This article will take an in-depth look at linear motion products.
The article will bring more detail to topics such as:
This chapter will cover the basics of linear motion products and explain the operation of linear actuators.
High-precision linear motion components are crucial in various applications, including machine tools and semiconductor manufacturing equipment. These components are designed to move objects along a straight path with minimal friction. Manufacturers have developed advanced bearings using various techniques to prevent motion from being impeded by sliding friction.
A linear actuator transforms the rotational motion of a motor into linear movement. Unlike traditional electric motors that rotate in a circle, linear actuators move back and forth. This push-and-pull action allows the device to slide, tilt, and lift objects with ease. The design provides operators with precise control over production processes. Linear actuators are energy-efficient due to their smooth operation and require minimal maintenance. They are also more cost-effective, compact, and easier to install compared to hydraulic or pneumatic systems.
Although not all linear motion designs and sizing projects will use every principle, understanding these concepts can help make more reliable and cost-effective design choices.
Some multi-axis systems offer six degrees of freedom and can support seven or more axes of motion. It's important to distinguish between "axes of motion," which refers to the system used to map movement within a Cartesian coordinate system, and "degrees of freedom," as described and illustrated below.
We typically use the Cartesian coordinate system for linear motion, but some applications, particularly those involving articulated robots, use the polar coordinate system.
Moments or torques result from a force applied at a distance. Understanding the difference between moment and torque is essential, as moment forces are static, whereas torque causes rotational movement in a component.
Yaw, pitch, and roll refer to rotational forces based on the axis around which a component rotates. These forces can lead to deflection and movement issues in linear guides.
When two surfaces with different radii contact each other under load, a narrow contact area forms, resulting in Hertz contact stresses. These stresses significantly impact a bearing's dynamic load capacity and L10 life.
The level of conformity between the ball (or roller) and the raceway affects the contact area’s position and geometry. Understanding ball conformity is crucial as it directly relates to the Hertz contact stress experienced by the bearing.
When a load-bearing ball (or roller) slips instead of rolling purely, it is due to the elliptical contact area and varying velocities along this area. This differential slip affects friction, heat, and the bearing's lifespan.
Friction, which lubrication helps to mitigate, is the primary cause of wear and often failure in linear bearings. Tribology, the study of wear, lubrication, and friction, explores the complex interactions among these phenomena.
Tension and compression loads in linear motion systems cause stress and strain in materials. These concepts are particularly important for components like fasteners, which may reach their yield point or tensile strength limit before other signs of system deterioration are noticeable.
Linear actuators move objects or machinery along a straight path with high precision and repeatability. They are designed to convert rotary motion into linear motion, which is essential when a linear movement is required from a rotary-based source.
Linear actuators work by converting rotary motion into linear motion. Most standard electric motors are rotary-based, and a flexible coupling or belt typically connects the motor to the linear actuator. This setup allows the motor to be positioned either axially or perpendicularly to the actuator, with various motor sizes available depending on the application.
In addition to rotary bearings that support the lead screw, ball screw, or belt pulleys, linear actuators incorporate linear bearings that support the moving payload. This design allows them to function as "stand-alone" devices, simplifying their integration into existing machinery and removing the need for expensive, custom-built parts.
To enhance load capacity and stability, a linear actuator system can be coupled with a payload moving between points, such as in an X,Y gantry-style stage. Typically, the two actuators in such configurations are synchronized using a shaft or belt.
This chapter will cover the various categories of linear motion products and their classifications.
The different types under the linear actuators category are:
A lead screw actuator translates rotational motion from a motor into linear motion using a simple screw and nut arrangement. Commonly used sources of rotational motion include manually operated screws or AC induction motors, which are often chosen for applications that require lower precision and are cost-effective. Compared to ball screw actuators, lead screw actuators are less efficient and have reduced capacity for "back driving." This characteristic can be beneficial in scenarios where maintaining the position of the payload when stationary is desired. They are frequently utilized in applications where safety and reliability are prioritized over precision and performance, such as in agricultural machinery and manual lifting systems.
