| 1. |
- Carvalho Bittencourt, André, et al.
(författare)
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Static Friction in a Robot Joint : Modeling and Identification of Load and Temperature Effects
- 2012
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Ingår i: Journal of Dynamic Systems Measurement, and Control. - : American Society of Mechanical Engineers (ASME). - 0022-0434 .- 1528-9028. ; 134:5
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Tidskriftsartikel (refereegranskat)abstract
- Friction is the result of complex interactions between contacting surfaces in down to a nanoscale perspective. Depending on the application, the different models available are more or less suitable. Static friction models are typically considered to be dependent only on relative speed of interacting surfaces. However, it is known that friction can be affected by other factors than speed.In this paper, the typical friction phenomena and models used in robotics are reviewed. It is shown how such models can be represented as a sum of functions of relevant states which are linear and nonlinear in the parameters, and how the identification method described in Golub and Pereyra (1973) can be used to identify them when all states are measured. The discussion follows with a detailed experimental study of friction in a robot joint under changes of joint angle, load torque and temperature. Justified by their significance, load torque and temperature are included in an extended static friction model. The proposed model is validated in a wide operating range, considerably improving the prediction performance compared to a standard model.
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| 2. |
- Ekström, Rickard, et al.
(författare)
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Evaluating Constant DC-Link Operation of Wave Energy Converter
- 2014
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Ingår i: Journal of Dynamic Systems Measurement, and Control. - : ASME International. - 0022-0434 .- 1528-9028. ; 136:1, s. 014501-
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Tidskriftsartikel (refereegranskat)abstract
- A wave energy converter (WEC) based on a linear generator and a point-absorbing buoy has been developed at Uppsala University. Interconnecting an array of WECs in parallel requires a point of common coupling, such as a common dc-bus. The dc voltage level seen by the generator is directly linked to the electromagnetic damping of the generator. A lower dc-level results in a higher damping factor and is important for increased absorption of the wave power. The drawback is increased losses in generator windings and cable resistance. There will be an optimal dc-level for maximum power output. This is a function of not only generator and buoy characteristics, but the current sea state. Experimental results of the full-scale system have been carried out, and used as validation of a simulation model of the system. The model is then used to evaluate how the dc-level seen by the generator influence the power output. The results indicate that higher dc-levels should be used at higher sea states, and power output may vary by up to a factor five depending on which dc-level is chosen.
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| 3. |
- Jonasson, Mats, 1969-, et al.
(författare)
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Utilization of Actuators to Improve Vehicle Stability at the Limit : From Hydraulic Brakes Toward Electric Propulsion
- 2011
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Ingår i: Journal of Dynamic Systems Measurement, and Control. - : ASME. - 0022-0434 .- 1528-9028. ; 133:5
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Tidskriftsartikel (refereegranskat)abstract
- The capability of over-actuated vehicles to maintain stability during limit handling is studied in this paper. A number of important differently actuated vehicles, equipped with hydraulic brakes toward more advanced chassis solutions, are presented. A virtual evaluation environment has specifically been developed to cover the complex interaction between the driver and the vehicle under control. In order to fully exploit the different actuators setup, and the hard nonconvex constraints they possess, the principle of control allocation by nonlinear optimization is successfully employed. The final evaluation is made by exposing the driver and the over-actuated vehicles to a safety-critical double lane change. Thereby, the differently actuated vehicles are ranked by a quantitative indicator of stability.
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| 4. |
- Moberg, Stig, 1962-, et al.
(författare)
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Modeling and Parameter Estimation of Robot Manipulators Using Extended Flexible Joint Models
- 2014
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Ingår i: Journal of Dynamic Systems Measurement, and Control. - : ASME International. - 0022-0434 .- 1528-9028. ; 136:3, s. 031005-
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Tidskriftsartikel (refereegranskat)abstract
- This paper considers the problem of dynamic modeling and identification of robot manipulators with respect to their elasticities. The so-called flexible joint model, modeling only the torsional gearbox elasticity, is shown to be insufficient for modeling a modern industrial manipulator accurately. Another lumped parameter model, called the extended flexible joint model, is therefore used to improve the model accuracy. In this model, nonactuated joints are added to model the elasticity of the links and bearings. The unknown elasticity parameters are estimated using a frequency-domain gray-box identification method. The conclusion is that the obtained model describes the movements of the motors and the tool mounted on the robot with significantly higher accuracy than the flexible joint model. Similar elasticity model parameters are obtained when using two different output variables for the identification, the motor position and the tool acceleration.
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| 5. |
- Norhirni, M.Z., et al.
(författare)
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Load and Stress Analysis for the Swash Plate of an Axial Piston Pump/Motor
- 2011
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Ingår i: Journal of Dynamic Systems Measurement, and Control. - : American Society of Mechanical Engineers (ASME). - 0022-0434 .- 1528-9028. ; 133:6, s. 064505-
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Tidskriftsartikel (refereegranskat)abstract
- In an axial piston pump design, the swash plate plays an important role in controlling the displacement of the pump, especially in a closed loop system. In this paper, the axial piston pump is incorporated into the design of a hydraulic regenerative braking system for hybrid vehicles. The pump in this configuration should function in dual mode, as a pump and as a motor. For this to occur, the swash plate should swing in two opposite directions. The swash plate presented in this paper is designed for stability and ease of control. Analytical analysis of torque and forces were conducted using MATLAB software to verify the motion of the swash plate. Furthermore, finite element analysis was also carried out to evaluate the rigidity and stress in the system. The analytical evaluation has shown that as the swash plate angle increases, the required control force and torque increase almost linearly. However, the change of the plate angle was found to have no effect on the force exerted on the X-axis and the torque exerted on the Z-axis.
