Many effective robot-manipulator control schemes using a disturbance observer have been reported in the literature in the past decades. Besides, the disturbance observer combined with the Kalman filter has attracted the attention of researchers in the field of motion control. The major advantage of a motion control system based on the Kalman filter and disturbance observer is the realization of high robustness against disturbance and parameter variations, effective noise suppression and wideband force sensing. This paper presents a survey of motion control based on the Kalman filter and disturbance observer, which have been previously introduced by the authors. Several control schemes, as well as formulations and applications of the Kalman filter and disturbance observer, are described in the paper. The performance and effectiveness of the control schemes are evaluated to give a useful and comprehensive design of the Kalman filter and disturbance observer in various motion control applications.
A method to suppress the residual vibration of relative displacement is proposed. In factory automation, the positioning machines are precisely controlled by servo motors; however, their reaction force will unavoidably vibrate the machine stand on which the motors are mounted. A common problem is that the resulting residual vibrations cause disturbances that prevent high speed and accurate positioning, due to the inherent flexible structures in the machine stand, thereby unexpectedly extending the settling time in some industrial applications. This paper presents machine stand acceleration feedback (MSAFB) control, which detects the acceleration signal of the machine stand using an accelerometer to improve the robustness against disturbances from the environment and uncertainty in the system. This feedback strategy is superior to input shaping strategy, which is based on feedforward control. Simulations and experiments show the effectiveness of the proposed MSAFB controller, which was designed specifically for mechanical plants with rocking mode vibration.
This study investigates kinodynamic object manipulation by a robot using a tool. Based on the conditions for maintaining contact between a held spatula and a manipulated object, a variety of movements satisfying such conditions are planned. Model predictive control is introduced to plan an optimal trajectory. Simulation results show that the proposed method plans a variety of turning over motions with different setups of cost functions. Experimental results demonstrate that the trajectory optimization method accomplishes turning over motion, which is a typical example of motion with kinodynamic constraints.
To realize flexible power flow control for DC power networks, we have proposed a bidirectional power flow controller (BPFC) based on a bidirectional buck-boost converter. It is possible to control the power flow by intentionally introducing additional voltage difference between two terminals. However, we have not investigated the efficiency of BPFC for power flow control in detail so far (in previous papers). Because many power converters are expected to be installed in future DC power networks, efficiency investigation is vital. In this paper, we first reveal the energy efficiency of BPFC and study ways to improve the efficiency. Then, we propose a novel structure of the BPFC, which drastically improves its efficiency. We call the proposed structure floating bidirectional power flow controller (F-BPFC). The efficiency and characteristics of the F-BPFC are experimentally compared with those of the BPFC and its superiority is clarified in this paper.
Inductor winding is often comprised of parallel-connected wires to suppress copper loss. However, in high-frequency inductors, the proximity effect can cause concentrated AC current distribution, hindering the suppression of the copper loss. Therefore, optimization of the physical inductor structure requires predicting the AC current distribution caused by the proximity effect. Certainly, simulators have been commonly employed for predicting the AC current distribution. However, simple analytical methods are also required for efficient design or invention of inductor structures that have more uniform AC current distribution among the parallel-connected wires. The paper proposes a novel simple analysis method for AC current distribution in parallel-connected wires of high-frequency inductors. The proposed method is based on a novel insight that AC current is distributed to give an extremum of the magnetic co-energy contributed by the AC flux under the given total AC current. Analysis of basic inductor structures revealed that the proposed method can derive the AC current distribution by straightforward calculation. In addition, experiments supported the analysis results. Consequently, the proposed method is suggested to be promising for developing inductor structures with less copper loss.
To improve the power density of a switching power supply, we attempt to reduce the transformer loss using a magnetoplated wire (MPW). Contrary to using a copper wire, the use of an MPW allows for a reduction of the winding loss component due to the proximity effect. In particular, we investigate the 1MHz LLC resonant converter using an MPW. An 8.8% decrease in the power loss is achieved, giving 33W at 1MHz and 1kW.
Recently, the dual transmitting resonator wireless power transfer system (DTR-WPT) has been proposed as a promising technique for the power supply of mobile apparatus. Although this technique has been reported to be effective for increasing the output power as well as for covering a wide area during wireless power transfer, the complicated magnetic coupling among two transmitting resonators and one receiving resonator makes it difficult to develop practical design optimization methods, thus hindering practical applications of this technique. The purpose of this paper is to propose a design optimization method for the load impedance of DTR-WPT. This method is derived based on a novel simple equivalent circuit model of the DTR-WPT. The optimum impedance derived using this method as well as the appropriateness of the equivalent circuit were verified experimentally, thus validating usefulness of the proposed method for the practical application of DTR-WPT.
