Aerial work platform with novel steering system and related method

Abstract

A vehicle steering system for a compact elevating work platform ("MEWP") or other vehicle and method for dynamically determining independent wheel steer angles to achieve a predetermined steering geometry between the vehicle's steerable wheels is described. The steering system determines adjustments for a plurality of independent wheels based on the angular differences of the plurality of steerable wheels. The independent master and independent follower wheels of the system are not mechanically linked, and there is no mechanical linkage between the plurality of independently steerable wheels, improving space efficiency and steering geometry accuracy. This independent operation facilitates the accommodation of steering actuators in limited side compartments, thereby allowing the machine lift mechanism to occupy space previously used for mechanical steering connections between wheel assemblies.

Description

[Technical field]

[0001] The present invention relates generally to a novel steering mechanism and control system for a motor vehicle. More specifically, the present invention relates to a compact steering system that does not require a steering linkage or other connection between a master wheel and a follower wheel. The steering system is operable to monitor the steering angles of the master wheel and the follower wheel and actively adjust the steering angle actuators of the follower wheels in response to the steering angle of the master wheel.

[0002] This application claims priority to U.S. Provisional Patent Application No. 63303042, filed January 26, 2022, which is incorporated herein by reference in its entirety. U.S. Patent Application "Aerial Work Platform with Novel Steering System and Related Method" Inventors: Matthew DYE, Gary CROOK [Background technology]

[0003] Background Discussion Aerial work platforms (MEWPs) are used to perform work at a variety of heights and locations. When performing work in a narrow space, such as a ceiling grid, if the MEWP has a footprint that is wider or longer than the narrow space, this can make the work difficult by limiting the allowable vertical movement of the platform. Traditional MEWPs typically have wheel assemblies connected by mechanical linkages that run throughout the vehicle. These mechanical linkages take up space in the center of the MEWP's chassis, which results in the chassis being larger than necessary.

[0004] Furthermore, due to stiffness and limitations of the mechanical linkage, the mechanical linkage causes the steering geometry (i.e., the relative angles of the wheels) between the wheels to not follow an ideal steering geometry. As the wheel assemblies rotate, the mechanical linkage cannot achieve the ideal relative angles between the wheel assemblies, for example according to the Ackermann steering geometry. This can cause wheel skidding and scuffing during turning maneuvers, wear and tear on the wheel assemblies, and damage to the riding surface. Summary of the Invention [Problem to be solved by the invention]

[0005] Therefore, there is a need for improved, efficient, reliable and compact steering systems and methods for MEWPs and similar small vehicles. Such improved systems would facilitate improved vehicle performance and utility. [Means for solving the problem]

[0006] Summary of the Invention The present invention provides a vehicle steering system for a MEWP or other vehicle and a method for determining independent wheel steering angles to substantially achieve a predetermined steering geometry between the steerable wheels of the vehicle. The steering system provides an improved alignment protocol that determines an angular position of an independent master wheel and an angular position of an independent follower wheel. In some embodiments, an Ackerman geometry is used and the system is operable to determine a rotational position of the master wheel and convert that position to a corresponding target position of the independent follower wheel without the need for a mechanical linkage between the two. The system according to the present disclosure adjusts the multiple independent wheels based on electronic data that provides the angular difference between the multiple steerable wheels and the predetermined steering geometry programmed into an electronic controller. Effect of the Invention

[0007] Vehicles using the present steering system (such as MEWPs) may achieve a lower profile, smaller vehicle chassis, and / or smaller vehicle footprint due to the elimination of the mechanical connection between the master wheel actuator and the follower wheel actuator. The elimination of the mechanical connection between the master wheel actuator and the follower wheel actuator allows flexibility in the placement of the master wheel steering actuator and the follower wheel steering actuator, allowing for more compact and efficient vehicle designs.

[0008] A further advantage of the steering system and method of the present invention is that the master and follower wheels can be more precisely adjusted to a given geometry (e.g., Ackermann geometry, parallel steering, etc.) than conventional systems that utilize mechanical linkages between multiple steerable wheels. Mechanical linkages can roughly approximate the dynamic shift of a pair of steerable wheels moving in concert to the steering geometry. However, the ability to match an ideal steering geometry is limited due to the somewhat crude mechanical arrangement of the rigid linkages connecting the steering yokes, etc. of the steerable wheels. The master and follower wheels of the present invention operate independently under the direction of an electronic controller (e.g., a microcontroller, a PLC system, or a general-purpose computer), allowing finer dynamic adjustment of the independent wheel assemblies, and allowing a greater approximation of the ideal steering geometry (e.g., Ackermann geometry, parallel steering, etc.) over the full range of toe angles (angular orientation of the tire relative to the centerline of the vehicle) of the master wheel. The approximation of the ideal steering geometry allows the wheels of the vehicle to skid or rub on the ground less during turning compared to mechanically linked systems. This increases the useful life of the vehicle and prevents damage to the surface the vehicle drives over.

