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Selecting the Right Linear Axis Actuator

A comprehensive guide to selecting the right Vention linear axis actuator for your application.

Selecting the Right Linear Axis Actuator main image.

Linear Actuators


Introduction

This Vention Design Tip features a comprehesive guide on selecting the appropriate linear axis actuator for your application based on available lengths, linear speed and maximum force capacity.

Vention’s belt-driven, ball screw, and rack and pinion linear actuators have been designed to simplify the design of automated equipment. Components are readily available in Vention’s 3D MachineBuilder™ and can be added to any assembly to create simple linear motion for light-duty and medium-duty applications. All linear actuators can be coupled with Vention all-in-one MachineMotion™ controller and MachineApps™ publicly available.


Ball Screw Linear Actuator Overview

Ball screw driven linear actuators are used for medium-duty applications requiring higher load and resolution.

Design and Construction

The assembly consists of a ball screw supported on each end by two angular ball bearings and support plates. The ball screw is 16mm in diameter and has a 10mm pitch. A ball nut housing connects the ball nut to the gantry plate. The outer frame consists of 45 × 90mm Vention extrusions. At one extremity of the assembly, a coupling housing provides a connection for any of Vention’s NEMA 34 stepper motors. 45 x 90 mm Vention extrusions link the two subassemblies together. Proximity sensors can also be added using an M18 sensor mounting bracket.

Available Lengths

Ball screw driven linear actuators are available in three different lengths: MO-LM-003-0585, MO-LM-003-0855 and MO-LM-003-1530, where the last four digits correspond to the linking extrusion lengths in millimeters.

Roller Wheel or Linear Bearing Configurations

Gantry loads can be supported by roller wheels or linear bearings, depending on the application. Roller wheels are made out of glass-filled nylon and use the extrusion’s V-shaped groove as guides. The linear bearings can be mounted to the same gantry plates and use hardened steel shafts directly mounted on the extrusion with support blocks. The shafts are available in the following lengths: 585, 855, 1530 and 2295mm.

Additional lengths available on request, contact support@vention.io for more info.

Exhibit 4. Internal components Exhibit 5. MO-LM-003 series shown with medium gantry, nylon wheels, stepper motor, and proximity sensors Exhibit 6. MO-LM-003 series shown with medium gantry, linear bearings and shafts

Belt-Driven Linear Actuator Overview

Belt-driven linear actuators are used for light and medium duty applications that require high speed and high acceleration.

Design and Construction

The assembly consists of two concealed timing belt pulleys, bolted at the extremities of a 45 × 90mm extrusion. The end-supports allow motor mounting options for any of Vention’s Nema 34 stepper motors on both sides. All lengths and configurations include a zero backlash steel-reinforced polyurethane timing belt. The timing belt’s open ends can be joined and tensioned using Vention’s timing belt tensioner for installation under any gantry plate. Add plastic bumpers on each end to protect the equipment. Bumpers also have a feature to mount M18 sensors for end of travel detections.

Available Lengths

Timing belt drives are listed as MO-LM-016-XXXX, where the notation “XXXX” in the part numbers corresponds to the extrusion length, ranging from 585mm to 1530mm in increments of 45mm, as well as length of 1980mm and 2295mm.

Roller Wheel or Linear Bearing Configurations

Gantry loads can be supported by roller wheels or linear bearings, depending on the application. Roller wheels are made out of glass-filled nylon and use the extrusion’s V-shaped groove as guides. The linear bearings can be mounted to the same gantry plates and use 16mm hardened steel shafts directly mounted on the extrusion with support blocks. The shafts are available in the following lengths: 585, 855, 1530 and 2295mm.

Additional lengths available on request, contact support@vention.io for more info.

Exhibit 1. Vention belt-driven linear actuator (MO-LM-016-0585) Exhibit 2. MO-LM-016-XXXX series shown with small gantry, nylon wheels, stepper motor, and proximity sensors Exhibit 3. MO-LM-016-XXXX series shown with small gantry, linear bearings and shafts

Rack and Pinion Linear Actuator Overview

Rack and pinion linear actuators are used for light and medium duty applications that require any combination of high speed, high acceleration, and high load.

Design and Construction

The assembly consists of rack segments mounted within the T-slot of Vention extrusion which mesh with a pinion. The pinion is mounted inside a housing which doubles as an enclosure for the pinion, shaft, and bearings. The housing also functions as a sturdy gantry plate capable of connecting to extrusions, assembly plates, other gantries, and many other Vention parts. The housing allows motor mounting options for any of Vention’s Nema 34 stepper motors or Vention's planetary gearbox on either side. 6061-T6 aluminum end stops protect the equipment and operator in case of actuator collision with the end stops. The end stops also have a feature to mount M18 sensors for end of travel detections.

Available Lengths

Rack segments are listed as MO-LM-020-XXXX, where the notation “XXXX” corresponds to the segment lengths of 540mm or 810mm. These lengths are designed to be installed in series to allow for a wide range of actuator lengths.

Roller Wheel or Linear Bearing Configurations

Pinion Housing loads can be supported by roller wheels or linear bearings, depending on the application. Roller wheels are made out of glass-filled nylon and use the extrusion’s V-shaped groove as guides. The linear bearings can be mounted to the same housing and use 16mm hardened steel shafts directly mounted on the extrusion with support blocks. The shafts are available in the following lengths: 585, 855, 1530 and 2295mm.

