Ken Masuya

Design of complementary filter for high-fidelity attitude estimation based on sensor dynamics compensation with decoupled properties

A high-fidelity attitude estimation technique for wide and irregular movements is proposed, in which heterogeneous inertial sensors are combined in complementary way. Although the working frequency ranges of each sensor are not necessarily complementary, inverse sensor models are utilized in order to restore the original movements. In the case of 3D rotation, the sensor dynamics displays a highly nonlinear property. Even if it is approximated by a linear system, the inverse model of a sensor tends to be non-proper and unstable. An idea is to decouple it into the dynamics compensation part approximated by a linear transfer function and the strictly nonlinear coordinate transformation part. Bandpass filters inserted before the coordinate transformation guarantee that the total transfer function becomes proper and stable. Particularly, the differential operator of a high-pass filter cancels the integral operator included in the dynamics compensation of the rate gyroscope, which causes instability. The proposed method is more beneficial than Kalman filter in terms of the implementation since it facilitates a systematic design of the filter.

COM motion estimation of a Humanoid robot based on a fusion of dynamics and kinematics information

A novel Kalman filter to estimate the center of mass (COM) of a Humanoid robot is proposed. In the conventional works, COM was estimated by some methods. First one is the kinematics computation based on the mass property of the robot and the global position and attitude of the body frame, but those errors degrade the estimation accuracy. Second is the double integral of COM acceleration computed by the measured external force. However, its accuracy suffers from the error accumulation with the integration and the initial error remains. Third is based on the relationship between COM and the zero-moment point (ZMP), but it ignores the torque around COM. Additionally, it only dealt with the horizontal movement. For those problems, the proposed method combines those informations in order to improve the accuracy. Particularly, in order to estimate three dimensional motion of COM, the proposed method reduces the offset included in the vertical component by utilizing the interference between the horizontal and vertical component of COM shown in third information. Through the simulation, the improvement by the proposed method is verified.

Nonlinear dynamics of twisted and coiled polymer actuator made of conductive nylon based on the energy balance

This paper proposes a novel dynamics model of the twisted and coiled polymer actuator (TCPA) which is one of the artificial muscles recently discovered. It can be driven by Joule heating and can contract up to 25%. Most of the conventional works employed the linear model of TCPA which represents the relationships between the input voltage, the temperature, and the displacement, but the real TCPA shows the nonlinearity. Although a nonlinear model was proposed based on the curve fitting, it is difficult to apply the model to the various TCPAs. Additionally, the conventional works cannot explain the effect of the convective heat transfer condition on the displacement behavior of TCPA. This paper aims to construct a general nonlinear model of TCPA based on the following two ideas: (1) The energy balance of TCPA and (2) the temperature and velocity dependence of the heat transfer coefficient. The temperature model is obtained from the time derivative of the energy balance, and the displacement model is derived as Lagranges equation of motion with the dissipation function. Through experiments, it is verified that the proposed model is closer to the real dynamics than the conventional linear model.

Dead reckoning for biped robots that suffers less from foot contact condition based on anchoring pivot estimation

A novel technique of dead reckoning for high-rate feedback control of biped robots is proposed. A fast position estimation of a robot is achieved by fusing information only from internal sensors including joint angle encoders, inertial sensors and force sensors. It combines the kinematics computation and the double integral of acceleration in a complementary way in order to improve the accuracy. The kinematics computation takes the movement of supporting foot, particularly, rotation about a fixed point and rolling on the terrain into consideration. The weights on each information are adjusted automatically based on the reaction force from the ground as it is expected to reflect the certainty of the contact condition of each foot. The validity of the proposed method is verified through computer simulations. Graphical Abstract

Position control of twisted and coiled polymer actuator using a controlled fan for cooling

Recently, artificial muscles made of fishing lines or sewing threads, namely twisted and coiled polymer actuators (TCPAs), have been proposed by Haines et al. A TCPA contracts by applying heat and returns to its initial length by cooling. A TCPA can be driven by voltage if the TCPA is plated by metal or if conductive wire such as nichrome is wound around it. Compared with the conventional electroactive polymers, advantages of TCPAs are low cost, simple structure, large actuation strain, and large force. However, a big disadvantage of TCPAs is slow response due to heat transfer. The problem becomes apparent during cooling, although the response of heating can be improved by feedback control. This paper proposes a control method of switching heating and cooling. In the proposed method, a TCPA is cooled by an electric cooling fan. When the TCPA is heating, the cooling fan is stopped. In a previous report, the response speed can be improved by keeping cooling fan always on; however, unnecessary energy consumption is required even during heating. In the proposed method, energy consumption during heating does not increase and the response speed can be improved using fan only during cooling. The proposed control law is as follows. Firstly, the desired control input is determined by PI-D control with respect to the length of the actuator. Then, the control inputs to the heater and to the cooling fan are switched according to the sign of the PI-D controller output. The effectiveness of the proposed control method is demonstrated by comparing the cases with and without the cooling fan in the experiments.

