This paper introduces the research field of real-world haptics that acts on real-world objects. This paper also reviews recent technical advances in real-world haptics, such as functionality and oblique coordinate control. As a catalyst for real-world haptics, a principle of this research area is explained through two simple examples: acceleration-based bilateral control and grasping/manipulating control. These two examples and the cited papers offer the view that a wide variety of system roles can be realized by combining pure position control and pure force control with an appropriate coordinate transformation. Real-world haptics has the capability of contributing toward supporting human activities.
This paper proposes a controller design method for the reproduction of multi-degree-of-freedom (DOF) motion. For the storage and reproduction of haptic information, a motion-copying system was proposed. In the conventional method, however, it is difficult to reproduce the saved motion when the environmental configuration in the motion-loading phase is different from that in the motion-saving phase. This problem can be solved by the proposed method. The proposed design procedures are divided into two steps. First, a control structure with a different environmental configuration is proposed, and it is shown that the difference in the environmental configuration influences the reproduction of force information. Second, a novel controller that is based on the abovementioned analysis is proposed. By using the proposal, we can reproduce the saved motion even though the environmental configuration is changed. In this study, the grasping/manipulation motion is considered to be a multi-DOF motion, and the validity of the proposal is confirmed via experiments.
Accurate current signals are required for precise current control of AC motor drives. However, current measurement errors that involve metering error and quantization error are unavoidable because of the inaccuracy of current sensors and the quantizing feature of analog-to-digital converters in all digital motion control systems. The quantization error contains harmonic components that can induce torque ripple, thus deteriorating the control performance. Therefore, it is necessary to suppress the quantization effects. In this paper, two dithered systems, namely, the subtractively dithered system and nonsubtractively dithered system, are presented in order to remove the quantization-based harmonic components of the measured current signals by whitening the quantization error. Moreover, for ease of practical implementation, the design of dither signals is analyzed for nonsubtractively dithered system, considering cases where the metering error is uniform noise or Gaussian noise. It is shown that by applying the dither having a suitably chosen probability density function, the total measurement error can be rendered spectrally white. The effectiveness of the proposed methods is verified through simulations and experiments using a high-precision linear stage.
Nowadays, fields that employ advanced techniques require a new type of education system that can reproduce a haptic sensation repeatedly. The environment-copying system has been developed for such an education system. The system is based on the bilateral control and can store and reproduce haptic data so that an operator can feel haptic sensation at any time and anywhere. Conventional environment-copying systems only treat the environment that has elastic characteristic. To solve this problem, two systems are proposed in this paper. One is the environment-identification system, wherein the saved force is divided into the force affected by the stiffness and the momentum of damper, using the Fourier transform to represent the environment with the identified mechanical impedance. The other is the state-to-state transition system, wherein the condition of the environment is considered from the view point of system connection. By using this system, dynamic environments such as these with nonlinear behavior can be expressed. The validity of the proposal is confirmed through experiments, and the experimental results show that the proposed system can satisfactorily store and reproduce the environment.
This paper proposes a method to automatically limit referential joint torques of a biped robot to prevent the feet from losing contact with the ground. This method can be used to implement active balancing, which is equivelent to position control as long as the torque limits are not exceeded. Therefore, unlike the zero-moment point feedback methods, the proposed method is robust against disturbances and has a good trajectory following ability without having the usual dangers associated with stiff, position-controlled methods. Furthermore, this method is based on force sensor data, and thus unlike inverse dynamic methods, it is robust to variations in robot dynamics that can arise when the robot carries loads. This paper also proposes a method to limit referential joint velocities to prevent overshoot of the robot. This is useful when the robots center of mass (COM) position moves near the edge of the support polygon, because if the COM exits the support polygon due to overshoot, then it will not be able to return to it. These two proposals are then combined to form a position control system that is robust against overshoot and can strongly interact with the environment without losing contact of the feet with the ground. Finally, this position control system is implemented on the biped robot MARI-3, and it is shown that near-zero overshoot position control with compliance is achieved.
This paper presents an improved method of a repetitive controller based on perfect tracking control (PTC) in order to reject the variable repeatable runout (RRO) of hard disk drives (HDDs). The author's group proposed repetitive PTC (RPTC) with a switching mechanism. RPTC is realized by using periodic a signal generator (PSG) and PTC. The PSG produces a feedforward signal from the periodic disturbance, and the PTC generates a control input to cancel the periodic error in the steady state. However, we have not considered the difference between the RROs of tracks. This paper proposes a re-learning scheme by taking into account the correlation of adjacent tracks. Finally, the advantages of RPTC using the proposed scheme are demonstrated through simulations and experiments using a hard disk drive equipment with discrete track recording media (DTR).
