Sign in to follow this  
Followers 0
mr_shadow

wireless start stop

19 posts in this topic

Hi all; Think a robot system or an automated production line in a factory. Basically there are start/stop buttons wired to start and stop the machine. I would like to learn from your experiences if you tried making this control wireless RF devices like car or garage door remote controllers. I do not want to try this with standart devices for cars and home automation,I need industrial devices seems like car remote controls. Could anyone direct me to a supplier or a company. Best wishes

Share this post


Link to post
Share on other sites
Control Chief and/or Telecrane for outright pendants. Control Chief is more expensive but slightly more rugged. On the other hand, I've seen Telecrane remotes very badly abused with zero problems (ie, Control Chief is awesome but unless you want the analog joysticks, there's no real advantage). The pendants in the McMaster-Carr catalog are Telecrane, and you can "special order" the ones that aren't in the catalog. The wiring on these things is dead simple. Look at the Telecrane manuals (online) for schematics. This isn't theoretical. I've actually used these. For basic digital signals or analog, there are a lot of vendors now. I kind of like Banner for simplicity. But this is only viable for monitoring-type functions. Beyond this, you can always use radio links for distributed control (Ethernet). It is possible to get to reliable levels of operation with Motorola Canopy, Dragonwave, or Ubiquity hardware. I wouldn't even consider cheap non-ISP grade equipment for this. If it involves a real start/stop function, then the transmitter has to have a "maintained on" type function which is what the crane/railroad pendants have if the operator is being relied on for safety functions (operator must watch the process and initiate start/stop). If the machine has ALL the other safeties and the operator control is a higher level function (basically just a request to start/stop), similar to what you have with an HMI/SCADA system, then you can have momentary start/stop controls but if you rely on the operator for E-Stop, again, must be a maintained signal (constantly transmitting) and absence of signal means stop. In terms of risk assessments, most companies (and safety codes) are leaning away from operator-initiated safety functions (E-Stops) anyways. If nothing else, the liability you get from doing this is enormous.

Share this post


Link to post
Share on other sites
Thank you for your reply, the products look ok but the device I am looking for is a small device like the device you open your car doors and garage doors

Share this post


Link to post
Share on other sites
mr_shadow the problem with these types of devices are that they only send data they don't receive anything. I have seen some that do but the price tag is a little high. Is this for a real application or a "this would be cooooool" dream? Banner has some remote I/O systems that are on battery power. You could use something like that for none critical applications. I just don't see a Robot being able to comply with any RIA standards if you have a wireless non safety rated device in the control circuit.

Share this post


Link to post
Share on other sites
i have a 12 channel device in my home i use for various functions, door locks, lights, etc., the relay board is wired directly to the plc and the transmitter (smaller than a credit card) runs on a AAA battery. it works great. check ebay thats where i bought mine for like $20 american.

Share this post


Link to post
Share on other sites
www.electronickits.com has a variety of these type of things. I used one in a farm application once where the guy wanted to turn a pump on and off from a remote on his tractor. Used the relay board to turn on a contactor. Worked like a champ.

Share this post


Link to post
Share on other sites
That's why I gave you the recommendation I did. The problem with industrial systems isn't trying to make them "small". It's trying to make them both operator friendly and operator resistant, err, I mean rugged enough for the environment. It's hard to make it much smaller and still be rugged. Those Telecrane units by the way are actually pretty darned small. The smaller 1 or 2 button units are a little smaller than your hand for the lower power series. Control Chief can get fairly large but even the really fancy locomotive controllers are about the size of an industrial/commercial radio and most railroad workers carry them around in a larger pocket. The "chest" carriers seem to be very popular for this since it leaves your hands free to hop on/off cars easily. If you want a car/home automation device, then buy a car/home automation device.

Share this post


Link to post
Share on other sites
If this is a real world application, I am not sure it is "safe." Is it? I would be concerned with a safety issue using wireless. I have never done this, nor have I seen it done before, but safety comes to mind first and foremost.

