Robust particle manipulation is a challenging but essential technique for single-cell analysis and processing of microfluidic devices. This paper proposes a micro-particle manipulation system with a microfluidic channel network. We built gravity-induced pressure actuators, which can generate high-resolution output pressure with a wide range so that the multiple particles can be delivered from the inlet of the chip. In this paper, we studied how to model the proposed multi-input-single-output system and sources of disturbances, and designed a robust controller using disturbance observer technique. The performance of the proposed system was verified through experiments.

Impedance control allows robots to manipulate physical interactions delicately. However, issues associated with path planning and impedance remain unresolved. Herein we propose a path and impedance planning method for impedance control in a robot based on programming by demonstration through telemanipulation using a surface electromyogram. We considered a task that requires quick and precise adjustment of path and impedance, that is, ball trapping. We implemented a teleoperated robot that can deliver an operator's impedance as well as position during the ball trapping task to the slave side. The operators were asked to perform demonstrations of ball-trapping tasks using the implemented teleoperated robot, where the slave side is a vertical robot with one degree of freedom. The path and impedance were recorded and programmed as control input profiles from a set of successful demonstrations using Gaussian mixture regression. The result showed that using the human demonstration, the robot could learn how to catch a dropped ball without rebounding.

A position-based proportional-derivative (PD) controller with inner torque feedback loops can be used as a simple controller to render compliant behaviors to hydraulic robots. However, using this control framework involves a tradeoff between the stability and performance of the closed-loop system (which includes the external environment) because the joint position sensors and control units (i.e., electrohydraulic servovalves) used in the control are separated (non-collocated) from the robot by their joint flexibility. To effectively overcome this limitation, this paper proposes a joint position-based PD control strategy for constructing an inherently stable and compliant hydraulic robot system. To this end, we use virtual internal leakage to separate the system by frequency into subsystems that include control units (i.e., servovalve), flexible joints, and robot manipulator, respectively. This architecture allows the hydraulic robot to behave as a passive system within its operating frequency region under the guidance of controllers designed to guarantee the stability of the passive subsystems within the respective frequency regions. The proposed approach was verified experimentally.

There has been consistent trials to make a hydraulic actuator to be effective in interactive robot applications that require high power and durability. However, conventional strategies to obtain this goal, such as force/torque servo control or adding elastic components, suffer from complexity, sensor problems, and reduced system robustness. In this paper, we show that introducing backdrivability to hydraulic system may be an ultimate solution to constructing interactive hydraulic robot systems, by analyzing the advantages of backdrivability for this application. Moreover, we show that the backdrivability of valve-controlled hydraulic system can be achieved by adding a load pressure feedback mechanism on the spool of the servovalve, using the similarity of its dynamics structure to that of a flexible joint robot. Finally, we show that the derived backdrivable servovalve dynamics is actually the dynamics of the pressure control valve, and we report experiments that verify the analyzed advantages of backdrivability.

Position-based proportional derivative (PD) controllers are known to be able to render compliant behaviors to a robot, and they are usually used in conjunction with a friction compensator to improve control performance. Existing methods are effective when applied to actuation systems with mechanical transmissions; however, they cannot be applied to actuation systems that use fluid transmissions owing to the characteristics resulting from fluid parameters. To solve this problem, we propose a stability-guaranteed PD control method that incorporates two observers: one for observing friction and the other is for observing flexible joint effects due to fluid compliance and internal leakage. This allows robots with fluid transmissions to asymptotically converge to the desired position. We verified the proposed approach by conducting simulations and experiments.

This paper proposes a passivity-based nonlinear disturbance observer (DOB) design for a powered upper-limb robot control. The proposed DOB allows for the nonlinearities of the robot dynamics, whereas the typical DOB designs cannot. Moreover, by virtue of the passivity property, human operator and environmental interactions can be embedded in the control loop. As a DOB, the proposed approach has a disturbance observation property that makes the actual robot behave like a nominal model selected by the user. Performance analysis proposes a gain tuning rule. In experimental validation, actual powered upper-limb robot is used to perform unknown payload carrying applications.

This paper proposes a simple model-free joint torque control strategy for hydraulic robots. The undesirable effect called “natural velocity feedback effect” is discussed by introducing mechanical impedance of the system. The proposed model-free joint torque control consists of internal-loop control and external-loop control (2 degrees of freedom (DOF)). Based on a mechanically represented hydraulic robot joint, the first-order internal-loop control is designed to reduce the mechanical impedance of a hydraulic robot joint in a passive manner. To improve joint torque tracking performance, a simple proportional-integral-derivative external-loop control is applied to the modified system by the internal-loop control. Robustness to external disturbance is demonstrated by transforming the proposed 2DOF control structure to the disturbance observer form. The proposed joint torque control strategy is validated on a 1DOF rotary hydraulic robot joint.

Admittance control is a well-established and popular control strategy in modern robotics. However, the standard admittance controller has several limitations. First, the passivity can be guaranteed by finding a set of control parameters that makes the admittance function positive real. However, this approach cannot be applied to multi degrees-of-freedom robot because it requires transfer function analysis. Second, standard admittance controller is not suitable when the system is exposed to unexpected environmental interaction (of which interaction force is not measured) due to the wall sticking effect. To overcome these limitations, this paper proposes an admittance controller of which structure can be constructed by feedback interconnection of passive subsystems. The proposed approach was verified using experiments and simulations.

This paper proposes joint torque servo control of an electro-hydrostatic actuator (EHA) for effective dynamic control of robot manipulators. In the control design, the fluid parameters are not considered to develop a simple low-level controller used for multi degree-of-freedom (DOF) robot manipulators. Instead, mechanical impedance, which represents the effect of joint velocity on joint torque, is reduced using a disturbance observer. The torque tracking performance of the modified system is then improved by a simple proportional-integral-derivative control. When evaluated on two 1-DOF EHAs, the proposed controller guaranteed robustness to external disturbances and variations in the fluid parameters, even though the fluid parameters are not considered.

Carrying unknown heavy payload is one of the classical problems in robotics. To realize heavy payload capability, the use of high reduction gears, which causes large motor-side inertia and large friction, is inevitable. This paper proposes a disturbance observer (DOB)-based approach that (1) reduces highly amplified motor-side inertia (2) compensates for large friction (3) compensates for the unknown heavy payload without sensory information. However, in principle, the DOB is applicable only for linear system. To overcome this, a concept of effective joint torque is introduced, which allows us to separate linear motor-side dynamics from the nonlinear robot dynamics. As a result, it becomes possible to apply high order DOB to compensate for the uncertainties. Mathematical analysis shows closed-loop stability, optimality, and passivity. Experiments and simulations are performed to verify the method.