[0009] The steering system of the present invention may utilize small electric actuators mechanically connected to each steering yoke and in electronic communication with an electronic controller. The electronic controller may be programmed with mechanical control programming operable to use position feedback from each electric actuator to calculate an ideal position of the follower wheels based on (1) the position change of the master wheel and (2) a selected ideal steering geometry. For example, the electronic controller may receive master wheel position data from a sensor (e.g., an encoder), calculate the position change of the follower wheels as the difference between a calculated target angle (e.g., the intersection angle of the follower wheel axis and the master wheel axis on a virtual pivot center according to an Ackermann geometry) and the current toe angle of the follower wheels based on the position feedback of the follower wheels (e.g., provided by an encoder), and then convert the position change value into an electrical signal that can be communicated to the motor of the electric actuator of the follower wheels. The steering system is operable to adjust the angular position of the wheels according to a predetermined steering geometry (e.g., Ackermann steering) based on the sensor data (e.g., encoder data) and / or electronic input from the electronic controller.

[0010] In some embodiments, the present invention provides a novel approach for determining a geometry (e.g., Ackermann geometry) state of a steering system. The system is arranged to receive a first signal representative of a first toe angle of a first steerable wheel (e.g., a master wheel) and a second signal representative of a second toe angle of a second steerable wheel (e.g., a follower wheel) when the first steerable wheel is located at a first toe angle. A target angle (e.g., according to the Ackermann geometry) of the follower wheel is calculated based on a wheelbase value representative of a length of a wheelbase of the vehicle, a wheelbase width value of the vehicle, and the first toe angle. The system determines an angle change of the follower wheel based on the current second toe angle and the calculated target angle (e.g., according to the Ackermann geometry). The disclosed method of achieving an ideal steering geometry provides an improved alignment procedure that generates a precise target angle of the follower wheel that closely matches the ideal angular relationship between the master wheel and the follower wheel according to a selected steering geometry. The present disclosure provides a novel procedure for determining a steering geometry based on a preferred steering geometry, which may be, but is not limited to, an Ackermann geometry.

[0011] In some embodiments, the electric actuator for the steerable wheels may be a linear actuator located at or near the outer wall of the vehicle. For example, the electric actuator may be a linear actuator with a stroke length in the range of about 10 mm to about 500 mm (e.g., in the range of about 50 mm to about 250 mm, in the range of about 75 mm to about 125 mm, in the range of about 100 mm, or any value or range between any values ​​therein). In other embodiments, the electric actuator may be a rotary actuator located at or near the outer wall of the vehicle chassis. For example, the electric actuator may be a rotary actuator with an angular range of about 10° to about 360° (e.g., in the range of about 30° to about 330°, in the range of about 60° to about 270°, in the range of about 90° to about 180°, or any value or range between any values ​​therein). There is no mechanical connection between the master wheel assembly and the follower wheel assembly, or between the steering actuator associated with the master wheel assembly and the steering actuator associated with the follower wheel assembly. This allows for a compact design as there are no cross-chassis mechanical linkages between the master and follower wheel assemblies. Each wheel assembly is housed and completely contained within its own side compartment with no cross-chassis mechanical linkages.

[0012] In some embodiments, the electric actuator may include an electronic position feedback device (e.g., magnetic position encoder, optical position encoder, potentiometer, etc.) operable to track changes in the toe angle of the wheel and provide such toe angle data to the electronic controller via wired or wireless electronic communication. The position of the master control wheel may be controlled by a human operator via a steering mechanism, such as a steer-by-wire system utilizing an operator-controlled handle steering (e.g., joystick steering mechanism), a rocker switch, a steering wheel, or other mechanism. A counterclockwise rotation or left movement of the steering mechanism may be adjusted to rotate the master wheel left toward a predetermined toe angle, and a clockwise rotation or right movement of the steering mechanism may be adjusted to rotate the master wheel right toward a predetermined toe angle. The rotational position of the master wheel may be monitored by a position sensing device (e.g., encoder) in the master wheel and electronically transmitted to the electronic controller. The electronic controller may be programmed to calculate steering commands to the follower wheels based on the changes in the position of the master wheel and a selected predetermined steering geometry programmed into the electronic controller of the steering system. Other suitable calibrations of the steering actuator may also be used.

