WO1998012498A1 - Procede et appareil de commande du mouvement d'un robot mobile - Google Patents

Procede et appareil de commande du mouvement d'un robot mobile Download PDF

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Publication number
WO1998012498A1
WO1998012498A1 PCT/US1997/015605 US9715605W WO9812498A1 WO 1998012498 A1 WO1998012498 A1 WO 1998012498A1 US 9715605 W US9715605 W US 9715605W WO 9812498 A1 WO9812498 A1 WO 9812498A1
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WO
WIPO (PCT)
Prior art keywords
base
calculating
motion
axis
wheels
Prior art date
Application number
PCT/US1997/015605
Other languages
English (en)
Inventor
Richard M. Legrand
James C. Slater
Original Assignee
Nomadic Technologies, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nomadic Technologies, Inc. filed Critical Nomadic Technologies, Inc.
Priority to AU42515/97A priority Critical patent/AU4251597A/en
Priority to EP97940826A priority patent/EP0939882A4/fr
Publication of WO1998012498A1 publication Critical patent/WO1998012498A1/fr
Priority to US09/263,163 priority patent/US6853877B1/en

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Classifications

    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D1/00—Control of position, course, altitude or attitude of land, water, air or space vehicles, e.g. using automatic pilots
    • G05D1/02—Control of position or course in two dimensions
    • G05D1/021—Control of position or course in two dimensions specially adapted to land vehicles
    • G05D1/0268—Control of position or course in two dimensions specially adapted to land vehicles using internal positioning means
    • G05D1/0272—Control of position or course in two dimensions specially adapted to land vehicles using internal positioning means comprising means for registering the travel distance, e.g. revolutions of wheels

