Precise Position Control of Holonomic Inchworm Robot Using Four Optical Encoders

In this paper, model-based precision force and position control of an ionic polymer metal composite (IPMC) is presented. A 23.8 mm × 3.4 mm × 0.16 mm IPMC strip was used as an actuator in a cantilever configuration. Open-loop force and position responses of an IPMC are not repeatable, and hence closed-loop precision control is of critical importance to ensure proper functioning, repeat-ability and reliability. After feedback controllers were designed and implemented with empirically obtained fourth-order plant transfer functions, the overshoot decreased from 460 to 2.8 per cent and the settling time was reduced from 37.5 to 3.22 s in force control. In position control the overshoot decreased from 333 to 20.3 per cent and the settling time was reduced from 21.5 to 2.56 s. Microscale precision force and position control capabilities of the IPMC actuator were also demonstrated experimentally. An 8 μN force resolution was achieved with a force noise of 0.5μN r.m.s., and the position resolution was 6 μm with a position noise of 2.5 μm r.m.s. The maximum force and tip displacement achieved with the IPMC actuator under closed-loop control were 2 mN and 5 mm respectively. The IPMC actuator could follow various commanded force and position trajectories such as sinusoidal and trapezoidal position profiles, and a velocity profile with a 3 mm/s maximum velocity. A novel hybrid force and position control strategy demonstrated its utility in practical micromanipulalion applications where the actuator force must be limited to prevent damaging micro-objects. High-precision control of the IPMC at low force level proved its potential for micromanufacturing and micromanipulation applications such as robotic and biomedical microgrippers.

Fluidic soft actuators have been widely used for applications where compliance is desirable – such as in delicate robotic manipulation. As their operation is based on pressurization, fluidic actuators typically rely on bulky, rigid pumps, valves, and pressure regulators for control. This dependence on rigid components hinders the development of compact and fully-soft robots. Soft regulation systems designed for control of these actuators have been recently developed based on soft valves using dielectric elastomer actuators, but precise control has not been achieved. In this work, we leverage these valves to introduce a soft regulation system capable of precise closed-loop position control of a soft hydraulic actuator with multiple controllers. We also achieve open-loop trajectory tracking based on a data-driven model of the fluidic system. Finally, we combine the valve system with wearable strain sensors to create the first teleoperated fluidic circuit where the sensor, actuator, and regulation system are all soft. This work presents control strategies for fluid-driven actuators with soft sensors and regulation systems, showing the potential for future all-soft motion control of soft hydraulic robots.

This paper investigates the problem of the position control in switched reluctance motor drives. Advanced proportional-integral (PI) and proportional-differential (PD) controllers for the speed and position control, respectively, are adopted. The parameters of the controllers are on-line fine tuned according to the load torque and rotor speed, for providing high dynamic performance and precise position control. In order to improve the set-point tracking of the drive performance, a low-pass filter is included in the position controller. The proposed four-quadrant control scheme is based on the average torque control method. The turn-on and turnoff angles are on-line determined through simple formulas and the proposed fine tuning regulator is capable of maintaining the torque ripple at an acceptable level over a wide speed range. This is important since the position precision is highly influenced from the motor torque ripple. Experimental results of the switched reluctance motor dynamic response are presented to verify the theoretical considerations and to demonstrate the effectiveness of the proposed control scheme.

Model-based precision position and force control of SMA actuators with a clamping application

Demands for high precision machine tools have been increased as technology advances. Such demands require higher position control to allow the machine tools to produce higher precision end products. To facilitate the position control, magnetic and optical encoders are been widely used in the machine tools. Due to its advantage in withstanding hard environment such as oil, grease and dust over an optical encoder, along with its wide applications in industrial position control, a magnetic encoder has become a desirable choice for machine tools. The objective of this study is to develop a polarity changeable magnetizer for manufacturing coding patterns in a rotary encoder which is used to monitor runout errors for rotating components in machine tools. As opposed to commonly used capacitive pulse magnetizer in which significant amount of energy is required for its electromagnets that potentially causes high energy hazard, in this study, a polarity changeable permanent magnet is proposed and investigated through parameter studies to overcome such issue with the aim placed on producing sufficient magnetization on a thin silicon steel plate to produce desirable coding patterns on the rotary encoders.