[0013] The steering system of the present invention may utilize open loop control for steering the master wheel and (1) monitoring the position of the master wheel, (2) monitoring the position of the follower wheel, and (3) closed loop control for steering the follower wheel. The electronic controller may include machine control programming that receives electronic data from a steering control mechanism operated by a human operator and determines the steering direction of the master wheel and the movement of the MEWP vehicle. The determination of the direction of the follower wheel may be determined using encoder data from the master wheel assembly and the follower wheel assembly. Both the master wheel assembly and the follower wheel assembly may include an encoder (e.g., an optical encoder, a magnetic encoder, a potentiometer, or other precision sensor) that is operable to provide precise position data to the machine control programming so that the controller can calculate the steering angle of the follower wheel. In some embodiments, steering input by the operator (e.g., directional movement of a joystick or rotation of a steering wheel) may be monitored by the controller and may be sufficient data provided to the machine control programming to precisely monitor the steering angle of the master wheel.

[0014] The machine control programming of the electronic controller may include machine executable instructions (e.g., software, firmware, and / or other programming) stored in memory that enable one or more processors of the electronic controller to receive input from the encoders regarding the position of the steerable wheels and use such data to control the steering angle of the follower wheels. The controller executing the machine control programming may be a microcontroller, a PLC system, or a general purpose computer, and is operable to use feedback position data from the master wheel position device to identify its position relative to a predetermined reference point within the range of toe angles. For example, the predetermined reference point may be the midpoint of the range of toe angles (e.g., where the wheels are parallel to the centerline of the vehicle), which may be the zero position. Rotation to either side of the toe angle may be expressed as a value relative to the zero position. For example, in the case of a linear actuator, the position of the wheel is determined by the distance of extension or retraction from a zero position measurement, which may be the mid-extension point of the linear actuator. In the case of a rotary actuator, the position of the wheel is determined by the angle of rotation, clockwise or counterclockwise, from the zero position measurement. The zero position measurement may be the rotational position where the wheels are parallel to the centerline of the vehicle chassis. A controller executing machine control programming is operable to switch to treat either front wheel assembly as master and to designate the master wheel between the left and right wheel assemblies. For example, the operator interface may have a selection mechanism for selecting the left or right wheel assembly as the master wheel assembly.

[0015] The machine control programming may be programmed to recognize the midpoint of the steering actuator of the master wheel assembly and the midpoint of the steering actuator of the follower wheel assembly as the zero position. The machine control programming may include an algorithm that utilizes position data provided by an encoder associated with the master wheel assembly and an encoder associated with the follower wheel assembly. For example, the machine control programming may utilize the following calculation for the linear actuator to turn the follower wheel when the master wheel is being controlled to turn left (e.g., with the linear actuator extended): y = 0.0168x 3 + 0.2869x 2 - 0.5817x + 1, where x = (Master 1 / 2 measured position) / (Master 1 / 2 full length position) Follower 1 / 2 actuator position = Master 1 / 2 full length position * y In this example, the machine control programming can utilize the following calculation to turn the follower wheel when the master wheel is controlled to turn right (e.g., the linear actuator is retracted): y = (0.0168x 3 + 0.2869x 2 - 0.5817x + 1) -1 Where: x = (Master 1 / 2 measured position) / (Master 1 / 2 full length position) Follower 1 / 2 actuator position = Master 1 / 2 full length position * y

[0016] In general, the controller may include one or more processors for the following purposes: (1) To receive electronic data from encoders, motors, steering mechanisms, and other electrical and electronic devices in the MEWP vehicle; (2) To execute machine control programming; (3) To read and store data stored on hard drives, RAM, and / or other memory in electronic communication with one or more processors; (4) To perform other functions typically performed by a processor, a memory, a data storage device for storing data, an input device for inputting data, and a bus that provides electronic communication among the input device, the memory, the data storage device, and one or more processors. The controller may be wired or wirelessly connected to one or more traction motors, encoders connected to the wheel assemblies, steering mechanism and operator interface, actuators of the telescopic lift mechanism, and other electrical devices and mechanisms present on the MEWP. The controller may be operable to send commands via electronic signals to each electrical device incorporated in the MEWP vehicle.

[0017] The steering system and method may be incorporated into a MEWP adjustable platform vehicle or a scissor lift. The scissor lift may include a vehicle chassis with a central cavity that houses a telescopic lift mechanism, a telescopic lift mechanism, a base, an actuator for extending and lowering the telescopic lift mechanism, and a platform assembly. The telescopic lift mechanism may extend from the central cavity by actuation of the actuator. The MEWP may have a telescopic lift mechanism. In some embodiments, the telescopic lift mechanism may be an extendable scissor lift mechanism. The scissor lift mechanism may include a series of linked foldable support members connected to each other using a central pivot pin and an outer pivot pin. The support members include a bottom foldable support member pivoted inside a central compartment of the chassis and a top foldable support member that may be pivoted to the underside of the platform assembly. Alternatively, the telescopic lift mechanism may be an extendable boom (e.g., a telescopic boom) that is storable and connectable to a central compartment of the chassis, and the distal end of the boom may be connected to the platform assembly, such as that disclosed in U.S. patent application Ser. No. 17 / 010,735, filed September 3, 2020, which is incorporated herein by reference in its entirety.

