Motion Control

Hybrid Stepper Advancements Improve Medical Pump Performance

Designers of medical pumps often have to deal with the challenge of implementing precise, yet low-cost motion control. For most medical pumps, there are three basic technology alternatives for implementing such electronic motion control: permanent magnet brush DC motors, brushless DC motors, or step motors. Step motors (sometimes called stepping motors, stepper motors, or simply steppers) are a solid choice for position or speed control. Steppers are inherently digital — a pulse applied to the drive electronics results in a shaft movement of one step. They are commonly used “open loop,” meaning without feedback, due to their ability to achieve the desired number of steps every time (if sized properly). The number of incoming pulses and the rate at which they are fed can be used to implement very precise, yet very simple motion (position, speed, and acceleration) control. As long as the speeds required are not too high (less than 3000 RPM, typically), steppers often offer a far simpler, lower-cost, and maintenance- free alternative.

Posted in: Features, Motion Control, Articles

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Factors to Consider When Selecting and Specifying LVDT Linear Position Sensors

Fitting the right type of linear position sensor to an application requires at least a working knowledge of the attributes of this electromechanical device. Starting with the basics, the LVDT (linear variable differential transformer) is a common type of linear position sensor widely used in electromechanical systems today. It consists of two basic elements: a stationary coil assembly and a movable core or armature. While most LVDTs are fundamentally AC-in/AC-out devices, some have electronics built-in to make them DC-in/DC-out devices. This gives rise to the terms “AC-LVDTs” and “DC-LVDTs”.

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Compact, Low-Force, Low-Noise Linear Actuator

This actuator has potential uses in military and automotive applications. Actuators are critical to all the robotic and manipulation mechanisms that are used in current and future NASA missions, and are also needed for many other industrial, aeronautical, and space activities. There are many types of actuators that were designed to operate as linear or rotary motors, but there is still a need for low-force, low-noise linear actuators for specialized applications, and the disclosed mechanism addresses this need.

Posted in: Mechanics, Tech Briefs, Mechanical Components, Motion Control, Briefs

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Ultra-Compact Motor Controller

Applications include industrial robotic arms, industrial machinery, and automobiles. This invention is an electronically commutated brushless motor controller that incorporates Hall-array sensing in a small, 42-gram package that provides 4096 absolute counts per motor revolution position sensing. The unit is the size of a miniature hockey puck, and is a 44-pin male connector that provides many I/O channels, including CANbus, RS-232 communications, general-purpose analog and digital I/O (GPIO), analog and digital Hall inputs, DC power input (18–90 VDC, 0–l0 A), three-phase motor outputs, and a strain gauge amplifier.

Posted in: Mechanics, Tech Briefs, Mechanical Components, Motion Control, Briefs

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Simulation of Fluid-Structure Interaction in Hydraulic Pump Design

Axial pumps with cam-driven commutation units — so-called PWK pumps — emerged as a result of a research project conducted in the Department of Hydraulics and Pneumatics at the Gdansk University of Technology. As for all axial hydraulic piston pumps, several cylinder chambers are positioned around the rotating shaft of an axial pump with cam-driven commutation units — called PWK pumps. The rotation of the shaft and the attached swash plate leads to movement of the pistons that alternately decreases and increases the fluid volume of the chambers. A window — which is part of the control sleeve or commutating bushing — connects the chamber between the pistons with the low-pressure and highpressure intake and outtake channels.

Posted in: Features, Motion Control, Articles

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Reducing Machine Controller Design and Deployment

Machine design and deployment requires integration of various technologies such as controls, mechanics, vision, lasers, data acquisition, and software, to mention only a few. These mechatronic solutions usually target a specific purpose such as part manufacturing, marking, packaging, etc. Often the controller is a key focus in the design because it must connect and coordinate all of the processes on the machine. Using separate programmable logic controllers (PLCs) and motion controllers necessitates integration, which is costly and time-consuming. Using a single controller for the machine eliminates the need for integration and shortens design and deployment time and cost.

Posted in: Features, Motion Control, Articles

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High-Accuracy Closed Loop Force Feedback

Benefits of serial servo digital presses for force gauge specifications. Hand-driven press assemblies, which require a specific amount of force applied for a given amount of time, present challenges when attempting to accurately measure or replicate results in production or quality control processes. In contrast, servo-driven digital presses are able to provide accurate, consistent, and repeatable results while outputting trackable data. By controlling position and current, the servo-driven digital press allows for stable, accurate, and repeatable control.

Posted in: Bio-Medical, Manufacturing & Prototyping, Motion Control, Medical, Briefs, MDB

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