Linear Motors vs Servos

  • I am trying to do a solder jetting application like this:

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    I thought cartesian robot will be best for this kind of application. I found this robot that uses linear encoders with servo motors:

    PrecisePlace_2300_pdf.pdf


    I called the jetting manufacturer and they weren't very confident on this working with their head because it didn't have linear motors. When I lookup linear encoder cartesian robots they seem to have same resolution 0.008mm vs 0.01mm. Signal needs to be pulsed in under 10ms. I am trying to understand the benefit of linear motors vs servo. They both seem fast and accurate to me? Not sure which one will last longer and have less vibration. The manufacturer was highly against belt driven systems.

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  • you do not seem to understand meaning of the term 'servo'.


    practically that it is any device that uses feedback to perform some sort of motion control. different types of servo exist and linear motor is just one of many variants of servos. in other words your question makes no sense - "what is difference between servomotor and servomotor?"


    any device means literally any device, regardless if operates using electricity, or hydraulics, or steam or, or something else. cartoons showing use of a carrot to control donkey pulling cart is an example of servo function. donkey is the motor and carrot is part of feedback.


    motion means anything that can move and term servo can apply to different aspects of the motion:

    - some may control speed,

    - some may control position,

    - some may control force or torque,

    - some may use combination of those....

    etc


    but it is always something that moves and uses feedback to make corrections.


    servos commonly used in robotics are doing position control (feedback is used to verify and correct target position of the motion).


    variable frequency drives are normally used to control motor speed (fan, conveyor, whatever). they are not considered to be servos - as long as they operate in basic form using open loop (no feedback). but once they use feedback to control position or speed they are operating as servos.


    encoder is one of commonly used type of feedback for position or velocity. but this is by no means the only type. feedback could be:

    - encoder

    - resolver

    - potentiometer

    - etc.


    accuracy of feedback sensors is a key factor that determines accuracy of servo.

    1) read pinned topic: READ FIRST...

    2) if you have an issue with robot, post question in the correct forum section... do NOT contact me directly

    3) read 1 and 2

  • as for linear servo... there too are different types construction and details of inner working determine speed, force, accuracy....


    some linear servos use rotary motor and some sort of screw as a transfer mechanism. this reduces speed but increases force. to move motor must overcome own inertia, inertia of the actuator (including any gearing) and inertia of the load. servos using linear motors (voice coil) are ultra fast since no mechanical gearing is used. as mentioned before, positional accuracy depends on type of feedback. most commercial products aim to meet demands of same applications which is why specs tend to be similar.

    1) read pinned topic: READ FIRST...

    2) if you have an issue with robot, post question in the correct forum section... do NOT contact me directly

    3) read 1 and 2

  • example of typical construction of a linear actuator. note the use of screw. this type of devices is strong, not back drivable and quite slow because one revolution of the screw only moves 2-3mm. so even with motor running at insane RPMs, you will never get 10m/s

    Linear Actuators | Progressive Automations™ |12 Volt Electric Linear  Actuators Canada – Progressive Automations Canada

    1) read pinned topic: READ FIRST...

    2) if you have an issue with robot, post question in the correct forum section... do NOT contact me directly

    3) read 1 and 2

  • linear actuators using belt transfer are much faster.

    ENDURO Linear Guide Actuator | Modern Linear, Inc.


    this type of transfer is used in SCARA robots. this is why industrial scara robots are fast.


    but one can also build custom one, since they use simple construction that could be optimized for particular application:


    SCARA Robot | How To Build Your Own Arduino Based Robot
    In this tutorial we will learn how to build an Arduino based SCARA Robot. I will show you the entire process of building it, starting from designing robot to…
    howtomechatronics.com


    Small Footprint Scara Laser Engraver Has Massive Build Area
    One of the limitations of the conventional Cartesian CNC platforms is that the working area will usually be smaller than its footprint. SCARA arms are one of…
    hackaday.com

    1) read pinned topic: READ FIRST...

    2) if you have an issue with robot, post question in the correct forum section... do NOT contact me directly

    3) read 1 and 2

  • VCM (voice coil motors) and VCA (voice coil actuators) use principle of voice coil. magnetic field is used to directly move actuator. and yes that is how speakers work. and they can move speaker cone back and forth at quite high frequencies, way faster than any rotary motor could.

    they can be simple construction, fast and accurate. essentially same principle like a rail gun. this is the fastest type of actuation possible.


    since there is no mechanical gearing involved, there is no risk of developing wear spots that may occur in other types of actuators that repeat many number of moves to same positions, but they do need proper cooling.

    1) read pinned topic: READ FIRST...

    2) if you have an issue with robot, post question in the correct forum section... do NOT contact me directly

    3) read 1 and 2

  • as you can see, not all linear actuators are built the same way and specs can be widely different. so simply saying "linear actuator" does not mean much since it only describes that some device can move on a straight line but not how.

    1) read pinned topic: READ FIRST...

    2) if you have an issue with robot, post question in the correct forum section... do NOT contact me directly

    3) read 1 and 2

  • place the stencil on top of PCB, drop whatever you are applying and spread it with putty knife, then remove stencil. should be no more than 10 sec. then roll your thumbs for 2min50sec.

    1) read pinned topic: READ FIRST...

    2) if you have an issue with robot, post question in the correct forum section... do NOT contact me directly

    3) read 1 and 2

  • I have 4 automatic stencil machines and 2 semi automatics. when dealing with near invisible components precision is critical, cant be done by hand, especially when making 50pcs per day. Solder paste has to be perfectly even and not creating shorts. 80% of errors come at this point in the process. Automatic stencil machines run $250k new and take alot of space. This little robot can fit in my closet.

  • Surprisingly, automatic units give alot of problems and solder paste cleanup, stencil alignment, etc take more 30 minutes in general to setup. Also, 30 minutes to clean stencils as well. We waste quite a bit of solder paste each day but that is not important to me. Storage of stencils is also a headache.


    With jetting no startup time, no cleanup time, no stencil needed. Small form factor but it is only good for ~15pcbs/per shift due to slow robotics. At this moment, I am planning on using the cartesian robot and will upgrade later to super fast delta/scara robots. I have seen some very expensive 6 jointed cobots reach 7.4m/s from ABB and others. I'm having a hard time finding info for super fast robots over 5m/s with short reach (prefer 10m/s). I would have thought based how fast small 3d printers move that there would be cartesian robots running alot faster. I contacted Yamaha but their units are only marginally faster.

    Edited once, last by Reckless ().

  • Linear motors are a type of electric motor that produces linear motion instead of rotary motion. They consist of a stator and a moving magnet, which are arranged in a linear configuration. Linear motors can provide high speeds, accelerations, and precision, and they are often used in high-performance applications where fast and precise motion control is required. However, linear motors can be more expensive and complex to implement than traditional rotary motors, and they require specialized control electronics.

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