The heart of the NXGEN servo system is the motion control board. The control board uses a high-speed RISC-processor which has a servo response time of 0.062 ms (16 kHz) — 16x faster than the Legacy servo controllers. This speed greatly increases the servo reaction time.
The difference is even audible. For example, on any machine with the Legacy control paired with Glentek brushless motors and amplifiers, the servos generate a “whining” buzz when not in motion. Now with our control, using the same servos, that “whine” is significantly reduced, in fact almost gone.
The inability to move to or hold position under load (weight/mass and cutting force) is measured as “following error” from the required position. A motor overload alarm occurs when this error becomes too large. In one test, to demonstrate the improved stiffness, we performed a static torque test. The test compared the original Legacy servo control board with the NXGEN system, using the same brushless motors and amplifiers while applying a 20 inch pound load at the motor shaft. The Legacy control measured .0004″ position deflection. With the NXGEN control, we measured only .0000125” deflection.
Servo stiffness directly relates to the ability of the servos to accurately control the machine slides while standing still or during motion resulting in more accurate and better finishes.
Having a higher stiffness is one of the features that enables us to achieve a true zero following error. The combined features previously described 10X Resolution, 30X Servo Stiffness and 16X Faster Servo Response, enable the motion control to significantly reduce following error. In most cases the servo system operation has zero following error. Without the normal servo lag as with most machines, now your parts will be consistently more accurate, even as you speed up the feed rates. Our goal is reducing your part cycle time without sacrificing accuracy.
While others worry about saving seconds during tool change time, we look to saving all the minutes during machining time!
Normally with CNC controls, you will see the position “dither” back and forth +-.0001” while “servoing” to hold position. With our new designs, using the standard AC motors, our Control achieves a stability of +-.000010, a factor of 10x better!
This velocity graph shows in red the acceleration taking place while making N1,N2 and N3 moves, then decelerating N3,N4 and N5 moves. This results in a smoother velocity during acceleration and deceleration as shown above. Even during G8 mode with ramping turned off, changes in velocity are automatically ramped up or down to maintain smooth motion regardless of the move length or feed rate. It automatically maintains the proper acceleration and deceleration profiles.
The ability to process small moves and not become buffer bound, causing the machine to pause or stop, is termed “Block Per Second Throughput” and it is measured by how many moves the control can process within one second. With the Legacy control, the fastest speed was 250 blocks per second in G90, 1000 blocks per second in G91.1 mode. With the NXGEN, we have three modes for Advanced Surfacing: No Ramps, Buffer, and High Speed.
The 511 block look-ahead with motion data pre-buffering increases the processing time up to 1900 blocks/second. The Legacy’s performance averaged at 250 blocks/second (depending on hardware and year), making the NXGEN perform 7.6x faster on average.
The Legacy’s maximum processing speed was using the command G91.1 for high speed incremental moves at a speed of 1000 blocks/second. The NXGEN has a high speed optional mode of 5000 blocks/second. That’s 5x times faster than the Legacy G91.1 or 20x faster than the average speed of 250 blocks/second.
Automatically accelerate and decelerate before interpolation. The iRAMP control feature uses a 511 block look-ahead buffer to determine when it needs to slow down for a direction change. The look-ahead will automatically generate at G9 ramp when needed then switch back to G8 mode. Simple to use, simply turn it on or off in the middle of the program or modify settings on-the-fly.
This diagram shows red dots where the control would automatically generate a ramp. This allows maximum high speed machining to be easily achieved by automatically ramping without slamming to a stop and banging at the start. The programmer is relieved from the normal complication of adding G9 and G8 in the program.
The iRAMP feature allows increasing feedrates without concern of excessive “slamming” into corners and thus reducing the cycle times without damaging the machine.
Create a Bi-Cubic Parametric Spline through original programmed points and use less data points (linear moves) to achieve a smooth finish. The motion control board interpolates in-between the original programmed points as it cuts the part. Requiring less linear moves simplifies the programming while actually providing the best possible finish.
The diagram below shows typical shape before and after the Smoothing function.
