Resonance Ratio Control Research Articles

Active Inertia Extended Resonance Ratio Control for Permanent Magnetic Coupling Transmission System

Active Inertia Extended Resonance Ratio Control for Permanent Magnetic Coupling Transmission System

[formula omitted]adaptive resonance ratio control for series elastic actuator with guaranteed transient performance

Series elastic actuator (SEA) technology is promising for the development of compliant robotic joints. Despite advancements in the realization of precise tracking, challenges persist in controlling the vibration and transient performance. This study enhanced the resonance ratio control (RRC) algorithm by integrating it with the L1 adaptive control (L1AC) method to address overshoot, static error, and vibration in SEA position control. Initially, the resonance between the motor and link sides caused by the elastic transmission structure was analyzed, which can result in overshoots and vibrations that affect the transient performance of the SEA control. Subsequently, a control scheme based on L1AC was introduced to enhance the performance. The stability of the proposed algorithm was demonstrated through a comprehensive exploration of key control parameters. Furthermore, the algorithm was augmented with gravity compensation, effectively reducing the predicted and reference errors. Consequently, the transient performance was improved. The efficacy of this enhanced algorithm was validated through simulations and experimental platforms, and comparisons with the RRC and model reference adaptive control algorithms. In all the experiments, the overshoot did not exceed 1.1%, the maximum jitter amplitude on the link side was within 0.2° , and a larger time constant in the controller could effectively eliminate the overshoot and vibration with a small response time delay. Furthermore, the algorithm exhibited a protective response during link side collisions by moderating link velocity and limiting motor current, to safeguard the contact environment, humans, and the SEA itself, which take advantage of the L1AC’s low-pass filter (LPF) properties in disturbance handling.

High-Robust Force Control for Environmental Stiffness Variation Based on Duality of Two-Inertia System

The conventional force control has proposed load-side torque control based on the resonance ratio control (RRC) enhanced by an instantaneous state observer using the acceleration sensor; however, environmental stiffness variation (K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> variation) is not considered in such systems. This article evaluates the robust stability of the conventional method based on open-loop characteristics and the stability analysis results indicate that the conventional method becomes unstable during K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> variation. To realize superior high-robust stability, this article proposes a high-robust force control based on the duality of the two-inertia system. This article constructs an equivalent RRC (ERRC) combining the motor-side velocity control and the load-side velocity observer and demonstrates a torque-velocity duality. The results confirm that the load-side torque control based on ERRC is robust against K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> variation through the analysis of open-loop characteristics, and illustrate that the ERRC has the same as the conventional RRC proposed in position or velocity controls. The effectiveness of the proposed control method is validated through numerical simulations and experiments.

Equivalent Resonance Ratio Control in Two-Spring System for Stable Contact Motion in Industrial Robots

Equivalent Resonance Ratio Control in Two-Spring System for Stable Contact Motion in Industrial Robots

Active vibration suppression for rolling mills vibration based on extended state observer and parameter identification

Rolling mills vibration is a key factor that hinders the production of thin-strip steel. Currently, vibration is mainly suppressed by adjusting rolling mill parameters which is not a common approach. Due to special working conditions, the information of work roll, such as displacement and velocity, cannot be directly measured. Therefore, based on extended state observer, new resonance ratio control method, which is a common approach, is proposed to suppress the rolling mill vibration. First, the equivalent mass of the back roll is identified. Then, the interaction force between the work roll and the back roll and the velocity of the back roll are estimated using the extended state observer. Finally, these values are introduced into the input of the servo valve to compensate. The simulation results indicate that vibrations of both the work roll and the back roll are suppressed, and this method has a great tolerance for the identification error of the back-roll equivalent mass, and extended state observer compensation possesses a more superior vibration suppression than disturbance observer compensation.

Design and Vibration Suppression Control of a Modular Elastic Joint.

In this paper, a novel mechatronic design philosophy is introduced to develop a compact modular rotary elastic joint for a humanoid manipulator. The designed elastic joint is mainly composed of a brushless direct current (DC) motor, harmonic reducer, customized torsional spring, and fail-safe brake. The customized spring considerably reduces the volume of the elastic joint and facilitates the construction of a humanoid manipulator which employs this joint. The large central hole along the joint axis brings convenience for cabling and the fail-safe brake can guarantee safety when the power is off. In order to reduce the computational burden on the central controller and simplify system maintenance, an expandable electrical system, which has a double-layer control structure, is introduced. Furthermore, a robust position controller for the elastic joint is proposed and interpreted in detail. Vibration of the elastic joint is suppressed by means of resonance ratio control (RRC). In this method, the ratio between the resonant and anti-resonant frequency can be arbitrarily designated according to the feedback of the nominal spring torsion. Instead of using an expensive torque sensor, the spring torque can be obtained by calculating the product of spring stiffness and deformation, due to the high linearity of the customized spring. In addition, to improve the system robustness, a motor-side disturbance observer (DOb) and an arm-side DOb are employed to estimate and compensate for external disturbances and system uncertainties, such as model variation, friction, and unknown external load. Validity of the DOb-based RRC is demonstrated in the simulation results. Experimental results show the performance of the modular elastic joint and the viability of the proposed controller further.

