Centroid OAK with C Axis Contouring

Post your completed retrofits for the world to see.

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Magneto
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Centroid OAK with C Axis Contouring

Post by Magneto »

We have recently finished up a major retrofit on a Cincinnati Avenger 250MT 3 axis lathe. This machine was originally controlled by a Acramatic 850SX IDS control that is supported by Siemens USA. It had a couple issues with it when we picked it up that made us want to do a Retrofit on it. Firstly the control boards had some kind of internal error that would be difficult to diagnose and fix, and secondly, the machine was designed for 480 VAC while we would want it to run on 220 VAC. Below is the control cabinet before the retrofit. Our goal was to replace as little as possible to make the retrofit as simple as we can make it while maintaining all original functionality of the machine. We decided to do a full control retrofit with new motors, drives, and control boards. We went with the Centroid OAK board as it allowed easy communication with the different drives and the expansion boards for additional I/O's.
Cabinet Before.jpg
The first simplification of the machine came from removing the unneeded original transformers. Additional transformers were used to transform the 480 VAC input into 220 VAC, 120 VAC, and 24 VDC. for use throughout the machine. With the change to 220 VAC input and the addition of the OAK power supply module, various transformers were removed to make the power supply simpler.

The X and Z axes are controlled by Yaskawa Sigma 7 ServoDrives. Both ServoPacks are the Sigma 7 SGD7S-180A00A 002 ServoPack with the X axis ran by the Sigma 7 SGM7G-20A6A6E ServoMotor and the Z axis ran by the Sigma 7 SGM7G-20A7D6S ServoMotor. This was a very simple replacement as the mounting lined up for the ServoMotors and the ServoPacks are very simple plug and play with the Centroid OAK board.
These axes move a Duplomatic BSV-N 200 12 tool turret. This turret has various sensors that plug into the OAK board with the required solenoids and motor contactors being controlled directly by the OAK board. This allows that OAK to easily move the turret to the desired tool with the 10 millisecond precision needed according to the turret manual. This turret also allows the use of live tooling ran by a Fanuc 3s AC spindle motor controlled by a Altivar Machine ATV320D11M3C VFD.

The live tooling functionality provided additional problems for the main spindle however. The main spindle is driven by a belt drive that is attached to a Fanuc 18s AC spindle motor controlled by a Emerson Commander SK 4203 VFD. As having a large spindle motor run in position mode is difficult to accomplish we opted for adding a ServoMotor into the belt system. This is a Sigma 7 SGM7G-20A7D6S ServoMotor controlled by a Sigma 7 SGD7S-180A00A 002 ServoPack. Additionally to avoid having the spindle motor drive the ServoMotor at speeds that would damage it, a clutch was added to the system. This clutch is a Mönninghoff type 546.32.4.4 electromagnetic clutch that is controlled via relay by the OAK board. We also added a 10:1 planetary gear reducer to the ServoMotor to allow for lower speeds, higher torque, and higher accuracy. This is a Porovin Technology High Precision Reducer model number TFG120-010-S2-P2 gear reducer. It was very simple to attach to the ServoMotor and we created a mounting system to mount the entire assembly to the cast body. This is shown below from a couple different angles.
C Axis System 1.jpg
C Axis System 2.jpg
C Axis System 3.jpg
The issue with having two VFDs however is that the OAK board only has one analog output. To get over this issue, we have ran separate enable signals to each VFD and ran the one analog output to both VFDs. Then we are able to toggle between which VFD we are wanting to control. This toggling is also able to engage the clutch and allow the ServoMotor to drive the main spindle in position control. The change between the two modes is controlled via M codes. We are using custom M codes to control switching between the two different modes. We attempted to use the CNC 12 C axis Enable and Disable but it never worked for us. The custom M codes are perfectly functional.


Another problem that had to be solved was with the main spindle encoder. Installed in the original machine was a main spindle resolver. This resolver wouldn't send the correct signals to the OAK board as that needs a Quadrature Encoder signal. To remedy this we purchased a VEGA 2796500 - COMPACT DIN RAIL RESOLVER TO DIGITAL CONVERTER BOARD, to convert the resolver to the needed Quadrature Encoder signal. This board is shown below installed into the machine. This board was very simple to plug in and is able to do what we needed to do.
Vega Board.jpg
Some additional functions of the machine is a chip conveyor, hydraulic pump, parts catcher, tool setter arm, spindle brake, tailstock and quill, and a coolant pump. Each of these systems are controlled by either contactors or directly from the OAK board.
We needed to make a new coolant tank and coolant pump mount as neither of those came with the machine. We also added a new monitor stand for the HP PC running CNC12. Then everything was given a new coat of paint to really make it look new. Below are some images of the control cabinet and the exterior of the machine.
Machine View.jpg
Machine View rear.jpg
Cabinet After.jpg
After the retrofit, the machine was moved into our production machine shop and parts were started to run on it. This production then releveled a couple different problems that we have had to solve. All of these problems were dependent of the Live Tooling and Milling capabilities of the machine. The V belts used in the Spindle drive system work very well when spinning at speed. However, when the C axis was activated, the belts introduced a unknown and varying amount of stretch. This stretch amounted in errors of ~0.2°. It caused the most issues when countersinking holes, causing the countersink to be off center of the first drill hole. In hindsight this is obvious but changing the system would require a complete redesign and rebuild. We attempted a software correction using Centroid but the inconsistent backlash proved to much.
We then tried a solution in the creation of a G code macro.
Centroid provides many different System Variables that can be accessed during machine runtime. These variables allow us to get the Current Encoder count and the Encoder count of the last index pulse. Using those variables we can accurately index the C axis. Then any hole that needed to have a countersink, would have both operations occur on the same encoder pulse. Now the machine is able to repeatably index the C axis for drilling operations and then do continuous mill-turn operations for less accurate operations. We have the example part below that worked quite well on the machine.
Mill-Turn Part.jpg
Overall we are very happy with where this retrofit has taken the machine. We are going to continue running different and more complicated parts on this machine until we are able to find the limits of it.
suntravel
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Re: Centroid OAK with C Axis Contouring

Post by suntravel »

Very nice retrofit.

The idea switching spindle control to the live tooling is great.

I have Acorn 6 with two 10V Outputs, but still waiting for the software to control them both independent....

Uwe
cnckeith
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Re: Centroid OAK with C Axis Contouring

Post by cnckeith »

wow! thanks for posting. impressive machine and installation. nice work!
do you have any video of it running a job? would love to see it in action.
Need support? READ THIS POST first. http://centroidcncforum.com/viewtopic.php?f=60&t=1043
All Acorn Documentation is located here: viewtopic.php?f=60&t=3397
Answers to common questions: viewforum.php?f=63
and here viewforum.php?f=61
Gear we use but don't sell. https://www.centroidcnc.com/centroid_di ... _gear.html
spikee
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Re: Centroid OAK with C Axis Contouring

Post by spikee »

cnckeith wrote: Fri Jun 14, 2024 12:50 pm wow! thanks for posting. impressive machine and installation. nice work!
do you have any video of it running a job? would love to see it in action.
This
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