Share this post


Link to post
Share on other sites
That is a very valid concern not to be taken lightly. With that said, I have worked with a hoist that had a remote (wireless) pendant that was guaranteed safe. They guaranteed us that no other wireless device could take control of the hoist, and that if the hoist controller lost communication with the remote pendant, it would shut down. Aside from going through six AA batteries a week, it worked as advertised (BTW when the batteries died, the hoist would shut down). So, there are products that exist that can be wireless and "safe" depending on your definition of safe (how much time must elapse before the receiver "knows" the remote is dead, etc.). Paul Edited by OkiePC

Share this post


Link to post
Share on other sites
Yes, wireless is safe. It can be just as safe as a wired system. Just as with a wired system, you have to give some thought to the various potential failure modes and plan for it. The same problems crop up in distributed control systems. Using a centralized control system with no consideration for equipment damage and claiming that this is safer because it is simple is simply irresponsible, but I see it go on all the time. Designing safe distributed control systems as a part of a larger system is relatively easy simply because there are diagnostic signals available, especially with wireless. Overall safe system design as a general principle is much more difficult because the vast majority of the failures are in the actuators or the operating environment. Yes, wireless crane pendants are safe. In fact most locomotives are run entirely by wireless for switching, and so are most cement pumper trucks. Even some robots have wireless "teach" pendants available. They all operate by using coded messages similar to garage door openers. However unlike garage door openers, the control boxes constantly broadcast an "I'm alive" signal, and the systems they control are configured to shutdown (go to safe state) if the signal disappears. Even crane pendants do this. All of the above usually rely on "maintained on" type controls as well in most cases...you have to hold the button to get the machinery to move. The moment you release, the equipment motion comes to a safe stop. Every so often you hear about a "runaway" with the above systems. Every investigation into this I've been close to usually either turns up some mysterious cable tie, wire, screwdriver jammed in the button, or some other mysterious operator defeat for the "maintained on" function, or else turns up a short circuit some place that forced the control system into an unsafe state (which would exist even in a non-wireless system). Sometimes nothing is found but the wireless system goes through a full checkout and a cause is mysteriously never found. I haven't actually seen an accident report yet for one of those runaway systems which actually turned out to be a failure of the wireless control system. Outside of these specialized controls (which are specifically designed with safety in mind), there are two other uses for wireless. You can use it for remote monitoring (where safety is simply a non-issue), and you can use it for infrastructure (replacing wired connections with distributed I/O) so long as diagnostics are available that allow you to safely shut down the system in the event of a communication fault, SAME programming that is necessary with a wired system. In fact the mine where I work at now uses both. We have several remote monitoring stations to monitor (but not control) the very extensive water handling/discharge system. This includes lots of data collection for environmental reporting purposes. In addition, we have pumps for slurry transport (at a rate of several hundred tons per hour). There are up to 4 booster stations connected in series as well as boosters on the water supply system. There is also a 7 mile long conveyor system with multiple conveyors and trippers as well (72" belt, >5000 TPH capacity). All of these systems are both monitored and controlled wirelessly. Both have been running via wireless for over a decade. The wireless systems in this case use heartbeat/ping-pong signals to monitor the network (which originally lacked any usable diagnostics). In the event that the heart beat signals are lost, the individual pumping/conveyor station goes into fail safe mode (shuts down). All the stations also include manual controls in the event that the radio system stops working and for troubleshooting purposes. In the context of a mining operation with cabling strung up and down walls and all over the benches, a wireless system is just as safe, and far more reliable because loss of wireless communication is easier to detect compared to say detecting every combination of shorted/open conductors if a wire gets cut/shorted out by a bull dozer (yes, I know that pilot pulses in modern safety relays have eliminated this possibility but this wasn't generally available in the 90's). Do NOT take your typical consumer grade wireless access point (nor any of the ones that a typical IT department will install) as an example of the reliability of wireless systems. This equipment is built to extremely low standards and is barely adequate for the intended purpose. A good friend of mine that owns and runs a large wireless ISP in the mountains of central Oregon has nothing but horror stories to tell about virtually all 802.11 wireless gear, either in terms of the interference that it generates or dealing with customers that complain about all kinds of connectivity problems that are caused by their low grade equipment. It is simply not reliable enough for "carrier grade" equipment, and that's the same level of reliability that industrial users are looking for. An example of carrier grade wireless communication equipment would be the Motorola Canopy system (warning...their radios are great, their software isn't), or a Dragonwave bridge. You can't buy any of that for $99 at Walmart.