[0018] The platform assembly may be mechanically connected and positioned above the telescopic lift mechanism and move vertically relative to the base with extension of the telescopic lift mechanism. The platform assembly may include a guard rail, cage, or basket within which a human operator may safely position, as disclosed in U.S. Patent Application No. 16 / 275,854, filed February 14, 2019, which is incorporated herein by reference in its entirety. Operator controls may be located and attached to an operator interface located within the guard rail, cage, or basket. The operator controls include lift, drive, and steering controllers. The steering controller may be a proportional drive joystick, steering wheel, two-axis rocker control, or other suitable steering mechanism. The operator interface may further include controls for directing boom functions (raise or lower or extend, platform height and platform rotation, engine start, and other functions). The operator controls may be in electronic communication with the electronic controller.

[0019] The chassis may house one or more motors mechanically connected to the wheels (e.g., rear wheels) to rotate the wheels and propel the vehicle. The one or more motors may be, for example, electric motors, hydraulic drives, or other suitable devices. In some embodiments, one or more propulsion motors may be mechanically connected to the rear wheels. The rear wheels may be directionally fixed so that they are not used to steer the vehicle. Each rear wheel may be mechanically connected to a separate motor, and each motor may be in electronic communication with a controller, which may send electronic control signals to the motors via a wired or wireless connection. The MEWP may also include a ground control panel within the chassis that allows lifting or other functions to be operated from the ground and allows a service technician, ground personnel, or others to operate the MEWP in certain situations (e.g., breakdown, emergency, etc.) or to override platform controls.

[0020] Other advantages of the present disclosure will become readily apparent from the following detailed description, which is merely illustrative and not limiting of the present disclosure. As will be understood, the present disclosure is capable of other different embodiments, and its several details can be modified in various obvious respects without departing from the present disclosure. Thus, the drawings and description should be regarded as illustrative in nature, and not restrictive. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a perspective view of a MEWP vehicle according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a first side view of a MEWP vehicle according to one embodiment of the present invention. [Diagram 3] FIG. 3 is a second side view of a MEWP vehicle according to one embodiment of the present invention. [Figure 4] FIG. 4 is a perspective view of a MEWP vehicle with the platform assembly removed to expose the undercarriage, according to one embodiment of the present invention. [Diagram 5]FIG. 5 is a front view of a MEWP vehicle according to one embodiment of the present invention with the front plate of the chassis removed to expose the internal structure. [Figure 6] FIG. 6 is a perspective view of a MEWP vehicle with the platform assembly extended and elevated in accordance with one embodiment of the present invention. [Figure 7] FIG. 7 is a top view of the interior chassis of a MEWP vehicle according to one embodiment of the present invention. [Figure 8] FIG. 8 is a close-up view of the interior of a wheel compartment of a MEWP vehicle in accordance with one embodiment of the present invention. [Figure 9] FIG. 9 is an overhead view of the interior of a MEWP vehicle chassis during a turning maneuver in accordance with one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Detailed Description of the Drawings Reference will now be made in detail to certain embodiments of the present invention. Examples of these embodiments are illustrated in the accompanying drawings. Although the present invention will be described with reference to these drawings and specific implementations and examples of the present embodiments, it will be understood that such implementations and examples are not intended to limit the present invention. On the contrary, the present invention is intended to cover alternatives, modifications, and equivalents that are included within the spirit and scope of the present invention as defined by the claims. In the following disclosure, specific details are set forth to provide a thorough understanding of the present invention. References throughout this document to various features of the "present invention" do not imply that all claimed embodiments or methods must include the referenced features. It will be apparent to one skilled in the art that the present invention may be practiced without these specific details or features.

[0023] Reference will now be made to the example figures of the accompanying drawings, in which like reference characters may be used to denote like or corresponding parts throughout the several views of the drawings.

[0024] 1-9, a MEWP vehicle 100 is shown. The MEWP vehicle 100 may be a scissor lift vehicle, a boom lift vehicle, or a similar vehicle, and is shown in FIG. 1 as a scissor lift. The MEWP vehicle 100 includes a vehicle chassis 101 having a central compartment 101a, a first side compartment 101b, and a second side compartment 101c, each of which may serve to house various components of the MEWP vehicle 100. The vehicle 100 includes a telescopic lift mechanism 105 that is stowed and stored within the central compartment 101a when in a retracted position. The telescopic lift mechanism 105 is coupled to the chassis 101 and may support a platform assembly 102. The platform assembly 102 may be connected to an upper portion of the telescopic lift mechanism 105 such that as the telescopic lift mechanism 105 extends from the central compartment 101A, the platform assembly 102 is raised.

