As I said before, an MT Connect agent provides the current status of the devices talking to it, by returning an XML string with all the details in it. Since the advent of AJAX it's been very common for developers to create web-based applications that hit a server for XML data, and on loading it, modify what's being shown on a web page (using DOM manipulation). This is basically the strategy I wanted to take, with the added feature of using the HTML canvas element included in modern HTML5-compliant web browsers. The canvas basically allows you to draw in 2D on a portion of a web page. The great thing about using HTML and JavaScript is, it works on any platform that supports HTML5 features (including iPad/iPhone/Android browsers).
One reason I chose the canvas element was because we had built a flash-based viewer a few years ago for a single machine, which just listed out some of the MT Connect data we were getting in real time (spindle speed, etc...). But now we have three machines (and maybe more in the future) that we'll want to be able to view at the same time, so I thought having an overhead view of our layout would be a cool way to get heads-up info on what's happening in our lab.
Luckily I had built a basic JavaScript library for creating and drawing 2D shapes on a canvas when learning JavaScript. So all I really had to do was write some code to interrogate the Agent, extract data on the machines I wanted to know about, update the 2D shape objects with the right information, and let my graphics library handle the graphics.
So to start, I used a VBA macro in Visio to export my 2D layout to JavaScript code that would create 2D shape objects in my graphics library format. So at this point I had a canvas element that would draw our machine lab layout, which was a great start.
I then added a JavaScript function that uses JQuery to get an XML string from my MT Connect Agent detailing the current status of my machines. I also used JQuery to convert the XML output into the JSON format, which converts the XML data into native JavaScript objects, and step through the XML tree to find what I need.
All that was required now was a function that would get the current status information as JSON data, and map that data to my 2D shape objects, and then call itself after some interval (using setTimeout). So I wrote that function, and it works pretty well, just turning machines different colors depending on their current state. You can click on a machine, and see some more detailed information pop up on the side.
I've also played with storing the last 150 spindle locations and drawing that on top of the machine, but the problem there is converting the spindle locations into relative locations within the bounds of its machine, otherwise the toolpath usually leaves the bounds of the machine. But if you watch long enough you see it follows the shape I set in my MT Connect machine simulator.
I've also started playing with pulling in other information, like temperature, and displaying that. Right now my simulator doesn't modify the temperature but that should be easy enough. I can see it working where there's a little thermometer shape next to the machine that changes color with increasing temperature. Or even a spindle shape that moves around drawing the toolpath line and changing color with temperature. There's also a power consumption aspect to this all, where maybe I draw bar gadgets next to the machines so you can see at a glance which machines are using the most electricity.
Regardless, MT Connect can provide some very interesting data, but there's a lot of it. At some point the really hard part will be in gleaning out what a user wants to see and only showing them that.
One issue I ran into while building this tool had to do with cross site request issues. An MT Connect agent is basically a webserver, except that it only serves XML strings based on what URL you go to. You can't serve arbitrary files (like JavaScript/HTML files). This isn't an issue if you're writing an application in VB/A, for instance, because the XMLHTTPRequest object provided by Microsoft doesn't care where the request is going to. However, the XMLHTTPRequest does care when it's being called in a web browser. Basically, any AJAX request you send has to be served by the same server that gave you the HTML document your JavaScript is running in.
So to get past this issue (which is a showstopper, if you can't actually get anything out of the agent) I used a PHP script that when called, retrieves /current from the agent, and returns that to the caller, keeping the request on the same domain, as far as the browser knows. So that works well enough, it seems, but it now means anyone who wants to do something similar in the browser has to also have php running (or some server side scripting that can do the same thing).
One other issue I'd like to mention is that I have to use a JQuery library for converting the XML output string of the agent into the JSON format, for creating native JavaScript objects. It'd be very cool if JSON was an option for output on the agent. Maybe that should be something I work on building, and if successful, contribute it to the project and try to get it included in a release.
For now, you can see the veiwer at ccat.us/mtconnect. At some point, I hope the simulated data goes away, and we can start showing the real status of our machines. I'd also like to work at automating the creation of these HTML pages so that other MT Connect users can view their shops using the same code I've written. We'll see where this all goes. In the meantime, I cobbled together another version of the viewer that shows the status of the simulated machine at agent.mtconnect.org as well as the toolpath the spindle is following (right now it only keeps about 20 points, and kinda looks like the game "snake", but I might up that value to show more points.
Contact me at jfournier@ccat.us if you have any questions about this.
2 comments:
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