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ABSTRACT: A problem of continuing interest in feedback control is handling conflicting time-domain performance specifications. Semiconductor manufacturing is one of the applications of particular interest in this context with the demanding feature sizes (on the order of a few tens of nanometers) to be produced on a wafer while still requiring high throughput (greater than 100 wafers per hour). In this brief, we propose a multiscale control design method based on a reduced-order model-following scheme for the dynamic systems with such conflicting time-domain performance requirements. This method uses a dynamic reference model to make the plant output track the model output as closely as possible without increasing the overall order of the control system. Optimal proportional-integral (PI) control is used, which is essentially a modification of the conventional optimal control. A detailed analytical proof is given to show that this control scheme effectively overcomes the limitations of the conventional optimal control techniques and provides consistent performances at nano- as well as macroscale positioning with fast rise and settling times. Benefits and limitations of the proposed control scheme are described and stability and performance analyses are discussed. A six-degree-of-freedom (6-DOF) extended-range magnetically levitated (maglev) nanopositioning stage, which is open-loop unstable, is used as a test bed to demonstrate the developed control strategy. Step responses under a variety of conditions are obtained to verify the effectiveness of the proposed method. This method exhibits significantly better and robust performances in terms of transient as well as steady-state behavior compared with conventional optimal-control schemes. Furthermore, it can be applied to a general class of higher-order linear time-invariant (LTI) systems with or without open-loop instability.
IEEE Transactions on Control Systems Technology 10/2007; · 1.77 Impact Factor
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ABSTRACT: The main objective of this paper is to demonstrate the feasibility of Inter-net-based real-time control. A novel client/server-based architecture for Inter-net-based supervisory control with a Common Gateway Interface/Hyper Text Markup Language (CGI/HTML) interface is presented. A real-time operating en-vironment was established for closed-loop control over Ethernet. We conceived of an autoregressive (AR) prediction scheme and a novel compensation algorithm to compensate for network-induced time delays and data-packet losses simultane-ously. We constructed an open-loop unstable ball magnetic-levitation (maglev) setup as a test bed to validate the two proposed control architectures. Experimental results proved the feasibility of Internet-based real-time control and verified the effectiveness of the proposed time-delay/packet-loss compensation algorithm in networked feedback control systems.
Asian Journal of Control 04/2007; 9:47-51. · 1.03 Impact Factor
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ABSTRACT: The main objective of this paper is to demonstrate the feasibility of Internet-based real-time control. A novel client/server-based architecture for Internet-based supervisory control with a Common Gateway Interface/Hyper Text Markup Language (CGI/HTML) interface is presented. A real-time operating environment was established for closed-loop control over Ethernet. We conceived of an autoregressive (AR) prediction scheme and a novel compensation algorithm to compensate for network-induced time delays and data-packet losses simultaneously. We constructed an open-loop unstable ball magnetic-levitation (maglev) setup as a test bed to validate the two proposed control architectures. Experimental results proved the feasibility of Internet-based real-time control and verified the effectiveness of the proposed time-delay/packet-loss compensation algorithm in networked feedback control systems.
