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Introduction to Electric Motors
Published in Wei Tong, Mechanical Design and Manufacturing of Electric Motors, 2022
Today, servomotors are increasingly being used in a variety of applications due to their high power density, high efficiency, and excellent dynamic performance as compared with other motor drive technologies. Servomotors operate with closed-loop control systems. The ability of the servomotor to adjust to differences between the motion profile and feedback signals depends greatly upon the types of control systems and servomotors. There are two types of servomotors: one is classical DC servomotor and another is AC servomotor. Generally, AC servomotors can handle higher current surges compared to DC servomotors. It is to be noted that in some references, AC servomotors are referred to as brushless DC motors, causing confusion to some readers. An AC servomotor or the so-called brushless DC motor is essentially a three-phase AC synchronous motor. It has a position transducer inside the motor to transmit motor shaft position to the drive amplifier for the purpose of controlling current commutation in the three phases of the motor windings.
Hardware Components for Automation and Process Control
Published in Stamatios Manesis, George Nikolakopoulos, Introduction to Industrial Automation, 2018
Stamatios Manesis, George Nikolakopoulos
When higher torque demands precise control, servomotors are then the best solution to be used. Servomotors are not a specific class of motors and the term “servomotor” is often used to refer to a motor suitable for use in a closed-loop control system. A servomotor consists of an AC or DC electric motor, a feedback device, and an electronic controller. In the case of a DC motor, this can be either a brushed or brushless type. Typically, the feedback device of a servomotor is some type of encoder built into the motor frame to provide position and speed feedback of the angular or linear motion. The electronic controller is a driver, supplying only the required power to the motor, in the simplest case. A more sophisticated controller generates motion profiles and uses the feedback signal to precisely control the rotary position of the motor and generally to control its motion and final position, thus accomplishing the closed-loop operation. Since the servo motors are driven through their electronic controllers, it is quite easily interfaced with microprocessors or other high level programmable controllers.
Imaging System Components
Published in Harry E. Martz, Clint M. Logan, Daniel J. Schneberk, Peter J. Shull, X-Ray Imaging, 2016
Harry E. Martz, Clint M. Logan, Daniel J. Schneberk, Peter J. Shull
The choices for the type of and the control protocol for the stages are large, and some of the distinctions are not consequential for system performance but can impact scan time. For the most part, there are three types of motor operation: stepper motor, AC servomotor, and DC servomotor. A stepper motor or step motor or stepping motor is a brushless DC electric motor that divides a full rotation into a number of equal steps. The motor's position can then be commanded to move and hold at one of these steps without any feedback sensor (an open-loop controller), as long as the motor is carefully sized to the application with respect to torque and speed. A servomotor is a rotary or linear actuator that allows for precise control of angular or linear position, velocity, and acceleration. It consists of a suitable motor coupled to a sensor for position feedback. It also requires a relatively sophisticated controller, often a dedicated module designed specifically for use with servomotors.
Review of ankle rehabilitation devices for treatment of equinus contracture
Published in Expert Review of Medical Devices, 2022
Kamila Dostalova, Radek Tomasek, Martina Kalova, Miroslav Janura, Jiri Rosicky, Marek Schnitzer, Jiri Demel
An intelligent custom-designed device for stretching spastic ankles adapted by the Illinois-based company Rehabtek has been developed for neurologically impaired patients [39]. Patients are strapped to the seat with their legs strapped to the leg support. Both the seat and the leg support are adjustable. The footplate is attached to the motor shaft with a six-axis force sensor. The servomotor is driven by a controller that reads the joint position and accordingly controls the velocity up to the extreme position of the joint, which can be held for a specified time. Position limits guarantee the safety of the device. Seventeen stroke patients and same number of healthy individuals as a control group participated in the study to quantify hemiplegic spacticity. Fifteen of the 17 stroke patients showed clinically enhanced Achilles’ tendon reflexes [40]. In another study by Sung et. Al [41]. 46 subjects participated in the study to investigate reliability of the device to measure ankle joint stiffness. Measurements were reproducible and consistent. Ten subjects with chronic ankle spasticity used the device for 4 weeks and results reported improvements in the passive ROM, maximum voluntary contraction, and ankle stiffness [42].
Finite element analysis of lower limb exoskeleton during sit-to-stand transition
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2021
Several types of actuators are employed to perform exoskeleton joint motion. The most common of them are DC Servo motor, stepper motor, brushless DC motor, hydraulic actuators, and pneumatic actuators. Each actuation system has its own advantages and disadvantages. The DC motors have been chosen for the proposed design. The major advantages of DC motors are compact in size, less weight, more efficient, and easier to control. The DC motors can be used in two different ways in an exoskeleton; (1) direct coupling and (2) linear actuation. The direct-coupled system uses the motor axis as the joint axis by directly placing the rotor in the axis of the exoskeleton joints. The major advantage of the direct coupling of motor is that the installation is easy and the assembly becomes compact. The linear actuation of DC motors enables higher torque output for the same specifications of the motor used in the direct coupling method. It is more preferred for the ankle joint where the requirement of the torque is higher. The linear actuation forms an additional arm between two exoskeleton segments, and this arm acts as a channel for the force during the support phase. In the proposed design, the direct coupling of DC motor is chosen as the actuation system which simplifies the design and analyzing the effects of weight on the exoskeleton. As the direct coupling will not protrude to any additional arms, the exoskeleton can be realized by the four-segment structure. Moreover, the joints of the segments can be treated as the axis of the motor.
Virtual commissioning for an Overhead Hoist Transporter in a semiconductor FAB
Published in International Journal of Production Research, 2020
Joo Y. Lee, Kwanwoo Lee, Sangchul Park
The main mission of an OHT is to move a FOUP from a starting point to a destination point, and it consists of four major steps; (1) Move to the starting point in an empty state, (2) Load a FOUP at the starting point, (3) Move to the destination point with the FOUP, and (4) Unload the FOUP at the destination point. Among the four steps, the FOUP loading and unloading steps require many tasks from shutter, slide, hoist and gripper. An OHT device has multiple motions requiring actuators such as ‘servo motors’ and ‘stepper motors’. While servo motors are used for precise control requiring feedback sensors (closed-loop control), stepper motors are suitable for less precise control without feedback sensors (open-loop control). Typically, an OHT has four servo motors (two for driving, one for slide, and one for hoist) and two stepper motors (one for shutter and one for gripper). Each motor has corresponding tasks. By analysing those tasks, we identify nine tasks, as shown in Table 1.