This paper aims to research the position control of the hydraulic cylinder controlled by the high-speed on-off valve to realize the precise position control. A compound algorithm of proportional integral & speed feedforward- displacement feedback is put forward based on the research on the relationship between the duty ratio and the past flow for the high speed on-off valve. The speed feedforward-displacement feedback algorithm can solve the hysteresis resulting from the feedback control and be considered as the certain duty ratio is given ahead, and the proportional integral control algorithm is designed and utilized to deal with the position error by adjusting to the duty ratio of high speed on-off valve. The genetic algorithm is used to tune the control parameters, including speed forward coefficient, proportional and integral coefficient of displacement feedback, output coefficient to gain the optimization result, on terms of the performance of the position control system. The mathematics modeling is analyzed and simulated with Simulink using the bulk-cavity-node method, and the hydraulic loop is established to verify the simulation result with the optimized results on the FESTO platform. the research finds that the proposed position scheme is effective to increase the position precision, and the position control parameters optimized by genetic algorithm can decrease the position error more. DOI : http://dx.doi.org/10.11591/telkomnika.v12i5.4218

Servo motor drives are systems involved in precision motion and position control used in multiple applications in industrial automation, e.g. robotic arm, conveyer belts etc. A typical servo motor drive receives position reference over industrial Ethernet from a motion controller and uses that reference to close the position/speed/torque loops to actuate the drive. The position reference is received over industrial Ethernet at a cyclic rate of 32 Khz i.e. every 31.25usecs and the position/speed/torque loops are closed at a cyclic rate of 100Khz, i.e. every 10usecs. In order to precisely control the servo motor drive, the SW blocks used to close the loops need to be synchronized precisely and with hard real-time limits set by cyclic rate of Ethernet communication and position/speed/torque loops. Additionally, modern servo drive systems need to control multiple servo drives, typically 3-axis servo drive to control a robotic arm in factory automation systems. This paper proposes a single chip solution to handle the industrial Ethernet protocols and multi-axis servo motor drive control software. The proposed solution uses multiple novelties namely, multi-core ARM R5F micro controllers to run the Ethernet and motor control loops, hard real-time offload to dedicated Programmable Real-time Units (PRUs), high precision time-sync to synchronize the SW blocks. The proposed implementation is done on TI AM243x SOC and is able to achieve 3-axis servo motor drive control, using < 10% R5F utilization, < 2MB of internal RAM and time-sync precision of < 20ns. This ensures the servo motor drive operates at the precise position/sneed/torque that is desired.

Nanotechnology is based on a combination of many technologies such as high precise positioning and force control, especially magnetic recording, biotechnology and semiconductor industry require the utilization of nanotechnology. Until now there have been various actuator systems proposed, but the structure models have only working distances of either under a millimeter or over ten millimeters. Structure models with working distance ranging several millimeters has been designed a little. Therefore we are proposing a new structure design of actuator that would allow us to build actuator systems with working distances between those parameters. This new actuator consists of a voice coil motor and a new guide with an elastic support mechanism. The elastic support mechanism (ESM) consists of a special spring which is restricted to moving in only one direction. This new ESM does not cause any lost motion, mechanical play or friction with motion. Since characteristically voice coil motor thrusts and displaces the elastic support mechanism linearly, highly precise positioning and force control can be realized using a simple controller. We will evaluate the force control method from the displacement of ESM. This paper will provide basic data for developing future Nano-Actuator systems.

Precise position control with an accuracy of 10 μ was impossible by mechanical means such as screw movement used so far. This is because continuous movement couldn't be expected due to sliding friction from a microscopic point of view. Also, it was impossible to avoid backlash even though mechanical pressure by spring may be adopted. The authors have developed practically precise control with an accuracy of 0.2 μ by a new method utilizing the electromagnetic force. In the new equipment, dynamic characteristics are also excellent because the damping time can be designed independently of characteristic frequency by electrical damping and because resistance to deviation from exact position can be selected widely by electrical feedback from a laser interferometer. For example, 66 g-wt is necessary to move it 0.1 μ in the case of only 0.56 W electromagnet, and the time taken for it to become stationary is less than 100 msec at the present stage.

The direct drive of the permanent magnet linear synchronous motor (PMLSM) requires excellent disturbance rejection capability to achieve precise position control. This article proposes an improved adaptive linear active disturbance rejection control (IALADRC) to improve trajectory tracking and disturbance rejection capability. First, we explain the difference between proportional–integral–derivative (PID) control and LADRC in terms of trajectory tracking and disturbance rejection. Unlike PID, which uses the integral controller to reject disturbances, LADRC uses the extended state observer (ESO) to decouple reference tracking and disturbance rejection. This simplifies the PMLSM control system to a second-order system, which in turn inspired the proposal of the improved LADRC (ILADRC). ILADRC reconstructs the disturbance from the position error using the inverse closed-loop model and injects it into the control output, resulting in better control performance. Due to the complex disturbance existing in the motion process of PMLSM, an improved adaptive ESO (AESO) is proposed to strike a balance between disturbance estimation and noise reduction. The ILADRC and the improved AESO are combined to form the IALADRC. Comparative experiments show that the IALADRC has excellent disturbance rejection capability and significantly improves the position control accuracy of the PMLSM system.