Definitions

  • a rigid body constrained to move in a plane i.e. a mobile base moving on the floor
  • three degrees of freedom (DOFs) such as, movement in the x direction, movement in the y direction and rotation. Combining these three DOFs results in movement in any direction while simultaneously rotating.
  • a holonomic mobile base has the ability move in this manner and change its motion at any time.
  • a mobile base out of wheels that each have two degrees of freedom (one for steering, one for translation) all three DOFs are possible under the proper control, and complex mechanisms found in synchro-drive mobile bases are no longer needed. Additionally, these 2-DOF wheels (2-DOFWs) can be easily integrated and manufactured as modular wheel assemblies.
  • This motion estimation can also be "summed-up" over time to create a “dead reckoned” position estimate of the mobile base with respect to fixed coordinates, which is also useful for autonomous tasks such as navigation. That is, consider a robot that wishes to navigate to a location (room) of which it knows the x-y coordinates. Motion estimation is also responsible for proper control of the mobile base, as will be described below. A control algorithm which minimizes wheel slippage will also allow for maximum motion estimation accuracy.
  • the present invention overcomes the deficiencies in the prior art described above, and provides motion control for a mobile robot base that is more accurate and more maneuverable. Referring to Figure 3 and the Detailed Description of the
  • a supervisory controller reads the input vector from a host processor, and maps the input vector to the desired axis motion vector (i.e. the desired motion of each axis) by using the equations in Section 2 below. It then predicts if the axes are capable of the desired motion by calculating their control envelopes (i.e. the motion possible within one control cycle ⁇ t .) as described in Section 3. If all axes are capable of the desired motion within one control cycle the desired axis motion vector is passed to the low-level controller. If one or more axes are incapable of the desired motion, a modified axis motion vector is calculated as described in Section 4 and passed to the low-level controller.
  • the modified axis motion vector lies within the control envelopes of all 2N axes while minimizing control error (i.e. the difference between the commanded input vector and the actual base motion.)
  • the control algorithm then estimates the motion of the mobile base since the last control cycle using the technique described in Section 5.
  • the estimated motion is then used to update the position and orientation yand, ⁇ of the base coordinate frame in the fixed world coordinate frame as described also in Section 5.
  • the updated position and orientation is then made available for the host processor to read.
  • the control algorithm then repeats the whole process by beginning another control cycle.
  • Figure 1 A is a perspective view showing a mobile base wheel with no castor offset.
  • Figure IB is a perspective view showing a mobile base wheel with a castor offset.
  • Figure 2 is a schematic diagram showing the flow of command information which controls the motion of the mobile base.
  • Figure 3 is a schematic diagram showing the steps of a method for controlling the motion of the mobile base.
  • Figure 4 is a perspective view schematically showing the layout of the mobile base wheels and the base and world coordinate systems.
  • a mobile base constructed according to the present invention includes as many two degrees of freedom wheels (2-DOFWs) as deemed necessary (N > 2 , where N is the number of 2-DOFWs). All of the wheels are mounted on the mobile base which is a rigid platform (depicted in Figure 4.).
  • Each 2-DOFW has two independent axes, one for steering and one for translation.
  • Figure IB shows an example of a 2-DOFW having a castor offset. In other words, the steering axis is offset from the translation axis by c m .
  • Each of the 2-DOFWs on the mobile base can have a different amount of caster if necessary.
  • a schematic diagram shows the flow of command information which controls the motion of the mobile base. Since each of the N wheels has two axes (i.e. steering and translation), the mobile base has a total of 2N axes. Controlling the 2N axes of the mobile base are 2N servo amplifiers connected to a set of low-level controllers that perform closed-loop, high servo-rate control of all axis positions. Positional feedback of each axis is provided by an accurate encoding scheme. A supervisory controller interfaced to the low-level controllers coordinates all 2N axes by sending position updates to the low-level controllers at each discrete control cycle.
  • the position updates are calculated by the control algorithm which takes into account the mobile base geometry, motor dynamics, and a 3-DOF input vector sent from a host processor interfaced to the supervisory controller.
  • the 3-DOF input vector completely describes the desired velocity-based motion of the mobile base, which is constrained to move within three DOFs as described previously.
  • a possible input vector for example, consists of an x- velocity, y- velocity, and rotational velocity with respect to the center of the mobile base, or alternatively, angle, magnitude, and rotational velocity with respect to a random fixed point (i.e. the representation is arbitrary as long as the axes of the input vector are independent.)
  • the control algorithm is optimal in that it controls the 2N axes such that the mobile base moves as commanded by the input vector as accurately and as quickly as possible within the physical limits of the motors. For example, if a motor is commanded beyond what it is physically capable of (i.e. it is commanded beyond its "saturation point") while other motors are commanded to within their physical limits, wheel slippage occurs.
  • the control algorithm is able to predict this situation and correct it before it occurs. It accomplishes this by anticipating velocities and saturation points with working models of each motor axis.
  • the control algorithm simultaneously minimizes wheel slippage and minimizes the difference between desired motion specified by the input vector and actual mobile base motion (motion error).
  • Section 2 Mapping the Input Vector to the Desired Axis Motion Vector This determines the motion required at each 2-DOFW and the corresponding motion at each axis such that the mobile base moves according to the commanded input vector (i.e. [ rf , j ⁇ , ⁇ ])- Thus, the mapping is from 9 ⁇ 1 to 9 ⁇ 2 ⁇ / . It is accomplished by first calculating the desired velocity to each wheel attachment point as below. The desired wheel velocity for each wheel is expressed as a 2-vector [ ⁇ jw, > jwi ] Dase coordinates ( Figure 4). ( V : l ⁇ i ⁇ N ) (i.e. for all wheels i):
  • y d w, y,, + r wl ⁇ d c ⁇ s ⁇ m )
  • y is the angle offset of 2-DOFW i with respect to the base origin in radians.
  • the desired steering axis velocity and desired translation axis velocity [j ⁇ ,, ⁇ ,] arc calculated for each 2-DOFW as below.
  • First the steering angle for each 2-DOFW is measured ( ⁇ mWl ) based on the raw measured encoder value of the steering axis ( s mWl ) and the encoder pitch ( ⁇ Wl ):
  • c Wl is the amount of caster offset in meters
  • ⁇ Wl is the encoder pitch for 2DOFW i expressed in encoders per radians
  • r Wl is the radius of the 2DOFW i
  • the control envelope for an axis describes the possible motion an axis can perform within a fixed time.
  • control envelope is determined by either maximum (negative) acceleration, or by the maximum possible (negative) velocity of the translation axis (i mmWi ), whichever is greater.
  • control envelope is determined by either the maximum (positive) acceleration, or by the maximum possible (positive) velocity of the translation axis, whichever is lesser.
  • the desired motion [ ⁇ ,, ⁇ , 1 lies within the control envelope for ⁇ t time duration if and only if
  • the desired motion [ ⁇ , , i dWl ] lies within the control envelope for ⁇ t time duration if and only if
  • Section 4 Calculating the Modified Axis Motion Vector
  • a desired base motion input vector ( m d ) and a current estimated base motion vector ( m e ) (calculated in Section 5)
  • m,(X) ⁇ (f d - m e ) + m e
  • Evaluating m,(0) results in m c , which is the current base motion vector.
  • Evaluating m,( ⁇ ) results in h d , which is the desired input vector.
  • Section 5 Estimating the Motion of the Mobile Base
  • For wheels with no caster ( c Wl 0 ), we begin by calculating the measured steering angle as in Section 1 :
  • Wl is the measured translation axis position at the beginning of the previous control cycle expressed in encoders.
  • the estimated base motion vector can be calculated by dividing by the time increment
  • the final step in motion estimation is determining the "summed-up" position of the mobile base in fixed world coordinates. This is accomplished by adding the rotation angle change ⁇ ⁇ e to the existing angle estimate
  • the present invention provides a method and apparatus for controlling the motion of a mobile base with increased accuracy and maneuverability.
  • the present invention is used on a mobile robot base having three wheels each with a predetermined amount of castor.
  • the mobile robot is controlled by an off-board host processor (as shown in Figure 2.)
  • the host processor sends command signals and receives motion feedback from an onboard supervisory controller by radio, cable, infrared, or similar type of link.
  • the motion control signals are mapped to axis control signals by the supervisory controller and sent to six low-level controllers. Each of the six low level controllers corresponds to either a steering axis or translation axis for one of the three wheels.
  • Each of the low level controllers in turn sends an axis control signal to an associated servo amplifier, which provides the proper voltage and current to drive the respective axis motor.
  • Each of the six motors has an encoder, which provides motor position feedback to both the low-level controller and the supervisory controller.
  • the host processor and supervisory controller are preferably microprocessors that are commonly used for embedded control. Propriety software code is written preferably in C programming language to implement the inventive control method on the microprocessors and low level controllers. The inventive method can be utilized with other configurations (not shown.)
  • the mobile base described above can be inverted with the positions of the mobile base and the surface it rolls on transposed.
  • two degree of freedom wheels can be mounted pointed upward on a stationary base, and can translate and rotate a horizontal surface resting on the wheels.
  • multiple bases, each having single or multiple wheels, can be pivotably linked together in a snake-fashion to form a non-rigid base which is controlled by the inventive method.

