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Command Shaping for Flexible Systems: A Review of the First 50 Years
William Singhose 한국정밀공학회 2009 International Journal of Precision Engineering and Vol. No.
The control of flexible systems is a large and important field of study. Unwanted transient deflection and residual vibration are detrimental to many systems ranging from nano-positioning devices to large industrial cranes. Thousands of researchers have worked diligently for decades to provide solutions to the challenging problems posed by flexible dynamic systems. The work can roughly be broken into three categories:1) Hardware design, 2) Feedback control, and 3) Command shaping. This paper provides a review of command-shaping research since it was first proposed in the late 1950’s. The important milestones of the research advancements, as well as application examples, are used to illustrate the developments in this important research field.
Command Shaping Control for Micro-milling Operations
Joel Fortgang,William Singhose,Juan de Juanes Márquez,Jesus Perez 제어·로봇·시스템학회 2011 International Journal of Control, Automation, and Vol.9 No.6
Micro milling requires both high speed and high accuracy in order to economically produce parts with features on the scale of 1 μm. Micro mills are smaller and more flexible than traditional large-scale machines. Therefore, vibration of the machine structure is a significant problem. Given that micro milling requires high positioning precision, even small vibrations in the controller dynamics are problematic. The small-scale operation has considerably lower tool/workpiece interaction forces than traditional-scale milling. These low cutting forces have minimal effect on the machine structural re-sponse. Therefore, the dominant dynamic factor in exciting vibration can be the machine tool motion, rather than the workpiece/tool interaction. Given this realization, properly shaping the motions of the micro mill is a promising approach to reduce vibration. This paper presents a nonlinear command-shaping technique to reduce the vibrations of a micro mill that can be implemented with a standard CNC controller. The robustness of this technique to modeling errors and disturbances is investigated. Theoretical proofs and experimental demonstrations of the command-shaping technique are presented. The improved performance from the command shaping enables higher throughput and improved accuracy of the micro mill.
입력성형 인자에 따른 XY 스테이지의 구동 특성 영향에 관한 연구
박상원,홍성욱,최훈석,William Singhose 한국공작기계학회 2006 한국공작기계학회 추계학술대회논문집 Vol.2006 No.-
This paper investigates the effect of input shaping parameters on driving characteristics of XY stage. When applying real time input shaping schemes to actual XY stages, time spacing and acceleration time are critical parameters to be determined. In order to evaluate these parameters on driving characteristics of XY stage, this paper implements input shaping algorithms with the time spacing and acceleration time. The results show that driving characteristics of XY stage can be significantly influenced by time spacing and acceleration time.
Control of Crane Payloads That Bounce During Hoisting
Jisup Yoon,Nation, Shelley,Singhose, William,Vaughan, Joshua Eric IEEE 2014 IEEE transactions on control systems technology Vol.22 No.3
<P>Crane payloads exhibit unwanted motions such as swings, twists, and bounces that cause safety hazards and decrease performance. Numerous controllers have been developed to reduce payload swing. However, much less consideration has been given to bouncing in the vertical direction, which in some cases can also excite pitching of the payload. This dynamic effect most often arises when the payload is heavy and the suspension cables are long. This brief presents a mathematical model of a bouncing crane payload. Then, a method for generating commands to suppress the oscillations is developed and evaluated. Experiments on a tower crane demonstrate the improved performance provided by the proposed control method.</P>
A Method for Identifying Human-generated Forces during an Extensor Thrust
Hong Seong-Wook,Patrangenaru Vlad,Singhose William,Sprigle Stephen Korean Society for Precision Engineering 2006 International Journal of Precision Engineering and Vol.7 No.3
Some wheelchair users with neuromuscular disorders experience involuntary extensor thrusts, which may cause injuries via impact with the wheelchair, cause the user to slide out of the wheelchair seat, and damage the wheelchair. Knowledge of the human-generated forces during an extensor thrust is of great importance in devising safer, more comfortable wheelchairs. This paper presents an efficient method for identifying human-generated forces during an extensor thrust. We used an inverse dynamic approach with a three-link human body model and a system for measuring human body motion. We developed an experimental system that determines the angular motion of each human body segment and the force at the footrest, which was used to overcome the mathematical indeterminacy of the problem. The proposed method was validated experimentally, illustrating the force-identification process during an extensor thrust.
[Invited Paper] Using Approximate Multi-crane Frequencies for Input Shaper Design
Joshua Vaughan,Jieun Yoo,William Singhose 제어로봇시스템학회 2012 제어로봇시스템학회 국제학술대회 논문집 Vol.2012 No.10
Cranes are the primary heavy lifter used in a wide array of industries. For the transport of large payloads, multiple cranes are often employed in a cooperative manner. One factor limiting the efficiency of all cranes is payload oscillation. For multi-crane lifts, the payload oscillation is a function of an array of crane and payload parameters, many of which are difficult to measure in real-time. This paper investigates the use of the estimates of the multi-crane natural frequencies in input shaper design. Two methods to design input shapers that rely only on the suspension cable lengths involved in the lift are presented. The accuracy of these estimations and the resulting effectiveness of input-shaping control are studied via simulation and experimental testing with a two-crane system.
Deflection-Limiting Commands to Slew Flexible Systems with Velocity Limits
Yoon-Gyung Sung,William E. Singhose 제어로봇시스템학회 2008 제어로봇시스템학회 국제학술대회 논문집 Vol.2008 No.10
A new method to generate deflection-limiting commands for flexible systems with actuator velocity limits is presented and evaluated. In addition to limiting transient deflection, the command profiles reduce residual vibration for rest-to-rest motion of oscillatory systems with one dominant mode. A beneficial advantage of the command profiles is that they are described by closed-form functions of the system frequency, deflection-limiting ratio, velocity limit, actuator force-to-mass ratio, and desired move distance. The performance of the commands is evaluated with respect to move duration, transient oscillation energy, maximum transient deflection, and robustness to modeling errors. The proposed approach is illustrated with a numerical simulation of a benchmark system.
A Feedback Control System for Suppressing Crane Oscillations with On-Off Motors
Keith A. Hekman,William E. Singhose 대한전기학회 2007 International Journal of Control, Automation, and Vol.5 No.3
Crane payloads frequently swing with large amplitude motion that degrades safety and throughput. Open-loop methods have addressed this problem, but are not effective for disturbances. Closed-loop methods have also been used, but generally require the speed of the driving motors to be precisely controlled. This paper develops a feedback control method for controlling motors to cancel the measured payload oscillations by intelligently timing the ensuing on and off motor commands. The effectiveness of the oscillation suppression scheme is experimentally verified on an industrial bridge crane.