Method and apparatus for controlled omnidirectional movement of payloads

A payload platform includes a platform and a castor assembly coupled to the platform. The castor assembly includes a body, a first wheel coupled to the body, and a second wheel coupled to the body. The first wheel and the second wheel are individually actuatable. A sensor is coupled to the body. A control unit is operably coupled to the sensor and operably coupled to the first wheel and to the second wheel. The sensor detects an area surrounding the platform, determines presence of obstacles, and transmits a signal to the control unit corresponding to the area surrounding the platform. The control unit directs the first wheel and the second wheel to rotate in a prescribed manner so as to achieve a prescribed movement of the platform.

BACKGROUND

Technical Field

The present disclosure relates generally to mobility systems for payloads and more particularly, but not by way of limitation to mobility systems utilizing actively-controlled split offset castors having embedded sensing and computation functions.

History of the Related Art

Movement of large payloads is common in the shipping and manufacturing industries. In the specific case of air and ocean transport, it is often necessary to maneuver large shipping containers to precise locations without impact or damage to surrounding items. Improper movement of a shipping container can damage the container, result in unstable packing of the container, and, in a worst case scenario, can result in the loss of the cargo or damage to the shipping vessel. Thus a need persists for methods and systems to provide controlled omni-directional movement to a payload.

SUMMARY

This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it to be used as an aid in limiting the scope of the claimed subject matter.

In one aspect, the present disclosure relates to a payload platform. The payload platform includes a platform and a castor assembly coupled to the platform. The castor assembly includes a body, a first wheel coupled to the body, and a second wheel coupled to the body. The first wheel and the second wheel are individually actuatable. A sensor is coupled to the body. A control unit is operably coupled to the sensor and operably coupled to the first wheel and to the second wheel. The sensor detects an area surrounding the platform, determines presence of obstacles, and transmits a signal to the control unit corresponding to the area surrounding the platform. The control unit directs the first wheel and the second wheel to rotate in a prescribed manner so as to achieve a prescribed movement of the platform.

In another aspect, the present disclosure relates to castor assembly. The castor assembly includes a body, a first wheel coupled to the body, and a second wheel coupled to the body. The first wheel and the second wheel are individually actuatable. A sensor is coupled to the body. A control unit is operably coupled to the sensor and operably coupled to the first wheel and to the second wheel. The sensor detects an area surrounding the body, determines presence of obstacles, and transmits a signal to the control unit corresponding to the area surrounding the body. The control unit directs the first wheel and the second wheel to rotate in a prescribed manner so as to achieve a prescribed movement of the platform.

In another aspect, the present disclosure relates to a method. The method includes detecting via a sensor, an area surrounding a payload platform. A desired movement of the payload platform is received via a control unit. Prescribed movement of a pivot point is computed, via the control unit. Prescribed rotation of a wheel associated with a castor assembly is computed via the control unit. A signal corresponding to the prescribed rotation of the wheel is transmitted, via the control unit, to the wheel. A desired movement of the payload platform is traversed, via the castor assembly.

DETAILED DESCRIPTION

Various embodiments will now be described more fully with reference to the accompanying drawings. The disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

FIG. 1is a perspective view of a payload platform100having a plurality of castor assemblies102attached thereto. By way of example, the payload platform100is illustrated inFIG. 1as being triangular in shape; however, in other embodiments that will be discussed hereinbelow, payload platforms utilizing principles of the disclosure could be any shape such as, for example, rectangular. A castor assembly102is attached at each vertex of the payload platform100. In the embodiment illustrated inFIG. 1, three castor assemblies102(a),102(b), and102(c) are utilized. The castor assemblies102(a),102(b), and102(c) are independently powered and are independently controllable and actuated. In a typical embodiment, the castor assemblies102(a),102(b), and102(c) are powered via battery arrays104; however, in other embodiments, the castor assemblies102(a),102(b), and102(c) may receive power from an external power source such as, for example, a payload disposed on the payload platform100. In a typical embodiment, the castor assemblies102(a),102(b), and102(c) together impart omni-directional motion to the payload platform100. In the embodiments described herein, the parent body (e.g. a payload) has a prescribed rigid-body motion that is specific to an application of interest. From the prescribed motion, the prescribed motion of a castor assembly pivot point (illustrated as (D) inFIG. 2D) is computed. The geometry of the castor assembly102and the associated mapping illustrated inFIG. 2Dthen provides the wheel speeds consistent with the prescribed velocity of the point (D) and the roll without slop of the wheels on each castor assembly102. In various alternative embodiments, the payload platform100may be altered to have a different shape. In such embodiments, the castor assemblies102could be positioned directly under the corners of a particular payload such as, for example, a shipping container. Commanding a plurality of castors such as, for example, three or more active castors consistent with the commanded velocity of the respective pivot points (D) ensures that a general, omni-directional motion ensues without the castors fighting each other.

