Linear Motion Actuators
A typical electromechanical actuator has an aluminum housing equipped with a load-bearing carriage propelled by a motor-driven ball screw, lead screw, or toothed belt.
Ball Screw Advantages
- High load capacity
Lead Screw Advantages
- Simple, quiet
- Less expensive
- Low maintenance
Belt Drive Advantages
- High acceleration, speed, rigidity
- Low friction, noise, vibration
- Long travel length
Miniature Linear Actuators
For precise linear travel and a small footprint, miniature lead screw-driven actuators are available for applications like medical and biotech testing, packaging, and military.
Many types are suitable for a linear actuator systems such as: stepper, DC (brush or brushless), and AC induction.
Static Load Capacity
Linear screw actuators have a static loading capacity, which means when the motor stops, the actuator locks in position. Braking force varies with angular pitch of the screw threads. Acme threads have a high static load capacity, while ball screws have a low load capacity.
All linear slides provide motion based on bearings. Movement for motorized linear slides is typically provided by a drive mechanism. Not all linear slides are motorized. Non-motorized roller and ball bearing slides can provide linear movement for manually operated equipment.
Rolling Element Bearings
- Ball Bearing Slides – Offer precise motion and are self-lubricating. Applications include instrumentation, robotic assembly, and cabinetry. They have a low load capacity and are less resistant to wear.
- Roller Slides – Often powered by hand for non-motorized mechanisms. They consist of steel-crossed rollers and are like ball bearing slides, except the bearings are cylindrical and offer improved repeatability and more load capacity.
Slide without balls or rollers and may or may not need lubrication. They are less rigid, corrosion-resistant, less sensitive to contamination, and can handle a wider temperature range than rolling-element types.
A linear stage consists of a platform and a base joined by a linear bearing, which restricts the platform to a single axis. Positioning of the platform is controlled by a linear actuator equipped with a lead screw or a toothed belt. A dual-axis stage can be assembled from two linear stages, with one mounted perpendicular to the other.
X-Y tables provide controlled horizontal motion for automated machines. They are typically mounted on ball bearing or roller slides and are available with a variety of linear bases. X-Y tables are lightweight, easy to use, and require little maintenance.
Other Types of Linear Actuators
Have no external piston rod, but rather an internal rod that is connected to an external carriage. Compressed air or hydraulic fluid is used to drive the piston and move the carriage. They require much less mounting space than conventional cylinders (up to 50%).
Rodless Mechanical Actuators
Also offer space advantages over conventional rod cylinders. Overall length is the same whether the actuator is extended or retracted. AC, DC, servo, step, or hydraulic motors can be used.
Often called solenoids, these are widely used for applications that require electromechanically-based linear motion. They are simple, cost-effective, and come in many configurations. The four main types are low-profile, tubular, open frame, and magnetically latched. They are not suited for harsh environments or applications where force needs to be applied slowly or in steps.
These use materials that stretch when subjected to a magnetic field and are used in applications that call for short linear movements. Similar to piezoelectric actuators, they use rods that stretch when an electric voltage is applied to the ends. A typical actuator consists of a magnetostrictive rod surrounded by a solenoid coil. Externally powered, the coil generates a magnetic field that causes the rod to become longer and thinner. They generally require a magnetic return path.
Consist of an input rotating shaft, an output linear motion shaft (screw), and support bearings, all in a housing. Three common types are:
- Machine Screw Jacks – Rotation of the input (worm) shaft turns the worm gear and drive nut. The lead screw (lifting screw or stem) has an Acme or modified square-thread form. It is threaded through the drive nut and converts rotary motion of the nut to linear motion.
- Ball Screw Jacks – The screw and nut are separated by a series of recirculating bearing balls. Higher lifting speeds and higher efficiency reduces the input power requirements to 2/3 of what is required for a machine screw jack.
- Roller Screw Jacks – Are more expensive than ball screws and commonly used in applications where load capacity, axial stiffness, speed, and acceleration and deceleration rates are stringent.
Before selecting a jack, determine:
- Number of lifting points
- Total load per jack
- Load direction (tension or compression)
- Speed at which load must move
- Distance load must move
Key Manufacturers of Linear Motion Actuators We Offer
- Danaher Motion
- Festo Corporation
- Lee Controls
- Nexen Group
- Nook Industries
- PBC Linear
- THK America
- Thomson Industries
- Warner Linear
Content on this page was created using excerpts from the Power Transmission Handbook (5th Edition), which is written and sold by the Power Transmission Distributor’s Association (PTDA). The Power Transmission Handbook is just under 400 pages and is a valuable resource for anyone involved or interested in the power transmission industry.