Development and testing of a high speedudhydraulic manipulator with single time scaleudvisual servoing

摘要

Automation of production processes has enabled to meet the dramatic demand forudmanufactured products that has grown out of the increase in world population. In existingudindustries greater production requirements and improvement in product qualityudcall for faster industrial robots. This study details the design and development of audhigh-speed visual servoing system for industrial applications. The proposed visualudservoing system consists of a high speed robotic manipulator, a high-speed cameraudsystem and an embedded controller.udThe proposed robotic manipulator has the configuration of a Selective CompliantudAssembly Robotic Arm (SCARA). It uses two custom-designed double vane rotaryudhydraulic actuators for driving the links of the robot. The SCARA system was mathematicallyudmodeled and simulated. Based on the simulation results, the hydraulicudactuators were sized for optimal performance. A prototype actuator was subsequentlyuddesigned, manufactured and experimentally evaluated. The test results show that theudproposed actuator is capable of reaching torques of up to 460 Nm in 30 ms with audpayload of 12 kg. This is not possible with electric motors of similar size. Then theudproposed SCARA was designed and fabricated using the proposed actuators. Theudend effector of this manipulator was capable of reaching velocities of up to 2.7 ms⁻¹udwith a payload of 5.3 kg. Comparable performance is not feasible with contemporary SCARA type robots.udThe proposed robot was designed for handling payloads up to 15 kg with speeds of upudto 2 ms⁻¹. This often results in flexing of the links and twisting of the support column,udadding external disturbances to the system. A high-speed camera system was designedudand built to obtain the position of the end effector as feedback for the controller. Ituduses a two dimensional Position Sensitive Detector as the image sensor. An electronicudcircuit was designed and built for signal conditioning and data acquisition from theudPosition Sensitive Detector. It was then calibrated to account for non-linearities onudthe image sensor. The camera was constructed using this Position Sensitive Detectorudcircuit, a lens and an infra red filter.It was then calibrated to estimate the extrinsicudand intrinsic parameters. This camera was capable of carrying out measurements atudfrequencies of up to 1350 Hz. The measurements made by this camera produced anudaverage absolute accuracy of 0.31 mm and 0.37 mm in x and y directions, respectively.udA Field Programmable Gate Array was used in this study as the platform for developingudan embedded controller for the robot. Using contemporary Field ProgrammableudGate Array technology, a powerful virtual processor can be synthesized and integratedudwith custom hardware to create a dedicated controller that out performs someudof the conventional microcontroller and microprocessor based designs. The Field ProgrammableudGate Array based controller takes advantage of both hardware featuresudand virtual processor technology. The input, output interfaces for this controller wereudimplemented using hardware. Complex functions that are difficult to be implementedudin hardware were implemented using a virtual soft processor. Four different typesudof controllers were implemented and tested. These include hardware proportional-derivative,udsoftware proportional-derivative, single time scale visual servoing and set point modification type controllers. The proposed implementation carried out singleudtime scale visual servoing at frequencies of up to 330 Hz.