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| 2. |
- Häggblad, Hans-Åke, et al.
(författare)
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On the fit of constitutive parameters through optimization
- 1983
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Ingår i: Scandinavian journal of metallurgy. - 0371-0459 .- 1600-0692. ; 12:6, s. 282-284
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Tidskriftsartikel (refereegranskat)abstract
- The need for more reliable finite element analyses of materials with complex behaviour has led to the development of new constitutive theories. These theories often have a large number of parameters which must be determined from experiments. A method is described of fitting constitutive parameters through optimization. An application is made to the Prevost multisurface plasticity theory. Good agreement is obtained between theoretical results and experimental data in the case of a multi axially loaded hard metal powder.
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| 4. |
- Lindahl, Olof, et al.
(författare)
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An improved optical eye movement detector for visual half-field studies of cerebral hemisphere memory
- 1988
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Ingår i: Journal of Medical Engineering & Technology. - : Informa UK Limited. - 0309-1902 .- 1464-522X. ; 12:3, s. 106-111
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Tidskriftsartikel (refereegranskat)abstract
- 106-11AB - An instrument for the evaluation of cerebral hemisphere memory using the visual half-field (VHF) technique is described. The object was to improve the existing VHF-techniques by means of an infra-red eye movement detector to control visual fixation, and to automatically control the presentation of visual stimuli. The instrument consists of four functional parts; visual presentation; optical eye movement control; electronic programming; and reaction time measuring. The instrument has been used on normal controls and in neuropsychological pre- and post-operative investigations on patients with drug resistant partial epilepsy. It has proved easy to use and reveals valuable information about hemisphere memory function. The use of an optical eye movement detector together with electronic logic has improved the accuracy and reliability of the VHF-test. A schematic outline of the instrument and a brief description of electronic circuitry are given.
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| 6. |
- Nilsson, Bernt, et al.
(författare)
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Active uncertainty reduction during gripping using range cameras-dual control
- 1995
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Ingår i: Human Robot Interaction and Cooperative Robots. ; , s. 406-413
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Konferensbidrag (refereegranskat)abstract
- This paper is on sensor based control for guiding a robot to correct gripping of objects having a large position uncertainty. An eye-in-hand mounted range camera is considered. A probabilistic problem formulation based on the requested posture at gripping and corresponding tolerances is presented. The problem is solved approximately using dynamic programming for a 1-degree-of-freedom manipulator. A five-step dual control law is studied in more detail. A typical case is that in the first part of the control sequence the robot steers towards the optimal sensing position and in the last part the error with respect to the gripping posture is minimized. Since range camera sensing introduces both range dependent noise and occlusion there is a need for `exploratory moves'. This behavior is formalized and includes `dual control'.
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| 7. |
- Nilsson, Bernt, et al.
(författare)
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Control of flexible mobile manipulators: positioning and vibration reduction using an eye-in-hand range camera
- 1999
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Ingår i: Control Engineering Practice. - 0967-0661 .- 1873-6939. ; 7:6, s. 741-751
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the positioning of a long flexible manipulator on a moving platform is investigated. The problem is to position the gripper at a requested relative distance in front of an object with unknown location. For this purpose, the gripper is equipped with a range camera giving the distance to surrounding objects within, ∼ 1% and with a sampling rate above 1 kHz. The range measurements are used in combination with internal angle measurements from joint encoders to estimate both the flexibility in the mechanical construction and the relative distance from gripper to object. This is solved satisfactorily by an extended Kalman filter (EKF). For the motion control of the manipulator, a time-scaled feedback controller is suggested. A fast inner loop is used to damp out oscillations and reject disturbances, both from the platform and the manipulator. An outer control loop, with a lower closed-loop bandwidth, then steers the gripper, based on the range measurements, to the requested final position in front of the object. This loop assumes a stationary and rigid platform and a rigid manipulator. At this moment, only simulations of a flexible manipulator on a rigid platform have been studied. However, the results show that the flexibility can be estimated from indirect measurements of the range to the object and the joint angles. Also, good damping and disturbance rejection are achieved, as long as the bandwidth of the actuators is sufficiently high compared to the oscillation. The use of range measurements of the surrounding objects makes the positioning task very robust against an uncertain platform position.
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| 8. |
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| 9. |
- Nilsson, Bernt, et al.
(författare)
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On‐range sensor feedback for mobile robot docking within prescribed posture tolerances
- 1997
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Ingår i: Journal of Robotic Systems. - 0741-2223 .- 1097-4563. ; 14:4, s. 297-312
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Tidskriftsartikel (refereegranskat)abstract
- The problem addressed is feedback from noncontact sensing for guiding robots during docking and gripping. The sensor used is a "range camera" onboard a mobile robot (MRb). To specify the docking task completely both the posture (position/orientation) and the required tolerances must be given. These tolerances are then used in the feedback control loop during docking. The algorithms are divided into three parts: the extraction of posture parameters from the "range camera," dynamic filtering for finding association gates and protecting the system against spuriousness in the measurements, and finally a feedback controller. The feedback controller is separated into geometric control and tolerance control. The geometric control uses a range varying LQG-designed feedback control law to generate the trajectories toward the object. The tolerance control adjusts the approach velocity so that the robot is given a sufficient number of observations and control cycles to meet the required tolerances. Thus, during the approach there is a conditional re-planning of the trajectory. For simplicity, only three kinematic state variables (x, y, θ) are used for the MRb. Gripping using an industrial robot (IRb) is an equivalent problem. Successful experiments were made with range resolution varying more than a factor of 50. Thus, the resolution volume in the (x, y, θ)-space varied by several orders of magnitude during the tests. The final errors in range and orientation are essentially limited by the resolution in the "range camera." A persistent conclusion from the experiments is the importance of correct association between the range measurements and the corresponding parts of the object.
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