Asian Journal of Control 02/2007; 9(1):45 - 49. · 1.03 Impact Factor
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ABSTRACT: A high-precision positioner using a novel superimposed concentrated field permanent magnet matrix is presented in this paper. It can generate all six-degrees-of-freedom (DOF) motions with only a single moving part. This extended range multi axis positioner is actuated by three planar levitation motors, which are attached on the bottom of the moving part. Three aerostatic bearings are currently used to provide the suspension force for the system against gravity. We designed and implemented digital lead-lag controllers running on a digital signal processor (DSP). To improve the closed-loop dynamic performance in the vertical directions, we implemented a controller in the minor feedback loop as well. The positioner demonstrates a position resolution of 20 nm and a position noise of 10-nm root mean square (rms) in x and y and 15-nm rms in z. The angular resolution around the x-, y-, and z -axes is of submicroradian order. The planar travel range is 160 mm times 160 mm, and the maximum velocity achieved is 0.5 m/s at the 5-m/s <sup>2</sup> acceleration, which can enhance the throughput in wafer processing. Several two-dimensional motion profiles are presented to demonstrate the positioner's capability of accurately tracking any extended range planar trajectories. The experimental results verified the utility of this extended range six-DOF high-precision positioner in semiconductor manufacturing and factory automation
IEEE/ASME Transactions on Mechatronics 01/2007; · 2.87 Impact Factor
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ABSTRACT: In this paper, we provide experimental results in the application of the results of [4]. Based on the theoretic work in [4], we propose an estimator-based delay-compensation algorithm to stabilize a networked con-trol system (NCS) with network-induced stochastic time delays, data-packet losses, and out-of-order data-packet transmissions. With the p-sampling-period delay upper bound, the NCS can also accommodate up to p À 1 successive packet losses. We also derive sufficient conditions for the stability of the NCS. The feasibility and effectiveness of the theoretic results of [4] are verified experimentally using an NCS test bed incorp-orating an open-loop unstable ball magnetic-levitation (maglev) system we constructed.
European Journal of Control 01/2007; 4:1-8. · 0.82 Impact Factor
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ABSTRACT: This paper presents the development of a novel real-time operating environment for networked control systems (NCSs). An open-loop unstable magnetic-levitation (maglev) test bed was constructed and used to develop an NCS with real-time application interface (RTAI). A client-server architecture on a local-area network was developed with the network communication based on the user datagram protocol. The control loop of our NCS is closed over the network. This NCS structure gives the best flexibility and has significant economical merits. The implementation of an event-driven server and a time-driven client presented in this paper facilitates a simple timing scheme that does not require clock synchronization between the client and the server. A novel prediction scheme with a multiple-step-ahead control-signal generator is used to maintain system stability in the presence of excessive time delays and data-packet losses in the communication network. The performance of this NCS, based on the predictor algorithm, is demonstrated experimentally. The current system can compensate for up to 20% data-packet losses without losing stability with the maglev real-time-control test bed in the communication network. Our real-time operating environment also improved the command-following capability by a factor of 4 in terms of command frequency. Note to Practitioners- With the advancement in the automation industry, the need to perform complex remote operations has grown. Ever-increasing computational capabilities and advancements in the networking technology have aided researchers to develop architectures to implement control from a distance. In large-scale control applications of the modern industry, the functional agents, such as sensors, actuators, and controllers are geographically distributed. For smooth working of a control application, all of the agents have to exchange information through communication media. The results of this paper can help to design practical real-time networked control systems in modern industry.
IEEE Transactions on Automation Science and Engineering 08/2006; · 1.46 Impact Factor
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ABSTRACT: We present and experimentally verify two control architectures: supervisory control and feedback control over network. With the client/server architecture we developed for supervisory control, a client can give the control commands, tune the control parameters, and receive the experimental results remotely and in real time. Real-time feedback control over network is also investigated with a ball magnetic-levitation (Maglev) system as a test bed. We devised a novel timeout scheme and derived an autoregressive (AR) prediction model for delayed/lost sensor data. By applying this timeout and prediction scheme to the cases of consecutive data loss, we showed that the test bed could survive sporadic delays of as long as three sampling periods without losing stability. The feasibility and effectiveness of the proposed network-based real-time control methodologies was demonstrated experimentally.