A ball screw actuator utilizes a precision nut equipped with ball bearings that roll along a threaded screw. This mechanism is similar to a ball bearing race, where the load is carried by the rolling elements. The advantages of this design include high accuracy and low friction, making it an efficient method for converting rotary motion into linear motion. Stepper or servo motors commonly provide the rotary drive. Ball screw actuators are ideal for applications requiring rapid, repetitive motion and precise positioning, such as in machinery, scientific instruments, and medical devices.
In a belt actuator system, a carriage is attached to a belt that loops around two pulleys. As the belt turns, it moves the carriage along the actuator. The belt is driven by a motor, which is generally positioned perpendicular to the actuator and connected via a flexible coupling to one of the pulleys.
Because they lack complex motion variations, belt-driven linear actuators are often a cost-effective choice for applications needing only straightforward linear movement. They are particularly advantageous in scenarios that involve extensive travel distances and high-speed linear motion, such as in packaging and automated material handling systems.
Hydraulic actuators are commonly used when significant force is required to operate valves, such as those found in large steam systems. The piston-type hydraulic actuator is the most widely used variant. It consists of a stem, hydraulic supply and return lines, a piston, a spring, and a cylinder. The piston moves vertically within the cylinder, creating two separate chambers: the upper chamber contains the spring, while the lower chamber is filled with hydraulic fluid.
The actuator's lower chamber is linked to the hydraulic supply and return lines, enabling hydraulic fluid to enter and exit this chamber. The stem transmits the piston's movement to a valve, which is kept in a closed position by the spring when there is no hydraulic pressure. When fluid is introduced, pressure in the lower chamber increases.
This pressure exerts a force on the piston that counteracts the spring's force. If the hydraulic force exceeds the spring force, the piston rises, the spring compresses, and the valve begins to open. As hydraulic pressure continues to build, the valve opens further. Conversely, when hydraulic fluid is removed from the cylinder, the piston lowers and the valve closes, as the hydraulic force becomes less than the spring force. The actuator's capability to control the flow of hydraulic fluid allows the valve to be adjusted to various positions between fully open and fully closed.
Pneumatic actuators come in two main types: piston-operated and diaphragm-operated. These devices use compressed air to generate the necessary force for operation. The air pressure acts on the piston or diaphragm, creating mechanical motion that moves the valve actuator along the valve stem. Pneumatic linear actuators are favored for two primary reasons: the safety of using air compared to other gases and the ease with which air can be compressed and managed.
Due to these advantages and the precise control over the conversion of compressed air into mechanical movement, pneumatic actuators are widely used in the industrial manufacturing sector.
Servo actuators are designed to provide precise position control using linear motion to ensure the correct functioning of other mechanisms or equipment. At its core, a servo operates by responding to feedback that corrects errors. A typical servo actuator consists of three main components: a servo motor, a set of gears, and an output bearing. These actuators can be powered through electromechanical, pneumatic, or hydraulic means, with electromechanical and pneumatic options being more commonly used than hydraulic ones. The choice of actuation type depends on the specific requirements for power, speed, and precision in the application.
Valve actuators are mechanisms that utilize various screw assemblies to enable linear motion in valves. This linear movement is often employed to adjust the valve's position, or to open and close it as needed. Valve actuators are used with a wide range of valve types, including metering valves, needle valves, globe valves, diaphragm valves, gate valves, pinch valves, and angle valves, among others.
The different types of linear guides are:
A ball rail system (BRS) consists of a guide rail and runner blocks. The system features four rows of balls arranged in an O-shaped configuration with a 45° contact angle. One or more runner blocks travel along one of the guide rail's four tracks. The guide rail can be mounted either from above or below, and V-guide rails are typically pressed into the base for secure installation.
The runner block is designed with either through-bores or threaded holes, allowing for direct attachment to adjacent structures based on specific requirements. Ball runner blocks come in various sizes, configurations, and preload options, making them versatile for different applications. Among profiled rail systems, the ball rail system stands out for its exceptional adaptability.
Linear roller guides operate similarly to other linear rails but utilize rollers instead of balls within their four raceways. This design provides a significantly larger contact area between the rail and slider. Roller slides are an effective type of linear-slide system for moving machinery or equipment. They are often noted for their quiet, low-noise operation, minimal slippage, and durability. Roller slide bearings, or roller tables, are commonly used in applications requiring high precision and consistent movement, such as in food processing and automotive manufacturing.
