A linear system is an assembly that moves and positions a load along a straight axis. Unlike a single linear guide, which only guides, a linear system includes all components needed for a controlled movement: guide, drive, sensors and control. Depending on the manufacturer and design, it is also called a linear axis, linear module or linear unit.
Linear systems are found in packaging machines, handling systems, medical devices and measuring systems. Wherever a tool, a sensor or a component has to be moved to a defined position, a linear system is at work.
Design of a linear system
- Guide: It carries the load, absorbs forces and moments and defines the direction of movement. Usually this is a linear guide consisting of a guide rail and a guide carriage.
- Drive: It generates the movement, for example via a toothed belt, a lead screw, a rack or a linear motor.
- Sensors:Limit switches limit the travel, position measuring systems report the position to the control.
- Control: It specifies position, speed and acceleration and controls the drive.
- Supporting structure: Profiles or base plates hold the guide and drive and connect the linear system to the machine.
Drive types at a glance
Which drive is suitable depends mainly on stroke, speed, force and accuracy:
| Drive | Strengths | Limits |
|---|---|---|
| Toothed belt | high speeds, long travel distances | medium accuracy and forces |
| Ball screw (spindle) | high accuracy, precise power transmission | less suitable for very long travel distances |
| Rack and pinion | long travel distances, high loads | moderate speed |
| Linear motor | power transmission without mechanical intermediate elements, high dynamics | usually higher costs |
How closely guide and drive can work together is shown by the application example water jet cutting machine: there, a linear motor is integrated directly into the rail profile of the Franke linear guide and moves the cutting head precisely.
Dimensioning a linear system: six steps
- Determine the load case: weight of the moving parts, machining forces and moments about all three axes.
- Define stroke and installation space: travel distance, installation height and available width. For large widths, a pair of profile rails with pair of roller shoes is a good choice because the guide width can be selected freely.
- Clarify the dynamics: speed, acceleration and cycle time. For high dynamics, the linear guide type FDH with carriage is designed with angular contact ball bearings.
- Check the environment: moisture (type FDC with carriage), magnetic fields (type FDD with carriage), food production and clean rooms (type FDE with carriage) or vacuum (type FDI with carriage).
- Select the drive: to match stroke, force and accuracy, see table above.
- Add sensors and accessories: limit switches for the end positions, cassettes with clamping to lock positions, metal scrapers against coarse dirt and cover caps for the holes in the rail.
The guide as the basis of the linear system
The linear guide determines how much load a linear system carries, how accurately and quietly it runs and how much maintenance it needs. Franke supplies this basis: linear guides made of aluminium with inserted wire raceways and large running rollers. The rolling bearings in the running rollers are lifetime lubricated, and the guide works maintenance free. More about this under The Franke principle for linear guides.
Because rails and carriages are made of aluminium, they fit particularly well into linear systems with aluminium profiles: temperature related distortions between guide and supporting structure are ruled out. At the same time, the moving mass is reduced, which benefits the drive and the dynamics. How far the weight can be reduced is shown on the page Linear guides in lightweight construction.
The entry point is the profile rail with carriage type FDA: quiet, smooth running and with sealed needle bearing running rollers. For cost sensitive linear systems there is type FDB with carriage with ball bearing running rollers.
Standard or individual linear system?
Many linear systems can be built with guides from the standard range. If installation space, weight, profile shape or material place special demands, Franke adapts rail profiles and carriages. Examples are shown on the pages Individual linear guides and Alternative materials. Answers to frequently asked questions about compatibility, speeds and maintenance can be found in the FAQ on linear guides.
Frequently asked questions about the linear system
What is the difference between a linear guide and a linear system?
A linear guide guides a load along a straight path and absorbs forces and moments. A linear system additionally includes drive, sensors and control and thus moves the load to a defined position in a controlled way.
Which drives are used in linear systems?
Common are toothed belts for high speeds and long distances, ball screws for high accuracy, racks for long distances and high loads, and linear motors for high dynamics.
What role does the linear guide play in a linear system?
It determines the load capacity, running accuracy, smooth running and maintenance effort of the linear system. Maintenance free linear guides such as those from Franke reduce the effort over the entire service life.
How do I dimension a linear system?
First, load case, stroke, installation space and dynamics are determined, then the ambient conditions are checked. This results in the guide type and the drive. Finally, sensors such as limit switches and accessories such as clamps are added.
Why are aluminium guides suitable for linear systems?
They have a low moving mass and expand with temperature changes in the same way as aluminium supporting structures. Temperature related distortions between guide and profile are therefore ruled out.
Further terms in the Franke glossary: Linear guide | Linear systems | Roller guides | Linear technology | Limit switches
Franke also manufactures linear guides individually to your specifications: Individual linear guides