Timothy N. Chang

Motion Control Firmware for High-Speed Robotic Systems

This paper addresses the hardware and software platforms of high-speed robot control systems, which are usually integrated with multi-modal sensing, multi-axis motion, and complex algorithmic capabilities. In this work, robot control is considered from software development cycles to actual applications. Cross platform and upward compatible software development is addressed. Finally, an example application of real time slewing control of a high-speed industrial robot is provided.

Web-based command shaping of cobra 600 robot with a swinging load

This work focuses on the real-time control of a swinging load through the Internet. In particular, command shaping is applied to move a cable suspended load at the end point of an Adept Cobra 600 4-axis SCARA robot, with the objective of minimizing load swing. The first part of this paper discusses inverse kinematics,pendulum dynamics calculations, the corresponding shaping control algorithm,and the effects of transmission time delay. Standardized Internet interface via the DataSocket software in LabVIEW is then addressed in the second part. Simulation and experimental results confirm the feasibility of real time command shaping control through the Internet.

Automated liquid dispensing pin for DNA microarray applications

This paper describes a new liquid dispensing/aspirating system that is capable of producing micron-size spots/droplets for molecular biology research and analysis. In particular, the application is focused on deoxyribonucleic-acid microarray fabrication with the goals of uniform spot morphology, smaller spot size, higher yield, more efficient use of biological materials, and the capacity to handle high viscosity liquids. The new system is based on active sensing and control and it is part of a fully integrated robotic microarray system for genomic and proteomic applications. The prototype system handles thick liquids such as 100% glycerol as well as aqueous solutions and generates uniform spots in a contactless manner with controllable spot size ranging from 80 microns to 200 microns. Note to Practitioners-Microarraying is a powerful tool that enables the expression profiling of a vast quantity genetic/proteomic materials in parallel. Current printing technology includes photolithography, impact pins, inkjet, etc. Although these designs have been successful in printing spot size down to 100 microns, a new approach is needed to handle the order of magnitude increase in density while reducing cost. The SmartPin described in this paper is a sensor-based motion-controlled print head created for printing the next-generation microarrays. It is capable of depositing any aqueous samples (e.g., deoxyribonucleic acid, protein, etc.) and has the flexibility and cost advantage of the printing approach and yet possesses high performance and telepresence accessibility. The system utilizes an optical-fiber-based sensor probe for both sensing and sample delivery. Sensing is then integrated with computer control so that it can generate the microarray with fully controllable spot density and size. By maintaining a uniform gap distance between the pin tip and the target slide, performance and reliability are enhanced. The current work is at the prototype development state and will need further refinement for commercialization.

Vibration control of linear robots using a piezoelectric actuator

This paper presents the results of vibration control strategy for high-speed linear robots using an auxiliary piezoelectric actuator. With acceleration reaching 3 g, rapid horizontal slewing motion inevitably excites the structural resonances of the robot and generates vertical vibration forces exceeding the tolerance of the end-effector. Instead of controlling the robot vibration from the main actuators (ac servomotors with limited bandwidth), a piezoelectric actuator is deployed to provide vibration suppression at the load in the z direction. This way the robot is treated as a disturbance generator while the piezoactuator is considered as the plant. A digital servocompensator is then designed and implemented to suppress these vibration modes. Typically, attenuation is achieved for the dominant mode with 30 dB and other modes with 15 dB. Suppression of vibration up to seven modes has been implemented satisfactorily.

Model Reference Input Shaper Design With Applications to a High-Speed Robotic Workcell With Variable Loads

In this paper, the model reference zero vibration (MRZV) control design is introduced to improve transient performance of robotic manipulators. MRZV consists of a zero vibration (ZV) shaper as the feedforward control while utilizing model reference control to improve robustness and performance under plant model parameter variations. Performance analysis of the MRZV control is given in terms of residual vibration and it is shown that MRZV can tolerate significantly larger plant model variations while maintaining the performance characteristics compared to standard shaper designs such as ZV and ZV and Derivative. A synthesis procedure is provided for the MRZV method to guarantee a prespecified level of residual vibration. Experimental verifications based on a standard cycle time test are carried out on an Adept Technology Cartesian robot. Results confirm the effectiveness of the proposed method.

Zero Vibration On–off Position Control of Dual Solenoid Actuator

Solenoids are low-cost high-speed nonlinear actuators commonly used in switching mode. This paper presents a dual-solenoid actuator system for high-speed positioning applications. A novel control method that combines on-off control and input shaping is used to obtain low-vibration smooth transients when compared with traditional proportional and integral control and on-off control. Simulation results and experimental data confirm that this dual-solenoid position actuator with the novel control method is effective and practical.

Analysis and control of monolithic piezoelectric nano-actuator

This paper describes the analysis and control of a 2-DOF monolithic piezoelectric actuator. This actuator is part of a 6-DOF manipulator capable of linear resolution to 2 nanometer and angular resolution to 1 arc-second. Design of this actuator differs from the existing ones in that it has a monolithic structure which enables a high bandwidth, low drift, and high force realization. A number of nonlinearities exist in the actuator, stemming from the geometry and materials properties. For example, coupling of the actuator elements can be modeled as a soft spring which increases scale factor at high actuation levels. In this work, a combination of feedforward (amplitude-dependent input shaping) and feedback control are applied to reduce the effects of 1) scale factor nonlinearities, 2) hysteresis, and 3) output oscillations. Application of this actuator include: optoelectronics assembly, optical fiber alignment, and semiconductor processing.

Development and implementation of an application programming interface for PC/DSP-based motion control system

This paper presents the results of a low cost, PC-DSP based motion control system development. The Texas Instruments TMS320C31 floating point Digital Signal Processor is selected for the real-time hardware platform while code development and user interface tasks reside on a standard, non real-time PC platform such as the Pentium/Windows 95 systems. An application programming interface has been implemented to facilitate open architecture code development. Finally, application to the control of an Adapt linear robotic workcell is made with 2 input shaper designs serving as the test algorithms.

Control of hysteresis in a monolithic nanoactuator

Deals with the characterization and control of hysteresis in a piezoelectric nanoactuator. First, the notion of normalized ratio is introduced to quantitatively measure the strength of the hysteresis. This ratio is based on the harmonic contents of the actuator output signal and is approximately invariant under a range of input signal frequency and amplitude. Second, an analytic expression relating the harmonics to the plant parameters is derived. This expression is then applied to determine the plant parameters so that a nonlinear observer can be synthesized to cancel the hysteresis. Third, the observer-based compensator is tested in the experimental system. It is determined that the proposed compensation scheme produces significant attenuation of the hysteresis in the actuator.

Method to detect cardiac abnormalities based on electrocardiography and sinoatrial pacemaker model

In this paper, a new method for detecting cardiac abnormalities (bradycardia and tachycardia) is proposed. Based on the YNI (Yanagihara, Noma, and Irisawa) model to analyze the pole-zero characteristics of the phase error between abnormal electrocardiography (ECG) and entrained YNI-response, it develops a diagnostic pacemaker system that can replace multiple sensors. The work derives for the first time the thresholds of poles and zeros to diagnose deadly bradycardia and tachycardia, respectively. Simulation analysis confirms that the proposed pole-zero characteristics of cardiac abnormalities is effective to complete a diagnostic process for a pacemaker in real time. The results of this study will be useful not only for detection and analysis of cardiac abnormalities but also for improvement of the performance of pacemakers.