[0025] As shown in FIG. 1, the telescopic lift mechanism 105 is a scissor lift structure that is comprised of an assembly of foldable support members 105A connected to one another using a central pivot pin 105B and outer pivot pins 105C. The central pivot pin 105B and outer pivot pins 105C pass through adjacent support members 105A to rotatably connect the support members 105A in a vertically telescopic assembly. The bottom foldable support member 105A may be rotatably connected to the central compartment 101A and the top foldable support member 105A may be rotatably connected to the underside of the platform assembly 102. FIG. 5 is a front view of the MEWP 100 with the front exterior panel of the chassis 100 removed. The telescopic lift mechanism 105 is shown in a retracted position. The telescopic lift mechanism 105 can be seen housed in the central compartment 101A of the chassis 101.

[0026] Adjusting the angular relationship between adjacent support members 105A vertically away from the chassis 101 and away from each other extends the telescopic lift mechanism 105, changing the position (height) of the platform assembly 102 relative to the chassis 101. The foldable support members 105A of the telescopic lift mechanism 105 can be folded and unfolded using lift actuators (not shown). The lift actuators can be, for example, hydraulic cylinders, pneumatic cylinders, electric linear actuators, or other suitable actuators. The lift actuators can be in electronic communication with the controller 140 and controlled by an operator via the operator interface 102 or the ground control device 131. The lift actuators selectively apply forces to the telescopic lift mechanism 105 to control the position of the telescopic lift mechanism 105. For example, extending the actuators raises the foldable support members, and moving the lift actuators in the opposite direction lowers the foldable support members 105A. FIG. 6 shows the telescopic lift mechanism 105 fully extended from the chassis 101.

[0027] 7-8 are internal views of the chassis 101, showing the internal structure. In some embodiments, the vehicle's propulsion may be driven by electric motors 107A and 107B mechanically connected to the rear wheels 104A and 104B. The electric motors 107A and 107B are operable to propel the rotation of the wheels 104A and 104B, respectively. The electric motors 107A and 107B may be in electrical communication with the controller 140, and their operation may be controlled by an operator via open-loop command operation inputted via the operator interface 102A. In such an embodiment, steering commands are routed directly from the steering input 102B to the electric motors 107A and 107B, or relayed via the controller 140 and routed to the electric motors 107A and 107B. The operator interface 102A may include a steering input 102B, which may be a rocker switch joystick or other mechanism. This mechanism allows an operator to select direction based on steering switch commands, etc., and adjust speed based on speed controls provided at operator interface 102 A. Steering input 102 B may be electromechanical or may be in electronic communication with controller 140.

[0028] In some embodiments, steering signals may be sent from the steering input 102B to the controller 140, which then relays them to the electric actuators 108A and 108B. Speed ​​may be controlled by a speed control mechanism (dial, throttle switch, depressible pad or switch, etc.) on the operator interface 102A. The controller 140 may cause the MEWP to track direction and speed as instructed by the operator via the steering input 102B. The rear wheels 104A and 104B may not have directional movement and may not be used to steer the vehicle. Additionally, they may be independently mounted to the chassis 101 and aligned but not mechanically connected. The absence of a rear axle between the rear wheels 104A and 104B may provide additional unobstructed space in the central compartment 101A to house the telescopic lift system 105. This allows the chassis 101 to be smaller in size and more compact.

[0029] The front wheel assemblies 106A and 106B and the rear wheel assembly 104 may be mounted on the sides of the chassis 101. The front wheel assemblies 106A and 106B each include a yoke (109A and 109B, respectively) for connection to an actuator that controls the steering of the wheel assembly. The steering system includes two independent steering actuators 108A and 108B, which are separately connected to the wheel assemblies 106A and 106B, respectively. The steering actuator 108A is mechanically connected to the wheel assembly 106A, and the steering actuator 108B is mechanically connected to the wheel assembly 106B. There is no mechanical connection between the first wheel assembly 106A and the second wheel assembly 106B, or between the steering actuators 108A and 108B. This allows for a compact design since there is no mechanical linkage between the first wheel assembly 106A and the second wheel assembly 106B across the central compartment 101A. The first wheel assembly 106A is housed and completely nested within the first side compartment 101B, and the second wheel assembly 106B is housed and completely nested within the second side compartment 101C.

[0030] In some embodiments, the electric actuators 108A and 108B for the steerable wheels 103A and 103B may be linear actuators located at or near the outer wall of the chassis. The electric actuators may be linear actuators with a stroke length in the range of about 10 mm to about 500 mm (e.g., in the range of about 50 mm to about 250 mm, in the range of about 75 mm to about 125 mm, about 100 mm, or any value or range therein). The actuators 108A and 108B are in electronic communication with an electronic controller 140, which provides control signals to the actuators 108A and 108B.

