An optimal wheel-torque control on a compliant modular robot for wheel-slip minimization
TL;DR: An optimal wheel-torque controller is proposed that minimizes the traction-to-normal force ratios of all the wheels at every instant of its motion to maintain static stability and desired wheel speed.
Abstract: This paper discusses the development of an optimal wheel torque controller for a compliant modular robot. The wheel actuators are the only actively controllable elements in this robot. For this type of robots, wheel-slip could offer a lot of hindrance while traversing on uneven terrains. Therefore, an effective wheel-torque controller is desired that will also improve the wheel-odometry and minimize power consumption. In this work, an optimal wheel-torque controller is proposed that minimizes the traction-to-normal force ratios of all the wheels at every instant of its motion. This ensures that, at every wheel, the least traction force per unit normal force is applied to maintain static stability and desired wheel speed. The lower this is, in comparison to the actual friction coefficient of the wheel-ground interface, the more margin of slip-free motion the robot can have. This formalism best exploits the redundancy offered by a modularly designed robot. This is the key novelty of this work. Extensive numerical and experimental studies were carried out to validate this controller.
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TL;DR: The results of this research imply how the accurate contact point detection aided by the new sensor yields a reliable approach for surface scanning and stability measure calculation.
10 citations
TL;DR: In this article, the concept and parameter design of a robust stair-climbing compliant modular robot, capable of tackling stairs with overhangs, is discussed, along with establishing a concept design, the robust design parameters are set to minimize performance variations.
Abstract: This paper discusses the concept and parameter design of a robust stair-climbing compliant modular robot, capable of tackling stairs with overhangs. Geometry modifications of the periphery of the wheels of our robot helped in tackling overhangs. Along with establishing a concept design, the robust design parameters are set to minimize performance variations. The Grey-based Taguchi method is applied to provide an optimal setting for the design parameters of the robot. The robot prototype is shown to have successfully scaled stairs of varying dimensions, with overhang, thus corroborating the analysis performed.
7 citations
TL;DR: The new sensor empowers a wheeled robot to scan the surface and to find stability margins during real-time locomotion without camera or laser sensors and enhances the ability of the real- time solution of the dynamic equations.
Abstract: In this paper, a new, simple and cheap sensor is proposed to detect the multipoint contact of a typical robotic wheel. The new sensor empowers a wheeled robot to scan the surface and to find stability margins during real-time locomotion without camera or laser sensors. Furthermore, it enhances the ability of the real-time solution of the dynamic equations. The new sensor is based on the total resistance of a circuit and can be classified into two types. In the first type, the resistive circuit includes a conductive path, a direct voltage source and some resistors by various values. The main advantage of this type of the new sensor is to determine the exact locations of multipoint contact only by means of an input data detecting the voltage of a resistor. The implementation of the new idea is easy to use and to be experimented. It can be used to improve the control process, especially on the rough surfaces and to enhance the locomotion stability. The second type of the new sensor contains a continuous resistive belt with higher accuracy than the first type. The algorithm of the multipoint contact detection is explained and the kinematics relations of the robot are obtained. The surface is scanned during the robot locomotion, and the error of the estimated surface profile is calculated. Finally, the static stability margins are extracted using the new sensor data.
6 citations
TL;DR: A new extendable platform for an unmanned ground vehicle to overcome the obstacle climbing issue is proposed based on scissor mechanism principles which have been innovated to achieve long and rigid displacement.
Abstract: This research proposes a new extendable platform for an unmanned
ground vehicle to overcome the obstacle climbing issue The new platform
is basically established on scissor mechanism principles which have been
innovated to achieve long and rigid displacement A couple of scissor
mechanisms are embedded in the rover platform adjusting the mass center of rover respect to the rear and front wheels Accordingly, it yields geometric control of the contact forces, which can simultaneously reduce the
slip of the wheels and increase the performance of the obstacle climbing
up To demonstrate the performance of the proposed platform, the 3D
kinematics is derived Subsequently, the stick-slip Euler-Lagrange dynamics
is derived and a three-level controller including the torque optimization is
implemented to simulate the rover facing obstacles Finally, without any
hardware prototyping, the extendable rover is simulated and compared
with a typical fixed-geometry rover to show the enhancement of the
climbing ability by using the proposed concept Moreover, controlling the
normal contact forces of the wheels yields the slip reduction, which subsequently, increases the traction force
6 citations
Cites background from "An optimal wheel-torque control on ..."