This paper presents an approach for a posture control method based on the vision-based posture estimation for a redundant manipulator. The redundant manipulator can provide dexterous task capability depending on the environmental information. In this paper, a hybrid motion controller including both a posture controller based on visual feedback and an end-effector motion controller based on encoder signal is proposed. In the proposed posture controller, the manipulator posture is estimated by using a particle filter, only based on the visual information. This means that posture control is completely achieved only by a vision sensor signal in the null space. The control performance of vision-based null space control is experimentally evaluated for several motions using the redundancy. A suitable control model for obstacle avoidance is also proposed by using an optical flow field, which is detected based on the visual information. The validity of the proposed method is evaluated by several experimental results.
This paper describes the development of a biologically inspired wide-angle fovea (WAF) lens well known as a significant part of a biomimetic vision sensor. The authors develop a micro WAF lens suitable for a board lens camera with a 1/3 inch imaging chip. The prototype of this Micro WAF lens has a smaller diameter and length, i.e., φ8mm × 15mm, than half of those of the WAF lens that the author produced formerly, i.e., φ16mm × 32mm. However, its central field of view (FOV), called herein fovea, has a much higher resolution; that is, its projected image is more highly distorted than that projected by the former WAF lens. The central FOV is approximately 10% of the entire FOV within an incident angle of 2.5° in Micro WAF lens, whereas it is approximately 10% within an incident angle of 10° in the former WAF lens. We mainly focus on determining its specification as the first step of a lens design procedure and discussing the results simulated using the lens design software.
Stiffness is an important factor for robots in a human environment. Therefore, many methods for stiffness control, which enable robots to setup stiffness, have been developed. Although the performance of stiffness control is quite an important factor, no methods for quantitative comparison of these methods exist. Thus, the characteristics and advantages of a stiffness control method are quantitatively investigated and compared, and certain evaluation criteria that can assist in guiding the design process of stiffness control systems are proposed. The experimental results show the quantitative comparison among three types of robot arms and investigate their property.
Conventional bilateral controllers have been designed on the basis of a tool coordinate system. However, from the viewpoint of versatility, a transformation technique based on physical features of an operator is advantageous. Therefore, this paper proposes a bilateral control technique that can be used to operate slave robots; the technique is based on motion features of an operator and facilitates intuitive operation. Here, motion features imply displacement ratios of joints. A coordinate transformation matrix containing the motion features of the operator is obtained by principal component analyses. The transformation matrix can be used to abstract the motion features, while other transformation matrices require symmetric motion or symmetric sensor placement. The validity of the proposed bilateral control method is experimentally verified. In an experiment, the proposed method is applied to a wearable robot hand and a forceps robot. A grasping motion extracted by the wearable robot hand is transmitted to the forceps robot on the basis of the obtained coordinate transformation matrix.
Sensorless vector control for induction motor drives is widely used. However, in the case of mass-produced closed-slot motors, it is difficult operate them at zero frequency with regenerative load. In this paper, a sensorless vector control method based on three-phase PWM carrier waves is applied to a mass-produced closed-slot induction motor. Further, methods to improve stability are proposed.
This paper describes an approach to achieve a high efficiency drive such a brushless AC (BLAC) drive by a Brushless DC (BLDC) drive. BLDC motors with an excited rectangular voltage for 120 electrical degrees per cycle are commonly used for low-cost applications of permanent magnet synchronous motors (PMSMs). This drive method yields low-order harmonic components in the current waveform. These harmonic components cause mechanical vibration and electrical losses. Therefore, a BLDC drive is not applicable to a sinusoidal back-EMF machine. However, with regard to the high-frequency loss caused by a pulse width modulation (PWM) carrier and a switching loss, the BLDC drive has the potential to achieve higher efficiency than the BLAC drive. This paper compares the overall efficiency, which includes the PWM carrier frequency loss, by using a coupling analysis between a finite element analysis (FEA) and a circuit simulator. Two surface-mounted PMSMs (SPMSMs) are tested. One has a sinusoidal back-EMF waveform (BLAC machine), and the other has a trapezoidal back-EMF waveform (BLDC machine). Both the driving methods of the BLDC drive and the BLAC drive are adapted to each machine and their efficiencies are compared by both simulations and experiments. The results show that the BLDC machine with a BLDC drive has higher efficiency than the BLAC machine with a BLAC drive.
An electromagnetic gear has been developed for variable-transmission applications such as wind power generators and electric hoists. It overcomes the problems of friction, noise, and the need for oil lubrication, which its mechanical counterparts suffer from. This paper explains how the gear operates according to the principle of magnetic gearing and how the concept of pole changing is utilized to change the gear ratio. The transmitted torques are derived and expressed in terms of the physical dimensions, and the optimization factors are identified. Simulation and experimental results confirmed the validity of the developed approach.