Accurate PMSM drive simulation, which utilizes a behavior model developed using FEA results to consider nonlinear characteristics, has been requested to evaluate driving performance. This paper proposes an advanced motor behavior model that is based on the flux linkage model instead of the inductance model to simplify the derivation of equations and to reduce the amount of table data produced from FEA results. The proposed model includes magnetic saturation, cross-coupling, and spatial harmonics. Its performance is verified in circuit simulation by comparing direct FEA results with measurement results. The results obtained using the proposed model are in good agreement well with the FEA results and measurement results.
We present a novel practical design optimization for the primary core in an induction heating roll, which significantly affects the heating performance. To optimize the 3D eddy current field problem within an acceptable CPU time, we effectively combine 2D magnetostatic optimization and 3D coupled magnetic-thermal FEM. For the 2D optimization, we adopt the level-set method, which has an advantage of being able to derive a feasible shape. However, the disadvantage is that its result occasionally falls into a local optimal solution. To overcome this disadvantage, we propose conducting the initial conceptual design with the linear level-set method before using the nonlinear level-set method to expand the search domain. Furthermore, we incorporate the parallelized move-limit strategy into the level-set method to prevent the configuration from undergoing excess deformation by the operation for the area constraint. Finally, the 2D optimal shape obtained using our new level-set method is converted into a straight line cross-sectional configuration to improve manufacturability, and the final 3D design is created with slits. The final 3D design obtained as a result of the 3D FEM successfully improves both the heating speed and temperature uniformity on the surface of the heating part under the same conditions of input AC current and material volume.
A sensorless control based on a pattern matching method is proposed for interior permanent magnet synchronous motors which have non-sinusoidal inductance spatial distribution, at a standstill and in very-low-speed regions. A previous study indicated that closed-loop-position sensorless control can be achieved under heavy load conditions. However, position control errors are generated at atypical rotor positions, and the reason for this has not been clarified. Moreover, there remains an issue in which this position error cannot be perceived before position sensorless control is carried out.
This study examines why position control errors are generated in the pattern matching method. Furthermore, an evaluation method that estimates position control error in advance is proposed using the clarified mechanism of position error generation. The effectiveness of the proposed method is demonstrated by comparing experimental and evaluation results.
An iterative dynamic programming (iDP) is proposed along with an adaptive objective function for solving optimal control problem (OCP) with isoperimetric constraint. Its application is investigated for optimal eco-driving control problem in electric vehicle (EV). The proposed method reduces the computational effort and enhances the global convergence of using iDP. Numerical calculations show that for the same computational time, the proposed method guarantees higher quality of solution when compared to basic iDP. In addition, the proposed method also achieves high accuracy of optimal solution with much less computational time than basic dynamic programming (DP), thus allowing for potential on-line implementation. Furthermore, the proposed iDP is successful in solving the optimal eco-driving control problem of EV with very long operational range.
A plant with unstable zeros is known as difficult to control because of initial undershoot of step response and unstable poles of its inversion system. There are two reasons why a plant has unstable zeros in a discrete time domain: 1) non collocation of actuators and sensors and 2) discretization by zero-order hold. Problem 2) has been solved using the perfect tracking control (PTC) method based on multirate feedforward control proposed by our research group. However, the conventional PTC method cannot achieve the perfect tracking for a plant with continuous-time unstable zeros because of the divergence of the desired state trajectories. This paper proposes a preactuation perfect tracking control (PPTC) method to solve problem 1) through the state trajectory generation based on a time axis reversal. The validity of the proposed method is demonstrated through simulations in comparison with three single-rate feedforward control methods.
In a teleoperation system with communication delay, the contact information on the slave side is transmitted to the master side with time delay. Hence, an operator may misunderstand that the slave has not contacted an object and may add more force. Eventually, excessive force by the slave may collapse the object. This paper proposes model predictive control with a variable dumping method to prevent collision on contact in a teleoperation system with time delay. The prediction method considers the distance to the object on slave side, and variable dumping is implemented on the master side. The proposed method is evaluated through numerical simulations and experiments.