The Basics of the Electric Linear Actuator

tech talk art O ne The Basics of the Electric P Linear Actuator

What is an electric linear actuator? drive spindle. These types of electric trial and medical grade columns are linear actuators are typically worm designed for applications such as medi- • An electric linear actuator is a device gear driven. These motors have fewer cal and bariatric beds and height-ad- that converts the rotational motion of gear ratio options, however because of justable industrial work stations, where an electric motor into linear motion that they are more efficient than spur worker and patient safety is essential. (push or pull movement). gear driven motors and operate with Our office ergonomic columns come in • It can be used anywhere a machine low noise. In addition, one of the key various colors, shapes, orientations, as pushes or pulls a load, raises or low- benefits of a worm gear driven, right well as 2 or 3 stages for BIFMA compat- ers a load, roughly positions a load, or angle electric linear actuator is in- ibility depending on user preference. rotates a load. creased self-locking ability. By Jon Mueller, Tyler Pocock, and Components of an Electric Linear Actuator Samantha Rosenfeld - TiMOTION

C There are many components and options to an actuator. We will discuss a new subject in each section related to the basics of an electric linear actuator C. Inline Actuators - An inline actuator and the factors to consider when pur- has a longer retracted length, but is de- chasing. In this section of the article signed specifically to fit into smaller or we will discuss the common styles and compact spaces. The inline actuator is configurations, and review the internal typically made up of a motor, planetary and external components of a linear ac- gear assembly and drive spindle. These tuator. Then, we will cover the safety re- usually operate at a higher noise level. lated options that can be added and ex- plain the various load and speed char- acteristics to consider and how it can be adjusted to meet your applications’ needs. We will follow that with the various levels of IP ratings an actuator can have for liquid and dust protection as D well as lubrication used, as well as consider the certifications and standards 1N050 Linar Drive D. Gear Motors - Gear motors allow for La Fox, IL 60542 that are needed to meet certain market economical and flexible designs, when Ph:630-208-9343 and country requirements. Lastly, we matching them with various external www.bitorq.com will discuss the importance of feedback spindle assemblies. The compact de- sensors in electric linear actuators. sign is typically worm gear driven and PRODUCTS TO SUIT ANY INDUSTRY Common Styles of Actuators an excellent choice for mechanical synchronization. AND A VALVE FOR EVERY TANK There are various styles of linear ac- E. Safety Stop - Located on the end of tuators that are all interchangeably Re-settable customizable to fit a customer’s ap- the spindle, its function is to prevent Block Valves plication needs. Some common styles the inner tube from overextension. of electric or electromechanical linear actuators include:

Automated F. Linear Slide Actuator - This actuator A Valves style creates a linear movement without the use of an outer tube. It uti- lizes a plastic slide mechanism which A. Parallel Drive Actuator - The motor travels across the actuator, attached is directly parallel to the drive spindle. to the frame of common household Typically, these types of electric linear furniture, such as power recliners and actuators are spur gear or belt driven couches. A slide actuator can even be with more gear ratio options. Parallel Thermal used in some medical furniture be- drive actuators allow for a wider range Shut-off Valves cause of its 60601 certification. of loads and speeds; however, they Sampling can operate louder than worm gear Valves driven actuators.

BI-TORQ Valve Automation’s unique group of products can be installed in any G modern industrial facility. From our industry leading thermal shut-off valves (FLP) and our innovative re-settable block valves (R-EBV), to our full suite of automated ball and butterfly valves, we have you covered. G. Electric Lifting Column - Lifting columns can cater to the industrial, medi- As part of the Strahman Valves family, we now offer a comprehensive line of B piston-style sampling valves. Available as stock items and with customizable cal, and ergonomic markets. The prima- options, you can be sure of the right fit for your application. ry advantage of a column is its ability to B. Right-Angle or “L” Drive Actuator - vertically lift high loads while retaining Contact us to start the conversation on how we can provide you a solution. The motor is set perpendicular to the a high degree of stability. Our indus-