A miniature version of the ball rail system has been developed to meet the needs of applications requiring compact ball-bearing longitudinal guides with high load capacities. This new design accommodates a wide range of ball diameters, ensuring consistent load ratings in all four directions. The system's excellent load-bearing ability in every direction helps to manage torque around the axes effectively. It features low friction and optimal performance. Both the runner block and the guide rail are made from martensitic steel, known for its corrosion resistance.
Unlike recirculating bearings, which come with a fixed preload determined by ball selection, cam roller guides require user-defined preload before installation. This allows for adjustments to maintain rigidity, speed, and performance as conditions change or components wear over time. The ability to adjust preload also ensures that bearing blocks and guide rails remain interchangeable, simplifying the process of replacement.
Linear motion products are essential components in the automation of transfer, positioning, and assembly machinery. To effectively utilize linear bushings, it is important to compare and understand the three main types of linear guides: linear bushings, slide guides, and oil-free bushings. Performance can significantly vary based on the load capacity of these components. For example, a machine using linear bushings or oil-free bushings on a shaft supported at both ends can experience elastic bending of the shaft due to the load.
A linear shaft is a precisely machined straight bar that serves as the foundation for a linear guide system, supporting or directing equipment movement in a linear manner. These shafts are compatible with various linear bearings and can be made from materials such as aluminum, 303 stainless steel, 316 stainless steel, hardened steel, and hardened stainless steel.
The different types of screw drives are:
The ball screw assembly consists of a screw, a nut, and balls that roll between the helical grooves of the screw and nut, providing the sole point of contact between these components. As the screw or nut rotates, the balls are guided by a deflector into the ball return system within the nut. They continuously travel through this return system to the other end of the ball nut. From there, the balls re-enter the raceways of the ball screw and nut, circulating in a closed-loop system.
Also known as roller screws, Planetary Screw Assemblies (PLSAs) are advanced, cost-effective screw drive systems that use precisely ground threaded rollers (planets) orbiting around the screw to convert rotational motion into linear motion. Their compact design makes them easy to integrate into applications requiring high load capacity, precision, and minimal environmental impact.
Various types of ball transfer units and tolerance rings include:
Ball transfer units consist of omnidirectional spherical balls housed within a restraining device. Functioning similarly to a computer trackball, they often feature a large central ball supported by several smaller bearings. These units are commonly used in an inverted position as part of conveyor systems, enabling efficient transfer of items between machines and different conveyor sections. They are prevalent in industrial settings and airports for handling goods and luggage.
Tolerance rings are specially designed components with wave-like features that secure cylindrical mating parts. As the tolerance ring is installed between the parts, the waves compress to hold them in place. Each wave acts as a spring, providing increased compression and force to ensure the components remain securely connected while meeting performance standards such as load-bearing requirements.
Linear axes come in various types, including:
Compact modules are characterized by their small size and high power density. Their distinctive feature is a relatively flat design, with a width-to-height ratio of approximately 2:1, making them easily recognizable externally.
A linear module is a mechanical device designed to generate linear motion, which can be oriented both vertically and horizontally. These modules can be combined to form complex motion systems, such as the X,Y axis or X,Y,Z axis configurations used in automation. Typically paired with a power motor, linear modules enable the creation of automated conveying systems by mounting workpieces on the slider and programming the motor for forward and reverse motion. This setup facilitates mass production and efficient manufacturing processes.
Precision modules are high-precision drive units known for their compact size and robust performance. They feature integrated ball-rail technology that ensures optimal travel, high load capacities, and exceptional precision. Equipped with a ball screw assembly and a backlash-free nut system, these modules offer precise positioning and repeatability. They also incorporate a double-floating bearing system and large screw diameters, enabling rapid movement while maintaining high accuracy.
Ball rail tables provide precise, pre-installed guiding systems within a compact format. Their modular design and favorable price-to-performance ratio make them versatile for various applications. Available with ball screw drives or as fully-integrated linear motor systems, these tables offer flexible configurations and high precision. The direct thrust on the load ensures dynamic and accurate movement without the need for mechanisms to convert rotary motion into linear motion, resulting in substantial stiffness.
