Linix Nursing Bed Actuator - Page 1
Forum section: electronics / projects

author: Dumpsterholic
author_rank: Regular Contributor
timestamp: December 22, 2017, 06:21:47 pm
content: Hi all.I recently salvaged what I believe to be a linear actuator from a treadmill. In its original use, it probably raised and lowered the belt, but I have other uses in mind. Problem is, the wire harness has me stumped. There are two wires going into the motor, plus six control wires to a box on the side. I tried applying 12VDC to the motor wires, but nothing happened. After reading several posts on linear actuators, I decided that maybe the thing requires some kind of control voltage in addition to the voltage for the motor itself. The model number for this device is Linix DTG110-92. Elsewhere, I have seen similar devices labeled "DTG12-XXX" or "DTG24-XXX, and I believe they run on 12VDC and 24VDC respectively. Based on the part number, I'm wondering if the motor I have may require 110VDC to run. Any advice or comments would be most appreciated. FWIW, the control wires are white, black, red, green, blue and yellow; the motor wires are heavier gauge black and red.

author: iainwhite
author_rank: Unknown
timestamp: December 22, 2017, 06:57:16 pm
content: I found this link:http://www.linixmotor.com/5-Nursing-Bed-Actuator.htmlLooks like the motor is DC and I think you are probably correct about the 110 volt ratingNot much data available from that link, however.

author: Dumpsterholic
author_rank: Regular Contributor
timestamp: December 23, 2017, 01:29:52 pm
content: Thanks Iain!I followed that link. There is a photo that very much resembles my little gem, so I believe they are in the same family. I have sent a request to the manufacturer for a data sheet and/or schematic.... Fingers crossed! In the event that they don't honor my request (after all, I am not a nursing bed manufacturer looking to buy 20,000 of them), I wonder if six-wire control harnesses are common for linear actuators. I have learned that limit switches often come built in to such devices, and that speed control via PWM is not uncommon. Elsewhere on other manufacturers' websites I have seen schematics incorporating multiple wires for feedback, limit sensing and control voltage, but none showing eight wires total. Also, Cytron Technologies at one time produced a motor control board, the manual for which shows it controlling a DTG24-100, (nearly identical to the unit I have, save for the number of control wires). Since the device I have came to me at zero cost, I may take the plunge and strip it down to parts I can readily identify, but before doing so I thought it wise to do as much research as possible.

author: Zero999
author_rank: Super Contributor
timestamp: December 23, 2017, 02:18:09 pm
content: This is the only thing I could find. It suggests there are three control signals: forwards, backwards and PWM, two wires are required for the 5V logic and another pair for power to the motor. That would make five wires for the logic/control. I don't know why there's an extra wire, it could be a motor healthy signal, which goes low if over:current/temperature is detected.http://www.robotshop.com/media/files/PDF/user-manual-mo-dtg24-100.pdf

author: Dumpsterholic
author_rank: Regular Contributor
timestamp: December 24, 2017, 01:19:15 am
content: Hero999:Much thanks. Your post helped me sort out some ideas circling around my muddled brain. BTW: The linear actuator may have comenotfrom the treadmill I scavenged, but rather from a sort of "massage chair" which lay right next to it in a junk pile outside a medical equipment supply company. Since there was a circulating pump for hot fluid (oil?) which was part of the so-called "massage" the unit delivered, it stands to reason that a "motor healthy" signal may need to have been incorporated into the circuitry in order to preventbad stufffrom happening.... Based on this knowledge, I think I'm ready to start poking around with some further tests. Even if I end up destroying the unit, it won't matter. The control circuitry can be sacrificed; at the very least I will end up with a rather robust motor and a gear train. I now know that in the area where I live, a sort of retirement destination for the well-heeled, such massage chairs, along with nursing home beds, treadmills and other exercise machines are plentiful.