18 Valve World Americas | February 2017 • www.valve-world-americas.net tech talk

Components of an Electric 2. Rotor: Also known as the armature Direct Current Motor Components Linear Actuator is the inner part of the motor which rotates. The rotor is mainly made up A. Front / Rear Clevis - Attachments on of silicon steel laminate, motor shaft, the front and rear of the actuator that al- commutator, and copper windings. low it to be mounted to the application. 3. Commutator: The commutator is Types of attachment styles include round, a pair of plates attached to the motor U-shaped (or slotted) or with a punched shaft. These plates provide two connec- hole. Clevises can be customized to best fit the application they are being used on. tions for the coil of the electromagnet. The commutator is used to reverse po- B. Outer Tube - Also known as the cover larity of current in the motor and essen- tube. This extruded aluminum or steel tially keep the motor rotating without tube protects the outside of the linear losing torque. actuator and houses all of the inner components of the actuator. 4. Carbon Brushes: Carbon brushes use sliding friction to transmit electri- C. Inner Tube - Also known as the exten- cal current from the stator to the rotor sion tube, drive tube, translating tube in the motor. or piston. This tube is usually made out of aluminum or steel. While retracted, 5. Motor Shaft: The motor shaft con- the inner tube is where the spindle is lo- nects the gear motor to the bottom of cated. It is attached to the threaded drive the stator on the DC motor. nut and extends and retracts when the 6. Output / Feedback Sensors: Output F. Manual Release - The manual release nut moves along the rotating spindle. (or feedback) sensors are used to com- is designed primarily for a medical patient hoist system. The manual release D. Spindle - Also known as the lead municate the actuator’s stroke position. allows the extension tube (inner tube) screw, rotating screw or lifting screw. The feedback that it gives is sent to the to release from the front attachment This part of the linear actuator rotates, control box MCU (micro control unit). (clevis) and spin freely. This allows the H extending or retracting the nut/inner Linear actuators with position feedback linear actuator to back-drive freely and tube, which creates a linear motion. are typically required when an applica- for a patient to be manually lowered Our steel spindle ensures durability and tion requires high level functions such from the patient hoist system. strength. The spindle can be threaded as synchronization and memory posi- motor shaft depending on whether the in different ways for various load and tioning. Additional details of this will be application will be pushing or pulling the speed capabilities. Additional details of covered in another section. F load. The motor brake gives the electric this will be covered in another section. actuator the added durability that en- Optional Safety Features sures longevity of the actuator. E. Safety Stop - Located on the end of the spindle, its function is to prevent Depending on the environment and the inner tube from overextension. duress that the actuator will be operat- ing in and undergoing, it is wise to re- J F. Wiper - A sealing component at- inforce the stability and strength of the tached to the end of the outer tube actuator. Some safety feature options G. Manual Crank - which prevents contaminants like dust to consider are: G and liquids from entering the spindle The manual area of the actuator. It also ensures a A. Overload Clutch - The overload clutch is crank is a safety proper seal between the inner and out- a built-in device that slips when the elec- feature designed J. Electromechanical Brake - The electro- er tubes which influences the IP rating tric actuator reaches a pre-set load limit. mainly for the mechanical brake slows or stops the mo- of the linear actuator. The overload clutch connects and dis- medical industry. connects the motor from the lead screw. It allows a medical tor using electromagnetic force to apply G. Drive Nut - The nut, which can be acme This slippage prevents the linear actuator practitioner to mechanical resistance to the spindle. or ball, is attached to the inner tube and from incurring possible damage. manually operate the The electromechanical brake is also in- travels along the spindle. The nut is the bed position in case stalled on the bottom of the motor shaft. component that allows extension or re- B. PTC Thermistor - A PTC Thermistor es- of emergency or K. Mechanical Brake - A mechanical traction of the inner tube. It can be made sentially acts as a fuse which cuts the power outages. brake can be added to reinforce stability of metal or plastic and is sometimes power to the motor, protecting the mo- keyed to prevent inner tube rotation. tor from overheating and burning out. H. Spring Coil Brake - A spring coil of the actuator when back drive can pos- Our electric motors have a UL certifica- brake is installed and wrapped around sibly be a factor with high weight loads. H. Limit Switches - Limit switches con- tion option that includes a PTC Thermis- the worm gear. It is a unidirectional no- trol the fully extended and retracted tor installed inside. back type brake that is activated auto- position of the inner tube by electri- matically by pinion winding and then cally cutting current to the motor. These C. Safety Nut - A safety nut is essen- For Part Two of this article please released when the motor turns. switches prevent the actuator from over tially a metal reinforced acme drive nut check out the March issue of extending or over retracting. In addition used to help the linear actuator support I. Motor Brake - The motor brake is in- Valve World Americas journal. to cutting current, limit switches can a higher load. A safety nut is recom- stalled either on the top or bottom of the also be used as a signal sending device. mended for loads of 6,000N or more. Many electric actuators also have the I. Gear - A gear is made of steel or plas- option to add this feature to ensure the tic and mates with other gears to alter strength and integrity of the product. the relation between the speed of a About the Authors driving mechanism (such as the engine D. Push-Only Nut - A standard drive nut of a vehicle) and the speed of the driv- will have threads to screw into the ex- Jon Mueller is Global Business Development and Market- en parts (the vehicle’s wheels). The gear tension tube whereas a “push only” ing Manager for TiMOTION. His primary responsibility connected to a power source, such as nut won’t have threads. This prevents is the strategic management of TiMOTION’s business de- the motor, is called the “drive gear”. obstructions (animals, people, other furniture, etc.) from being damaged by velopment and marketing strategies in Europe, Asia and J. Motor Housing - The motor housing a retracting linear actuator system. This North America. He works out of the TiMOTION USA office contains all the internal parts to the can be helpful for example in a recliner, based in Matthews, North Carolina. gear motor without leaving anything where if the foot of the recliner is going exposed for external damage. Many from an extended to retracted position motor housings are typically made of and there is an object below the feet of high quality plastic. Tyler Pocock is a Business Development the chair. The foot of the chair will not Associate for TiMOTION’s North American K. DC Motor - The DC (Direct Current) continue to push force on the object it market. He also is currently located in motor is where all the power is gen- comes into contact with. Matthews, North Carolina. erated for the electric linear actuator. E. Quick Release – A handle or cable There are several types of DC motors, which allows the actuator to be quick- including brushed DC motors which are ly back driven when it is released. The composed of: quick release is designed mainly for Samantha Rosenfeld is a Marketing Associ- 1. Stator: The stationary, outside por- medical bed applications for when the ate for TiMOTION’s North American office. tion of the motor made up of the motor back rest of a medical bed needs to be She is also working out of the Matthews, housing, two permanent magnets, and quickly laid flat (in case of emergency North Carolina office. motor caps. The stator generates a sta- CPR). Our medically certified linear ac- tionary magnetic field that surrounds tuators can come with this option, de- the rotor. pending on the application needs.

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