• Journal of Mechanical Science and Technology
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• v.17 no.10
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• pp.1431-1442
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• 2003

A new method of estimating the pose of a mobile-task robot is developed based upon an active calibration scheme. The utility of a mobile-task robot is widely recognized, which is formed by the serial connection of a mobile robot and a task robot. To be an efficient and precise mobile-task robot, the control uncertainties in the mobile robot should be resolved. Unless the mobile robot provides an accurate and stable base, the task robot cannot perform various tasks. For the control of the mobile robot, an absolute position sensor is necessary. However, on account of rolling and slippage of wheels on the ground, there does not exist any reliable position sensor for the mobile robot. This paper proposes an active calibration scheme to estimate the pose of a mobile robot that carries a task robot on the top. The active calibration scheme is to estimate a pose of the mobile robot using the relative position/orientation to a known object whose location, size, and shape are known a priori. For this calibration, a camera is attached on the top of the task robot to capture the images of the objects. These images are used to estimate the pose of the camera itself with respect to the known objects. Through the homogeneous transformation, the absolute position/orientation of the camera is calculated and propagated to get the pose of a mobile robot. Two types of objects are used here as samples of work-pieces: a polygonal and a cylindrical object. With these two samples, the proposed active calibration scheme is verified experimentally.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.6
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• pp.2689-2708
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• 2016

Multi-camera systems which integrate two or more low-cost digital cameras are adopted to reach higher ground coverage and improve the base-height ratio in low altitude remote sensing. To guarantee accurate multi-camera integration, the geometric relationship among cameras must be determined through platform calibration techniques. This paper proposed a combined two-step platform calibration method. In the first step, the static platform calibration was conducted based on the stable relative orientation constraint and convergent conditions among cameras in static environments. In the second step, a dynamic platform self-calibration approach was proposed based on not only tie points but also straight lines in order to correct the small change of the relative relationship among cameras during dynamic flight. Experiments based on the proposed two-step platform calibration method were carried out with terrestrial and aerial images from a multi-camera system combined with four consumer-grade digital cameras onboard an unmanned aerial vehicle. The experimental results have shown that the proposed platform calibration approach is able to compensate the varied relative relationship during flight, acquiring the mosaicing accuracy of virtual images smaller than 0.5pixel. The proposed approach can be extended for calibrating other low-cost multi-camera system without rigorously mechanical structure.

• Journal of Electrical Engineering and Technology
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• v.13 no.1
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• pp.438-444
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• 2018

Structured light vision system has been widely used in 3D surface profiling. Usually, it is composed of a camera and a laser which projects a line on the target. Calibration is necessary to acquire 3D information using structured light stripe vision system. Conventional calibration algorithms have found the pose of the camera and the equation of the stripe plane of the laser under the same coordinate system of the camera. Therefore, the 3D reconstruction is only possible under the camera frame. In most cases, this is sufficient to fulfill given tasks. However, they require multiple images which are acquired under different poses for calibration. In this paper, we propose a calibration algorithm that could work by using just one shot. Also, proposed algorithm could give 3D reconstruction under both the camera and laser frame. This would be done by using newly designed calibration structure which has multiple vertical planes on the ground plane. The ability to have 3D reconstruction under both the camera and laser frame would give more flexibility for its applications. Also, proposed algorithm gives an improvement in the accuracy of 3D reconstruction.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.8
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• pp.2081-2087
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• 1994

Touch trigger probes are widely used for inspection purposed in the CMM(Coordinate meauring machine) or machine tool. The errors introduced by measurement probe are fairy systematic, thus can be calibrated and compensated properly. This paper presents a technique for the error calibration and compensation of the probe errors, which can be easily applicable to the manufacturers and users of the measurement probe. The probe coordinate system is defined for the probe error assessment, and a reference sphere ball is measured, and the probe errors are calibrated. The calibrated probe errors are represented in the 3D error map and 2D error map along probing direction. Detail algorithms for the error compensation are proposed.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.5
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• pp.1182-1191
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• 1994

This paper presents an enhanced method of slit beam projection intended for the rapid measurement of 3-dimensional surface profiles of dies and molds. Special emphasis is given to optimizing the design of optical system so that the measuring accuracy can be maximized by adopting two-plane camera calibration together with sub-pixel image processing techniques. Finally, several measurement examples are discussed to demonstrate that an actual measuring accuracy of $\pm$ 0.2 mm can be achieved over the measuring range of 500 mm{\times}300mm{\times}200mm$.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.521-526
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• 2001

This research develops a low-cost and high accurate kinematic calibration method for a parallel typed machining center tool. A planar table is used for a mechanical fixture restricting the platform to place at the constrained pose and a low-cost and high accurate digital indicator is employed for a device checking if the constrained movement is satisfied within the established range. The kinematic parameters calibrated with respect to a single plane aren't influenced from the misalignment of the plane. A parameter observability is successfully obtained even through one planar constraint, which guarantees that the kinematic parameters is estimated by minimizing the cost function.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.7
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• pp.986-991
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• 2004

For volumetric error measurement and calibration for machine tools, manufacturing machine or coordinate measuring machine (CMM), are studied using a Ball-bar artifact. A design of the Ball-bar is suggested manufactured by Invar, which is a low thermal expansion material, and precision steel balls. The uncertainty for the artifact method is discussed. A method of the Ball-bar artifact for obtaining 3-D position errors in CMM is proposed. The method of error vector measurement is shown using the Ball-bar artifact. Finally, the volumetric error is calculated from the error vectors and it can be used for Pitch error compensation in conventional NC machine and 3-D position Error map for calibration of NC machine tools.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.6
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• pp.1431-1440
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• 1993

This paper presents a new NC machine performance test and calibration system. In order to measure NC machine erros in simpler, and less time-comsuming way, some indirect measuring systems such as circular disk system and double ball bar system have been developed instead of laser interferometer. But these indirect measuring systems have shown their limits in identifying each of NC machine error sources in absolute numerical value. Therefore, we developed an unique NC machine error measurement system which provides a simple measuring process like other conventional indirect methods and still can indentify each of NC machine error sources in absolute numerical value.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.9
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• pp.53-57
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• 2009

There are technical requirements to manufacture large size functional parts with not only simple geometries like a flat or spherical surface but also sculptured geometries. In addition, the required machining accuracy for these parts is becoming more severe. In general, the form accuracy of machined parts is determined by the relative position between workpiece and tool during machining process. To improve machining accuracy the relative position errors should be maintained within the required accuracy. This study deals with the estimation and calibration of depth of cut using the AE signal in micro-machining. Also, this sensing technique can be applied to detect the initial contact between workpiece and tool.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1219-1224
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• 2004

The objective of this study is to propose an experimental calibration facility in which a heat flux sensor can be calibrated under conductive condition by using helium gas. The heat flux calibration facility was designed, simulated and manufactured for use in a high heat transfer condition. It delivers heat fluxes up to a maximum of 35 KW $m^{-2}$. A copper block heated electrically with 3.5 KW power is designed to produce uniform temperature up to 600 K across its face. High heat fluxes are provided between hot plate and cold plate by 1 mm height helium filled gap. A cold plate is maintained around 300 K through pool boiling using a refrigerant and water-cooled heat exchanger. A simulation was conducted to verify the design of the main test section. To verify the performance of calibration facility, a heat flux sensor was examined. The measured heat fluxes were compared to the calculated one.