| 1. |
- Ingvast, Johan, et al.
(författare)
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The PVT, an elastic conservative transmission
- 2006
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Ingår i: The international journal of robotics research. - : SAGE Publications. - 0278-3649 .- 1741-3176. ; 25:10, s. 1013-1032
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents an innovative transmission called the passively variable transmission (PVT) that has a high torque ratio for large loads and a low velocity ratio for small loads. The change in these ratios depends passively on the load, in contrast to the continuous variable transmission (CVT), where the transmission ratio is controlled explicitly. Another difference from the CVT is that the PVT is elastic and the term transmission ratio is therefore not applicable. A theory section formulates alternative ways of describing the torque and velocity relations for elastic conservative transmisions as well as other important properties. This theory is used to analyze and illustrate the characteristics of a PVT. The theory is also used to compare the PVT with another novel elastic conservative transmission, called load sensitive CVT. The nonlinearities and elasticity of the PVT make it difficult to control using linear control theory. Feedback linearization was therefore used to design a torque controller, and experimental results show low impedance at small loads. Further, the controller tracks a reference torque well as long as the reference rate does not cause motor saturation. The abilities of the PVT are also illustrated by comparing it with an actuator having a traditional transmission. The load case is recorded joint torques and angles from the carpus joint of a walking horse. Simulation show that the required peak power is reduced by more than 20% and the product of the maximum torque and the maximum angular velocity is reduced by approximately 30%
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| 2. |
- Ridderström, Christian, et al.
(författare)
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Combining control design tools : from modelling to implementation
- 2001
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Ingår i: International Conference on Robotics and Automation.
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Tidskriftsartikel (refereegranskat)abstract
- Good tools are needed in order to develop roboticsystems efficicntly. Today, in addition to CAD/CAM,there are tools for model derivation, control design andimplemcntation. There are also tools for exporting modelsto a control design environment, as well as from controldesign to implementation (rapid prototyping tools). It ishowever, still difficult to combine these tools, especiallywhen working with large systems (i.e. a lot of signalsand parameters). We have therefore combined, interfacedand augmented some of these tools into a method thatbridges the gaps between automatic model derivation andcontrol implementation. Analytically derived functions(from Maple) are used for control design, simulation,visualization, evaluation (MATLAB) and implementation(Real-Time Workshop and xPC Target). The method andtools are illustrated by application to a four-legged robot inboth simulation and reality. Generality is also examplifiedby applying the method to a simulated SCARA robot.
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| 3. |
- Ridderström, Christian, et al.
(författare)
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Improving a trotting robot's gait by adapting foot trajectory offsets
- 2001
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Ingår i: International Conference on Climbing and Walking Robots.
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a method to adapt the foot reference trajectory offsets in order to improvea specific trotting gait. The trot gait used, is expected to have each leg on ground the sameamount of time and the adaptation offsets the supporting diagonals of the feet to minimize thedifferences in time. The controller is thus indirectly controlling the centre of mass position withrespect to the support without an explicit measure of the actual position of the centre of mass.The functionality of the controller is verified by experiments: trotting in place and trotting up aslope.
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| 4. |
- Ridderström, Christian, 1973-
(författare)
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Legged locomotion : Balance, control and tools - from equation to action
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is about control and balance stability of leggedlocomotion. It also presents a combination of tools that makesit easier to design controllers for large and complicated robotsystems. The thesis is divided into four parts.The first part studies and analyzes how walking machines arecontrolled, examining the literature of over twenty machinesbriefly, and six machines in detail. The goal is to understandhow the controllers work on a level below task and pathplanning, but above actuator control. Analysis and comparisonis done in terms of: i) generation of trunk motion; ii)maintaining balance; iii) generation of leg sequence andsupport patterns; and iv) reflexes.The next part describes WARP1, a four-legged walking robotplatform that has been builtwith the long term goal of walkingin rough terrain. First its modular structure (mechanics,electronics and control) is described, followed by someexperiments demonstrating basic performance. Finally themathematical modeling of the robot’s rigid body model isdescribed. This model is derived symbolically and is general,i.e. not restricted to WARP1. It is easily modified in case ofa different number of legs or joints.During the work with WARP1, tools for model derivation,control design and control implementation have been combined,interfaced and augmented in order to better support design andanalysis. These tools and methods are described in the thirdpart. The tools used to be difficult to combine, especially fora large and complicated system with many signals and parameterssuch as WARP1. Now, models derived symbolically in one tool areeasy to use in another tool for control design, simulation andfinally implementation, as well as for visualization andevaluation—thus going from equation to action.In the last part we go back to“equation”wherethese tools aid the study of balance stability when complianceis considered. It is shown that a legged robot in a“statically balanced”stance may actually beunstable. Furthermore, a criterion is derived that shows when aradially symmetric“statically balanced”stance on acompliant surface is stable. Similar analyses are performed fortwo controllers of legged robots, where it is the controllerthat cause the compliance.Keywordslegged locomotion, control, balance, leggedmachines, legged robots, walking robots, walking machines,compliance, platform stability, symbolic modeling
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| 5. |
- Ridderström, Christian, et al.
(författare)
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The basic design of the quadruped robot WARP1
- 2000
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Ingår i: International Conference on Climbing and Walking Robots.
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the basic design of a walking robot platform, in terms of its mechanics,electronics and control. The four-legged robot weighs about 60 kilograms, has three actuatorsin each leg and uses a distributed control system over six CAN busses. Basic strength and speedis demonstrated by experiments where the robot performs walking motions and goes down onits knees and then up again. A brief discussion of experiences from designing and implementingthe platform is included.
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| 6. |
- Ridderström, Christian, et al.
(författare)
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WARP1: Towards walking in rough terrain : control of walking
- 2003
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Ingår i: Climbing and walking robots: and their supporting technologies. ; , s. 467-474
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Konferensbidrag (refereegranskat)abstract
- This paper describes further results from making the four-legged robot WARP 1 capable of walking in rough terrain. In this work, WARP1'S special foot length sensors (FLS) are used to improve leg control during footfall, footlift and support. It is shown that using the FLS can reduce the duration of a footfall without increasing disturbances on the trunk. This strategy has been used for walking over obstacles, as described in a companion paper.
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