...The slip reduction algorithms estimate dynamics of UGV platforms at the current moment and calculate the appropriate torque of motors so that the slip is minimized (Xu et al., 2016; Kobayashi et al., 2018; Siravuru et al., 2017)....
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25 Jul 2019
TL;DR: An improved formulation for rover optimization using smooth functions is improved, which enables use of powerful gradient based nonlinear programming (NLP) solvers for finding solutions.
Abstract: We address the problem of improving mobility of rovers with rocker-bogie suspension. Friction and torque requirements for climbing a single step were considered as performance parameters. The main ...
5 citations
References
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17 Feb 2000
TL;DR: Shrimp as discussed by the authors is a high mobility wheeled rover for uneven terrain off-road that uses passive locomotion concept robot on uneven terrain, and is based on the SHRIMP concept.
Abstract: Keywords: passive locomotion concept robot uneven terrain off-road ; SHRIMP : High Mobility Wheeled Rover Reference LSA-CONF-2000-003View record in Web of Science Project Web Site: http://asl.epfl.ch/research/systems/shrimp/shrimp.php Record created on 2006-12-07, modified on 2016-08-08
156 citations
"An optimal wheel-torque control on ..." refers background or methods in this paper
...Wheel-torque optimization is carried out using the three objective functions as given in Eqs (11)– (13) at all the set points between 0 and hmax ....
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...(11)) performs consistently well on all the metrics....
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...Therefore, for phase-1, the equality constraints are obtained from Eqs....
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...Optimization Results and Discussion Wheel-torque optimization is carried out using the three objective functions as given in Eqs (11)– (13) at all the set points between 0 and hmax ....
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...(1)–(5) and for phase-2, it is obtained from Eqs....
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01 Jan 2001
TL;DR: In this paper, the authors focus on the configuration of wheeled robotic locomotion through the formulation and systematic evaluation of analytical expressions called configuration equations, which capture quantitative relationships among configuration parameters (e.g., wheel diameter, chassis articulation location), performance parameters (i.e., drawbar pull, maximum gradeable slope) and environmental/task parameters (eg soil geophysical properties, density and size of obstacles).
Abstract: Through their ability to navigate and perform tasks in unstructured environments, robots have made their way into applications like farming, earth moving, waste clean-up and exploration All mobile robots use locomotion that generates traction, negotiates terrain and carries payload Well-designed robotic locomotion also stabilizes a robot's frame, smooths the motion of sensors and accommodates the deployment and manipulation of work tools Because locomotion is the physical interface between a robot and its environment, it is the means by which it reacts to gravitational, inertial and work loads Locomotion is the literal basis of a mobile robot's performance
Despite its significance, locomotion design and its implications to robotic function have not been addressed In fact, with the exception of a handful of case studies, the issue of how to synthesize robotic locomotion configurations remains a topic of ad hoc speculation and is commonly pursued in a way that lacks rationalization This thesis focuses on the configuration of wheeled robotic locomotion through the formulation and systematic evaluation of analytical expressions called configuration equations These are mathematical functions which capture quantitative relationships among configuration parameters (eg, wheel diameter, chassis articulation location), performance parameters (eg drawbar pull, maximum gradeable slope) and environmental/task parameters (eg soil geophysical properties, density and size of obstacles) Solutions to the configuration equations are obtained in parametric form to allow for comprehensive characterization of variant locomotion concepts as opposed to searching for point designs Optimal configuration parameters are sought in the context of three indices of performance: trafficability, maneuverability and terrainability
The derivation of configuration equations, the estimation and optimization of configuration parameters and predictions of performance are performed in a computational framework called Locomotion Synthesis (LocSyn) LocSyn offers a practical approach to rationalizing configuration design of robotic locomotion through quantitative studies
The configuration of Nomad, a planetary prototype robot for exploration of barren terrain is a case illustrating the implementation and evaluation of the Locomotion Synthesis (LocSyn) framework put forth by this thesis
146 citations
"An optimal wheel-torque control on ..." refers background in this paper
...(1)–(5) are obtained by eliminating the constraint forces (f xli , fyli ,f xwi and fywi) from the above equations....
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...∑ Fx = 0 N1 − F2 − F3 − F4 = 0 (1) ∑ Fy = 0 3wl + 4ww − F1 − N2 − N3 − N4 = 0 (2) ∑ MJ1 = 0 F1(lcosφ1 + r) + N1lsinφ1 − wl[(l/2)cosφ1-csinφ1] − k1φ1 − wwlcosφ1 = 0 (3) ∑ MJ2 = 0 F2r + N2l − wwl − wl(l/2) − [wl + ww − F1](l + l0) − k2φ2 + k1φ1 = 0 (4)...