Omega modules (OBB) are designed to achieve speeds of up to 5.0 m/s using ball rail systems with toothed belt drives. These modules are customizable and can be installed in various positions, with lengths extending up to 5,500 mm. Their design is particularly suited for applications where the frame extends into the working area, providing flexibility in installation and operation.
Feed modules are precise, ready-to-install linear motion systems that offer high performance in a compact form factor. They are ideal for tasks requiring significant force and torque transmission while maintaining high precision. Feed modules are especially effective for vertical motion in Z-axes due to their low moving system mass.
Linear slides, also referred to as linear guides or linear-motion bearings, facilitate smooth, frictionless movement along a single axis. These components are crucial for machine tools, robotics, actuators, sensors, and other mechanical systems that require straight-line motion across any of the three-dimensional axes. Friction, which opposes free translational movement, arises from the interaction between moving bodies and the surface they contact. The amount of frictional force depends on the load applied and the coefficient of friction, which describes the surface's resistance to movement.
A ball screw consists of a shaft, a nut with balls, and a bearing. The balls facilitate the transfer of force between the screw and the nut, efficiently converting rotational motion from a motor into linear motion. This makes ball screw units a common choice for driving components in various linear guide systems. Typically, when the shaft is powered, the nut is attached to the moving component. However, there are cases where the screw itself moves linearly while the nut is driven.
Linear actuators play a crucial role in linear-motion control by covering a wide range of applications. These mechanical devices generate linear motion by converting energy from various sources, such as air, electricity, or hydraulic fluid, into straight-line movement.
Multi-axis systems are designed with various combinations of directly-driven linear modules, differing in type, size, and configuration. The choice between two-axis setups or three-axis portals depends on the specific automation task. These systems come in various sizes tailored to application requirements, including load capacity, stroke length, dynamic performance, and positioning speed. Multi-axis systems offer at least two linear movements for precise placement. Multiple series are available to suit different applications. Successful integration of these systems relies on high precision, repeatability, and dynamic movement accuracy. With rapid control cycles, multi-axis systems facilitate exceptionally accurate cutting and positioning tasks.
Captive linear actuators, often referred to as electric cylinders or electromechanical cylinders, are designed as modular systems. These electric cylinders are increasingly replacing pneumatic cylinders across various industries due to their lower maintenance costs, enhanced motion control, and numerous additional benefits. They feature internal guiding and anti-rotational mechanisms, making them well-suited for z-axis and dual-axis (z-theta) applications. Additionally, the tubular design of electric cylinders shields the leadscrew or ball screw from debris and environmental factors, allowing them to operate effectively in demanding conditions.
This chapter will explore the various factors to consider when selecting linear motion products.
Typically, considerations for selecting linear motion products can be categorized into the following areas:
Generally, a ball screw or linear motor-driven system is preferred for applications requiring high precision or repeatability. Conversely, a belt or pneumatic actuator might be considered a viable option for applications with lower accuracy requirements. However, relying solely on these generalizations could lead to a system that is either underperforming or excessively expensive.
Several factors influence a system's precision and repeatability, including gearboxes, couplings, connecting shafts, deflection, and temperature variations. To determine the required accuracy and repeatability of a linear system, it is essential to consider these elements along with the type of feedback and control systems used. For instance, a typically lower-accuracy device, such as a belt-driven actuator, can achieve high precision and repeatability by incorporating external feedback mechanisms like linear scales. Additionally, basic servo controls can compensate for expected errors in travel, such as lead deviation in ball screw drives.
In gantry and Cartesian systems, typically only the base (often referred to as the "X" axis) is fully supported. In gantry configurations, the "Y" axis is usually mounted only at the ends, leaving a substantial portion of the length unsupported. Similarly, in Cartesian setups, the secondary horizontal axis (commonly the "Y" axis) generally has support at one end and is only partially supported along its length.
Unsupported actuator deflection can lead to binding and premature wear. To calculate beam deflection, it is often sufficient to model the actuator as a beam with either a point load or a uniform load. You can then compare the calculated deflection with the maximum deflection recommended by the manufacturer.
