Nicholas Krouglicof

An Efficient Camera Calibration Technique Offering Robustness and Accuracy Over a Wide Range of Lens Distortion

In the field of machine vision, camera calibration refers to the experimental determination of a set of parameters that describe the image formation process for a given analytical model of the machine vision system. Researchers working with low-cost digital cameras and off-the-shelf lenses generally favor camera calibration techniques that do not rely on specialized optical equipment, modifications to the hardware, or an a priori knowledge of the vision system. Most of the commonly used calibration techniques are based on the observation of a single 3-D target or multiple planar (2-D) targets with a large number of control points. This paper presents a novel calibration technique that offers improved accuracy, robustness, and efficiency over a wide range of lens distortion. This technique operates by minimizing the error between the reconstructed image points and their experimentally determined counterparts in “distortion free” space. This facilitates the incorporation of the exact lens distortion model. In addition, expressing spatial orientation in terms of unit quaternions greatly enhances the proposed calibration solution by formulating a minimally redundant system of equations that is free of singularities. Extensive performance benchmarking consisting of both computer simulation and experiments confirmed higher accuracy in calibration regardless of the amount of lens distortion present in the optics of the camera. This paper also experimentally confirmed that a comprehensive lens distortion model including higher order radial and tangential distortion terms improves calibration accuracy.

Design and control of a high performance SCARA type robotic arm with rotary hydraulic actuators

This study proposes a Selective Compliant Assembly Robotic Arm (SCARA) with two revolute joints for poultry deboning. The joints of the arm are based on two high performance rotary type hydraulic actuators. These actuators are operated by servo valves, which control hydraulic fluid flow and direction. A PID based independent joint control system is considered for controlling the position of each joint. The system was modelled using the MATLAB - SIMULINK toolbox. The simulation results show that the arm was capable of covering a work envelope of 0.9 m × 0.9 m, reaching controlled velocities of up to 7.5 m/s with an average of 5.8 m/s. Obtaining such high speeds and torques would be a difficult task with electrical actuators of the capacity as the hydraulic counterparts considered here.

Machine vision system for the automatic identification of robot kinematic parameters

This paper presents an efficient, noncontact measurement technique for the automatic identification of the real kinematic parameters of an industrial robot. The technique is based on least-squares analysis and on the Hayati and Mirmirani kinematic modeling convention for closed kinematic chains. The measurement system consists of a single camera mounted on the robots wrist. The camera measures position and orientation of a passive target in six degrees of freedom. Target position is evaluated by applying least-squares analysis on an overdetermined system of equations based on the quaternion representation of the finite rotation formula. To enhance the accuracy of the measurement, a variety of image processing functions including subpixel interpolation are applied.

High speed electro-hydraulic actuator for a scara type robotic arm

This study details the development of a high performance servo-hydraulic actuator for a Selective Compliant Assembly Robotic Arm (SCARA). The arm is intended for high speed food processing applications; specifically on-line poultry deboning. The system is mathematically modeled and simulated. Based on the simulation results, the hydraulic actuators are sized for optimal performance. A prototype actuator is subsequently designed, manufactured and experimentally evaluated. The tests results demonstrate that the prototype actuator is capable of producing unprecedented torques and associated accelerations relative to its size and mass. Comparable performance is not feasible with contemporary electrical actuators of similar size.

Propeller dynamometer for small Unmanned Aerial Vehicle

This paper details the design and development of a small scale air propeller dynamometer based on thin beam strain gauge load cells. The dynamometer will be used to characterize the performances of small propellers for Unmanned Aerial Vehicles (UAVs) in order to obtain an accurate system model and design an appropriate controller for hovering and smooth flight. A brief description of the design concept and calibration procedure along with test results is presented here. A static calibration was performed to determine thrust/torque measurement sensitivity as well as cross-sensitivity. Measurement data was captured and processed using a sigma-delta data acquisition board. Test results confirm that the dynamometer can be used to reliably measure thrust and torque produced by UAV propellers up to 10 inch in diameter with an accuracy of ±1% of full scale.

