Universal axis controller

Initial Thoughts

Along the lines of a universal power unit like the power cube it makes sense to create a universal controller that can be "plugged in" to whatever actuator system you need to control. Why let the control electronics/software for a system sit idle? Take the controller with you and use it in the machine you happen to be operating at the moment.

I assume this would be a distinct system in that it wouldn't be automated. So, automation systems could utilize the universal axis controller, but it would primarily be used by people as they move between different machines.

Characterizing an arbitrary arrangement of actuators isn't really straight-forward, but it will probably yield to some kind of nomenclature. Some sort of hardware description language is in order.

For example, an electric drill would have only one axis (or degree of freedom) which can be moved positively or negatively at different velocities. Drill

• Single axis
• Rotation
• positive/negative
• (angular) velocity

Or, arguably, the drill doesn't know or care that something is spinning, let alone how fast it's spinning. More accurately its "axis" is the variable-resistance switch that sends electricity to the motor. The state of the switch is what's important; the motor's actions are just a dependent variable.

That implies a high-level characteristic should be whether or not the axis control is closed-loop. If it is, then the feature being measured is important. If it isn't, then nothing at all is being measured, so things are much simpler. Okay, so the universal axis controller (UAC) should be an interface between an operator (human or automated) and the system with the axes. It should interface with and understand the signals of any sensors, translate those signals into whatever the operator needs to know, then translate control signals into whatever the axes need to move correctly. That's beginning to sound like a robot control system. Something like this Basic Input Output Elements thing.

If the point of it is to be easy to unplug from the machine and walk away with, then it would need to be a single unit. Just a box you can unclip or something. That means there will probably have to be some sort of associated family of sensor/actuator interfaces that are physically distributed throughout the machine. For example, maybe stepper motors would have their step control boards right next to them and the UAC would just send step signals to wherever the steppers physically are. In the same way, end-stop sensors would have their circuitry right there at the place where the sensing is happening and would just return ON or OFF signals to the UAC. That's how open source 3D printers are built, except that the stepper drivers are usually mounted on the central controller itself instead of next to the motor. It wouldn't make sense to clutter up the UAC with a dozen stepper drivers just in case that many were necessary for one machine.

Perhaps the UAC could be implemented in a FPGA. Or, rather, in an FPGA slaved to a computer. The computer would be the primary interface with the operator. The FPGA would be "programmed" with the correct "image" for whatever machine needed to be controlled. That would supply precisely timed signals to the hardware (operating systems don't work in real time). It would also mean the control systems could be simulated as they were needed, rather than having to be all sitting next to each other "just in case." An FPGA could simulate a few stepper drivers and end-stops and thermistors and whatnot for a 3D printer, or it could simulate a dozen stepper drivers for an industrial robot, or it could simulate a machine vision system for an automated crane...or whatever. If each control module is programmed the FPGA can just be loaded with a custom control image for each application.

Fiber Optics

In terms of multi-mission flexibility and future-proofing, fiber optics are superior to metal wire. Wikipedia has this to say:

• physically flexible and has a small cross section
• 10 or 40 Gbit/s is typical in deployed systems
• Each fiber can carry many independent channels, each using a different wavelength of light
• a single fiber can carry much more data than electrical cables such as standard category 5 Ethernet cabling, which typically runs at 1 Gbit/s.
• Fiber is also immune to electrical interference; there is no cross-talk between signals in different cables, and no pickup of environmental noise.
• Non-armored fiber cables do not conduct electricity, which makes fiber a good solution for protecting communications equipment in high voltage environments, such as power generation facilities, or metal communication structures prone to lightning strikes. They can also be used in environments where explosive fumes are present, without danger of ignition.
• Wiretapping (in this case, fiber tapping) is more difficult compared to electrical connections, and there are concentric dual core fibers that are said to be tap-proof.
• Sensors that vary the intensity of light are the simplest, since only a simple source and detector are required
• ...is usually a fiber of silica glass that confines the incident light beam to the inside...Plastic optical fibers (POF) are commonly step-index multi-mode fibers with a core diameter of 0.5 millimeters or larger. POF typically have higher attenuation coefficients than glass fibers, 1 dB/m or higher, and this high attenuation limits the range of POF-based systems...POF has been called the "consumer" optical fiber because the fiber and associated optical links, connectors, and installation are all inexpensive. Due to the attenuation and distortion characteristics of the traditional PMMA fibers are commonly used for low-speed, short-distance (up to 100 meters)
• Silica can be drawn into fibers at reasonably high temperatures, and has a fairly broad glass transformation range. One other advantage is that fusion splicing and cleaving of silica fibers is relatively effective. Silica fiber also has high mechanical strength against both pulling and even bending, provided that the fiber is not too thick and that the surfaces have been well prepared during processing. Even simple cleaving (breaking) of the ends of the fiber can provide nicely flat surfaces with acceptable optical quality. Silica is also relatively chemically inert. In particular, it is not hygroscopic (does not absorb water).
• The light is "guided" down the core of the fiber by an optical "cladding" with a lower refractive index ...
• The cladding is coated by a "buffer" that protects it from moisture and physical damage...These coatings are UV-cured urethane acrylate composite materials applied to the outside of the fiber during the drawing process. The coatings protect the very delicate strands of glass fiber
• Modern cables come in a wide variety of sheathings and armor, designed for applications such as direct burial in trenches, high voltage isolation, dual use as power lines, installation in conduit, lashing to aerial telephone poles, submarine installation, and insertion in paved streets
• Fiber cable can be very flexible, but traditional fiber's loss increases greatly if the fiber is bent with a radius smaller than around 30 mm. This creates a problem when the cable is bent around corners or wound around a spool, making FTTX installations more complicated. "Bendable fibers", targeted towards easier installation in home environments, have been standardized as ITU-T G.657. This type of fiber can be bent with a radius as low as 7.5 mm without adverse impact.
• Some fiber optic cable versions are reinforced with aramid yarns or glass yarns as intermediary strength member. In commercial terms, usage of the glass yarns are more cost effective while no loss in mechanical durability of the cable. Glass yarns also protect the cable core against rodents and termites
• Optical fiber can be used to transmit power using a photovoltaic cell to convert the light into electricity...the efficiency is not nearly that of electricity (the efficiency of the photovoltaic is around 40 to 50%)