Optimal linear feedback controller synthesis methodologies have the potential to become a worthy alternative to standard design methodologies, particularly for high-end complex systems. Although these design methodologies have been around for more than two decades, the majority of industrial control engineers are still reluctant to adopt this new design paradigm. Motivated by these observations, the MECO Research Team at KU Leuven is developing a Linear Control Toolbox (LCToolbox). LCToolbox is an open-source ᴍᴀᴛʟᴀʙ toolbox providing a high level of abstraction to apply linear optimal controller design methods. Its key features are the signal-based modeling framework that allows the user to construct the control configuration, the identification module that interfaces several routines in a uniform manner, and the control module that allows the user to specify an optimal feedback controller design problem in an intuitive way and solve it as such. Moreover, LCToolbox supports state-of-the-art B-spline-based linear parameter-varying (LPV) modeling and controller design techniques, unlocking the true potential of advanced feedback controller synthesis methodologies. The design of an LPV controller for an overhead crane is used as a running example throughout the paper to illustrate all features of LCToolbox.
Sensorless external torque estimation is important for industrial applications. The load-side torque in a two-inertia system with a load-side encoder can be estimated by using either of the two observers that present different levels of robustness against modeling and measurement errors on the motor side and transmission part. By combining these observers, we propose a load-side external torque observer with high estimation accuracy even under modeling and measurement errors. Analyses of the observer with and without a joint torque sensor unveil the advantages and limitations of applying a joint torque sensor for external torque estimation. In addition, we derive a systematic design method for the proposed observers to minimize the estimation variance by considering the variance of the plant parameters and sensor measurements. The advantages of the proposed method are evaluated through simulations and experiments.
Advanced rehabilitation requires a measurement system that quantitatively analyzes the actions of each individual. Joint moment is an indice used to quantitatively evaluate an individual's actions. Conventionally, force plates and high-speed cameras have been used to analyze joint moments. However, these devices need to be fixed in a laboratory, which limits the measurable motions and measurement range. Further, these sensors are expensive. Hence, it is difficult to use them in medical or nursing care facilities. Therefore, this study aimed to estimate joint moments using inexpensive and wearable sensors. This paper proposes a practical joint moments estimation system using inertial measurement units, which is a wearable sensor. The proposed method uses wearable sensors to measure continuous motion without limitation. It is also cheaper than conventional systems. The effectiveness of the proposed system was verified by comparison with the method using force sensors.
Ball-screw-driven stages are feed systems that are widely used in industrial equipment such as numerically controlled machine tools. They require precise position control; however, rolling friction in the ball-screw mechanism deteriorates its control performance. Therefore, for precise control of ball-screw-driven stages, rolling friction must be compensated. Iterative learning control (ILC) is an effective method of friction compensation. However, industrial applications of ILC are limited because of its vulnerability to task variation, such as variation in position reference. In conventional studies, projection-based ILC employing basis functions has been proposed to deal with multiple tasks. In this paper, we propose basis functions for position control of ball-screw-driven stages based on their physical association with rolling friction. Simulations and experiments validate the effectiveness of our proposal.
In this research, we developed a system to insert an intelligent power module (IPM) in a circuit board automatically. The pin row spacing of a target IPM is not reformed in advance and is not the same as the hole row spacing of the board. Hence, after the pin row of one side is inserted, the opposite side must be inserted while applying a force to the already inserted pin row in order to reform the spacing. To this end, a parallel link robot consisting of servo motors was developed. Also, visual feedback control using two webcams is utilized for the alignment and insertion. Moreover, by using the information obtained from a six-axis force sensor installed on the motion base of the robot, it is possible to confirm the grasping IPM and prevent the damage. In the experiment, the developed system was used to perform insertion 100 times, and a 100% success rate was achieved. The average insertion time was 29 seconds.
Communication delays between the master robot and slave robot could destabilize a bilateral control system. Recent researches have shown that an adaptive controller that dynamically determines the controller gain of the master depending on the stiffness of the contact object is effective in improving stability. However, the resulting delay in estimating the stiffness of the object degrades the performance and stability of the control system. This paper therefore proposes a novel adaptive controller that utilizes the position of the contact object. The validity of the proposed controller is demonstrated through frequency domain analysis as well as simulation and experimental results. These results indicate that the proposed controller suppresses overshoot, because the proposed controller changes the controller gain before the slave robot comes into contact with an object. In addition, the control system works well if the contact object moves during a contact motion.