FIG. 2Ais a front view of a castor assembly102.FIG. 2Bis a side view of the castor assembly102.FIG. 2Cis a rear view of the castor assembly102.FIG. 2Dis a schematic top view of a castor assembly102. Referring toFIGS. 2A-2Dcollectively, the castor assembly102includes a first wheel202and a second wheel204. In a typical embodiment, the first wheel202and the second wheel204are of similar construction and comprise an equivalent diameter and coefficient of friction. The first wheel202and the second wheel204are independently controlled and may be actuated in a forward direction or in a backward direction at a variety of rotational speeds. The first wheel202and the second wheel204are rotatably connected to a body206and arranged such that a center of rotation of the first wheel202is on the same axis of rotation205as a center of rotation of the second wheel204. Further, the first wheel202and the second wheel204are arranged such that the first wheel202rotates in a plane that is generally parallel to a rotational plane of the second wheel204. The first wheel202and the second wheel204are displaced from a centerline of the body206by a distance, which is noted as (d) inFIG. 2D. The body206is rotatably coupled to the payload platform100at a pivot point (D). In a typical embodiment, the pivot point (D) is offset by a distance (L) from the axis of rotation205of the first wheel202and the second wheel204.

Referring specifically toFIG. 2D, a turn rate ({dot over (θ)}) about a center of rotation (O) of the body206is given by Equation 1:

θ.=rd⁢(ωr-ωi)Equation⁢⁢1
Where (r) is the radius of the first wheel202and the second wheel204, (ωr) is a rotational speed of the first wheel202and (ωt) is a rotational speed of the second wheel204. The velocity of the pivot point (D) is given by Equation 2:
{dot over (r)}D=r(ωr+ωl)ĉ1+{dot over (θ)}{circumflex over (l)}2Equation 2:

Referring again toFIGS. 2A-2D, a first motor250is operably coupled to the first wheel202and a second motor252is operatively coupled to the second wheel204. A first encoder254is positioned proximate the first wheel202so as to sense a rotational velocity of the first wheel202and convert the rotational velocity of the first wheel202into an electrical signal. Similarly, a second encoder256is positioned proximate the second wheel204so as to convert the rotational position of the second wheel204into an electrical signal. In a typical embodiment, the first encoder254and the second encoder256are electrically coupled to a control unit. In a typical embodiment, the control unit is a proportional, integral, derivative (“PID”) control.

FIG. 3is a schematic diagram of a castor assembly102. As previously discussed, the first wheel202and the second wheel204are separated from a centerline of the body206by a distance (d). The axis of rotation205of the first wheel202and the second wheel204is offset from a pivot point (D) by the distance (L). In a typical embodiment, the body206, together with the first wheel202and the second wheel204is able to rotate about an axis208. Thus, the body206, the first wheel202, and the second wheel204are able to rotate about the axis208in a plane that is generally orthogonal to a direction of travel of the first wheel202and the second wheel204. Such rotation of the body206ensures that the first wheel202and the second wheel204will maintain contact with a surface in the event the payload platform encounters uneven areas in the surface.