IEEE Transactions on Control Systems Technology 02/2006; · 1.77 Impact Factor
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ABSTRACT: We present a six-axis magnetic-levitation (maglev) stage capable of precision positioning down to several nanometers. This stage has a simple and compact mechanical structure advantageous to meet the performance requirements in the next-generation nanomanufacturing. It uses the minimum number of linear actuators required to generate all six axis motions. In this paper, we describe the electromechanical design, modeling, and control, and the electronic instrumentation to control this maglev system. The stage has a light moving-part mass of 0.2126 kg. It is capable of generating translation of 300 μm in the x, y, and z axes, and rotation of 3 mrad about the three orthogonal axes. The stage demonstrates position resolution better than 5 nm rms and position noise less than 2 nm rms. Experimental results presented in this paper show that the stage can carry, orient, and precisely position a payload as heavy as 0.4 kg. The pull-out force was found to be 8.08 N in the vertical direction. Furthermore, under a load variation of 0.14 N, the nanopositioner recovers its regulated position within 0.6 s. All these experimental results match quite closely with the calculated values because of the accurate plant model and robust controller design. This device can be used as a positioning stage for numerous applications, including photolithography for semiconductor manufacturing, microscopic scanning, fabrication and assembly of nanostructures, and microscale rapid prototyping.
IEEE Transactions on Industry Applications 10/2005; · 1.66 Impact Factor
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ABSTRACT: This paper addresses nanoscale path planning and motion control, which is essential in key nanomanufacturing applications such as microstereolithography (μSTL), dip-pen-nanolithography (DPN), and scanning applications for imaging and manipulation of nanoscale surface phenomena, with the magnetic-levitation (maglev) technology. We identified motion trajectories commonly used in industrial applications along with the challenges in optimal path planning to meet the nanoscale motion-control objectives and achieve precise positioning and maximum throughput simultaneously. Key control parameters in path planning are determined, and control design methodologies including a well-damped lead-lag controller and an optimal linear quadratic regulator are proposed to satisfy the positioning requirements. The proposed methodologies, individually and collectively, were implemented, and experimental results are presented in this paper to illustrate their effectiveness in planning optimal trajectories. The damped lead-lag controller exhibited the command overshoot of as small as 0.37%, and the multivariable LQ controller reduced the dynamic coupling between the axes by 97.1% as compared with the decoupled single-input-single-output (SISO) lead-lag controllers. The position resolution of 5 nm was achieved in x and y with the errors in command tracking as small as 4.5 nm. The maglev stage demonstrated excellent performances for the chosen nanomanufacturing applications in terms of position resolution and accuracy, and speed.
American Control Conference, 2005. Proceedings of the 2005; 07/2005
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ABSTRACT: This paper discusses the real-time aspects of networked control systems' (NCSs) operating environments. An open-loop unstable magnetic-levitation (Maglev) test bed was constructed and used to develop an NCS with a real-time application interface (RTAI) operating environment. A client-server architecture on a local area network (LAN) was developed with the network communication based on the user datagram protocol (UDP). The implementation of an event-driven server and a time-driven client presented in this paper facilitates a simple timing scheme that does not require clock synchronization between the client and the server. A novel prediction scheme involving the multiple-step-ahead generation of control signals is used to maintain system stability in the presence of excessive time delays and packet losses in the communication network. The current system can compensate for up to 20% data-packet losses without losing stability with the Maglev real-time-control test bed in the communication network.
American Control Conference, 2005. Proceedings of the 2005; 07/2005
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ABSTRACT: A novel model-predictive-control strategy with a timeout scheme and p-step-ahead state estimation is presented in this paper to overcome the adverse influences of stochastic time delays and packet losses encountered in network-based real-time control. An open-loop unstable magnetic-levitation (maglev) test bed was constructed and employed for its experimental verification. The compensation algorithms developed in this paper deal with the network-induced stochastic time delays and packet losses in both the forward path and the feedback path simultaneously. With the p-sampling-period delay upper bound, the networked control system (NCS) can also accommodate up to p - 1 successive packet losses. Experimental results demonstrate the feasibility and effectiveness of this networked real-time control strategy.