author: Dumpsterholic
author_rank: Regular Contributor
timestamp: January 06, 2018, 03:45:28 pm
content: I'm happy to report that I have decoded this linear actuator. Having requested a data sheet from the manufacturer, I waited for awhile and finally gave up. Since the thing cost me nothing, and since I don't have a pressing need for it, I decided to just open it up and have a look inside. The result was less than surprising. There is a lead screw connected to a sliding tube; the motor has a gear train which moves the lead screw back and forth. The two heavy black and red wires connect to the motor itself, while the remaining six wires connect to a pair of SPDT limit switches, one on each end of the tube. The Wikipedia article on linear actuators has an illustration which matches up nicely with the unit I have.Since I stupidly did not salvage the control circuitry, I can only guess that speed and direction were controlled via the motor leads, while the six limit-switch wires probably just kept the tube from moving too far in either direction of its travel. I have attached a rather crude drawing which calls out the various wires and shows how they are connected internally. Soon I will test the motor by applying a varying voltage of around 50 to 110VDC and watch what happens. I know from reading a number of online articles that a relatively hefty motor like this (weight of a brick, size of a beer can) can draw a lot of current, so I have purchased a variac and am waiting for a 50A 1000V bridge rectifier to which I will affix a big aluminum heat sink. Any warnings or advice would be appreciated, but I think I know what I'm doing....

author: Zero999
author_rank: Super Contributor
timestamp: January 06, 2018, 07:04:28 pm
content: Bear in mind that any DC power supply, derived from a variac+rectifier, won't be isolated from the mains. 110VDC is considered to be safer than 110VAC, because AC interferes with the rhythm of the heart more than DC and it has a much higher peak voltage. This means the motor will not have sufficient insulation for mains voltages. Only ever do this for test purposes and don't touch the motor's metal frame when doing this. Put it on an insulated mat and keep your hands away before powering it.

author: Dumpsterholic
author_rank: Regular Contributor
timestamp: January 07, 2018, 06:23:33 am
content: Thanks again!I will follow your advice once I have received the rectifier and hooked it up to a test jig. I gather that placing an isolation transformer between the mains power and the variac would mitigate some of the danger, but I don't see any justification for spending that kind of money while I still lack such basic test equipment as a function generator, an oscilloscope or a quality power supply. Even if the LA is operational, I will more than likely consign it to the junk box, since at this time I have no use for it.I do see some potential uses for LA's; should I stumble upon one that runs on a lower, safer DC voltage (12V or 24V) I might do some experiments. Can't wait to prototype my Arduino-driven burger flipper, mustard squeezer and bun butterer so I can be ready to cash in when McDonald's finally decides to replace all their employees with robots....

author: Dumpsterholic
author_rank: Regular Contributor
timestamp: January 10, 2018, 06:09:41 pm
content: Solved!"Eppur, si move!"OK, after much nail-biting, I finally built a test jig as discussed above and powered up my linear actuator. Thanks to the help, support, advice and warnings of Hero999 and iainwhite, the experiment came off without a hitch. No sparks, no smoke, no grinding of gears; just a quiet, steady advance of the cylinder.Because I know that inductive loads can produce large voltage spikes when powered down, I ramped up the voltage slowly on the variac, advanced the tube a few centimeters, then gradually reduced the voltage back to zero. Don't know if that was really necessary, but I believe in being careful. I have not yet bothered to disconnect the crimped-on terminals which connect to the DC output of the rectifier to reverse their polarity, but my guess is that simply swapping these two leads will allow me to power the LA in the opposite direction. Problem solved!Now, I'm curious about what kind of control circuitry was originally involved. I've seen various "black boxes" that allow a nursing bed to be raised and lowered, but haven't had the chance to tear one apart. And since they cost a bundle, I don't want to buy one. Based on circuits I've seen posted here and elsewhere, what I need is a hefty DC power supply for the motor plus the control circuit itself. This might incorporate an H-bridge, a momentary toggle switch and a power transistor (MOSFET?), and a lower-voltage input to fire the transistor. I will likely also need a snubber circuit incorporating a couple of diodes (one for each direction of current flow) and a resistor. Since I don't yet have any reliable specifications for the motor, designing this circuit is not a big priority right now. But if anybody can point me to an example circuit to get me in the ballpark, that would be most appreciated.The DTG110-92 is about the size and shape of a 12oz beer can and runs on 110VDC. Absent any test gear, I can't even guess how much current it draws, let alone what the induced voltage spikes might look like, though I guess a DMM set to measure current in series with the load while it's powered up would get me started, right? From there I could presumably calculate power dissipation and start looking through datasheets to find parts that will stand up to use in a such device.Hmmm, speaking of 12oz beer cans.... Gotta go!