FIG. 4is a schematic top view of a payload platform400having three vertices and three castor assemblies102.FIG. 5is a schematic top view of a payload platform500having four vertices and four castor assemblies102. Referring toFIGS. 4-5collectively, the castor assemblies102are located at vertices of the payload platform400,500and are coupled to a control unit (not explicitly shown). The control unit receives a command related to a desired motion of the payload platform400,500. By way of example, the desired motion could include, for example two-axis translational motion or rotational motion about a vertical axis. In a typical embodiment, the control unit resolves the desired motion into translational and rotational components. The required velocity of each castor assembly102is then determined according Equation 3:

[V1V2]=[cos⁢⁢ψ-sin⁢⁢ψsin⁢⁢ψcos⁢⁢ψ]⁡[Vcx1+Ryi⁢ψ.Vcy1+Rxi⁢ψ.]Equation⁢⁢3
where ψ is the heading angle of the payload platform400(illustrated inFIG. 4), Ryiand Rxiare components of the position vector of the body206of the ith castor assembly102from an origin, Vcxiand Vcyiare prescribed wheel velocities expressed in a reference frame attached to the body206(b1and b2illustrated inFIG. 5). In similar fashion, the required speed of each wheel of each castor assembly is determined according to Equation 4:

Still referring toFIGS. 4-5, a plurality of sensors470are disposed about the castor assembly102and, by installation, serve as ancillary sensors of the payload platforms400,500. In a typical embodiment, the plurality of sensors470are proximity sensors including, but not limited to range sensors such as, for example, radar, optical sensors, and laser-range sensors, optical sensors such as cameras, other motion/object detection sensors such as, for example, ultrasonic detectors, photodiodes, and inertial measurement units including accelerometers and rate gyroscopes. Mechanical devices such as, for example track balls and laser odometery systems may also be integrated into the plurality of sensors470. Angular encoders at the pivot point (D) measure the heading angle of the castor assembly102with respect to a specified reference body direction such as, for example, b1.

During operation, the plurality of sensors470detect the area immediately surrounding the payload platform400,500and determine the presence of potential obstacles such as, for example, barriers to movement or other impact or instability risks. The plurality of sensors transmit this information to the control unit onboard each castor assembly102. The control unit then plots a course from a present location of the payload platform400,500to a desired location of the payload platform. The course is then reduced by the control unit to a series of movements to be traversed by the center of mass of the payload. This control logic is further broken down into individual castor differential velocity commands and communicated to corresponding castor assemblies. The command, control, and communication logics are accomplished by embedded computers integrated into each castor assembly102. Wireless network established between the castors at the outset enables the command and control information exchange. In an embodiment, one of the castor assemblies102assumes a role of leader and carries out a guidance scheme of computing a series of movements for the payload and the individual castor velocities necessary to negotiate a payload traversal and reorientation process. The movements of the center of mass of the payload are further reduced to required movements of each castor assembly. Finally, the movements of each castor assembly are reduced by the control unit to rotational speeds of each wheel in the castor assembly. Additionally, each castor assembly is equipped with a measurement device471. In a typical embodiment, the measurement device471is, for example, an inertial measurement unit (“IMU”); however, in other embodiments, the measurement device471is, for example, a laser measurement device, or a mechanical device such as, for example, a track ball. During operation, the measurement device471tracks rotational and translational movement of the castor assembly, converts the movement to an electrical signal, and transmits the electrical signal to the control unit.

FIG. 6is a flow diagram of a process600for maneuvering a payload platform400. The process600starts at block602. At block604, the sensors470detect the area immediately surrounding the payload platform400. At block606, the control unit receives a desired movement of the payload platform400. In various embodiments, the desired movement of the payload platform includes both rotational and translational movement. At block608, the control unit determines a desired movement of a pivot point in order to execute the desired movement of the payload platform400. At block610, the control unit determines a prescribed rotation of a wheel associated with a castor assembly. In various embodiments, the wheel may be the first wheel202or the second wheel204. At block612, the control unit transmits to the wheel a signal corresponding to the prescribed movement. At block614, a castor assembly causes the payload platform to traverse the prescribed movement of the payload platform400. The process600ends at block616. By way of example, the process600has been described herein relative to the payload platform400; however, one of ordinary skill in the art will recognize that the process600could also apply to the payload platform500.

Depending on the embodiment, certain acts, events, or functions of any of the algorithms, methods, or processes described herein can be performed in a different sequence, can be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the algorithms, methods, or processes). Moreover, in certain embodiments, acts or events can be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors or processor cores or on other parallel architectures, rather than sequentially. Although certain computer-implemented tasks are described as being performed by a particular entity, other embodiments are possible in which these tasks are performed by a different entity.