Share this post


Link to post
Share on other sites
Paul, I know crane operations are safe. A lot of people use them. The issue I have is the reaction time. As I have never done this, nor have I looked at it, I am no expert. I have always had issue with a few things: 1) What is the reaction time and how long does it take before the "machine" stops? 2) What about frequencies? If you have multiple wireless devices, would there be interferences? Not saying this ever happens, but what if someone had something with the same frequency broadcasting and an accidental start/stop occurred? 3) How would you decide the "heartbeat" time? I guess it would be broadcast timeout. You need it long enough to not cause faults, but yet short enough to not have a big lag. 4) What about line of site? I always like to have line of site for any commanded motion. My theory is, if I want to have line of site, why do I need wireless? The crane is different because there are issues with going over things in which you cannot always climb over. Back to number 2, which is my biggest concern and I will explain why here. We had numerous stand alone welding machines we had been running for years with no issues. We added some sensors to these machines when we added automatic nut feeders. They were standard off the shelf Turk sensors. I was working on a machine next to it when all of a sudden the machine cycled for no apparent reason. This happened a few times while I was standing there. I called my boss out to look at this with me as I did not see anything where and why it would cycle by itself. He looked, I looked, and then the production supervisor came over to ask what was going on because, of course, he saw it cycle and they "NEED" to run production. I told him what happened and he got on his radio and called his boss. As soon as he keyed his mic, the machine cycled. We did this several more times with the same outcome. To make a longer story shorter. Come to find out, Turk made some sensors with the wrong switching frequency. The same frequency as our radios. Which, by the way, need to be registered with the FCC and can only broadcast on a certain frequency band. This is why I have the issue with it. Now, if you tell me the manufacturer can without a doubt guarantee this will never happen, I would be very interested in wireless. But until then, I have my doubts because of the above. Please don't take this as wanting to start an argument or anything bad. I just wanted to voice my thoughts. I am all for wireless. I have used it for robots before and works great for I/O in non-critical applications.

Share this post


Link to post
Share on other sites
It has been 7 years since I worked with the crane with wireless controls, so I don't recall the mfg name. I do remember asking similar questions, and their response was that the signal was encrypted and proprietary and they simply guaranteed it to work with no possibility of interference causing unexpected motion. They said that excess interference on the same frequency would cause the controller to shut down. The reaction time as far as button operations was not noticeably any different than with hardwired controls. I am sure that in the event of a comms loss between the controller and the pendant, there would have to be some sort of timeout period, probably less than half a second, but I don't know that for sure. The other Paul can probably fill us both in on the nitty gritty of these things... Ours did not require line of site. You could operate the crane from within about a 200' radius, even standing behind control panels, etc. Paul Edited by OkiePC

Share this post


Link to post
Share on other sites
I am not concerned with the crane controls. I am concerned in other operations especially where an operator would be interfacing with such equipment. You are correct about the crane controls. We had our Demag crane control rep come out and keep (for lack of better or the right word) "pinging" close frequencies and exact frequencies to our crane and it did shutdown. I guess you could do that in other applications, but is it cost effective?