Additional lengths available on request, contact support@vention.io for more info.

Rack and Pinion series shown with linear bearings, stepper motor, and proximity sensors


Technical Characteristics

Belt Driven Linear Actuator

Ball Screw Linear Actuator

Rack and Pinion Linear Actuator

Characteristics
Typical Applications High-speed Applications
  • General linear robotic
  • High-speed vision systems
  • Robot's 7th axis (RTU)
  • Pick and place equipment
Precise, High-load Applications
  • General linear robotics
  • CNC routers
  • Handling systems
  • Automated gantries
High-speed, High-load Applications
  • General linear robotics
  • CNC machines
  • Long 7th axis systems
  • Z-axis acutator
Available Lengths 585mm to 1530mm in 45mm increments + 1980mm, 2295mm

Net displacement is equivalent to the extrusion length minus the gantry's longitudinal dimension
585mm, 855mm and 1530mm

Net displacements are equivalent to 405mm, 675mm and 1350mm respectively
Combinations of 540mm & 810mm

Net displacements are equivalent to total segment length minus 190mm to account for hosuing and end stops
Compatible Gantries
Compatible Guides Linear bearings (MO-LM-010-0001) on 16mm hardened steel shaft (MO-LM-014-XXXX)
  • Suitable for high duty cycle applications requiring minimum friction
  • Shaft available in lengths of 585mm, 855mm, 1530mm and 2295mm
  • Bearing capacity: 1kN each
Roller wheels, concentric (MO-LM-001-0028) and eccentric (MO-LM-001-0027)
  • Wheel material: fiber glass reinforced nylon
  • Mounted on 2× double-sealed deep-groove ball bearings
  • Roller radial and axial capacity: 280N each
Speed Ratio (mm/turn) 150 10 157.08
Linear Force / Torque Ratio (N/Nm) 42 565.5 40
Linear Force Capacity (N) 320 3,700 1000
Repeatibility (mm) ±0.25 (with roller wheels)
±0.025 (with linear bearings & shafts)
±0.023 per 300mm length
±0.025
Max Linear Speed (mm/s) 3,000 500 3,000
Back Drive Resistance Low High Low
Motor Compatibility NEMA 34, 14mm shaft
MO-SM-001-0001, MO-SM-002-0001, MO-SM-003-0001

Calculating Actuator Forces

It is important to calculate the forces that your machine will be subject to which includes the loads on the actuator. The forces present are dependant on the assembly but here we will discuss some basic factors to consider when calculating the forces applied to actuators.

As a general practice a safety factor should also be used to ensure that any uncertainties and variables won’t make or break the operation of an actuator. A recommended safety factor of 1.2 should be used when calculating these forces.

Horizontal actuators:

When calculating the operating loads of a horizontal actuator the main consideration is simply the payload of the actuator and how much acceleration will be required to perform the intended operations.

F = ma

Therefore, it is as simple as knowing the mass (kg) of the moving section of the actuator and its desired acceleration (m/s²). Friction in the system is a factor to consider however it is very low and is highly assembly dependant. This makes it difficult to provide a general calculation for all actuators and instead can be absorbed into the use of a safety factor.

Vertical actuators:

Lifting a mass vertically is more challenging than horizontally because the actuator must fight the acceleration of gravity, not just the desired accelerations of the actuator. The updated force calculation for vertical actuators is:

F = m(a + 9.81 m/s²)

This equation is like that used for horizontal payloads with the addition of the acceleration of gravity 9.81 m/s².

Example:
If a 2-axis system, one horizontal and one vertical, is being designed with the following performance characteristics:
- 2 m/s² horizontal acceleration
- 1 m/s² vertical acceleration
- 50 kg payload
- Safety factor or 1.2

Using these values, we can easily calculate the required horizontal actuator and vertical actuator forces:

Fh = 1.2 X 50kg X 2m/s² = 120N

Fv = 1.2 X 50kg (1m/s² + 9.81 m/s²) = 645.6N

Selecting the Right One

The figure below demonstrates a comparison of the linear force output as a function of the linear speed of the ball screw, belt-driven, and rack and pinion linear actuators.


Exhibit 7. Force as a function of linear speed comparison between the ball screw, belt-driven, and rack and pinion linear actuators. Note the rack and pinion is equiped with a 5:1 gearbox in this comparison as the parts were designed to be used together.

Observing the ball screw actuator's behaviour from the graph and table above, its maximum force capacity sharply decreases as linear velocity increases. In comparison, when observing the belt-driven actuator's behaviour, its maximum force capacity slowly declines as linear velocity increases, remaining relatively consistent at all speeds. Both actuators intersect at a linear speed of 435 mm/s, representing a maximum force capacity of 265 N. The rack and pinion, when equiped with Vention's 5:1 gearbox, provides a performance which is a balance between the other two actuators.

Consequently, if your application requires higher force capacites, higher torque, and higher precision, we recommend the ball screw or rack and pinion. If your application requires higher speeds with a large range of available lengths, we recommend the belt-driven actuator. Finally, if your application requires very long axes, or fast operating z-axis we recomend the rack and pinion.


For more help selecting your linear actuator, make sure to use the flowchart below to help you narrow down your options:


Choose your Actuator Flowchart

For more details on each actuator we recomend that you visit their respective Technical Data Sheets:
Ball Screw Linear Actuator Datasheet
Belt Driven Linear Actuator Datasheet
Rack and Pinion Linear Actuator Datasheet



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