This paper presents a vision based motion control and trajectory tracking strategies for microassembly robots including a self-optimizing visual servoing depth motion control method and a novel trajectory snake tracking strategy. To measure micromanipulator depth motion, a normalized gray-variance focus measure operator is developed using depth from focus techniques. The extracted defocus features are theoretically distributed with one peak point which can be applied to locate the microscopic focal depth via self-optimizing control. Tracking differentiators are developed to suppress noises and track the features and their differential values without oscillation. Based on the differential defocus signals a coarse-to-fine self-optimizing controller is presented for micromanipulator to precisely locate focus depth. As well as a novel trajectory snake energy function of robotic motion is defined involving kinematic energy, curve potential and image potential energy. The motion trajectory can be located through searching the converged energy distribution of the snake function. Energy weights in the function are real-time adjusted to avoid local minima during convergence. To improve snake searching efficiency, quadratic-trajectory least square estimator is employed to predict manipulator motion position before tracking. Experimental results in a microassembly robotic system demonstrate that the proposed strategies are successful and effective.

Precise force control and position control is essential for many robotic applications. During unilateral or bilateral object handling remote applications, human operators apply excess forces on the actuators with the intention of better grip and it is possible to damage the handled objects. This paper proposes position control and force control techniques when human applies excess force. The controllers consist of predefined force and equilibrium position which are correspond to remote environmental object safety. The operator applied excess force is modeled as a spring force through a virtual stiffness model. The paper introduces proportional derivative position control loop to conventional virtual stiffness controller. The force control loop and the position control loop references are combined in the common dimension of acceleration to produce current reference to the actuator. The sensorless sensing techniques of disturbance observer and reaction force observer are utilized to disturbance suppression and external force estimation. In the force controller, estimated reaction force is reduced to desired value by introducing virtual force loop between reaction force observer output and reaction force feedback input. The position control is achieved by introducing a scaling factor to reaction force feedback path. The switching between force control and position control is possible with scaling factor value. The performances of proposed methods are compared with conventional method and validity of the proposed methods is verified by simulations and experiments.

Thickness measurements using an ultrasonic contact test is a well-known nondestructive evaluation technique. However, its implementation in a robotic system with a closed-loop feedback control for artificial intelligent measurements requires precise information of positioning and force of the ultrasonic probe. In this work, we describe an ultrasonic probe developed in our lab that uses a semispherical soft membrane made from an elastomer. The aim is to develop a methodology for precise positioning and force control of a dry contact ultrasonic probe based on the ultrasonic signal information processed using sparse matrix optimization and Fourier analysis techniques. The results show that the proposed methodology makes easy to achieve a fine tuning of the probe orientation with high sensitivity to load and misalignment in order to perform accurate thickness measurements.

For solving dynamic position error problem and improving synchronization position control precision in electrohydraulic servo system, a dynamic particle swarm optimization algorithm is established by means of the introducing of moving windows and forgetting factor in searching regional, and an electro-hydraulic servo system synchronization position control method is presented by dynamic particle swarm optimization algorithm. Finally, this method was demonstrated and validated by a sample. It has shown the proposed method can improve the benefit of position control precision in electro-hydraulic servo system synchronization control, and provide a support for adapting to complex and dynamic synchronization control in electro-hydraulic synchronization position servo system (EHSPSS).

The experience of the design of the nonlinear position control confirmed the remarkable potential of backstepping and fuzzy logic in the development of effective decision laws capable of overcoming the inherent limitations of model-based control strategies. This paper focuses on design of hybrid backstepping and fuzzy position logic controls of mobile robot that satisfied a good position tracking performance with simultaneously satisfactory control of velocities, which has an impact on wheel torques. In our previously designed backstepping controller a good tracking performance was obtained. However, its main shortcoming is unsatisfactory control velocities values, particularly at the beginning of tracking. Control parameters of backstepping controller and membership functions of fuzzy controller are adjusted by genetic algorithms. Advantage of the proposed fuzzy controller, and also hybrid backstepping controller, lies in the fact that control velocities (and consequently, the control torques) cannot exceed certain limits. Consequently, these controllers radically decreased the control velocities without major impact on tracking performance. Finally, from the simulation results obtained, it can be concluded that the proposed hybrid backstepping and fuzzy design achieve the desired results. Future work will include the investigation of a fuzzy stability of the proposed fuzzy logic position system.