[0031] The electronic controller 140 may be one or more general purpose computers with at least one processor (central processing unit [CPU]) operable to execute machine executable instructions and provide control signals to the actuators 108A and 108B, the boom actuators, the motors 107A and 107B, and other electrical and electronic components of the vehicle 100. The system may further include other components required for the functionality of a general purpose computer, well known to those skilled in the art, such as a power supply, a hard drive, a random access memory (RAM), an internet connection device, software, etc. The system may include a logic unit for receiving and processing electronic data, such as a package of executable instructions stored on a hard drive and executable by a processor. The machine control programming is stored in the memory of the controller 140 and is accessed and executed by one or more processors of the controller 140. The controller 140 executing the machine control programming receives electronic data from the encoder of the electric actuator 108A of the master wheel to accurately determine the steering angle of the master wheel. The steering angle of the follower wheel (e.g., wheel assembly 106B) may be determined in part from encoder data from the follower wheel motorized actuator 108B. This data may be used by the controller 140 executing the machine control programming to calculate the steering angle command for the follower wheel (e.g., wheel 103B).

[0032] The controller 140 is operable to treat either front wheel assembly as the master and to switch the master wheel designation between the left and right wheel assemblies. For example, the operator interface may include a selection mechanism for selecting the left or right wheel assembly as the master wheel assembly. The wheel assembly selected as the master wheel may be under the direct control of the operator interface 102A. For example, wheel assembly 103A may be treated as the master wheel. The MEWP may utilize open-loop control for steering the master wheel (e.g., wheel assembly 103A) and closed-loop control for the follower wheel (e.g., wheel assembly 103B). Pressing a rocker switch on the operator interface 102 (or in some embodiments lateral movement of the joystick to the left) can adjust the master wheel to rotate left at a predetermined toe angle, and movement to the right can adjust the master wheel to rotate right at a predetermined toe angle. The rotational position of the master wheel may be monitored by a master wheel position sensing device (e.g., an encoder in the motorized actuator 108A) and may be electronically transmitted to the electronic controller 140, providing the controller 140 with position data of the master wheel (e.g., wheel 103A). The electronic controller 140, running the machine control programming, may then calculate steering commands to the follower wheel (e.g., wheel 103B) based on the changes in steering direction of the master wheel, the positions of the follower wheels, and the predefined steering geometry selected and programmed for this machine control programming.

[0033] When the steering input of the steering input 102B initiates rotation of the master wheel (e.g., wheel 103A), the encoder data from the master wheel electric actuator 108A and the follower wheel electric actuator 108B can be used to determine the target angle of the follower wheel (e.g., wheel 103B). The encoders of the master wheel assembly and the follower wheel assembly can be operative to provide accurate position data to the controller 140, allowing the controller 140 to calculate the target steering angle of the follower wheel (e.g., wheel 103B). The electronic controller 140, which executes the machine control programming, can be operative to receive feedback position data from the encoder of the master wheel (e.g., wheel 103A) and can identify its position relative to a predetermined reference point within the toe angle of the master wheel (e.g., wheel 103A). The position of the master wheel (e.g., wheel 103A) is determined by the distance of extension or retraction from a reference point, which may be the mid-extension point of the linear actuator 108A. The position of the follower wheels (e.g., wheel 103B) is also determined by the distance of extension or retraction from a reference point, which may be the mid-extension point of the linear actuator 108B. The controller 140 executing the machine control programming can calculate the target angle of the follower wheels based on the steering angle of the master wheel and the steering angle of the follower wheels whenever the steering angle of the master wheel changes. The calculations performed by the controller 140 utilize the encoder position data from each linear actuator 108A and 108B and the predefined steering geometry of the system. The encoders for these wheel steering actuators are not shown separately since they may be built into the linear actuator devices 108A and 108B. In some embodiments, the predefined steering geometry is an Ackerman steering geometry.

[0034] FIG. 9 illustrates an exemplary turning maneuver according to the present invention, where the predetermined steering geometry is the Ackermann geometry. The fixed rear wheels 104A and 104B are mounted in line but independently to rotate without a connecting axle. The steerable master wheel assembly 103A and the follower assembly 103B are mounted at or near the front of the chassis 101 in line laterally to rotate but independently to rotate without a connecting axle between them. The lack of axles between the front and rear wheels allows them to be fully contained within the side compartments 101B and 101C of the chassis 101. This design allows space in the central compartment 101A of the chassis 101 to accommodate the telescopic lift mechanism 105.

