Integrating lead screws with stepper motors is a simple and cost-effective method for getting precise linear motion. But achieving that precision requires anti-rotational guidance, which must either be added externally by the user or designed in by the manufacturer. Determining which option makes sense for you requires an analysis of your need for a guidance system and weighing the advantages and disadvantages of each approach.
THE NEED FOR ANTI-ROTATIONAL GUIDANCE
The main components of a traditional motorized lead screw (MLS) are a stepper motor, lead screw, and a nut that connects to the load in various ways. When the motor turns the lead screw, the nut and connected load should travel forward or backward to achieve the positioning required for the application. But if that nut is unsecured, it will rotate with the screw and no motion will translate across the axis.
BUILDING YOUR OWN SYSTEM
If you already utilize a motorized linear actuator (MLA) and have the technical knowledge and resources, you can design and add an anti-rotational assembly yourself. If your application has stroke lengths longer than 2.5 inches, loads heavier than 200 lbf, and speeds faster than 20 in/s, an external system may be your best choice. Building your own guidance system can be a time-consuming and somewhat risky process.
THE BENEFITS OF A BUILT-IN SYSTEM
To ensure accurate pipetting, tiny, precise, and repeatable vertical motion is required. Integrating motorized lead actuators simplifies your z-axis, while motorized lead screws provide precise and horizontal motion. (Image courtesy of Thomson Industries, Inc.)
SELECTING THE RIGHT BUILT-IN TECHNOLOGY
Generally, stepper motor linear actuators are available for standard stepper motor sizes (NEMA 8, 11, 14, 17, and 23 motor frame sizes), single or double stacked, with a variety of motor winding options and linear resolution options ranging from 0.063 to 7.5 μin of linear travel per step. Available offerings may differ in their ability to handle radial and moment loads, capability to integrate other devices, visibility of rotating parts, mounting options, and customization capability, so it is wise to consider your needs in these areas before purchasing one.
This is hybrid stepper motors are normally used for positioning, and are not known for their speed. This calculator computes the maximum speed of a stepper motor, which is limited by the time it takes for the coil to energize to it's maximum holding current, and then de-energize as polarity flips.
Current through the coil is proportional to the time that the voltage has been applied, and inversely proportional to the inductance.
For one step the current must go from 0 to Imax and back to 0, or alternatively from -Imax to +Imax.
T is the number of seconds for a single step.
To compute maximum revolutions per second - divide seconds per step by steps per revolution.
Rev/sec = V/(L*2*Imax)/(steps/rev)
Pmax occurs not when the motor is going max speed because the current is a triangle wave. Pmax occurs when the slope of the current is small compared to the on holding time of the step pulse.
aragraph text. Double click here to edit and add your own text.