Power transmission shafts — on motors and gearboxes, for example — are subjected to torque loads that result in torsion, or twisting of the shaft about its axis. Similar to structures under tension or compression, two important mechanical properties of shafts under torque loads are shear stress and shear strain. Stress is a material’s resistance […]
Mechanical properties of materials: Stress and strain
Every component in a linear motion system experiences some form of loading due to applied forces or motion. The component’s reactions to these loads are described by its mechanical properties. For components subjected to tension or compression — such as load-carrying balls and rollers, shafts mounted vertically, or fastening and joining hardware — the mechanical […]
What is servo tuning and why is it important?
Unlike stepper motors, which rely on even pulses of current to turn the motor in discreet steps, servo motors operate with continuous current to reach a specified position, velocity, or torque. The precise amount of current to be delivered to the motor is determined by the servo controller, based on information supplied by an encoder […]
How does closed-loop stepper control work … and why not just use a servo?
Stepper motors are inherently open-loop devices. They don’t require feedback because each pulse of current delivered by the drive equals one step of the motor (or a fraction of a step in the case of microstepping). Plus with small step sizes (or step angles) the motor’s position can be determined very precisely without the need […]
What is Abbé error and how does it affect linear systems?
When evaluating the accuracy of a linear motion system, the area of focus is often the positioning accuracy and repeatability of the drive mechanism. But there are many factors that contribute to the accuracy (or inaccuracy) of a linear system, including linear errors, angular errors, and Abbé errors. Of these three types, Abbé errors are probably […]
Follow these four tips when using L10 life to size linear bearings
The well-known bearing life equation, often referred to as L10 life, is a fundamental element in the sizing and selection of recirculating linear bearings. Through statistical analysis and real-world testing, the L10 life equation can predict, with 90 percent reliability, the life that a recirculating bearing can be expected to achieve. But even this universally […]
What’s the difference between backlash and hysteresis in linear systems?
In linear systems, backlash and hysteresis are often referred to as the same phenomenon. But while they both contribute to lost motion, their causes and methods of operation are different. Backlash: The enemy of linear systems Backlash is caused by clearance, or play, between mating parts, which introduces a dead band when the direction of […]
When did the most common linear-actuator options come about?
This is the first of several technical notes on the technology known as moving coil actuators. Here we provide a brief history of linear actuators used in automation — and hint at where moving coil actuators are suitable. By Ed Neff • President | SMAC Moving Coil Actuators (MCA) Hydraulic actuators came first. These devices […]
Why are planetary gearboxes preferred for servo applications?
In a servo application — one in which a feedback device is used to control torque, position, or speed of a linear or rotary system — the ratio of the load inertia to the motor inertia is a critical factor in system performance. A lower inertia ratio allows the motor to more precisely control the load […]
How to size a rack and pinion drive
In linear motion applications, ball screws are widely recognized for their ability to provide high thrust forces, while linear motors are gaining market share in high-speed applications, and belt drives continue to maintain their reputation as the best solution for long travel lengths. But rack and pinion drives are the often-overlooked workhorses behind gantry and […]
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