This study investigated the effect of display response delays, i.e., the time lag between operation input and display output, on human–machine interface (HMI) device operation, emphasizing commander-type devices, e.g., those used for in-vehicle infotainment. While operating the HMI device, simultaneous processing of visual and tactile information, e.g., operating the device while gazing at the display, is required. This investigation was conducted to clarify how varying response delays in visual feedback after tactile feedback with device operation affect usability in terms of various aspects, e.g., task efficiency, subjective workload, and the sense of agency (SoA). This study employed a targeting task, in which the participants engaged in HMI device operation under a delay time ranging from 0–120 ms. The subjective workload was evaluated using NASA Task Load Index (NASA-TLX) scale, and the SoA was assessed quantitatively through Near-infrared Spectroscopy (NIRS) measurements of cerebral hemodynamics, which provide insights into the user’s psychological and physiological responses to delay. The findings revealed a nuanced relationship between response delays and usability during HMI device operation. We found that slight delays (40– 80 ms) do not necessarily detract from user workload or efficiency. Instead, the slight response delays can enhance the user’s SoA, which suggests that there is an optimal delay window that balances immediate feedback with the cognitive and sensory processing times inherent to human perception. These findings suggest that incorporating slight delays within the software framework of HMI system design effectively enhances the SoA, thereby enabling more intuitive user interactions and improving usability.

This study clarifies the effects of follower–leader information asymmetry, which is due to a target position and a transport cycle, on brain activities during human–human 1-DOF parallel reciprocating transport work. Elucidating the effects of information asymmetry on leader–follower brain activities by analyzing brain activity and hand movements in humans with visual information and humans without visual information will reveal the behavioral characteristics of humans for cooperative work. Therefore, in this study, we simultaneously measured brain activities, the forces applied to a 1-DOF transportation mechanism, and the hand positions of two people during human–human 1-DOF parallel reciprocating transport work using a transport cycle of 3 s. Three levels were set for the follower side to antisymmetrize the information of a follower with respect to a leader: i) the follower was asked to wear an eye mask and not be informed of a target position and a transport cycle (Level 1), ii) the follower was informed of a target position but not a transport cycle (Level 2), and iii) the follower was informed of a transport cycle and a target position by a metronome sound (Level 3). In the evaluation of brain activity, brain activation was assessed by the amount of change in the concentration of oxygenated hemoglobin (Oxy–Hb), which had the highest correlation with changes in cerebral blood flow. The results showed that Level 2, which corresponded to cooperative work between humans with visual information, demonstrated significant synchronization changes in both cerebral blood flow in mirror neurons and hand inertia/stiffness compared to Level 1, which corresponded to cooperative work between humans with visual information and humans without visual information, suggesting a relationship between them. In addition, the evaluation of brain activation and impedance change suggests that cooperative work among humans with visual information did not involve voluntary movements but smoother cooperative work from both neuroscientific and kinematic perspectives.

With the recent diversification of operating devices, the demand for input operations that require confirmation of the effect of differences in display response on operability has increased. Regarding display response, previous studies have investigated the threshold time and sense of agency for a delayed response during device operation. However, these studies only focused on subjective evaluations. Therefore, this study aims to clarify the human motor characteristics and activated brain regions based on the differences in display response time during device operation. The target motion is the rotational operation of the cylindrical rotary controller using the index finger and thumb. The experimental conditions involve four types of display response times (the duration from the operation to the indicated response). We measured the brain activity using near-infrared spectroscopy, the muscle activity from a surface myoelectric potential measurement device, and the force data of the index finger and thumb tip obtained from two independent six-axis force/torque sensors. Although the experimental results showed no significant difference in the muscle activity and gripping force, a significant difference was observed in the brain activity and the questionnaire survey by the difference in display response time. This investigation reveals that the difference in display response time affects brain activity and subjective information, clarifying the relationship between brain activity and subjective information.

