Experimental Hardware System Research Articles

Operational Space Iterative Learning Control of Coupled Active/Passive Multilink Cable-Driven Hyper-Redundant Robots

Abstract The operational space control (OSC) of multilink cable-driven hyper-redundant robots (MCDHRs) is required to perform tasks in many applications. As a new coupled active-passive (CAP) MCDHR system, due to the multiple couplings between the active cables, the passive cables, the joints, and the end-effector, the OSC becomes more and more complicated. However, there is currently no robust and effective control method to solve the OSC problem of such types MCDHRs. In this paper, an OSC framework of CAP-MCDHRs using a dynamics-based iterative-learning-control (ILC) method is proposed, considering multivariate optimization. First, the multi-coupling kinematics and the series-parallel coupling dynamics equation (i.e., cable-joint-end) of the CAP-MCDHR are derived. Then, a dynamics-based trajectory tracking framework was constructed. Moreover, an OSC accuracy evaluation model based on a high-precision laser tracker was also designed. The framework allows the tracking of operational space trajectories (OSTs) online with the feasible cable tension and the joint angle. It is also shown that the tracking performance can be improved through the ILC when the desired trajectory is repeatedly performed. Finally, a simulation and an experimental hardware system are built. The results show that the proposed control framework can be easily and effectively applied to the CAP-MCDHR used in real-time.

Defects Detection Algorithm of Harumanis Mango for Quality Assessment Using Colour Features Extraction

Visual defects detection is one of the main problems in the post-harvest processing caused a major production and economic losses in agricultural industry. Manual fruits detection become easy when it is done in small amount, but the result is not consistent which will generate issue in fruit grading. A new fruit quality assessment system is necessary in order to increase the accuracy of classification, more consistencies, efficient and cost effective that would enable the industry to grow accordingly. In this paper, a method based on colour feature extraction for the quality assessment of Harumanis mango is proposed and experimentally validated. This method, including image background removal, defects segmentation and recognition and finally quality classification using Support Vector Machine (SVM) was developed. The results show that the experimental hardware system is practical and feasible, and that the proposed algorithm of defects detection is effective.

Extended NLCS Algorithm of BiSAR Systems With a Squinted Transmitter and a Fixed Receiver: Theory and Experimental Confirmation

This paper proposes an extended nonlinear chirp scaling (CS) image formation algorithm for the bistatic synthetic aperture radar systems with the squinted transmitter and a fixed receiver. Since the transmitter with the squint mode was adopted in the system, two main problems, i.e., the spatial variance of the frequency-modulation rate and cubic phase terms, were introduced in the image formation algorithm. The former problem was solved by the linearity approximation of parameter <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$p$</tex></formula> and deduced <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$q$</tex></formula> (the second- and third-order coefficients of CS factors in range, which could be used to remove the spatial variation and high-order phase in the range direction) along the range domain while the latter one was compensated by a cubic analytical phase term in the frequency domain. A corresponding experimental hardware system and the bistatic experiments were also described in this paper. Both the simulation and experimental results validated the proposed algorithm.

Computer vision based system for apple surface defect detection

A novel automated apple surface defect sorting experimental system based on computer image technology has been developed. The hardware system has the advantage of being able to inspect simultaneously four sides of each apple on the sorting line. The methods, including image background removal, defects segmentation and identification for stem-end and calyx areas, were developed. The results show that the experimental hardware system is practical and feasible, and that the proposed algorithm of defect detection is effective.

Vibration Suppression of a Flexible Concrete Distributor Arm. 2nd Report, Application to Actual Arm.

The 1st report of this subject modeled a flexible concrete distributor arm as a multi-link flexible arm and a DVFB control of the 1st joint was shown to be effective for suppressing the vibration of the arm of an experimental hardware system. The present paper illustrates a difference between the experimental hardware system and an actual concrete distributor arm. It is shown that the control law which was suitable for the experimental system is not directly applicable to the actual system due to nonlinear frictions existing in the joints and actuator dynamics. The DVFB control law is modified by considering equivalent damping torques corresponding to the actual frictions including Coulomb friction, etc. In order to design a control law of the distributor system, a numerical simulator incorporating such nonlinear elements is further developed by using MATLAB/ SIMULINK. The simulator enables us to design a control system taking account of the nonlinearity in the system. The designed control system is successfully applied to the vibration suppression of the actual concrete distributor arm.

Experimental Demonstration of an Indoor GPS-Based Sensing System for Robotic Applications

The objective of this research is to demonstrate that an indoor sensing system consisting of pseudo-satellites (pseudolites) and modified commercial GPS receivers can be used to sense and control the relative position and attitude of prototype robotic space vehicles in a laboratory environment. The long-term goal for this research is to develop technologies that will enable robotic vehicles to perform complex maneuvers such as autonomous navigation, rendezvous, multivehicle formation flying, and assembly in space. An experimental hardware system consisting of a prototype space robot, target vehicle, and GPS system has been devised to closely emulate real space systems. Since the experiments take place indoors where GPS satellite signals cannot be received, several GPS pseudolite transmitters have been built and installed around the perimeter of the laboratory to provide the GPS signals. The indoor GPS environment created by the close-range pseudolite transmitters required development of new algorithms for resolving vehicle positions and attitudes from the carrier-phase measurements. Therefore, the most novel aspect of this research has been the development of GPS for indoor sensing, where it has the potential to be applied to indoor mobile robots and to automated manufacturing systems. This paper presents the theoretical formulation and experimental results of the use of this indoor GPS system for performing rendezvous between a prototype space robot vehicle and a passive target vehicle.

A data flow processor array system

This paper presents the architecture of a highly parallel processor array system which executes programs by means of a data driven control mechanism. The data driven control mechanism makes it easy to construct an MIMD (multiple instruction stream and multiple data stream) system, since it unifies inter-processor data transfer and intra-processor execution control. The design philosophy of the data flow processor array system presented in this paper is to achieve high performance by adapting a system structure to operational characteristics of application programs, and also to attain flexibility through executing instructions based on a data driven mechanism. The operational characteristics of the proposed system are analyzed using a probability model of the system behavior. Comparing the analytical results with the simulation results through an experimental hardware system, the results of the analysis clarify the principal effectiveness of the proposed system. This system can achieve high operation rates and is neither sensitive to inter-processor communication delay nor sensitive to system load imbalance.