COM motion estimation of a biped robot based on kinodynamics and torque equilibrium

A novel technique to estimate motion of the center of mass (COM) for a biped robot is proposed. A Kalman filter is synthesized where the time evolution of COM is predicted from the external force and corrected based on kinematic estimation and torque equilibrium. They complementarily work to compensate the initial estimation offset, the error accumulation, and errors in modeled mass properties. It makes use of the authors’ previous method to estimate the translational and rotational motion of the base body from inertial information and joint angle measurements. The information about torque equilibrium helps to reduce an uncertainty of the height of COM and to improve the estimation accuracy of it by utilizing an interference of the horizontal and vertical motion of COM. The parameters are tuned based on error analyses in mass properties and sensor signals. A comparative study showed a better performance of the proposed method than other methods through dynamics simulations. Graphical Abstract

Dead reckoning of biped robots with estimated contact points based on the minimum velocity criterion

A novel technique of dead reckoning for biped robots, which could be utilized for agile motion controls, is proposed. A complementary filter combines the estimations of the position of robot body from both the kinematic computation and the acceleration information, where the former is relied on in the lower frequency domain and the latter is done on in the higher domain. Even though the supporting foot of the robot happens to roll and rotate on the terrain, the estimation accuracy of the kinematics is improved by taking such movements into consideration. We suppose that the contact point moves with respect to the ground at the instantaneously minimum velocity, and thus name it the instantaneous minimum velocity point (IMVP), which is estimated by an optimization. IMVP can be computed for each foot, so that the weighted sum of them by the magnitude of reaction forces on each foot is adopted as a candidate of the contact point under an assumption that the contact condition is more steady when a larger reaction force is applied. Finally, it is merged with the twice-integrated acceleration through the complementary filter, where the crossover frequency is also determined by the reaction forces. Hence, it is robust against the change of contact conditions. Results of computer simulations will show that the proposed method reduces the estimation error comparing with the conventional methods.

A dual-stage complementary filter for dead reckoning of a biped robot via estimated contact point

This paper proposes a novel technique of dead reckoning for biped robots. The trunk position of a robot with respect to the inertial frame is estimated only using internal sensors in a short interval, so that it is available for high-rate feedback control. It is a complementary filter in which (1) the low-frequency component of the motion of the trunk is inversely computed from the relative motion of the contact point with respect to the trunk, where the rotation and rolling of the support foot about the contact point are taken into account, (2) the high-frequency component of that is estimated by double-integral of acceleration, and (3) the crossover frequency to combine those estimations is automatically adjusted based on the ground reaction force. The efficacy of the proposed method was verified through some simulations.

Gray-box modeling and control of torsional fishing-line artificial muscle actuators

This paper focuses on the torsional motion of a torsional type fishing-line artificial muscle actuator, so to speak, Twisted Polymer Fiber (TPF) actuator. TPFs are expected as limited rotation motors or limited angle motors for mechatronic applications. Aiming to construct a gray-box model for TPF actuators, this paper derives the first-order transfer function as the model from the applied electrical power to the generated torque of an actuator. The relation from the temperature to the generated torsional torque is simply assumed as a linear function of which coefficient is the torsional rigidity. In the experiment, the validity of the obtained model is evaluated, and then the blocked torque of the TPF actuator is controlled.

Development of Actuator Unit consisting of Multiple Twisted and Coiled Polymer Actuators

An actuator unit consisting of multiple twisted and coiled polymer actuators (TCPA) with the feedforward controller is proposed. TCPA is made by two methods: 1) overtwisting the fiber and 2) winding the twisted fiber around the mandrel. The former output the larger force than the latter, while the former shows the smaller stroke. In order to realize the coexistence of large stroke and large output force, we combine multiple TCPAs fabricated by the latter method. The performance of the actuator unit is investigated through the experiment. Additionally, it is verified that the feedforward controller based on the authors’ nonlinear displacement model can reduce the offset error compared with that based on the linear model.