Components of a servo system

[sdswp5]

Hello,

I have a NOOB question from someone who probably jumped in too early: what components are required for a servo CNC system. I currently use Mach 3 for my stepper controlled Taig mill and will use it for my lathe project. I have already purchased the servodisc motors with attached encoders. Do I have to acquire a driver and a controller for each of the motors? What components have I not mentioned that are necessary for successful assembly of a closed loop servo control system? Thanks for the help.

[Kelinginc]

check here for components: Driver, Power supply, Breakout borad
http://www.kelinginc.net/ServoMotor.html
http://www.kelinginc.net/CNC34ServoMotorPackage.html
http://www.kelinginc.net/CNC23ServoMotorPackage.html

[CoAMarcus]

To expound a little bit, you will need a servo motor, an appropriate line count encoder for each one, a motor controller for each one, a breakout board to connect to the computer and the drives, and a power supply. To figure out your optimal encoder line count, you must take your step pulse frequency and divide it by your revolutions per second. You then divide the whole mess by 4 to take quadrature into account, and the answer will be your optimal line count. Choose the closest standard line count below that number and you will have very few problems or complaints. I have laid it out in formula form below:

(Step pulse frequency / RPS) / 4 = Encoder Line Count

Example for a 3000 RPM motor and a 45kHz step pulse signal:

First, take 80% of your no load RPM to find your maximum loaded RPM and divide by 60 to find your revolutions per second. For 3000RPM, this number will be 40.

(45000 / 40) / 4 = 281.25 lines

I believe a standard line count is 275 lines, so that will work perfectly for this equation.

Also, I assume you were talking about just the electronics end of the setup but do not forget to properly gear your machine. When you are using servos, gearing is one of the most important things you can take into account.

Marcus Freimanis

[sdswp5]

Thanks Marcus for the info, that was precisely what I was needing to know. One question that has nagged me to this point, in your reply I see mention of controllers in the list of items and drives in reference to the connection established by the breakout board, are these the same item or are there drives connected to the computer which in turn connect to the controllers? I already have the motors and encoders, as well as the appropriate gearing. With this particular application, speed is not the primary function of the machine as it is primarily for high precision prototyping. The gearing I have will provide for a max transverse of 25ipm but the mechanical precision is astounding. The physical precision of the lathe is obviously subject to my attention and precision in the assembly, we'll see how that goes.

[CoAMarcus]

The computer has the CNC program running on it which outputs the step and direction signals through the parallel port. The parallel port goes to your breakout board, which then goes to your drives. You have the power supply, motors, and encoders hooked up to your drives.

Marcus Freimanis

[sdswp5]

Thanks again Marcus for the explanation. Now to address acquiring the drives, I think the UHU controller may be the direction I ultimately take on this portion.

[lamicron]

Marcus, can you explain a little more ?
I ´ve already understood the first part, it seems in mAch you work almost the same as in the steps motors. What about the encoder sets in Mach?
Thanks
Luis

[sdswp5]

Marcus,

In my last response I was still far from understanding the components you were speaking of. After a little more research I decided to pursue the A.M.C. family of servo drives and am in the process of acquiring them. Several of the A.M.C. drives claim opto-isolation is built in. If one of these were utilized, would it be necessary to insert a break-out board in the system or would that be additional insurance against the dreaded smoke? Thanks for the great info provided to this point.

[CarbideBob]

You won't be able to use the AMC drives directly with Mach.
These drives expect a +/- 10 volt signal from a controller board like those from Galil or Delta-Tau where the servo loop is closed on the controller card.

Since Mach outputs step signals you need an intelligent drive which closes the servo position loop in the drive itself. Gecko makes a drive with this intelligence built in. Sanyo-Denki drives also have the ability to understand step/dir signals.

I have seen references here to using a Pixie card between Mach and a typical servo drive where the Pixie card controls the servo loop.
Bob

[sdswp5]

Thanks for the info Bob. I spoke with one of the system engineers at AMC yesterday. They offer a digital series that can accept step/direction inputs. I've also looked into Copley and the Gecko offerings. I haven't researched the Geckos as completely as I intend, but I have printed the information. One major obstacle, and one major plus for the Geckos, is I am alas forced to put the system together as budget allows and the cost of these various drives is substantial. We'll see how this turns out!

[zook]

Does each servo require a seperate power supply?

Thanks,
pat

[Al_The_Man]

Originally Posted by zook Does each servo require a seperate power supply? Thanks, pat

If you are talking A-M-C they offer two types, either having PS built in or using a common supply for several drives.
Al.