Vision-based kinematic calibration of a H4 parallel mechanism : Practical accuracies (original) (raw)
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Vision-based kinematic calibration of a H4 parallel mechanism
In this article, we present the kinematic calibration of a H4 parallel robot using a vision-based measuring device. Calibration is performed according to the inverse kinematic model method, using first the design model then a model developed for calibration purpose. With a precision of the order of magnitude of 0.2mm and 0.03 • , our vision system allowed us to obtain a final positioning accuracy of the end-effector lower than 0.5mm. Conclusions are given on the use of a vision-based measuring device for the calibration of this class of mechanisms.
Combining end-effector and legs observation for kinematic calibration of parallel mechanisms
— In this paper, an original approach is proposed for the kinematic calibration of parallel mechanisms. The originality lies in the use of vision to get information on all parts of the mechanism, i.e. its end-effector as well as its legs. Metrological redundancy is therefore maximized to improve the calibration efficiency. The approach is implemented for the calibration of the I4 parallel mechanism [1], with the use of the Jacobian matrix. No accurate camera location is needed so that the experimental procedure is easy to achieve. The calibration algorithm is detailed and experimentally demonstrated more efficient than other calibration methods based on legs observation or end-effector observation.
ON VISION-BASED KINEMATIC CALIBRATION OF n-LEG PARALLEL MECHANISMS
A vision-based kinematic calibration algorithm is proposed for parallel mechanisms with end-effector connected to the base by n legs. The joint between corresponding leg ends can be a passive or actuated prismatic joint, which include constant-length legs. Information on the position and orientation of the mechanism legs is extracted from the observation of these elements with a standard camera. No workspace limitation nor installation of additional proprioceptive sensors are required. The algorithm is first detailed, then an evaluation of the method is achieved for a Stewart-Gough platform, with experimental measurement accuracy evaluation and simulation of the identification process.
Kinematic Calibration of Parallel Mechanisms: A Novel Approach Using Legs Observation
—In this paper, a novel approach is proposed for the kinematic calibration of parallel mechanisms with linear actua-tors at the base. The originality of the approach lies in the observation of the mechanism legs with a camera, without any mechanism modification. The calibration can hence be achieved online, as no calibration device is linked to the end-effector, on any mechanism since no additional proprioceptive sensor installation is necessary. Because of the conditions of leg observability, several camera locations may be needed during the experimentation. The associated calibration method does not however require any accurate knowledge of the successive camera positions. The experimental procedure is therefore easy to perform. The method is developed theoretically in the context of mechanisms with legs linearly actuated at the base, giving the necessary conditions of identifiability. Application to an I4 mechanism is achieved with experimental results.
This paper presents kinematic calibration of parallel manipulators with partial pose measurements using a device that measures a rotation of the end-effector along with its position. The device contains a LVDT, a biaxial inclinometer, and a rotary sensor. The device is designed in a modular fashion and links of different lengths can be used. Two additional kinematic parameters required for the measurement device are discussed, kinematic relations are derived, and cost function is established to perform calibration with the proposed device. The study is performed for a six degree-of-freedom (DOF) fully parallel HexaSlide Mechanism (HSM). Experimental results show significant improvement in the accuracy of the HSM
Kinematic calibration of linear-actuated parallel mechanisms from leg observation
In this article, an original algorithm is proposed to achieve the kinematic calibration of parallel mechanisms with linear actuators on the base, using vision as an exteroceptive sensor to perform measurements on the legs of the mechanism. The calibration can be performed without adding proprioceptive sensors or restricting the mechanism's workspace during the calibration process. The algorithm is implemented for the calibration of the I4 parallel mechanism with experimental results.
Sensors, 2013
This paper presents a novel method for the calibration of a parallel robot, which allows a more accurate configuration instead of a configuration based on nominal parameters. It is used, as the main sensor with one camera installed in the robot hand that determines the relative position of the robot with respect to a spherical object fixed in the working area of the robot. The positions of the end effector are related to the incremental positions of resolvers of the robot motors. A kinematic model of the robot is used to find a new group of parameters, which minimizes errors in the kinematic equations. Additionally, properties of the spherical object and intrinsic camera parameters are utilized to model the projection of the object in the image and thereby improve spatial measurements. Finally, several working tests, static and tracking tests are executed in order to verify how the robotic system behaviour improves by using calibrated parameters against nominal parameters. In order to emphasize that, this proposed new method uses neither external nor expensive sensor. That is why new robots are useful in teaching and research activities.
Optimal pose selection for vision-based kinematic calibration of parallel mechanisms
In this paper, a new pose selection criterion for the kinematic calibration of parallel mechanisms is proposed. It enables one to take into account the measurement noise amplification that may occur for parallel mechanisms, as well as the variation of amplitude and anisotropy of the measuring device accuracy. This new criterion is applied to vision-based calibration of an Orthoglide mechanism, both in simulation, with comparison to existing criteria, and experimentally.
Sensors, 2010
This paper presents an overview of the literature on kinematic and calibration models of parallel mechanisms, the influence of sensors in the mechanism accuracy and parallel mechanisms used as sensors. The most relevant classifications to obtain and solve kinematic models and to identify geometric and non-geometric parameters in the calibration of parallel robots are discussed, examining the advantages and disadvantages of each method, presenting new trends and identifying unsolved problems. This overview tries to answer and show the solutions developed by the most up-to-date research to some of the most frequent questions that appear in the modelling of a parallel mechanism, such as how to measure, the number of sensors and necessary configurations, the type and influence of errors or the number of necessary parameters.
Calibration of three dimensional mechanism-novel calibration method for 3 DOF parallel mechanism
2002 IEEE International Conference on Industrial Technology, 2002. IEEE ICIT '02.
Many types of three dimensional mechanisms (3Dmechanism) are used in modern industry. Specially, in automation technology, product engineering and robotics, 3D-mechanisms play the key roles of complicated manipulation, 3D positioning and 3D measurement. Usually, the repeatability of 3D-mechanism is tested and evaluated. However, when we use 3D-mechanism in wide purposes and in wide conditions, the absolute calibration is the key technique to control the mechanism precisely. In this article, we analyze theoretically the method of the absolute calibration for 3D-mechanisms, such as a Cartesian mechanism, an articulated mechanism and a parallel mechanism. After theoretical analysis, we introduce a novel 3DOF parallel mechanism for a coordinate measuring machine (CMM) and a micro milling machine and a novel calibration method for these parallel mechanisms.