This study aim to confirm the effect of viscosity characteristics differences on the rotational manipulation of a cylindrical rotary controller with the index finger and thumb through a quantitative analysis and evaluation of muscle and brain activations. The target motion was a rotary manipulation with the index finger and thumb of a cylindrical rotary controller with a 50 mm diameter. The rotary motion of the controller produces a click sensation at every 12 degrees in the rotation. The experimental conditions were three conditions with different viscosity characteristics related to the rotary motion of the controller. The subjects were six right-handed healthy males with a mean age of 21.7 (S. D.: 1.03) years. We analyzed the brain activity from a near- infrared spectroscopy measurement system, the muscles activity using a surface myoelectric potential measurement device, the force data at the index finger and thumb tip using two independent six-axis force/torque sensors, and the position data using a 3D position measurement device. The experimental results showed that there was no significant difference in the questionnaire survey, muscle activity, and grasping force, respectively; however, a significant difference in brain activity was observed with increased controller viscosity. Therefore, it became clear that there was a change in the brain activity when rotating the cylindrical rotary controller with the viscosity characteristics related to the rotary motion.

There have been numerous studies on human- machine cooperative systems. In such studies, it is generally preferable to consider human maneuverability and motion during machine operation as well as considering mechanical parameters. However, many of the current studies only evaluate the mechanical parameters. Although some studies have evaluated human parameters, these remain subjective. Therefore, in this study, upper extremity movement and muscle and brain activation during machine operation with inertia and friction were measured quantitatively. The experimental conditions were divided into nine classes. These were then combined into the following frictional and mass conditions: the friction during machine operation was 3.3 ± 1.2, 8.6 ± 2.7, or 11.5 ± 3.8 N; the mass of the machine was 2.2 ± 0.1, 3.2 ± 0.2, or 4.4 ± 0.2 kg. The experimental results revealed significant differences in upper extremity muscle activation with both friction and mass (p <; 0.05). Although the brain analysis results showed no significant difference with friction, significant differences were found with mass (p <; 0.05). The experimental results showed that the trajectory of the hand position, upper extremity muscle activation, and brain activation tended to be affected by mass.

In this paper we address a robot motion control scheme for a human-robot cooperative task. From the viewpoint of improving the operative efficiency of the cooperative task, we designed a novel robot control system, in which inherent dynamics of the target task and the object is conserved. The proposed control scheme differs widely from an ordinary impedance control scheme in that the inherent dynamics of the target task and the object is substituted by impedance characteristics. Under the proposed control scheme, the dynamics of the target task and that of the robot motion are uncoupled and independent. The proposed control system enables the human operator to carry out the cooperative task intuitively by only considering the inherent dynamics of the target task and the object. To confirm the effectiveness of the proposed control system, an experiment base on a peg insertion task involving human-robot cooperation is carried out. The experimental results show that the proposed control scheme is effective for cooperative tasks requiring precision.

The development of a robot motion control scheme and a mechanical load adjuster with a motion measurement interface is addressed in this paper. To improve the efficiency of a task involving human-robot cooperation, we designed a novel robot control system, in which a multiple-load state can be provided for a human operator. This system also can provide a multiple-dynamics state during a task involving human-robot dynamical cooperation. The multiple-load state including its transition is effective and efficient in such a task. A single load state can be easily provided by the impedance control of the robot motion thus far; however, the multiple-load state and its transition are difficult to realize using a conventional control scheme. The proposed control scheme differs widely from a conventional impedance control scheme in that the multiple- load state as well as both active and passive states cannot be induced in the single robotic system. Under the proposed control scheme, the load state can be adjusted with the various dynamics in the active or passive state. To confirm the effectiveness of the proposed control system, human-robot cooperative experiments were carried out. Results showed that the proposed control scheme can provide the multiple-load state for use in a human-robot cooperative task system.

