Want to know how to choose a linear actuator? First, understand the common types available on the market, then combine that with your specific needs to find the most suitable one.
Linear drive is about moving a load along a straight line, and there are many methods. The characteristics and performance of each actuator are closely related to its core technology. Below, we'll discuss six common commercial linear actuators and how to choose the right one.
1. What is Linear Motion?
Simply put, linear motion is movement along a straight line, which can be clearly explained using a single dimension. It can be uniform (constant speed or no acceleration) or variable (variable speed or acceleration), and the direction can be up and down, left and right, or any angle.
2. Six Common Linear Actuators
There are six main types:
- Pneumatic cylinder (piston rod or slider type)
- Hydraulic cylinder (piston rod type)
- Screw-driven actuator (rod or slider type)
- Belt-driven actuator (slider type)
- Linear motor (slider or rod type)
- Telescopic actuator
These technologies can all be made in rod or slider styles. Different styles have different performance characteristics and are suitable for different scenarios.
2.1 Carrier Type
This type of actuator has a carriage (or slider) supported by guide rails fixed at both ends. The guide rails can be round, profiled, or other structures that can support the carriage and withstand the torque it generates. Applying force to the carriage causes it to move back and forth along the guide rails.
2.2 Rod Type
This type consists of a rod (usually round) with a bushing at the front end, allowing it to extend or retract from the housing. This type can only push or pull loads along the direction of the rod and cannot withstand lateral forces or torques.
3. Power Source: How is the actuator driven?
Whether it's a slide-type or rod-type actuator, the power source (fluid/air or electricity) is crucial.
Hydraulic and pneumatic actuators rely on hydraulic oil or compressed air—sent to the actuator via a pump or compression system, and then controlled by control elements to adjust the flow and pressure, generating force and motion.
Electric actuators, on the other hand, receive electricity from an amplifier/controller, which adjusts the motor's current and voltage to generate force and motion.
Generally, the power and control equipment is housed in a control cabinet or machine room, supplying power to the actuator via hoses, valves (for hydraulic/pneumatic actuators) or cables (for electric actuators). With technological advancements, it's increasingly common to integrate the drive and actuator into a single unit.
Linear motors come in various types, including coreless flat-plate, coreless T-type or U-slot, and tubular types.
4. Comparison of Six Actuators
4.1 Pneumatic Cylinder
After the invention of the compound air compressor in 1829, people began to use air pressure to move things; in 1867, New York even had a pneumatic subway, using air pressure to push the carriages. Pneumatic cylinders are still commonly used in industry today.
A pneumatic cylinder uses air to drive a piston, causing a rod- or carriage-based structure to move back and forth. It is a mature technology, simple in structure, and inexpensive, but its advantages and disadvantages are also obvious:
- Common applications: stamping, simple and quick moving of objects, or places with large impacts.
- Advantages: Low initial investment in basic applications; with advancements in compressors, valves, and control circuits, it can run very fast and accelerate quickly.
- Disadvantages: Not suitable for precise positioning, consumes more electricity than other technologies, and has high long-term operating costs.
4.2 Hydraulic Cylinder
Hydraulic technology is similar to pneumatics, developed during the Industrial Revolution. Around the 1650s, Blaise Pascal discovered that pressure could be transmitted through fluids. Early manually operated pump-driven hydraulic cylinders were used in cranes and presses.
Hydraulic cylinders use fluid to drive a piston, causing a rod-like structure to move back and forth. The technology is mature, simple, and inexpensive. Its characteristics include:
- Common applications: Suitable for extremely high-force stamping (push or pull), large impacts like those from bulldozers, and large industrial tractors.
- Advantages: Durable, long-term use with proper maintenance, low initial investment.
- Disadvantages: Requires a large space for fluid storage and pumping equipment; high noise level; low efficiency; potential for oil leaks, causing maintenance problems and environmental impact.
4.3 Lead Screws in Screw Drives
There are three types of lead screws in screw drive actuators: roller screws, ball screws, and trapezoidal screws. Each type has different characteristics and costs, and the screw's "lead" (how far it travels per revolution) also differs. For example, a 5mm lead means it travels 5mm per revolution. The appropriate lead screw must be selected based on the required motion of the application.
- Roller Screws: Introduced in the 1960s, they use a planetary structure to distribute the load over a larger area. They have a long lifespan and can reach speeds of up to 60 inches per second. They are expensive, but offer excellent load capacity, speed, and durability.
- Ball Screws: Patented in the late 19th century, they add balls to the nut of a traditional screw, reducing friction, resulting in high efficiency and less wear. They are now commonly used in various industries, but their speed is slower than roller screws, approximately 24-30 inches per second.
- Trapezoidal Screws: These may have existed as early as 234 BC in ancient Greece, becoming widespread after the Industrial Revolution. They are inexpensive but less efficient, and can self-lock, making them suitable for vertical applications (ball and roller screws can be reversed, making them unsuitable for vertical self-locking).
4.4 Screw Drive Actuators
Unlike pneumatic/hydraulic actuators which rely on fluid pressure, screw drives rely on mechanical levers: the motor rotates the screw, and the nut moves accordingly, converting rotation into linear motion.
- Suitable Scenarios: Load handling requiring precise control of position and speed, such as machine tools, packaging machines, and factory automation equipment.
- Advantages: Available in various sizes to handle diverse loads; performance close to hydraulic systems under heavy loads; no need for additional air compressors or pumps, easy to install; simple maintenance, requiring only regular lubrication and inspection; motor-driven, high efficiency.
4.5 Belt-Driven Actuators
Like lead screw actuators, belt actuators are driven by electric motors. However, instead of a lead screw, belt actuators use a belt and pulley system. Linear force is generated by connecting the belt and pulley system to the rotational motion of the electric motor. As the belt rotates back and forth between the pulleys, it is converted into linear motion.
- Suitable Applications: Belt drives are an excellent choice for high-speed indexing applications requiring position and speed control, such as multi-axis Cartesian coordinate systems and long-span gantry systems, but are not recommended for stamping applications.
- Advantages: High speed, rapid acceleration, and high efficiency; while some types of belts may stretch over time, material improvements and new belt technologies have mitigated this issue. Many belt drives are equipped with pre-tensioned belts. With proper maintenance, belt drives can operate for extended periods.
4.6 Linear Motor Actuator
Directly driven, without mechanical transmission components. The load is directly connected to the slider assembly and driven by the linear motor itself. Generally, a brushless servo motor is used, with position controlled by a linear encoder.
- Suitable Scenarios: Can replace belt/screw drives or hydraulic/pneumatic drives, especially suitable for multi-axis equipment requiring rapid movement, rapid stopping, and high precision.
- Advantages: High speed and acceleration (depending on current and guide rail capacity); compact structure (no transmission components), allowing for thinner designs to save space; low power consumption, no hydraulic oil required, more environmentally friendly.
4.7 Telescopic Actuator
Similar to a lever actuator, but can extend to 2-3 times its retracted length, achieved through internal segment extension. Generally used for lifting, pushing, or retracting objects.
- Drive Method: Can use lead screws or belts (with servo or stepper motors), or pneumatic or hydraulic.
- Common Scenarios: Lifting or lowering loads, pushing parts into or pulling them out of machines.
- Features: Capable of handling medium weights; robust structure and long lifespan when driven by a lead screw or belt; however, it may misalign due to torque at its maximum extension, making it unsuitable for horizontal use.
Summary
When selecting a linear actuator, do not only consider price or a single parameter, but also take into account load size, stroke length, operating speed, positioning accuracy, installation space, maintenance costs, and working environment. If you have any questions, please feel free to contact us!