Precise control of manipulators in contact with constrains in their environments is a prerequisite to feasible application of robot manipulators to complex handling and assembly problems in industry and space. An important step toward achieving such control is to control simultaneously position and force trajectory. Through recent advances in robotics technology many control design methodologies have been proposed for the control of robot manipulators. The hybrid technique is well known technique in these methodologies. In this technique coordinate system on the constrains plays an important role. But decision scheme of the coordinate system has not been proposed clearly.
This paper analyzes the hybrid technique based on the constrained control system and proposes a new conceptually simple approach to the hybrid technique. The new approach is able to control simultaneously manipulator impedance and position trajectories on the constrains. The coordinate system is appropriately selected and divided into two coordinate systems. These two coordinate systems represent two independent input spaces where the hybrid technique is realized.
Finally we also present the results of experiments that explore application of the hybrid technique to a control of a two degrees of freedom manipulator.

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Vector Controlled Induction Motors (VCIM) have been increased in popularity and their application fields are expanding. In this paper, the software implemented high performance control system of VCIM with torque feedforward using load torque observer is presented. In the proposed system, load torque is estimated by the minimal order state observer based on torque component of VCIM, and the robust control system against load torque variation is realized using the torque feedforward. Moreover, the design of speed controller with the torque observer is discussed.
The prototype was constructed using a 3.7 kW induction motor and an eccentric load with an arm and a weight which produced sinusoidal gravitational torque. The whole processing (vector control including current loop, speed control and observer control) could be performed within 104 μs by DSP-TMS 32010. Experimental results showed the improvement of speed control characteristics, the robustness of control loop against system parameters change and the improvement of disturbance suppression in low frequency range.

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This paper proposes the robust force & compliance control of DD actuator based on the new model following acceleration control system without speed sensor. The new model following acceleration control system has the faculty to suppress the state error caused by not only the force disturbance but also the system structure variation completely. The DD actuator controlled by this acceleration control system has only two integral elements, and it has no mechanical system parameter. Therefore, each joint of DD robot manipulator is regulated by the acceleration command ω^cmd. This structure is very effective for both the virtual inertia based force control and the virtual impedance based compliance control. Moreover, the hybrid control of force and position is realized by the proposed acceleration control method. In this paper, all of the proposed control systems is constructed by the software algorithm of DSP (digital signal processor) and the microprocessor. The experimental results show that the proposed method is valid for the robust force and compliance control of DD actuator. Using the proposed acceleration control system, the hybrid control of force and position is well regulated in the tested 2-degrees-freedom DD robot manipulator.

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Since direct drive (DD) motors have high stiffness and no backlash, they can realize precise position control. However, DD motors are easily affected by the disturbance and the parameters variation compared with motors with reduction gears. To suppress the effect of disturbance, the disturbance observer which estimates the total disturbance of motors from torque current and speed or position signal has been proposed. The feedback of the estimated disturbance makes the motors robust against the parameters variation and the disturbance, and requires less calculation effort. The disturbance compensation by the disturbance observer is a realization of two-degrees-of-freedom control system. First, we analyze the characteristics of the system with the disturbance feedback and realize acceleration control. Next, a controller which realizes desired response of position, speed and acceleration is constructed based on the acceleration controller. Finally, the continuous path control is performed by a linear synchronous motor which is a kind of DD motor. The disturbance is estimated by an observer whose input is torque current reference and position signal. Robust and precise control with micron order accuracy is realized experimentally.

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In recent years, ultrasonic motors (USM) as new actuators have attracted special interest. Some sorts of constructions and characteristics of USMs have been reported so far. Of these USMs, a traveling-wave type USM has many characteristics such as high torque at low speed range, large holding torque based upon frictional force, flexible free forms, compactness in size and low magnetic noise. In practice, an inherent mechanical resonant frequency and a velocity amplitude of USM are largely changed according to operating temperature due to frictional drive, load disturbance torque, and applied voltage levels. Therefore, it is necessary to develop a new control system which solves these items and always supplies the required power with high-efficiency and high-performance in the practical applications. This paper is mainly a newly-proposed sensorless high-performance control scheme of inverter-fed ultrasonic motor, which is based upon a control system technology with two feedbacks incorporating an automatic resonant frequency tracking and a constant velocity amplitude control strategies. This control system is realized in terms of high-frequency chopper and two-phase series/parallel resonant inverter. The experimental results are demonstrated and discussed as compared with the theoretical ones.