This paper presents stability analysis for an impedance control of a specific robot system in a human-robot cooperative task system. In the stability analysis, we consider these conditions such as an impedance characteristic of the robot, time delay of a human operator and a control of the robot, a compliance of structure of the robot, and an environment stiffness respectively. The stability analysis simulation reveals that these conditions have significant influence on the stability of the system. In order to investigate the usefulness of the stability analysis simulation, a verification experiment using a Mitsubishi PA-10 robot arm was carried out. Experimental results illustrate that the investigated stability analysis is useful and effective to simulate and reveal the stability of the human-robot cooperative task system.

This paper presents a novel control method for a human-robot cooperative task. There is a problem that a cooperative fitting task, i.e., peg-in-hole task, could not be performed precisely using a conventional impedance control. A proposed controller changes a control mode according to the task. An impedance control based on a position control is used in a carrying task and a torque control with compensation for its dead weight and friction is used in the fitting task. In order to confirm the usefulness of the proposed control, a human-robot cooperative carrying and peg-in-hole task was performed. Experimental results illustrate that the proposed control is effective for the human-robot cooperative task.

This paper presents a measurement method and its results for a compliance of a vertical-multi-articulated robot. In order to calculate the compliance of a robot, a stiffness of each joint of the robot is required. In this paper, a stiffness of each joint of the robot is measured by using a force/torque sensor and a 3-D motion and position measurement system OPTOTRAK 3020. The proposed measurement method is applied for a 7-DOF robot PA-10 made by MITSUBISHI heavy industries. At first, an 11-DOF link model with 4-virtual joints, i.e., the link model includes virtual 4-DOF, is proposed. Then, a compliance matrix is obtained using a measured joint stiffness matrix of the PA-10 and a Jacobian matrix of a proposed 11-DOF link model. In order to investigate accuracy of the measured joint stiffness, and to confirm effectiveness of the measurement method for the joint stiffness and the proposed link model, experiments measuring the compliance of the PA-10 are conducted. In the experiments, the proposed 11-DOF link model is compared with a 7-DOF link model. Experimental results illustrate that the measured joint stiffness are accurate, and the measurement method and the proposed link model are effective for calculating the compliance of the PA-10.

This paper presents a novel variable impedance control method for a human-robot cooperative task. An impedance control system based on a positioning control of a robot with time delay of the robot and a human operator can become unstable when the stiffness of a human arm or body is increased in the human-robot cooperative task. The proposed variable impedance controller varies the viscosity coefficient of the robot in proportion to an estimated value of the stiffness of the tip of the human arm. A method of a proposed variable impedance control makes the human-robot cooperative system stable and the cooperative task easy. In order to confirm the usefulness of the proposed control method a cooperative calligraphic task, that is writing a Kanji character with a writing brush, is performed. Experimental results illustrate that the proposed control method is effective for the human-robot cooperative task.

This paper presents a novel variable impedance control for a human-robot cooperative task. Cooperative positioning tasks cannot be performed easily using a conventional position based impedance controller. The proposed controller has a virtual stiffness term in order to make the cooperative positioning task easy and precise. It generates a virtual force in the positioning task using the virtual stiffness term. The virtual force helps the human operator to perform the positioning task easily. In order to confirm the usefulness of the proposed control, a cooperative peg-in-hole task was performed. Experimental results illustrate that the proposed control is effective for the human-robot cooperative task.

This paper presents a novel strategy of adjusting impedance parameters of a robot's end effector in a man-machine cooperation-work. In the proposed strategy, the impedance parameters are settled with regard to a working process of a human operator that is identified using a passivity index and an extreme value of force applied by the human operator. This approach enables to perform the cooperation-work with a robot easily. In order to confirm the usefulness of the strategy, the cooperation-work to which the robot's end effector is moved in the horizontal plane was performed. It is shown that the proposed strategy gives the manipulator a better characteristic than the invariable impedance control and the conventional variable impedance control. Furthermore, by a subjective evaluation test performed to subjects, the proposed control strategy is evaluated better than the other ones. Experimental results illustrate that the proposed control strategy for the robot is suitable for the cooperation-work.