Share this post


Link to post
Share on other sites
First off, you are comparing apples to oranges. The situation that you described relies on ON/OFF keying. That is, the receiver (a sensor in this case) is only looking to receive a sine wave signal, whether data is modulated onto it or not. Load cells are even worse because by nature the input system is looking for millivolt or microvolt signals and the long wiring that you typically have around a truck or railroad scale are nothing but antennas. ANY radio transmission nearby will cause problems. This type of system is almost never used for a couple reasons. First off, one has to decide how strong a signal to react to. This makes them very unreliable and susceptible to interference. Second, with an on/off keying system you need roughly 3 times the transmitter power to make it work compared to other alternatives (1/3 in a carrier, 1/3 in each of 2 identical sidebands). This MIGHT be fine with a sensor like you described, but it would be a total disaster with a system that is specifically meant to work as a radio. What if it requires a sequence of 3 frequencies, played in a certain order and that only one can be received at a time? In this case, your example of a commercial/industrial radio, EVEN if it had the right (wrong?) frequency, would not trigger the receiver. Even a broadband noise source such as an arc in a metal halide light cannot do it. And if the system is digital, it is very easy to construct an even more complicated pattern which has an exponentially decreasing probability that interference will inadvertently trigger something. This would be an example of frequency modulation. Actual digital radio systems usually use frequency modulation (transmitting different frequencies) or phase modulation (single carrier, but the phase changes). Actual modern systems are digital. At the end of a message, there's always a self-checking code of some sort because that's the primary way that the system determines whether the data is garbled or not. This wikipedia article describes one of the most common check codes, the cyclic redundancy check code: http://en.wikipedia.org/wiki/Cyclic_redundancy_check Notice that CRC's are "non-secure" methods for verifying that a message was not garbled. That just means that it is pretty easy for someone to intentionally create a fake digital message and cause harm to the system. If there is a secret or public key cryptography system involved, then you get digital signatures, which are a way of proving that a message was not garbled which is secure (the data cannot be forged), even if (in the case of public key systems) all of the information is publicly available. Both nonsecure and secure systems make these claims with a given level of probability (the chance of faking out the system). If you really need iron-clad lawyer-backed secure controls then use a crane pendant system. If you want the best of the best of the best, then call Control Chief. They have been through this issue dozens of times. Their market niche is not so much cranes as it is much bigger equipment that can easily kill lots of people. They sell remote controls for cement pumper trucks and especially locomotives. They pay lots of lawyers to defend law suits when wirelessly operated heavy equipment causes damage or destroys something. If you are looking for something with a TuV or SIL rating, I haven't yet seen a product that passes those specifications. It can be done, and it's just a matter of time before someone starts selling one. Right now it seems like the safety market is just getting over the idea that hard wired mechanical relays are less reliable than solid state ones with self-checking diagnostics.

Share this post


Link to post
Share on other sites
Paul, that was an excellent read...thank you very much...

Share this post


Link to post
Share on other sites
Paul, Thank you for the replies and the time to spell it all out for me. After reading your posts, I am indeed a more knowledgeable man about the wireless systems and how they operate. I believe I was thinking in the wrong direction and wireless can be just as safe as wired. You are a very knowledgeable man about wireless and hopefully more people can learn from this post. Again, thanks for the replies and thanks for keeping it civil for/with me. Most people would have gotten a little irate with me asking the same things over again. Corey

Share this post


Link to post
Share on other sites
In college, I studied communications. I've tried to keep up with it. When I was going to college, IEEE 802.11 just recently became a standard. It was intended to support noncritical applications like wireless LAN's in offices and houses at relatively low speeds (1-3 Mbps). It was NEVER intended to go in many of the places that it is now in use, and not to handle high speed. Many subsequent modifications have improved it but it is still very inadequate in many applications such as industrial wireless or "long" distance communications (more than a hundred meters).

Share this post


Link to post
Share on other sites
We have a number of cranes that are operated by wireless pendants - they are about the size of a multi-meter. They are problematic, but not because they don't work. On the contrary they work very well and have been very reliable. The problem is we usually can't find the remotes - no one puts them away when they are done.

Share this post


Link to post
Share on other sites
I worked in a shop that had 5 wireless controls atleast they where junk they couldn't even handle being ran over by a small 30,000 lbs forklift with 25,000 lbs of steel on it. No realy they where great I wish I had them at the house so I could use both cranes by myself and didn't have to ask my 4 year old to run one of them. He still can't look at me when he pushes the button. His little ears hear the contactor pull in and the head turns to see what is moving. Dad can't stop laughing because I have my little man helping me.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0