The decrease in iron loss in a DC-DC converter is one of the most important issues for energy apparatuses. To reduce the iron loss under the magnetic hysteresis B-H curve caused by the current ripples in the reactor core built in the DC-DC converter, where B and H are the magnetic flux density and magnetic field intensity, respectively, we apply a numerical calculation method based on a suitable magnetic hysteresis model using the play model. When the operating current (corresponding to the magnetic field), on the reactor core is constant, there are two points of magnetic flux density in the B-H curve because of the nonlinear magnetic characteristics, the higher magnetic flux density and lower magnetic flux density. At the higher B and lower B operating points, minor loops appear in the B-H curve when the operating current on the reactor core is varied and has ripples. The calculation results for all three cases show that the performance of the higher B operating point is significantly better than that of the lower B operating point. In particular, a higher B operating point has lower iron loss, smaller magnetic flux density ripples, and larger energy density of the magnetic field caused by the smaller minor loop.
Geared motors require oil for lubrication; however, the oil may leak if no sealing is provided. One method for preventing leaking is to mount oil seals on the input and output sides of the gear. However, this increases the effects of nonlinear friction in the motor, causing stick-slip during velocity zero-crossings. This paper proposes a stick-slip suppression method based on a velocity-driven N-order stick compensator (VDNSC) and a slip suppressor. The proposed stick compensator is based on a motor-side normalization compensator (MNC) and works as an order-variable friction observer, while the proposed slip suppressor is based on velocity-switched high frequency damping. The validity of the proposed method is confirmed through experiments with low-velocity control.
In this paper, a cross-coupled 2-DOF SPM motor with Halbach array is proposed. In the proposed 2-DOF motor, the permanent magnets (PMs) are arranged in both the linear direction and the rotational direction so that the motor generates thrust force in the linear direction and torque in the rotational direction. The Halbach array is applied to both the linear direction and the rotational direction. The proposed motor is analyzed using 3-D FEA. In the analysis, the model with Halbach array only in the linear direction, the model with Halbach array only in the rotational direction, and the model with Halbach array in both the linear direction and the rotational direction are compared. The analysis results show that the model with Halbach array in both directions generates higher force and torque than not only the model without Halbach array but also the models with Halbach array in either the linear direction or the rotational direction. In the analysis, the magnetic flux is also analyzed in addition to the force and torque. Additionally, experiments are conducted to confirm the effectiveness of the Halbach array.
To reduce vibration, overshoot, and tracking error of the rotor in an open-loop micro-step drive of a stepping motor, we propose a novel pre-compensator using a low-pass type filter without control delay. The pre-compensator consists of a low-pass filter that removes the natural frequency component causing the vibration and a zero-phase filter that removes the control delay. Finally, a position control experiment demonstrates the validity of the pre-compensator.
We have been focusing on automatic train operation (ATO) as a suitable method to evaluate energy-saving operation effects and to improve speed profiles and scheduling. Our previous studies showed some methods of energy-saving operation using ATO. For example, one is to generate “hidden time”, for energy-saving control. Another is to use such a “hidden time” effectively and to apply energy-saving control such as coasting operation. This paper shows an additional method for energy saving by optimizing running time scheduling. ATO controls a train with accuracy such that the optimized schedule can be implemented to minimize the energy consumption. The speed profiles based on this scheduling were installed on the ATO system, and experiments were carried out on track. The results show that the proposed train control and optimized scheduling can save energy by 17% compared with conventional operation processes. The relationships between energy consumption and running time are explained in detail in this paper.
In a linear motor which is used in various industrial applications, improvement of thrust density to minimize instrument size is desired. This paper presents a structure to increase the magnetic flux generated from a permanent magnet by three-dimensionally configuring magnetic poles. We constructed an analytical model of a cylindrical-type linear motor with the developed magnetic pole structure and compared the general SPM (Surface Permanent Magnet) structure with the permanent magnet quantity. As a result, the magnetic flux linkage of the developed model increased to about twice that of the comparison model. For this reason, it was confirmed by analyzing that the thrust increases to about twice that of the comparison model by increasing the air gap magnetic flux density without increasing the surface contributing to the generation of the force and the volume of the electric motor.