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| 6. |
- Nässelqvist, Martin, et al.
(författare)
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A methodology for protective vibration monitoring of hydropower units based on the mechanical properties
- 2013
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Ingår i: Journal of Dynamic Systems Measurement, and Control. - : ASME International. - 0022-0434 .- 1528-9028. ; 135:4
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Tidskriftsartikel (refereegranskat)abstract
- It is important to monitor the radial loads in hydropower units in order to protect the machine from harmful radial loads. Existing recommendations in the standards regarding the radial movements of the shaft and bearing housing in hydropower units, ISO-7919-5 (International Organization for Standardization, 2005, "ISO 7919-5: Mechanical Vibration-Evaluation of Machine Vibration by Measurements on Rotating Shafts-Part 5: Machine Sets in Hydraulic Power Generating and Pumping Plants, " Geneva, Switzerland) and ISO-10816-5 (International Organization for Standardization, 2000, "ISO 10816-5: Mechanical Vibration-Evaluation of Machine Vibration by Measurements on Non-Rotating Parts-Part 5: Machine Sets in Hydraulic Power Generating and Pumping Plants, " Geneva, Switzerland), have alarm levels based on statistical data and do not consider the mechanical properties of the machine. The synchronous speed of the unit determines the maximum recommended shaft displacement and housing acceleration, according to these standards. This paper presents a methodology for the alarm and trip levels based on the design criteria of the hydropower unit and the measured radial loads in the machine during operation. When a hydropower unit is designed, one of its design criteria is to withstand certain loads spectra without the occurrence of fatigue in the mechanical components. These calculated limits for fatigue are used to set limits for the maximum radial loads allowed in the machine before it shuts down in order to protect itself from damage due to high radial loads. Radial loads in hydropower units are caused by unbalance, shape deviations, dynamic flow properties in the turbine, etc. Standards exist for balancing and manufacturers (and power plant owners) have recommendations for maximum allowed shape deviations in generators. These standards and recommendations determine which loads, at a maximum, should be allowed before an alarm is sent that the machine needs maintenance. The radial bearing load can be determined using load cells, bearing properties multiplied by shaft displacement, or bearing bracket stiffness multiplied by housing compression or movement. Different load measurement methods should be used depending on the design of the machine and accuracy demands in the load measurement. The methodology presented in the paper is applied to a 40MW hydropower unit; suggestions are presented for the alarm and trip levels for the machine based on the mechanical properties and radial loads
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| 7. |
- Roebuck, Richard, et al.
(författare)
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Implementation of Trailer Steering Control on a Multi-Unit Vehicle at High Speeds
- 2014
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Ingår i: Journal of Dynamic Systems, Measurement and Control, Transactions of the ASME. - : ASME International. - 0022-0434 .- 1528-9028. ; 136:2, s. Art. no. 021016-
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Tidskriftsartikel (refereegranskat)abstract
- A high-speed path-following controller for long combination vehicles (LCVs) was designed and implemented on a test vehicle consisting of a rigid truck towing a dolly and a semitrailer. The vehicle was driven through a 3.5 m wide lane change maneuver at 80 km/h. The axles of the dolly and trailer were steered actively by electrically-controlled hydraulic actuators. Substantial performance benefits were recorded compared with the unsteered vehicle. For the best controller weightings, performance improvements relative to unsteered case were: lateral tracking error 75% reduction, rearward amplification (RA) of lateral acceleration 18% reduction, and RA of yaw rate 37% reduction. This represents a substantial improvement in stability margins. The system was found to work well in conjunction with the braking-based stability control system of the towing vehicle with no negative interaction effects being observed. In all cases, the stability control system and the steering system improved the yaw stability of the combination.
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| 8. |
- Sarin, H., et al.
(författare)
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Comparing time histories for validation of simulation models : Error measures and metrics
- 2010
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Ingår i: Journal of Dynamic Systems Measurement, and Control. - : ASME International. - 0022-0434 .- 1528-9028. ; 132:6
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Tidskriftsartikel (refereegranskat)abstract
- Computer modeling and simulation are the cornerstones of product design and development in the automotive industry. Computer-aided engineering tools have improved to the extent that virtual testing may lead to significant reduction in prototype building and testing of vehicle designs. In order to make this a reality, we need to assess our confidence in the predictive capabilities of simulation models. As a first step in this direction, this paper deals with developing measures and a metric to compare time histories obtained from simulation model outputs and experimental tests. The focus of the work is on vehicle safety applications. We restrict attention to quantifying discrepancy between time histories as the latter constitute the predominant form of responses of interest in vehicle safety considerations. First, we evaluate popular measures used to quantify discrepancy between time histories in fields such as statistics, computational mechanics, signal processing, and data mining. Three independent error measures are proposed for vehicle safety applications, associated with three physically meaningful characteristics (phase, magnitude, and slope), which utilize norms, cross-correlation measures, and algorithms such as dynamic time warping to quantify discrepancies. A combined use of these three measures can serve as a metric that encapsulates the important aspects of time history comparison. It is also shown how these measures can be used in conjunction with ratings from subject matter experts to build regression-based validation metrics.
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