Landscapes

  • Engineering & Computer Science (AREA)
  • Aviation & Aerospace Engineering (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Automation & Control Theory (AREA)
  • Control Of Position, Course, Altitude, Or Attitude Of Moving Bodies (AREA)

Abstract

Une base de robot mobile se déplaçant par rapport à une surface, ladite base étant composée des éléments suivants: au moins deux roues montées de façon à pivoter et à être en rotation par rapport à la base, chacune des roues ayant un axe de direction et un axe de rotation; un mécanisme d'entraînement qui assure la rotation des roues sur la surface; un mécanisme de direction qui fait pivoter les roues par rapport à la surface; et une unité de commande qui commande le mouvement de la base. Cette unité de commande est équipée d'un dispositif qui assure la lecture d'un vecteur de mouvement d'entrée provenant d'un processeur central, met en correspondance, pour chacun des axes, le vecteur d'entrée avec un vecteur de déplacement d'axe souhaité, calcule une enveloppe de référence pour chacun des axes, détermine, pour chacun des axes, si le vecteur de déplacement d'axe est compris dans l'enveloppe de référence, calcule un vecteur de déplacement d'axe modifié quand celui-ci n'est pas compris dans l'enveloppe de référence, transmet, pour chacun des axes, le vecteur de déplacement d'axe ou le vecteur de déplacement d'axe modifié à une unité de commande des axes, estime le mouvement accompli par la base pendant un intervalle de temps discret Δt, calcule une position et une orientation de la base dans un ensemble de coordonnées universelles, et répète continuellement cette série de mesures jusqu'à ce qu'elle reçoive l'instruction d'arrêter.
PCT/US1997/015605 1996-09-06 1997-09-05 Procede et appareil de commande du mouvement d'un robot mobile WO1998012498A1 (fr)