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The paper presents a method of the collision detection and the continued avoidance motion after that. In an industrial robot control, if an unknown obstacle exists on the trajectory, it is required to detect the collision against the obstacle and to avoid it autonomously. In the proposed method, the collision is known by the signal of disturbance observer. The paper shows the algorithm how the robot knows the collision. When the collision occurs, the recovery motion and the obstacle avoidance motion start. The function of the collision detection is similar to that of the tactile sensor or the torque sensor. The algorithm is simple and it is easy to apply to the robot system.
Moreover more intelligent robot control system is realized by fusing the function of the collision detection and the vision sensor. The experimental results are shown to verify the prposed method.

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We propose a new design method on robust servomechanism and apply it to advanced motion control of robot manipulators. Our servomechanism is based on the two degrees of freedom controller. We can specify the command input response and the disturbance response to arbitrary reference models independently by choosing two parameters appropriately. Furthermore, we can eliminate the speed sensor which has been required for the high performance control of robot manipulators. The efficacy of the proposed method is confirmed with some laboratory experiments showing robustness to inertia variation, disturbance suppression and mechanical impedance control performances. This controller realizes complete decentralized motion control of robot joints because we can eliminate all the interference torques caused by the robot motion. We also propose a novel trajectory control method where we solve the inverse kinematics by using the simple Newton method.

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PM motors are attracting growing attention for a wide variety of industrial applications. So far as we know, the i_d=0 control method, in which a direct axis component of the armature current does not exist, is applied in general because of avoiding a demagnetization of the permanent magnet. The recent development of the permanent magnet materials, however, has brought magnets with large coercivity. Therefore, there is no need to be a slave to the i_d=0 control method. Several remarkable performance characteristics can be obtained by controlling the direct axis component of the armature current actively.
In this paper, the control method of armarture current is examined in order to obtain the maximum output in all speed range. The effects of the motor parameters and the rotor configulations are examined in detail and the optimum motor parameters to expand the operating limits are clarified.

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This paper describes an induction heating system of 1kW 450kHz which is developed for dental casting machines. This system consists of a single-phase diode rectifier, a voltage-source inverter using four power MOSFET's, and a series resonant circuit with a matching transformer of turn ratio 8:1. No capacitor is connected on the DC side of the rectifier except for a high frequency capacitor of 0.47 μ F. Thus, the DC voltage across the high frequency capacitor is fluctuating at 100Hz, that is, twice as high as the line frequency of 50Hz as if no capacitor were connected. Not only does the fluctuation have no effect on heating or melting but also the fluctuation plays an essential role in shaping the line current of the rectifier into sinusoid and unity power factor, because it is seen from the DC side of the rectifier that the inverter plus the resonant circuit acts as a pure resistance.
The power control covering a wide range from 50W to 1kW is achieved by power factor control of the inverter which takes the place of DC voltage control of the rectifier.
The system efficiency is estimated to be 76% by sophisticated measurement of the actual heating power, which is based on Lissajous's figures for voltage and charge.

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A magnetic suspension system is required to keep a stable state even if the system parameters vary. In this study, a sliding mode control is applied in order to enhance the robustness to the parameter variations. First, the sliding mode control is applied to the system whose manipulated variable is pulse width of a DC chopper replacing a conventional linear amplifier for current control of the magnetic coil. We refer the system to as a voltage control type. In this case, the control system becomes equivalent to that of which manipulated variable is the current of the magnetic coil because sliding mode operation reduces the system order by one. However, the manipulated variable can be current without using the sliding mode control when hardware of control device is changed and a current-source controller is used. Next, hence, the sliding mode control is applied to the system referred to as a current control type.
As a result, the control system achieves enhancement of the robustness to practically imrportant parameter variations such as a mass of a suspended body, and an equilibrium point. Besides, it is found that the sliding mode control system is more robust to step disturbance input than an optimal control system.

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A inverter-fed permanent magnet synchronous motor with a rotor position sensor and a speed sensor is used in many industrial applications as a DC-brushless motor. In this paper, a strategy which determines the rotor position and the speed of the permanent magnet synchronous motor by using the instantaneous values of phase voltage and phase current sensing is explained.
In a permanent magnet synchronous motor, the permeance of the stater magnetic circuit is altered by rotating the rotor position; the inductance of a phase winding changes according to rotor positions. Hence, the phase voltages and currents of the motor have close relations with the rotor positions. Measured values of phase voltages and currents and the values of the equivalent circuit parameters are substituted to the voltage equation of the synchronous motor. Then, we can calculate the value of the rotor position angle by that voltage equation. The rotating speed of the rotor can be calculated from the voltage equation by substituting the rotor position angle. In these calculations, we used a 16-bit micro-computer and a DSP, and for sensing phase voltages and currents, 12-bit high quality A/D converters are used.
Experimental results obtained by using the prototype system were congruous values of the rotor position angles and the rotating speed.

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