Show Posts
This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.
I have been working way too much and was off fixing a servo system on a Lathe for a local shop... Now with a little bit more rest I should do a bit better job! 
You are sending commands to the Drive telling it that it needs to be at X position and you get a report back that it is only at x-.2. If this is true the PID loop is bad on the drive (we are talking about a servo system in this example) It needs to have a bit more “I” to move the motor into position over time. By telling the Drive to move an other .2 units you are in fact telling the drive and it should be a position X+.2 .This is not the position that you would like to have the motor... The PID loop is still trying to move into position and could jump ahead to the X+.2 position … This would be NO good! You could have two loops working against each other and that would be no fun ;( On the other hand I do think that you should know where the motors are all the time . You can do cool things like use Fiber optics... Yes that has been done in the past! There is an Unbuffered encoder line that comes out of the drive and this is used to monitor he following error of the drive... So in the end a good servo system should monitor the error of the machine and fault if there is anything that goes wrong. Now about steppers.... well they have there place and I like to have encoders on the steppers that I run I am not a big fan of lost position! If you were to see the mill that I have here for testing you would say "Why the HECK to have motors like THAT!" ... I run AC brushless servo motors on my test mill here.... I can rapid my knee mill at 500 IPM and has 1.3 Hp per axis (I love that thing) But just the motors and drives cost me 5000.00 ! On the small bench top test mill that I have is all stepper and it works but at 100IPM it is nice But the price for the machine and drive box with motors was only 2500! That is a deal... On a machine like the one that you have I would not use anything but servos because I would want to have the fast movement and so on. But then there are people on the other end like me ... I have Skype running (talking to people allover the world) as well as my E-mail and a few web pages open at the same time I am cutting a part on my laptop... This is not the best thing to do but I have never crashed out when doing it So the more you do the risk you have and I think that is the same for Linux and windows.
There are a few ways that this can be done and I would be happy to tell you more about the pro's and con's of each system... There is the Galil card (I am not telling you to get one by the way) that is a good system to run a +-10V amp... I have done a conversion with this and it works well ONLY if the accel of each axis is about the same. Why is this??? Well it all has to do with how galil chains the moves... I would like to change the galil to use an other mode but I don't think we can move data to the buffer as fast as we need to in that mode. The other way is to do what Hood told you and use a Pixi... This is one way that it can be done and is the lowest cost solution... There is an encoder board from Ron Rogers that works well... I made the code for the plugin and I can tell you that it works The Pluging is watching the encoders and tracking the following error of the axis. You could say "IT is not right because it is not telling the axis to correct the error"... To that I say WRONG! The servo is driven by the Pixe that has a PID loop.. THIS is where the error is taken out NOT in the computer! the computer will track the error and IF you get over on following error it will fault out. Yes this is how a Fanuc or any other works... I could add code that could look at the following error and slow the feed to try to limit the error that it is getting... This is not a big deal and can all be done with 2 P ports... So why would you use P Ports if you could have something so grand as a Galil! For 1400.00 I got a 6 axis one here for testing! The P port is going to be far less and there is going to be a NEW USB board that can run your machine at up to 4MHz pulse rate! Now you may be saying .. I want the standard!!!! +/-10V uuummmm... Not any more The new way is digital drives and I have also worked on bus systems that only send data! So for me I would take the new USB board and a few Pixies to get the best closed loop that I can for the money... For the people that are hard core and need to have it all one one board because it makes them feel better there is the Galil BUT you need to know that there is a limitation of the accel needing to be the same AND that I have not coded in the probing One thing that it will do VERY well is homing to an index pulse If there are people out there that think they can do better... I have the plugin code and if you think you can handle the code I would be willing to work with you... You need to have VS2003.. I have seen machines that have every home and limit hooked to one input!!! Having said that I have run a machine in the past for a few years that has G320's and it worked well.. the problem is that it is not the best sounding servo system but they are a very good price! Have you tuned the drive with the pots on the back?? there are instructions that tell you how to do this from Gecko.
Guest