[0035] In Ackermann steering geometry, the outside wheel must turn a smaller angle than the inside wheel to prevent wheel scrubbing as the vehicle turns. The centerlines of the rear and front wheel axes are represented by wheel axes A, B, and C. Lines A and B represent the axes of the master wheel assembly 103A and follower assembly 103B, respectively, and line C represents the aligned axis of the rear wheel. A steering system with perfect Ackermann geometry will have an optimal turning motion relative to point D, where axes A, B, and C intersect. When the master wheel turns to change direction as a result of actuation of the master wheel actuator 108A as commanded by the steering input 102B, (1) an encoder on the master wheel assembly 103A measures the change in the toe angle (e.g., angle A) of the master wheel to provide accurate data to the controller 140; (2) an encoder on the follower wheel assembly 103B measures the toe angle of the follower wheel to provide accurate data to the controller 140; (3) The controller calculates the target toe angle (e.g., angle B), (4) The controller 140 sends a control signal to the follower wheel actuator 108B to rotate the follower wheel from the current toe angle to the target toe angle (e.g., angle B) so that the master wheel axis and the follower wheel axis intersect at the rear wheel axis (e.g., point D) to achieve the Ackermann steering geometry. This process is continually repeated as the operator operates the MEWP vehicle 100, each time the operator inputs various steering inputs to the steering mechanism.

[0036] The steering system of the present invention is operable to more precisely adjust the toe angles of the master and follower wheels according to a predetermined geometry (e.g., Ackermann geometry) through the dynamic process of driving and steering the MEWP vehicle 100 than conventional systems that utilize mechanical linkages between the steerable wheels. Mechanical linkages somewhat reduce the ability of such systems to match the ideal Ackermann steering geometry. Because the master and follower wheels of the present invention operate independently under the direction of the electronic controller 140, finer, more dynamic adjustments of the independent wheel assemblies are possible, allowing for greater approximation of the ideal steering geometry over the full range of steerable wheel toe angles. Approaching the ideal steering geometry results in less slippage or rubbing of the vehicle's wheels on the ground during turning compared to mechanically linked systems.

[0037] It is to be understood that variations, modifications, and substitutions of the embodiments of the present invention and their uses can be made without departing from the scope of the present invention. It is also to be understood that the present invention is not limited by the specific embodiments, descriptions, or illustrations, or combinations of components or steps disclosed herein. These embodiments have been selected and described in order to best explain the principles of the invention and its practical application, thereby enabling those skilled in the art to best utilize the invention and its various embodiments with various modifications suited to the particular use envisaged. Although reference has been made to the accompanying drawings, it is to be understood that these drawings are illustrative and are not intended to limit the scope of the present invention. It is intended that the scope of the present invention be defined by the claims appended hereto and their equivalents.

Claims

1. a. a vehicle chassis; b. an independently steerable first wheel; c. a first linear steering actuator mechanically coupled to the first independently steerable wheel; d. an independently steerable second wheel; e. a second linear steering actuator mechanically coupled to the second independently steerable wheel; a first wheel rotatably coupled to a first steering axis that is geometrically fixed relative to the vehicle chassis; a second wheel rotatably coupled to a second steering shaft that is geometrically fixed relative to the vehicle chassis; a first linear steering actuator housed in the first side compartment; a second linear steering actuator housed in the second side compartment; The aerial work platform, wherein there is no mechanical steering connection between the first independently steerable wheel and the second independently steerable wheel.

2. the vehicle chassis includes a central compartment; 2. The vehicle of claim 1, wherein the central compartment extends from the front of the vehicle chassis to the rear of the vehicle chassis.

3. 10. The vehicle of claim 1, further comprising a plurality of independently rigid rear wheels mounted at or near the rear end of the vehicle chassis, the plurality of rear wheels having no mechanical linkages therebetween.

4. 3. The vehicle of claim 2, wherein a first steering actuator is housed in a first side compartment and is not present in the center compartment.

5. 3. The vehicle of claim 2, wherein a second steering actuator is housed in a second side compartment and is not present in the center compartment.

6. 10. The vehicle of claim 1, further comprising a controller having a processor for processing data, a memory, and a data storage device for storing data.

