Collaborative robot zero moment control for direct teaching based on self-measured gravity and friction

The focus of this study is a moment compensation control algorithm driven by a direct current servo motor. Zero moment robot teaching is achieved with a joint moment compensation algorithm. The moment equilibrium equation is derived based on moment compensation. The current signal detected by a Hall effect sensor is multiplied by a torque constant to estimate the torque value of the robot joint. The compensation current is obtained through parameter identification to overcome gravitational and friction torques. The two variables of speed and position are separately controlled, allowing the compensation current of Coulomb friction and viscous friction force to be separated from the compensation current of friction torque. This study presents the system research, design, and development of a high-precision position control theory of a robot zero moment teaching control method. A collaborative robot is used as the test and verification platform to confirm the feasibility and effectiveness of the proposed theoretical method and implementation technology.

Dynamics of a Moving Body With the Hole in Its Center and Characteristics of Fluid Flow in a Small Diameter Tube

A rigid body moving with fluid in a narrow tube is expected to be developed for future engineering applications such as a capsule endoscopy, and it is also applied to some parts of industry. This paper deals with the flow characteristics around a single rigid body with a hole in its center and transient motion of the body when the body is influenced by pressure force from upstream. The model considered the width of the gap between the body and the wall is smaller than a diameter of a tube so that the force on the body can be numerically and analytically estimated as a viscous friction force. It was assumed that the flow is axisymmetric, laminar and taken to be Newtonian and incompressible. It was obtained that, with the hole in its center, the terminal velocity of the body becomes smaller than the average velocity at the inlet. Moreover, because there is a stagnation on the body, the pressure increases behind the body.

Transient Motion of a Rigid Body Through a Narrow Tube and Characteristics of Surrounding Fluid Flow

A multibody transportation system that moves with fluid inside a small-diameter tube has been studied by a lot of researchers. It is expected to be developed for future engineering applications such as a micro machine that transports medicines to a certain part of a body. This paper deals with the flow characteristics around a single rigid body and transient motion of the body when a body is influenced by pressure force from upstream. The model considered a body smaller than a diameter of a tube so that the force on the body can be numerically and analytically estimated as viscous friction force. It was assumed that the flow is axisymmetric, laminar and taken to be Newtonian and incompressible. It was obtained that the axial component of the fluid velocity decreases and pressure increases near the body like stagnation flow. Moreover, the pressure rapidly increases behind the body and decreases in front of the body with increasing diameter of the body.

Dielectrophoretic Separation Motion of a Particle From Electrolyte Solution in Micro-Channel

Dielectrophoresis (DEP) based on the processes of particle separation and particle detection in micro-channel is one of the most important operations required for many lab-on-a-chip devices. To understand the mechanism of the DEP, a theoretical analysis of dielectrophoretic separation motion of a spherical particle in a rectangular micro-channel filled with an aqueous electrolyte solution is presented in this paper. The dimensions of micro-channel are 100 μm in width and 200 μm in length. In this study, driven forces on the particle are analyzed in detail. At the gravitational direction, it is assumed that the density of the spherical particle is higher than that of the solution, and thus the gravitational effect is considered coupled with the buoyancy force and the electric double layer interaction force as well as the van der Waals force. Both the DEP force and the viscous friction force drive the particle separation motion from the solution in micro-channel. The particle separation distance of the particle from the bottom wall by the action of these forces and its motion behavior are analyzed and calculated. The DEP motion along the channel in an applied non-uniform electric field is simulated. Effects of particle’s size, electrolyte solution concentration and applied electric field strength on the DEP motion are discussed.

Adaptive Output Force Tracking Control of Hydraulic Cylinders With Applications to Robot Manipulators

An adaptive output force control scheme for hydraulic cylinders is proposed by using direct output force measurement through loadcells. Due to the large and somewhat uncertain piston friction force, cylinder chamber pressure control with Coulomb-viscous friction prediction may not be sufficient enough to achieve a precise output force control. In the proposed approach, the output force error resulting from direct measurement is used not only for feedback control, but also to update the parameters of an appropriate friction model which includes the Coulomb-viscous friction force in sliding motion and the output force dependent friction force in presliding motion. The L2 and L∞ stability is guaranteed for both the pressure force error and the output force error. Under bounded desired output force and its derivative, asymptotic stability of both the pressure force error and the output force error is also guaranteed. The experimental results demonstrate that a good pressure force control system does not necessarily guarantee a good output force control, and that adaptive friction compensation is superior to fixed-parameter friction compensation. The output force control transfer functions of a robot joint driven by two hydraulic cylinders in pull–pull configuration are limited by ±1.5dB up to 20Hz, tested in free motion and in rigid constraint. The excellent output force (joint torque) control performance implies the dynamic equivalency between a hydraulic cylinder and an electrically-driven motor within the prespecified bandwidth. This allows to emulate an electrically-driven robot by a hydraulic robot.

Modelling and Analysis of a Grout Delivery Mechanism in the Remote Spray Lining of Shafts

A thorough analysis on the characteristics of a grout delivery mechanism in the lining of shafts has been accomplished. The dynamic equation of this spraying mechanism has been established and can describe the system’s performance properties under different conditions of viscous friction forces. The analysis introduces a combined viscous damping coefficient c* and a ratio λ between viscous friction force and inertia force. It is proved theoretically that the relative velocity of the grout is less than the implicate velocity and the emission angle α described in the paper is always larger than 45 °. Numerical simulations are performed by feeding various different parameters into the model. A full discussion of the effects of different variables is presented. Additionally, a formula for calculating the driving torque and power is developed. These studies provide an understanding of the properties of this mechanism and should prove useful in guiding its design and operation.