Sensorless cutting force estimation for full-closed controlled ball-screw-driven stage

Process monitoring technology has been studied in order to realize higher efficiencies and greater automation of the machining process. The cutting force is widely regarded as being the most valuable physical quantity to be gathered when monitoring a metal-cutting process. However, a practical, wideband, and indirect means of measuring the cutting force has not yet been attained for ball-screw-driven machine tools. In recent years, full-closed ball-screw-driven stages mounting linear encoder have been widely used for high-end machine tools. Considering indirect cutting force estimation using servo information from a full-closed controlled ball-screw-driven stage, three pieces of information are available as servo signals of the feed drive: the motor current command, the rotation angle of the motor, and the displacement of the stage. In this study, a high-precision and wideband sensorless cutting force estimation method was proposed for full-closed controlled ball-screw-driven stages using a multi-encoder-based disturbance observer (MEDOB). The MEDOB was originally proposed for estimating the external force on the load side of flexible robots, and was used for resonance ratio control, which was intended to suppress low-frequency vibration. This study aimed to develop an estimation technique for high-frequency cutting forces that exceed the bandwidth of current control loops for the highly stiff ball-screw-driven stage. The influence of extra phase lag on the control signals was considered in order to apply MEDOB to an actual ball-screw-driven stage. The validity of the proposed method was verified using both an analytical simulation and cutting experiments.

Advanced Motion Control for Next-Generation Industrial Applications

In this special section, a total of ten papers are included, covering a variety of aspects of advanced motion control for industrial applications. The first two papers are on the control of the robotic elastic joint. The classical two-degrees-of-freedom robot control is extended by the virtual torsion sensor in the loop. The proposed control is experimentally evaluated on a single-joint robot consisting of an actuator with harmonic-drive gear and inertial load under additional impact of gravity. Also proposed is an acceleration-based robust controller for the position and force control problems of a novel variable stiffness series elastic actuator (SEA). The vibration of the novel SEA and external disturbances are suppressed by using the resonance ratio control and arm disturbance observer, respectively. The intrinsically safe mechanical structure and high performance motion control system provide several benefits in industrial applications.

An Acceleration-Based Robust Motion Controller Design for a Novel Series Elastic Actuator

This paper proposes an acceleration-based robust controller for the motion control problem, i.e., position and force control problems, of a novel series elastic actuator (SEA). A variable stiffness SEA is designed by using soft and hard springs in series so as to relax the fundamental performance limitation of conventional SEAs. Although the proposed SEA intrinsically has several superiorities in force control, its motion control problem, especially position control problem, is harder than conventional stiff and SEAs due to its special mechanical structure. It is shown that the performance of the novel SEA is limited when conventional motion control methods are used. The performance of the steady-state response is significantly improved by using disturbance observer (DOb), i.e., improving the robustness; however, it degrades the transient response by increasing the vibration at tip point. The vibration of the novel SEA and external disturbances are suppressed by using resonance ratio control (RRC) and arm DOb, respectively. The proposed method can be used in the motion control problem of conventional SEAs as well. The intrinsically safe mechanical structure and high-performance motion control system provide several benefits in industrial applications, e.g., robots can perform dexterous and versatile industrial tasks alongside people in a factory setting. The experimental results show viability of the proposals.

Contactless magnetic gear for robot control application

SummaryThis paper describes the application of a magnetic gear to a robot by fulfilling the essential requirements for a robot control, which are velocity control, position control, and force control. A magnetic gear is a transmission device that realizes contactless torque transmission by applying a magnetic force. When using a magnetic gear, cogging torque and spring characteristics need to be considered. In this paper, we introduce an approximate model of cogging torque. This model is used for velocity control to attenuate the disturbance due to cogging torque. In the case of position control, the oscillations due to the spring effect of the magnetic attractive force become a problem. To reduce the adverse effect due to these oscillations, resonance ratio control is applied. We also propose to use a magnetic gear for realizing force sensorless bilateral control of teleoperation. Because of the frictionless transmission of a magnetic gear, the force sensorless estimation of a reaction force can be realized using a reaction force observer. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(4): 32–41, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22414

Design for Sensorless Force Control of Flexible Robot by Using Resonance Ratio Control Based on Coefficient Diagram Method