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...(1) is obtained by substituting the values f xl2, f xw3 and f xw4 from the above into Eq....
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...(1)–(5) and for phase-2, it is obtained from Eqs....
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...Equations (1)–(5) and (6)–(10) contain the minimal set of static-equilibrium equations for the first and second phases of climbing of the robot as shown in Figs....
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18 Apr 2005
TL;DR: The proposed method for wheel-ground contact angle measurement and a traction control strategy minimizing slip in rough terrain has the advantage to avoid relying on complex wheel-soil interaction models, whose parameters are generally unknown in challenging terrains.
Abstract: This paper presents a method for wheel-ground contact angle measurement and a traction control strategy minimizing slip in rough terrain. The slip minimization algorithm has been tested and compared with a standard speed control in simulation, which allows to verify the validity of the assumptions taken during the modeling phase. The simulations show clearly the advantage of torque control versus speed control. Furthermore, the proposed method has the advantage to avoid relying on complex wheel-soil interaction models, whose parameters are generally unknown in challenging terrains.
79 citations
"An optimal wheel-torque control on ..." refers background in this paper
...(1)–(5) are obtained by eliminating the constraint forces (f xli , fyli ,f xwi and fywi) from the above equations....
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...∑ MW4 = 0 F3r + N3l − wwl − wl(l/2) − [2(wl + ww) − F1 − N2](l + l0) + k2φ2 + F4r = 0 (5) ∑ Fx = 0 N1 − F3 − F4 = 0 (6) ∑ Fy = 0 3wl + 4ww − F1 − N3 − N4 = 0 (7) ∑ MJ1 = 0 F1(lcos(φ1 + φ2) + r) + N1lsin(φ1 + φ2) − wl[(l/2)cos(φ1 + φ2) − csin(φ1 + φ2)] − k1φ1 − wwlcos(φ1 + φ2) = 0 (8) ∑ MJ2 = 0 [F1 − (wl + ww)](l + l0)cosφ2 − wl(l/2cosφ2 − csinφ2) − wwlcosφ2 + k1φ1 − k2φ2 + N1(l + l0)sinφ2 = 0 (9) ∑ MW4 = 0 F3r + N3l − wwl − wl(l/2) − [2wl + 2ww − F1](l + l0) + k2φ2 + F4r = 0....
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...(v) Equation (5) is obtained by substituting values of fyl2, fyw3, τw3 and τw4 from item − ii above, Eqs....
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...(1)–(5) and for phase-2, it is obtained from Eqs....
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...Equations (1)–(5) and (6)–(10) contain the minimal set of static-equilibrium equations for the first and second phases of climbing of the robot as shown in Figs....
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07 Jun 2004
TL;DR: In this article, a quasi-static modeling of a six-wheeled robot with a passive suspension mechanism is presented together with a method for selecting the optimal torques considering the system constraints: maximal and minimal torques, positive normal forces.
Abstract: Navigating in rough terrain is a complex task that requires the robot to be considered as a holistic system. Algorithms, which don't consider the physical dimensions and capabilities of the mobile robot lead to inefficient motion and suffer from a lack of robustness. A physical model of the robot is necessary for trajectory control. In this paper, quasi-static modeling of a six-wheeled robot with a passive suspension mechanism is presented together with a method for selecting the optimal torques considering the system constraints: maximal and minimal torques, positive normal forces. The aim of this method is to limit wheel slip and to improve climbing capabilities. The modeling and the optimization are applied to the shrimp rover.
79 citations
01 Jan 2006
TL;DR: In this paper, the locomotion concept CRAB is compared to RCL-E (Concept E by RCL); the simulations include the MER (Mars Exploration Rover by NASA) as well.
Abstract: Many exploration rovers have been proposed in the past, but none was compared to other systems. Therefore, this paper not only introduces the locomotion concept CRAB, but also compares it to other rovers regarding obstacle negotiation capabilities. Instead of relying only on simulation, a comparison was also performed with real breadboards. In reality the CRAB is compared to RCL-E (Concept E by RCL); the simulations include the MER (Mars Exploration Rover by NASA) as well. The simulations predict significantly superior performance of CRAB compared to RCL-E, which is confirmed by the tests on hardware. The performance of CRAB and MER is similar; however, the CRAB has the same behavior in forward and backward motion because it is a symmetrical structure, while the MER has significantly inferior performance in backward motion.
65 citations