Linear Motors and the Opportunity for Complex Assembly Automation


Our customers look to us to design and build systems to automate their most complex assembly processes.  Installing instrument panels into cars, loading seats into SUVs, and securing windshields to truck cabs are all critical operations that have the potential for full automation if the right drive system is selected and configured for the application.  At Eckhart, we tackle dozens of these big projects every year and believe that linear motors are the drive system that’s unmatched with respect to precision, speed, and uptime.  In this blog post, we review linear motor technology and highlight specific applications in complex assembly where a linear motor makes sense.


What is a linear motor?


A linear motor is a class of servomotor that uses magnets laid on a track to produce a linear force as opposed to a torque, such as in a traditional rotary motor.  When coupled with an encoder for positional feedback, a linear motor becomes a drive system that can precisely navigate a load along an overhead rail or gantry.  Linear motors have the speed and precision of a robot and are capable of moving loads greater distances than the reach of even the largest robot.   

While linear motors are at the heart of high-tech systems like maglev trains, their use in industrial applications dates back to the mid-1980s.  All major automation component suppliers like Rockwell, THK, and Danaher consider linear motors a core product offering.  

Linear motors are the preferred drive system for automating processes that require precision, speed, long travel distance, and often heavy loads.  Key advantages include: 

  • Mechanical simplicity – Traditional rotary drive systems (e.g. belt drives, rack & pinions) require a rotary-to-linear force conversion mechanism which adds inertia, friction, backlash, and mechanical complexity to an automation system.  Linear motors have no contacting parts and directly generate a one-dimensional force which results in a simpler, lighter, and lower maintenance drive system.
  • Faster acceleration & higher traverse velocity – Whereas the ability for traditional rotary drive systems to generate a linear force is governed by gearing and transmission components, the force produced by linear motors is governed entirely by electrical transmission.  An automation system’s ability to accelerate and brake is now controlled by the gain and current from the voltage bus and not gearboxes and leadscrews.
  • Smoother motion -  The lighter system weight, on-board encoder, and lack of kludgy mechanical transmission allow for motion profiles that are perfectly smooth and precise.  Linear motors instill confidence in plant personnel that complex movements of high loads can be executed with a high degree of precision and safety. 

 
Where in the manufacturing plant do linear motor drive systems make sense? 


A linear motor drive system can replace any process where an operator is maneuvering a heavy load within a station or cell.  Two linear motors can be placed orthogonal to one another to create high precision and high speed XY-plane navigation.  Unlike a robot with a limited range, linear motors operate on a track that can be extended to any length needed.  
Linear motors are the best drive system option for companies looking to automate:

  • the placement of windshields, seats, and instrument panels into vehicles
  • assembly operations that need to track a moving line.  Eckhart uses linear motors to automate how a large automaker secures wheel lugnuts to vehicles on a continuously moving line.
  • the transfer of parts from one build line to another.  For example, moving a large truck frame from a fixed pallet to a rotating carrier typically occurs over a large distance and with a need for precision that requires one or sometimes two operators.  A material handling system with a linear motor drive system can eliminate the need for operator involvement.
  • quality inspection equipment like scanners and cameras that need to travel with fast moving conveyance.  A large home appliance company uses two linear motors to position a camera in 6 unique locations on a water heater line that has a 12 second takt time.  

 

Other considerations

We’ve found that the Total Cost of Ownership of linear motor applications represents a more cost effective drive system option than traditional rotary motors.  None of the linear motors currently on the market specify a mean time between failure (MTBF) due to the lack of contacting components.  On the other hand, a typical MTBF for an equivalent rack & pinion system is 25,000 hours.   

As the price of linear motors decreases, they become a viable option for use in systems where the operator will remain involved.  Operators appreciate that linear motors are quieter than their rotary counterparts and that the motion profile for maneuvering heavy loads feels truly “zero G”.  

At Eckhart, we expect to see linear motors take on a greater role as the drive system of choice for complex assembly operations.  Connect with us through our website or at info@eckhartusa.com to see if linear motors make sense for your application.