to summer <b>819,</b> which produces the basic balancing torque command for the wheels, in the general manner described above in connection with <figref idref="f0003">Fig. 4</figref> above. The output of summer <b>819</b> is combined with the output of the yaw PID loop <b>816</b> (described below) in summer <b>820,</b> then divided in divider <b>822</b> and limited in saturation limiter <b>824,</b> to produce the left wheel torque command. Similarly, the output of summer <b>819</b> is combined with the output of PID loop <b>816</b> in summer <b>821,</b> then divided in divider <b>823</b> and limited in saturation limiter <b>825,</b> to produce the right wheel torque command.

0029The average of the compensated linear velocity input signals rθ̇_wl any rθ̇_wr, determined via summer <b>817</b> and divider <b>818,</b> produces a linear velocity error signal ẋ. Displacement error signal x is derived by integrating rθ̇_wl and rθ̇_wr in integrators <b>810</b> and <b>809,</b> limiting the results in saturation limiters <b>812</b> and <b>811,</b> and then averaging their outputs via summer <b>813</b> and divider <b>815.</b> The difference between these displacements determined via summer <b>814,</b> produces the yaw error signal ψ.

0030The yaw error signal ψ is run through a standard proportional-plus-integral-plus-derivative (PID) control loop <b>816,</b> the output of which is combined with the output of the basic balancing torque command of summer <b>819</b> to produce the individual wheel torque commands, which cause the wheels to maintain fore-aft stability and also cause the wheelchair to maintain a forward direction of travel.

0031The controller accepts inputs of wheelchair inclination or rate of change of inclination from the pitch sensor and wheel rotation from the wheel rotation sensors and provides commands altering the braking of the manually driven wheels. As a result, the wheelchair accelerates or decelerates so as to maintain balance on two wheels.

0032While <figref idref="f0007">Fig. 8</figref> shows control algorithms schematically, they may be implemented in a number of embodiments including the use of analog control algorithms or microprocessor programmed digital control, both wholly within the scope of the present invention.