The question of accuracy with geometric camera calibration

In the field of machine vision, camera calibration refers to the experimental determination of a set of parameters which describe the image formation process for a given analytical model of the machine vision system. An accurate, reliable calibration procedure is essential for most industrial machine vision applications including mechanical metrology, robot assembly, reverse engineering, stereo vision etc. One of the most systematic calibration procedures for 3D machine vision applications was proposed by Heikkilä in which a comprehensive set of camera parameters is automatically evaluated by observing a calibration target consisting of two perpendicular planes, each with 256 circular control points. Other similar techniques employ a checkerboard pattern as a target and use the vertices of the squares as control points. While these techniques are sound from a theoretical point of view, they do not adequately speak to the question of measurement accuracy. The objective of this work is to gain and understanding of the problems associated with Geometric Camera Calibration through the application of Design of Experiments. A response surface methodology, namely a CCD Design, is carried to analyze the effects. This paper also highlights the issue of calibration accuracy by addressing the following fundamental question: Assuming a certain tolerance or uncertainty in the calibration target, what is the expected error with respect to the measured camera parameters and what is the impact on the final 3D machine vision application?

Moving target detection for sense and avoid using regional phase correlation

This paper outlines a video-based method for detecting intruder aircraft to assist with sense and avoid for small, unmanned aerial vehicles (UAVs). A key consideration is that the algorithm is suitable for real-time implementation on field-programmable gate arrays (FPGAs). The method begins by estimating the motion in the scene using regional phase correlation, and then fitting the positional predictions obtained using these regional motion vectors to an affine model representing the effect of camera motion on the background imagery. A combination of metrics, including phase correlation peak height (a confidence measure) and the error between the position predicted by the affine model and that obtained using the measured phase correlation vector, is used to indicate regions of interest where moving targets are present. The ability of the algorithm to detect approaching aircraft is analyzed using a number of aerial video sequences with different encounter geometries.

Development and testing of a novel high speed SCARA type manipulator for robotic applications

This paper proposes using servo hydraulics for high speed robotic manipulation. It details the development of a novel double vane rotary type actuator custom designed for use in a Selective Compliant Assembly Robotic Arm (SCARA). The system, which is mathematically modeled and simulated, consists of an electro-hydraulic servo valve, double vane rotary actuator, manipulator and a controller. Based on the simulation results, hydraulic actuators were sized for optimal performance. A prototype of the proposed manipulator was built and tested. The test results show that the proposed actuator is capable of reaching torques of up to 860 Nm. The end effector of the manipulator is capable of reaching average velocities in excess of 2.7 ms−1 with a payload capability of 5.3 kg. Comparable performance is not feasible with contemporary SCARA type robots with electric motors.

A single time scale visual servoing system for a high speed SCARA type robotic arm.

A high speed image based visual servoing (VS) technique is developed in this study for a Selective Compliant Assembly Robotic Arm (SCARA) manipulator with rotary hydraulic actuators. This study has developed a 2D position measuring system which comprise a high speed camera with a position sensitive detector as the image sensor. The input output interface and the controller for the VS system was implemented using a field programmable gate array (FPGA) providing a single chip solution for the embedded system. This camera was capable of providing position measurements of the end effector (EE) with an accuracy of up to 0.95 mm at a frequency of 1340 Hz. The proposed control strategy produced a better tracking performance with an EE payload of 12 kg with speeds of up to 1.3 m/s.

Digital hardware implementation of an active disturbance rejection controller for a highly dynamic parallel orientation manipulator.

This paper details the development of a tracking controller for a highly dynamic parallel orientation manipulator that is capable of achieving high angular acceleration. The adopted control algorithm is derived from the active disturbance rejection control (ADRC) technology. The ADRC algorithm must be evaluated on the control hardware at a frequency consistent with the dynamics of the system without creating any inter-channel latency for a successful implementation. In this regard, the field programmable gate array (FPGA) is preferred because of its superior speed and parallelism. While there is a clear demand for FPGA controllers in the military and the aerospace domain because of the improved SWaP (size, weight, and power) capabilities, the literature provides a few examples of such controllers that mostly employ expensive high logic density FPGA chips. In contrast, this paper describes how an advanced controller can be efficiently prototyped on a relatively low-cost, low logic density FPGA hardware. The controller was tested in a co-simulation approach (wherein the digital implementation of the control algorithm and the dynamics of the manipulator are simulated together) to ensure a robust FPGA implementation. In addition, a hardware evaluation was also conducted using a linear voice coil actuator under varying inertial loads. Experimental results obtained from the simulation study and hardware testing confirm the robust performance of the designed controller.