Generally, the flexible robot system can be modeled as the two-mass system which consists of a motor and load connected by a spring. Thus, its elasticity causes resonance in the system. By using the conventional PID controller, this method cannot perform well in this situation. Much research has proceeded with the aim of reducing vibration. A new effective control method, the resonance ratio control, has been introduced as a new way to guarantee the robustness and suppress the oscillation during task executions for a position and force control. In this paper, three techniques are proposed for improving the performance of resonance ratio control. Firstly, a new multi encoder based disturbance observer (MEDOB) is shown to estimate the disturbance force on the load side. The proposed observer is not necessary to identify the nominal spring coefficient. Secondly, coefficient diagram method (CDM) has been applied to calculate a new gain of the force controller. A new resonance ratio gain has been presented as 2.0. Finally, the MEDOB and load side disturbance observer (LDOB) are employed to identify a spring coefficient of flexible robot system. By using the proposed identification method, it is simple to identify the spring coefficient and easy to implement in the real flexible robot system. The effectiveness of the proposed identification method is verified by simulation and experimental results.

非接触磁気歯車のロボット制御への適用

Summary This paper describes the application of a magnetic gear to a robot by fulfilling the essential requirements for a robot control, which are velocity control, position control, and force control. A magnetic gear is a transmission device that realizes contactless torque transmission by applying a magnetic force. When using a magnetic gear, cogging torque and spring characteristics need to be considered. In this paper, we introduce an approximate model of cogging torque. This model is used for velocity control to attenuate the disturbance due to cogging torque. In the case of position control, the oscillations due to the spring effect of the magnetic attractive force become a problem. To reduce the adverse effect due to these oscillations, resonance ratio control is applied. We also propose to use a magnetic gear for realizing force sensorless bilateral control of teleoperation. Because of the frictionless transmission of a magnetic gear, the force sensorless estimation of a reaction force can be realized using a reaction force observer. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(4): 32–41, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22414

Vibration Suppression of Two-Wheel Mobile Manipulator Using Resonance-Ratio-Control-Based Null-Space Control

A two-wheel mobile manipulator has the potential to become a multiskilled robot in the field of robotics, and it is already implemented by using inverted pendulum control. The center of gravity (COG) position is controlled to achieve the balancing of the robot. Since the vibrations of manipulator arms affect the COG positions of the inverted pendulum, balancing of the robot deteriorates. Therefore, the vibration control of manipulator arms of the two-wheel mobile manipulator is proposed in this paper. The virtual double-inverted pendulum is modeled using a “4-DOF” manipulator, and it is controlled in work space and null space. Resonance ratio control is utilized for vibration-suppression control. The resonance ratio of a system can be determined arbitrarily by the feedback of reaction torque, and reaction torque observers are implemented for each and every manipulator motor. The feedback signal for vibration suppression is introduced to the null space of the manipulator. Simulations and experiments were carried out to check the validity of the proposed method, and results prove the effectiveness of the proposed vibration controller.

Motion Stabilization by Using Laser Distance Sensor for Biped Walking Robot with Flexible Ankle Joints

This paper describes an approach to motion stabilization by using laser distance sensors for biped robots with flexible ankle joints. To avoid the vibrated zero moment point (ZMP) behavior caused by mechanical resonance, a vibration control method is proposed in the paper. In our approach, the deformation of the ankle joint is measured by using laser distance sensors, and the detected deformation is translated into the equivalent reaction force at the center of gravity. The feedback of the reaction force enables the stabilization of the walking motion in a manner similar to resonance ratio control. The validity of the proposed method is evaluated by several experimental results.

Vibration suppression control of redundant manipulator with flexible structure by considering nullspace motion

AbstractA redundant manipulator is useful for posture control while maintaining the desired end‐effector position by using its redundancy. This makes it possible to perform agile motions such as obstacle avoidance while achieving the target task. However, as the number of degrees of freedom of motion increases, the stiffness of the redundant manipulator decreases, which induces unacceptable vibration in manipulator motion. To address this issue, this paper describes a strategy of vibration suppression by using a workspace observer and resonance ratio control based on nullspace control. The validity of the proposed approach is confirmed by simulations and experiments. © 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 92(2): 1–9, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10050

Observer-Based Tuning of Two-Inertia Servo-Drive Systems With Integrated SAW Torque Transducers

