FILENAMES: servamps.jpg servback.jpg servencoder.jpg servflychip.jpg servfrnt.jpg servfullserv.jpg servxen.jpg servxy.jpg servxyz.jpg servyax.jpg sergzax.jpg DESCRIPTION: These are pictures of the latest servo based CNC conversion project by Dan Mauch and Bill Wainright . Dan provided the following description: ======================================================================== Pictures: Servamps.jpg: A picture of the complex electronics. Fitting it all into a 12/X10X6 was a challenge considering that there are three power supplies, 3 amplifiers, a db25 junction opto isolated board and a power distribution board. The controls seem to be rock solid once adjusted. Servback.jpg This picture shows the X-Y-Z motor power leads. Two wires are used for each motor. The other inputs are IEC power entry module, and a DB25 connector for the parallel port. Servfrnt.jpg This shows the three motor encoder connectors and the lighted power switch on the prototype controller. Servyax.jpg shows the Y axis servo motor. It is a ball bearing DC brush type motor with a 200 count HP encoder. This installation was on a Shoptask which made this CNC installation easy. Servzax.jpg shows the z axis drive motor. The Z axis servo system is installed on the Shoptask with the quadralift modifications. ServBack.jpg is another picture of the back of the controller case. servFront.jpg self explanatory. servEncoder.jpg a detailed picture of the 200 count encoder and it mounting on the motor. servFullserv.jpg is a picture of the servo system installed on my mill drill. The mill drill was retro fitted with ball screws. It does 120 IPM+ servXy.jpg shows the XY servo motor installation. Since I was using a stepper motor system before I made adapters to adapt the existing motor mounts to the servo motor mounts. servZ.jpg is a straight view of the Z axis . It uses the fine feed but is plagued by the common problem of most mill/drills in that there is excessive backlash in the drive gears. I will replace it in the future with a ballscrew drive. Description: It is awesome to watch my mill drill run with a table speed of 120+ IPM. It is dazzling to see how smooth a servo system is when compared to a stepper system. It is very impressive to see the servo system do circular and linear interpolation fast and smoothly. Bill Wainwright (billmw@isomedia.com http://www.isomedia.com/homes/billmw and I (dmauch@seanet.com http://www.seanet.com/~dmauch )have been working on something better than a conventional stepper motor systems. Stepper motors have their place but servo systems are generally superior with respect to speed and smoothness. The biggest problem with stepper motors is that they do not have a feed back system. They are open loop systems. Servo systems on the other hand have an encoder that feeds back it's position. This coupled with the built in Proportional, Intregral, Derivative (PID) filter and error amplifier corrects positioning errors to 8 bits. Here is how a Bill Wainright's servo system works. Using one of the low cost Computer Numerical Control (CNC) Programs such as Maxnc, DeskNC, Dancam, Supercam, Stepster, or BasicCNC, a number of pulses are sent to the parallel port. The number of pulses is set in configuration files and is determined by the encoder used, the pitch of the leadscrews and the motor pulley ratio. It is best to have a minimum of 8 counts (.000125) or more per .001". On my mill drill I am using a 2/1 ratio with a .2" pitch ball screw and 200 count encoder when in quadrature is 800 counts per revolution. Thus 800X 2(Ratio)X .2(pitch)X5(threads per inch)= 8000 counts per 1" of travel or .000125 resolution. If the CNC program orders the servo system to move 1.000 inches then 8000 pulses will be sent via the parallel port to an opto-isolated junction board. Each axis servo is connected to this interface. The servo then compares the number of pulses received and while it is moving the servo motor in time with the incoming pulses checks t o see if there are any errors between what was received and what the encoder connected to the motor reports. If the error between the received pulses and the encoder increases over zero error then the Proportional, Integral, Derivative (PID) filter sends the servo signals to the servo amplifier to increase or decrease the power necessary to keep up with the motor encoder. Bill uses an 8-bit error amplifier to keep the delta low. When the axis reaches the targeted location the motor stops and a magnetic brake keeps the ball screws from back spinning. The power to the motor decreases since the encoder and the servo error amplifier has compared the error to be zero. If you were to manual try to turn a lead screw by hand with no change in destination then the comparator would generate a counterbalancing force to move the lead screw back to the last positioned order. Running several axes simultaneously is always neat to watch and each servo comparator would detect any error for that axis and would compensate so that along each axis travel there would be a minimum of error. Bill and Dan