7. The data storage device, upon execution of instructions by the processor, causes the system to: receiving a first signal representing a first toe angle of said first independently steerable wheel, wherein said first signal corresponds to a position of said first linear steering actuator; b. calculating a target toe angle for the second independently steerable wheel based on the first toe angle and a predetermined steering geometry; c) receiving a second signal representing a starting second toe angle of the second independently steerable wheel; d. calculating an angular difference between the target toe angle and the second toe angle to determine an angular adjustment for the second independently steerable wheel; e. sending a steering command from the controller to the second linear steering actuator of the second independently steerable wheel to turn the second independently steerable wheel in accordance with the angle adjustment; 7. The vehicle of claim 6, further comprising machine-readable instructions stored thereon to cause the vehicle to: Claim 8: A vehicle chassis having a central compartment, a first side compartment, and a second side compartment; b) an independently steerable first wheel mounted for rotation about a first steering axis that is geometrically fixed relative to the vehicle chassis; c. a first linear steering actuator mechanically coupled to a first independently steerable wheel and housed in the first side compartment; d. an independently steerable second wheel mounted for rotation about a second steering axis that is geometrically fixed relative to the vehicle chassis; e. a second linear steering actuator mechanically coupled to a second independently steerable wheel and housed in the second side compartment; f. A controller having a processor for processing data, a memory, and a data storage device for storing data; Equipped with there is no mechanical linkage between the first independently steerable wheel and the second independently steerable wheel; The data storage device comprises the machine-executed steps of: i. receiving a first signal representing a first toe angle based on a position of the first linear steering actuator of the first independently steerable wheel; ii. calculating a target toe angle for the second independently steerable wheel based on a predetermined steering geometry and a position of the first linear steering actuator; iii. receiving a second signal representative of a second toe angle of the second independently steerable wheel; iv. calculating an angular difference between the target toe angle and the second toe angle to generate a steering command, and transmitting the steering command from the controller to the second linear steering actuator of the second independently steerable wheel to turn the second independently steerable wheel toward the target toe angle; An aerial work platform storing instructions for causing the processor to perform the above.

9. A first signal representing a first toe angle is determined by a movement of the position of the first linear steering actuator; a neutral position of the first linear steering actuator such that the first independently steerable wheel is aligned with the first side compartment; 9. The aerial work platform of claim 8, wherein the first and second linear steering actuators are operatively connected to the first and second independently steerable wheels, respectively, such that actuation of the first and second linear steering actuators causes corresponding rotational movement of the corresponding independently steerable wheels about a fixed steering axis.

10. An aerial work platform as described in Claim 9, wherein the second signal representing a second toe angle is measured by an electromechanical sensor and compared with the position of the second linear steering actuator to calculate the angular difference between the target toe angle and the second toe angle.

11. An aerial work platform as described in Claim 10, wherein the comparison between the position of the second linear steering actuator and the second toe angle generates a steering command for the second linear steering actuator to rotate the independently steerable second wheel to a target toe angle until the angular difference between the target toe angle and the second toe angle becomes zero.

12. A method for determining steering geometry for a vehicle of a type having independently steerable first and second wheels, comprising: each of the first and second independently steerable wheels mounted for rotation about a steering axis that is geometrically fixed relative to the vehicle chassis; the steering system includes a wheel angle sensor device for generating a toe angle signal representative of the toe angle of the steerable wheels; The method includes machine-executed steps: i. receiving a first signal representative of a first toe angle of a first independently steerable wheel; ii. calculating a target toe angle for a second independently steerable wheel based on a predetermined steering geometry; iii. receiving a second signal representative of a second toe angle of a second independently steerable wheel; iv. calculating an angular difference between the target toe angle and the second toe angle to generate a steering command, wherein the steering command eliminates scrub of the independently steerable second wheel; v. transmitting the steering command from the controller to a linear steering actuator of a second independently steerable wheel to turn the second independently steerable wheel. determining an Ackermann angle of the second independently steerable wheel based on a second toe angle of the first independently steerable wheel; b) calculating an electrical signal value that will activate the linear steering actuator of the second independently steerable wheel to achieve the Ackermann angle; c) transmitting the electrical signal value from an auxiliary controller to the electrical linear steering actuator of the second independently steerable wheel; The method of claim 12 further comprising:

14. The controller is further operable to receive a third signal representing a third toe angle of the first independently steerable wheel when the first independently steerable wheel is turned in a second direction by operation of a steering mechanism; 13. The method of claim 12, wherein the third toe angle is determined by the position of the linear steering actuator.

15. The method of claim 14, further comprising calculating a second target toe angle for the independently steerable second wheel based on the third toe angle and the predetermined steering geometry.

16. The method of claim 15, further comprising calculating a second angular difference between the second target toe angle and the toe angle of the independently steerable second wheel to generate a second steering command.

17. The vehicle of claim 1, further comprising a telescoping lift mechanism operable to be extended from and retracted into the vehicle chassis.

18. A vehicle as described in claim 17, further comprising a telescopic lift mechanism actuator operable to extend the telescopic lift mechanism from the vehicle chassis and to retract the telescopic lift mechanism into the vehicle chassis.

19. A vehicle as described in claim 17, further comprising a platform assembly positioned at an upper end of the telescopic lift mechanism and operable to move vertically as the telescopic lift mechanism is extended.

20. The vehicle of claim 6, further comprising an operator input device for inputting data.

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