American Control Conference, 2005. Proceedings of the 2005; 07/2005
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ABSTRACT: In this paper, we present the design, control, and testing of a 6 degrees-of-freedom magnetically-levitated system with nanometer-precision positioning capability and several-hundred-micrometer travel range. This system levitates a triangular single-moving-part platen, and produces the six-axis motion with six single-axis linear actuators. One of the prominent advantages of this magnetic levitation (maglev) system is that there is no physical contact between the moving part and the stator, which eliminates friction, wear, backlash, and hysteresis. As compared to other traditional devices, the present system is very compact with the minimum number of actuators for six-axis motion generation. The maglev device presented herein shows the position resolution better than 5 nm with 2-nm rms position noise, and is capable of a velocity of 0.5 m/s and an acceleration of 30 m/s<sup>2</sup>. The nominal power consumption is only 15 mW by each horizontal actuator, and 320 mW by each vertical actuator. The actuators are sized to be able to orient and position a maximum payload of 1 kg. The key application of this maglev device is the manipulation at nanoscale for microassemblies and manufacture of their parts. Other potential applications are stereolithography, vibration-free delicate instrumentation, and microscale rapid prototyping.
IEEE/ASME Transactions on Mechatronics 07/2004; · 2.87 Impact Factor
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ABSTRACT: This paper presents a novel design for a tubular linear brushless permanent-magnet motor. In this design, the magnets in the moving part are oriented in an NS-NS-SN-SN fashion which leads to higher magnetic force near the like-pole region. An analytical methodology to calculate the motor force and to size the actuator was developed. The linear motor is operated in conjunction with a position sensor, three power amplifiers, and a controller to form a complete solution for controlled precision actuation. Real-time digital controllers enhanced the dynamic performance of the motor, and; gain scheduling reduced the effects of a nonlinear dead band. In its current state, the motor has a rise time of 30 ms, a settling time of 60 ms, and 25% overshoot to a 5-mm step command.. The motor has a maximum speed of 1.5 m/s and acceleration up to 10 g. It has a 10-cm travel range and 26-N maximum pull-out force. The compact size of the motor suggests it could be used in robotic applications requiring moderate force and precision, such as robotic-gripper positioning or actuation. The moving part of the motor can extend significantly beyond its fixed support base. This reaching ability makes it useful in applications requiring a small, direct-drive actuator, which is required to extend into a spatially constrained environment.
Industry Applications Conference, 2003. 38th IAS Annual Meeting. Conference Record of the; 11/2003
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ABSTRACT: The main objective of this research is to demonstrate experimentally the feasibility of using the Internet for distributed real-time control. A magnetic ball levitation system was developed as a test bed for the experimental verification of the real-time supervisory control scheme via the Internet. This supervisory control is based on the client/server architecture. With CGI (common gateway interface) and HTML (hypertext markup language) codes, it has been shown that a client can change the position commands, modify the control parameters, and receive the experimental results in real time. We propose a methodology of using timeout and sensor data estimation along with the controller to stabilize the system with bounded sporadic time delay in the Internet. The algorithm increased the mean allowable time delay following a uniform distribution from 90 μs to 836 μs. This algorithm also ensures the system stability at a sampling frequency of 333.3 Hz in the presence of bounded sporadic surges in time delays.
American Control Conference, 2003. Proceedings of the 2003; 07/2003
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American Control Conference, 2003. Proceedings of the 2003; 02/2003
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ABSTRACT: The main objective of this research is to demonstrate experimentally the feasibility of using the Internet for distributed real-time control. A ball magnetic levitation (maglev) system was developed as a test bed for the experimental verification. In the first part of this paper we present the successful establishment of supervisory control of the test-bed via the internet. With the supervisory control it has been shown that a client can change the position commands, modify the control parameters, and receive the experimental results in real time. in the latter part of the paper a methodology to increase the upper bound for time delays that can be accommodated in the control loop has been presented. The upper bounds of time delays that can be accommodated in the control loop for a lead-lag compensator designed in the continuous domain were estimated experimentally for various sampling frequencies. The mean time delay that can be accommodated in the control loop is 90 /spl mu/s when the time delays vary according to uniform distribution. To increase this upper bound of time delays a new lead-lag compensator was designed directly in the digital domain and a methodology of timeout and sensor data estimation has been proposed. The methodology of sensor data estimation and the new digital lead-lag controller running at a sampling frequency of 333.3 Hz increased the upper bound of mean time delay from 90 /spl mu/s to 836 /spl mu/s for delays following a uniform distribution.
