The No SPIN Zone

About steppers and servos...

 

Reliable: Let's face it, you're going to crash you gantry some day. Either the plate is going to warp, or your programming will be off by one decimal place, and eventually it's going to hit something.  Closed loop design DOES NOT require system re-initialization.  In fact, you can disable the power to the motors, allowing you to manually push the Gantry and Torch around tour table.  The onboard encoder will ALWAYS keep track of the motors position and when you re-apply power to the motors, they will know EXACTLY where they are.  No need to re-home!  If the system does crash, the brain of the servo motor will prevent it from breaking a gear tooth or burning up. Steppers will just skip steps, and leave you lost, requiring a re-homing... and at <300 ipm, that is going to be painful (see below).  And with dual X motors, if something happens to one motor, the motors are smart enough to discuss amongst themselves what has happened, and who needs to make the adjustment to get back inline again. Steppers? They are both lost...

High Speed: We think 1000 ipm is a good speed, in fact 2000 ipm is even better, but since we cannot go that fast, then 1000 is just right.  Time is money, waiting for the gantry to travel 20 feet (yes we have many users with 20 and one with a 40 foot table) at 300 ipm is just downright painful.  But, how often do you make a move like that anyway?  Believe me, it's more often than you think. 

High Accuracy: Our standard gantry drive system has a scaling factor of 15274 encoder pulses per inch. Our motors can repeat with one encoder pulse.  So electronically we can repeat within 65 millionths of an inch.  If we did a terrible job of  tuning or motor, we could have a positioning error of 15 pulses, then we would be off by 982 millionths of an inch (or about one thousandth)  Therefore, electronically we eliminate any doubt in the accuracy of the motors and can spend more time with the mechanical aspects of the machine.  So, not only can we make a 0.000065" per second slow move, we can also do a 1000" per minute fast move.  Now that is quite a versatile operating range.

Smooth and Quite: Servos for the most part are silent operating.  Unlike steppers that are very noisy.  The smoothness is also quite apparent, as the system is much more analog than the digital type stepper. And the high precision gearbox we chose to use has helical cut gears for a quite operation.  What we are left with is the rack and pinion on the machine to making the noise. (and we are looking at new technologies to quite that down)

Latest Technology: At one time, cost was the major consideration for the motor choice. Today, the servos have come down quite a bit and with their advantages, are actually less costly in the long run.  Now consider the technology. At one time, a servo system needed a "controller", usually housed in the PC or a stand alone box in the control panel.  They also needed an "amplifier", something to convert the controller signal over to power that went to the motor.  This amplifier was also housed in the control panel.  Then of course the motor, which by the way needed an encoder and commutation signals to go back to the controller and amplifier to close the loop.   Today, with the Smartmotor, the controller and amplifier are housed in the back of the motor, so the encoder and commutation wires are all internal.  All that's needed is a couple power wires going to the motor and a couple serial RS232 wires to issue commands from the host PC.

Technology advancements are a good thing, and the same holds true for the motion control market.  Yes, my Sony walkman compact cassette works just fine, but compared to an iPod which is 1/8 the size and holds 300 cassettes worth of music, there just is NO comparison.  It's like my kids say, "Dad, get with it, it's 2007...  Nobody uses walkmans anymore....   and what's that hissing noise I hear in your headphones... Dolby noise reduction, what's that button do?, why do you need it?  Look Dad, I can program my iPod to control the TV ! I think I might be able to control your motors with this thing Dad.."  "Soon my son, you probably will, very soon..."  In the meantime, we just keep adding more features to our current system 

For an even more in-depth discussion on why we use servos instead of steppers, click here.