Contaminants such as dirt, dust, chips, and liquids can adversely affect the performance of a linear system. To protect against these, use systems with robust seals or covers, such as linear actuators with well-maintained enclosures. Alternatively, positioning the system horizontally or vertically can prevent contamination. However, note that the actuator's orientation will influence the loads and forces on the drive and guiding mechanisms.
Temperature variations, often overlooked, can also impact performance. Materials may expand or contract with temperature changes, potentially causing issues in environments with significant temperature fluctuations, either due to ambient conditions or the operational process. For example, aluminum expands about twice as much as steel, which could lead to binding or excessive stress if an actuator with an aluminum base and steel guides is used in an environment with extreme temperature shifts.
Linear actuators can be mounted using various methods, such as clamps on the sides, holes in the base, or slots in the housing. The chosen mounting method can affect both deflection and the space required for the actuator. In high-precision gantry or Cartesian setups, actuators might also be pinned to ensure accurate parallelism and perpendicularity between axes. Additionally, the mounting arrangement impacts ease of maintenance and replacement; a system that is easier to install and remove will reduce downtime and simplify upkeep.
Most actuators require basic lubrication, involving the application of grease or oil to contact points between metals. Centralized lubrication, through one or more ports that distribute lubricant to all necessary parts, is often the simplest approach. However, some designs may not support central lubrication, necessitating individual lubrication of each component. This can be inconvenient, potentially leading to insufficient lubrication and future costly problems.
Consider the actuator’s lubrication access when planning maintenance. If side lubrication ports are obstructed by other components, alternative lubrication methods or mounting configurations may be required.
This chapter will explore the various applications and advantages of linear motion products.
Some machines, which are often utilized in machine tools and equipment for producing semiconductors, are built with high-precision linear motion products. The core purpose of linear motion products is, simply, to help move products along a straight line. High-performance bearings have been developed by numerous manufacturers using various techniques to help prevent motion from slowing down as a result of the friction that occurs during sliding.
The rotating motion of a motor is transformed into a line of motion by a linear actuator. While traditional electric motors revolve in a circle, linear actuators move in forward or reverse directions. Their push and pull motions allow these gadgets to slide, tilt, and lift things with the touch of a button. Because of their design, operators have precise and accurate control over the production process.
A linear actuator is a device that transforms rotational motion into push or pull linear motion, which can then be used to lift, lower, slide, or tilt machinery or materials. They offer effective, maintenance-free motion control...
Electric actuators are devices capable of creating motion of a load, or an action that requires a force like clamping, making use of an electric motor to create the force that is necessary...
A linear actuator is a means for converting rotational motion into push or pull linear motion, which can be used for lifting, dropping, sliding, or tilting of machines or materials. They provide safe and clean...
A linear actuator actuates, moves, in a linear, straight, line to complete or start a process. There are a variety of terms used to describe a linear actuator such as ram, piston, or activator. They are very common in...
Ball screws are mechanical linear actuators that consist of a screw shaft and a nut that contain a ball that rolls between their matching helical grooves. The primary function of ball screws is to convert rotational motion to linear motion. Ball nuts are used in...
A lead screw is a kind of mechanical linear actuator that converts rotational motion into linear motion. Its operation relies on the sliding of the screw shaft and the nut threads with no ball bearings between them. The screw shaft and the nut are directly moving against each other on...
Linear bearings are a type of bearing that "bear" or support the load of the carriage during its single-axis linear movement and provide a low friction sliding surface for the guide rails. In a linear guide, the carriage is the component that travels in a straight line, back and forth, along the length of the guide rail...
Linear Rails are ideal for moving items through a production process with great precision and as little friction as possible if creating, packing, and distributing products. Linear Rail is a type of gadget that...
Linear slides, also referred to as linear guides or linear-motion bearings, are types of bearings that allow smooth and near-frictionless motion in a single axis. Machine tools, robots, actuators, sensors, and other...
A roller table is a small, stiff, limited linear guide device with an integrated cross-roller guide. Electrical or mechanical drive systems are frequently used to move a roller table, making it easy to transfer heavy loads...