Intelligent Control. 2003 IEEE International Symposium on; 02/2003
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ABSTRACT: The authors have developed a novel extended-range linear
magnetostrictive motor using the peristaltic motion of a laminated
Terfenol-D (Tb<sub>0.3</sub>Dy<sub>0.7</sub>Fe<sub>2</sub>) element.
This element migrates in the opposite direction of the traveling
magnetic field generated by prevailing three-phase armature commutation.
The actuator mechanical design is in an open structure in order to allow
easy assembly and access to internal actuator components. Eight sets of
Belleville washers guarantee uniform squeeze preload in spite of wear,
thermal expansion, or motion of the moving element. We incorporated a
laminated Terfenol-D slab in this actuator to reduce the eddy current,
leading to high-frequency high-speed operation. We have also designed
and constructed the power electronics and control units for the
magnetostrictive actuator's open-loop and closed-loop operations. With a
series-resonant capacitor, we were able to achieve a near-unity power
factor and decrease the reactive power requirement by a factor of 20.
The magnetostrictive motor has demonstrated 12-mm/s speed at excitation
frequency of 1600 Hz, and shown 140-N load capacity. The effective
travel range of the present motor is 25 mm, and can be extended further.
This linear magnetostrictive motor shows great potential in high-force
precision positioning applications such as automotive actuators,
robotics, and flight control surface actuators
IEEE Transactions on Industry Applications 06/2002; · 1.66 Impact Factor
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Won-jong Kim
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ABSTRACT: We have developed a high-precision magnetically levitated (Maglev) stage with large planar motion (50 mm×50 mm) capability. The key element of this stage is a linear motor capable of providing forces in both suspension and translation without contact. To deal with the dynamic coupling in the platen, we designed and implemented a multivariable linear quadratic regulator, and performed time-optimal control. In this paper, we address issues related to the stochastic modeling of the stage including transfer function identification and noise/disturbance analysis and prediction. Provided are recent test results on precision dynamics, such as fine settling, effect of optical table oscillation, and position ripple. We demonstrate how the performance of the current Maglev stage can be improved with these analyses and test results. The Maglev stage operates with positioning noise of 5 nm RMS in x and y, acceleration capabilities in excess of 2 g (20 m/s<sup>2</sup>), and closed-loop cross-over frequency of 100 Hz.
American Control Conference, 2002. Proceedings of the 2002; 02/2002
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ABSTRACT: Presents high-precision control of a magnetically levitated (maglev) linear actuator with novel geometric configuration. The linear actuator is used as a unit actuator in the development of a maglev instrument with six-axis nanopositioning capability. The novel configuration in this design concept leads to a lightweight and compact size. The objective of development of this maglev linear actuator is to verify the underlying theory and fundamental working principles. The device allows a linear motion range of ±500 μm with nanoscale positioning resolution. We present electromechanical design, controller design and implementation, and preliminary closed-loop experimental results with various step sizes for this linear actuator.
American Control Conference, 2002. Proceedings of the 2002; 02/2002
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Won-jong Kim
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ABSTRACT: Nanoscale science and engineering is an emerging technological
field and,has immense economic and societal impacts. This paper presents
a high-precision magnetic levitation (maglev) technology that can be
used in many crucial research activities in nanotechnology and, other
precision applications dealing with delicate motions and forces. They
include manufacture of nanoscale structures, atomic-level manipulation,
assembly and packaging of microparts, vibration isolation for
instrumentation, and seismic motion detection. A compact, lightweight,
single-moving part that holds the specimen can be magnetically
levitated-in all six degrees of freedom. This paper has demonstrated the
applicability of this maglev technology in nanoscale science and
engineering
Nanotechnology, 2001. IEEE-NANO 2001. Proceedings of the 2001 1st IEEE Conference on; 02/2001
