Simple Torque Control Research Articles

Simple Torque Control Method for Hybrid Stepper Motors Implemented in FPGA

Stepper motors are employed in a wide range of consumer and industrial applications. Their use is simple: a digital device generates pulse-bursts and a direction bit towards a power driver that produces the 2-phase currents feeding the motor windings. Despite its simplicity, this open-loop approach fails if the torque load exceeds the motor capacity, so the motor and driver should be oversized at the expense of efficiency and cost. Field-Oriented closed-loop Control (FOC) solves the problem, and the recent availability of low cost electronics devices like Digital Signal Processors, Field Programmable Gate Arrays (FPGA), or even Microcontrollers with dedicated peripherals, fostered the investigation and implementation of several variants of the FOC method. In this paper, a simple and economic FOC torque control method for hybrid stepper motors is presented. The load angle is corrected accordingly to the actual shaft position through pulse-bursts and direction commands issued towards a commercial stepper driver, which manages the 2-phase winding currents. Thanks to the FPGA implementation, the control loop updates the electrical position every 50 μs only, thus allowing a load angle accuracy of −1/100 rad for a rotor velocity up to 750 rev/min, as shown in the reported experiments.

Variable-Friction Finger Surfaces to Enable Within-Hand Manipulation via Gripping and Sliding

The human hand is able to achieve an unparalleled diversity of manipulation actions. One contributor to this capability is the structure of the human finger pad, where soft internal tissue is surrounded by a layer of more rigid skin. This permits conforming of the finger pad around object contours for firm grasping, while also permitting low-friction sliding over object surfaces with a light touch. These varying modes of manipulation contribute to the common ability for in-hand-manipulation, where an object (such as a car key) may repositioned relative to the palm. In this letter, we present a simple mechanical analogy to the human finger pad, via a robotic finger with both high- and low-friction surfaces. The low-friction surface is suspended on elastic elements and recesses into a cavity when a sufficient normal force is applied (∼1.2 to 2.5 N depending on contact location), exposing the high-friction surface. We implement one “variable friction” finger and one “constant friction” finger on a 2-DOF gripper with a simple torque controller. With this setup, we demonstrate how within-hand rolling and sliding of an object may be achieved without the need for tactile sensing, high-dexterity, dynamic finger/object modeling, or complex control methods. The addition of an actuator to the finger design allows controlled switching between variable-friction and constant-friction modes, enabling precise object translation and reorientation within a grasp, via simple motion sequences. The rolling and sliding behaviors are characterized with experimentally verified geometric models.

Prediction of lower relative stability states In case of speed control of DC motor

Abstract- In industries, the control of direct current (DC) motor is a common practice thus the implementation of DC motor of speed control is important. The main purpose of motor speed control is to keep the rotation of the motor at the preset speed and to drive a system at the demanded speed. When used in speed application, speed feedback control the DC motor's speed or confirms that the motor is rotating at the desired speed. To maintain the speed, it requires the speed feedback at all times. The speed of a DC motor usually is directly proportional to the supply voltage. For instance, if we reduce supply voltage from 5 Volts to 2.5 Volts the motor will run at half or lower the speed. The advantages used DC motor is provide excellent speed control for acceleration and deceleration with effective simple torque control. This paper considers the method that are used to control speed of DC motor is phase locked loop (PLL) with proportional and data acquisition system (DAS) based to monitor the dynamic of the system and predict the change of stability for system. In this project, the method use to indicate how far the system from instability and take the reaction rapidly before system goes to unstable and to be out of control and problems occur in the rest of dependable parts on that system and useful for preventive maintenance which effective approach for reliability enhancement for the system so a failure can be detected early or even predicted is the key point. This project presents a failure prediction method for help in preventive maintenance with rapid indication for system stability and design via bode diagram to get phase margin and gain margin by program (G-code) on LabVIEW before system operations .

BioMot exoskeleton - Towards a smart wearable robot for symbiotic human-robot interaction.

This paper presents design of a novel modular lower-limb gait exoskeleton built within the FP7 BioMot project. Exoskeleton employs a variable stiffness actuator in all 6 joints, a directional-flexibility structure and a novel physical humanrobot interfacing, which allows it to deliver the required output while minimally constraining user's gait by providing passive degrees of freedom. Due to modularity, the exoskeleton can be used as a full lower-limb orthosis, a single-joint orthosis in any of the three joints, and a two-joint orthosis in a combination of any of the two joints. By employing a simple torque control strategy, the exoskeleton can be used to deliver user-specific assistance, both in gait rehabilitation and in assisting people suffering musculoskeletal impairments. The result of the presented BioMot efforts is a low-footprint exoskeleton with powerful compliant actuators, simple, yet effective torque controller and easily adjustable flexible structure.

Herbert: Design and Realization of a Full-Sized Anthropometrically Correct Humanoid Robot

In this paper we present the development of a new full-sized anthropometrically correct humanoid robot Herbert. Herbert has 33 DOFs: 1) 29 active DOFs (2 × 4 in the legs, 2 × 7 in the arms, 4 in the waist and 3 in the head); 2) 4 passive DOFs (2 × 2 in the ankles). We present the objectives of the design and the development of our system, the hardware (mechanical, electronics) as well as the supporting software architecture that encompasses the realisation of the complete humanoid system. Several key elements, that have to be taken into account in our approach to keep the costs low while ensuring high-performance, will be presented. In realising Herbert we applied a modular design for the overall mechanical structure. Two core mechanical module types make up the main structural elements of Herbert: 1) small compact mechanical drive modules; and 2) compliant mechanical drive modules. The electronic system of Herbert, which is based on two different types of motor control boards and an FPGA module with a central controller, is discussed. The software architecture is based on ROS with a number of sub nodes used for the controller. All these supporting components have been important in the development of the complete system. Finally, we present results showing our robot’s performances: demonstrating the behaviour of the compliant modules, the ability of tracking a desired position/velocity as well as a simple torque controller. We also evaluate our custom communication system. Additionally, we demonstrate Herbert balancing and squatting to show its performance. Moreover, we also show the simplicity of the higher level supporting software framework in realising new behaviours. All in all, we show that our system is compact and able to achieve comparable human performances and has human proportions while being low cost.