Priority Applications (3)

Application Number Priority Date Filing Date Title
AU42515/97A AU4251597A (en) 1996-09-06 1997-09-05 Method and apparatus for mobile robot motion control
EP97940826A EP0939882A4 (fr) 1996-09-06 1997-09-05 Procede et appareil de commande du mouvement d'un robot mobile
US09/263,163 US6853877B1 (en) 1996-09-06 1999-03-05 Method and apparatus for mobile robot motion control

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US2540696P 1996-09-06 1996-09-06
US60/025,406 1996-09-06

Related Child Applications (1)

Application Number Title Priority Date Filing Date
US09/263,163 Continuation-In-Part US6853877B1 (en) 1996-09-06 1999-03-05 Method and apparatus for mobile robot motion control

Publications (1)

Publication Number Publication Date
WO1998012498A1 true WO1998012498A1 (fr) 1998-03-26

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US1997/015605 WO1998012498A1 (fr) 1996-09-06 1997-09-05 Procede et appareil de commande du mouvement d'un robot mobile

Country Status (3)

Country Link
EP (1) EP0939882A4 (fr)
AU (1) AU4251597A (fr)
WO (1) WO1998012498A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1037129A1 (fr) * 1999-03-05 2000-09-20 Nomadic Technologies, Inc. Procédé et appareil de commande du mouvement d'un robot mobile
US6948576B2 (en) 2002-01-10 2005-09-27 Jorge Angeles Driving and transmission unit for use in rolling vehicles

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4657104A (en) * 1983-07-23 1987-04-14 Cybermation, Inc. Concentric shaft mobile base for robots and the like
US5559696A (en) * 1994-02-14 1996-09-24 The Regents Of The University Of Michigan Mobile robot internal position error correction system
US5568030A (en) * 1989-04-25 1996-10-22 Shinko Electric Co., Ltd. Travel control method, travel control device, and mobile robot for mobile robot systems
US5576947A (en) * 1994-06-30 1996-11-19 Siemens Corporate Research, Inc. Robot hallway traveler

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2566935B1 (fr) * 1984-06-27 1986-12-12 Commissariat Energie Atomique Systeme de commande optimisee des mouvements d'un mobile sensible et actif par rapport a un environnement local passif a l'aide de capteurs proximetriques locaux
US5609216A (en) * 1995-03-01 1997-03-11 Cybermotion, Inc. Mobile base having leg assemblies with two wheels
JP3647538B2 (ja) * 1996-02-12 2005-05-11 本田技研工業株式会社 車両操舵装置

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4657104A (en) * 1983-07-23 1987-04-14 Cybermation, Inc. Concentric shaft mobile base for robots and the like
US5568030A (en) * 1989-04-25 1996-10-22 Shinko Electric Co., Ltd. Travel control method, travel control device, and mobile robot for mobile robot systems
US5559696A (en) * 1994-02-14 1996-09-24 The Regents Of The University Of Michigan Mobile robot internal position error correction system
US5576947A (en) * 1994-06-30 1996-11-19 Siemens Corporate Research, Inc. Robot hallway traveler

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of EP0939882A4 *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1037129A1 (fr) * 1999-03-05 2000-09-20 Nomadic Technologies, Inc. Procédé et appareil de commande du mouvement d'un robot mobile
US6948576B2 (en) 2002-01-10 2005-09-27 Jorge Angeles Driving and transmission unit for use in rolling vehicles

Also Published As

Publication number Publication date
EP0939882A4 (fr) 2001-04-11
EP0939882A1 (fr) 1999-09-08
AU4251597A (en) 1998-04-14

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