This paper proposes controller design and tuning methodologies that facilitate the rejection of periodic load-side disturbances applied to a torsional mechanical system while simultaneously compensating for the observer's inherent phase delay. This facilitates the use of lower-bandwidth practically realizable disturbance observers. The merits of implementing fulland reduced-order observers are investigated, with the latter being implemented with a new low-cost servo-machine-integrated high-bandwidth torque-sensing device based on surface acoustic wave (SAW) technology. Specifically, the authors' previous work based on proportional-integral-derivative (PID) and resonance ratio control (RRC) controllers (IEEE Trans. Ind. Electron., vol. 53, no. 4, pp. 1226-1237, Aug. 2006) is augmented with observer disturbance feedback. It is shown that higher-bandwidth disturbance observers are required to maximize disturbance attenuation over the low-frequency band (as well as the desired rejection frequency), thereby attenuating a wide range of possible frequencies. In such cases, therefore, it is shown that the RRC controller is the preferred solution since it can employ significantly higher observer bandwidth, when compared to PID counterparts, by virtue of reduced noise sensitivity. Furthermore, it is demonstrated that the prototype servo-machine-integrated 20-Nmiddotm SAW torque transducer is not unduly affected by machine-generated electromagnetic noise and exhibits similar dynamic behavior as a conventional instrument inline torque transducer

Force Servoing by Flexible Manipulator Based on Resonance Ratio Control

This paper presents a force servoing method to suppress torsional vibration of two-mass resonant system. The resonance ratio control is one of the effective control methods of two-mass resonant system. In this method, the ratio between the resonant frequency of motor and arm is determined arbitrary according to the feedback of estimated reaction torque. The reaction torque is estimated by using a position sensitive detector (PSD). Since the estimation method does not need the parameter identification, the torsion information is obtained with accuracy. To attain the affinity and adaptability to environment, motion systems should control the reaction torque from the environment. In the force servoing system, the force command is given as a disturbance of the arm portion. The arm disturbance is observed by the arm disturbance observer without force sensors. The proposed force servoing system is based on both the conventional PD control and the resonance ratio control, and the determination method of pole placement is discussed. The proposed force servoing system can realize both the suppression of the inner torsional reaction torque and the adaptation to unknown outer force inputs. The numerical and experimental results show the viability of the proposed method

Vibration Suppression Control of Redundant Manipulator with Flexible Structure by Considering Nullspace Motion

Redundant manipulator is useful for posture control with keeping the desired end-effector position by using its redundancy. This makes it possible to realize dexterous motion such as obstacle avoidance motion with achieving the target task. However, the more degree-of-freedom motion increase, the smaller the stiffness of redundant manipulator is. This induces unacceptable vibration in the manipulator motion. To address this issue, this paper describes a strategy of vibration suppression by using workspace observer and resonance ratio control based nullspace control. The validity of the proposed approach is confirmed by simulations and experiments.

Pushing Operation by Flexible Manipulator Taking Environmental Information Into Account

Vibration suppression in a motion-control system is an important problem in industry applications. Recently, a number of studies about flexible manipulators have been reported. However, there is little published on pushing operation by flexible manipulators. Contact motion to an unknown environment is difficult, because the motion system should recognize the environmental stiffness and adapt to it at the time of collision. This paper proposes a pushing control by a flexible manipulator based on a resonance ratio control. The environmental information is estimated more accurately by using a position sensitive device. The proposed method is composed of three modes: 1) approaching; 2) touching; and 3) pushing. In the approaching mode, the resonance ratio control is applied to suppress the torsional vibration. Compliance control is installed in order to relax an impact force in the touching mode. Finally, a two-step controller is proposed for the pushing mode. In the first step, friction effects are identified by a friction-torque observer. Then, the pushing operation with compensation of the stick-slip friction is controlled based on the identification results in the second step. It is possible to remove an object to a desired position. The experimental results show viability of the proposed method

High-Performance Control of Dual-Inertia Servo-Drive Systems Using Low-Cost Integrated SAW Torque Transducers

This paper provides a systematic comparative study of compensation schemes for the coordinated motion control of two-inertia mechanical systems. Specifically, classical proportional-integral (PI), proportional-integral-derivative (PID), and resonance ratio control (RRC) are considered, with an enhanced structure based on RRC, termed RRC+, being proposed. Motor-side and load-side dynamics for each control structure are identified, with the integral of time multiplied by absolute error performance index being employed as a benchmark metric. PID and RRC control schemes are shown to be identical from a closed-loop perspective, albeit employing different feedback sensing mechanisms. A qualitative study of the practical effects of employing each methodology shows that RRC-type structures provide preferred solutions if low-cost high-performance torque transducers can be employed, for instance, those based on surface acoustic wave technologies. Moreover, the extra degree of freedom afforded by both PID and RRC, as compared with the basic PI, is shown to be sufficient to simultaneously induce optimal closed-loop performance and independent selection of virtual inertia ratio. Furthermore, the proposed RRC+ scheme is subsequently shown to additionally facilitate independent assignment of closed-loop bandwidth. Summary attributes of the investigation are validated by both simulation studies and by realization of the methodologies for control of a custom-designed two-inertia system