author: Zero999
author_rank: Super Contributor
timestamp: January 10, 2018, 07:33:03 pm
content: There are plenty of h-bridge motor driver ICs which will be suitable for that motor. It's very important to know what current it draws, which will be dependant on the load.The inductive kick-back isn't a problem and is absorbed by diodes across the transistors, which divert it back into the power supply. Providing the power supply has enough decoupling capacitors, the inductive kick-back won't cause any overvoltage. The only potential issue is if the drive performs active braking, when the motor's role is reversed and it behaves as a dynamo, injecting a considerable voltage and current into the supply, but letting it freewheel to a stop is fine.

author: Dumpsterholic
author_rank: Regular Contributor
timestamp: January 11, 2018, 01:21:03 am
content: Excellent!I gather that building up an H-bridge from separate MOSFETs, IGFETs or other transistors is not worth the effort. I just spent a bit of time Googling various motor driver ICs and kept being directed to the ubiquitous L293D and L298N, which though dirt-cheap apparently aren't rated for supply voltages above 35V or so. And I found quite a few ready-made complete motor controller boards in $50-$100 range, which seems a little spendy for my budget, considering what I paid for the LA....So I dug around at Digi-Key, Jameco, and Mouser and became thoroughly bewildered; I then visited company websites for Infineon, International Rectifier, ST Microelectronics and Texas Instruments and spiraled further down the rabbit hole. I now have a bunch of data sheets and sales brochures in .pdf form saved on my laptop, plus a greater awareness of the vastness of the industrial-control market. I learned new vocabulary terms such as "gate driver" and "quadruple half-H bridge", but still find myself at sea.So, I'm hoping somebody can point me in the direction of an IC that I can base a motor-control circuit on. I realize that without a current rating, it won't be realistic to start the design process, but let's just guess that my motor draws 10A @ 110VDC and go from there. Though-hole components would be preferable, but from what I've seen the kinds of ICs I'm looking for may only be available in SOIC packages. That's OK. There are plenty of people soldering these things onto PCBs by hand. Way back in the '90s I worked for a company whose lead engineer showed me some circuits he was building using with these flea-sized ICs; he warned me that the DIP packages I was used to might someday become obsolete, and he was most prescient indeed. FWIW, I am proficient enough at soldering, metalworking and reading application notes schematic diagrams that I feel confident that my circuitwilleventually work. And if it doesn't, oh well. I will take full responsibility for my failures, and share the credit for my successes with those of you who have chimed in on this forum so far.

author: Zero999
author_rank: Super Contributor
timestamp: January 11, 2018, 10:18:23 am
content: Actually, at this sort of power level and voltage, it makes sense to use discrete MOSFETs and a separate driver IC, to translate the logic levels into the drive signals for the MOSFETs. One thing you need to beware of is many of these drivers use bootstrapping capacitors, to drive the high side, which means the output can't go high for too long, as the capacitor needs time to recharge. This limits the duty cycle to below 100%. The only way to get 100% duty is with an isolated DC:DC converter for the high side, which increases complexity.https://www.semicon.sanken-ele.co.jp/sk_content/sma2404m_ds_en.pdfhttps://www.intersil.com/content/dam/Intersil/documents/an90/an9010.pdfhttp://www.st.com/content/ccc/resource/technical/document/application_note/09/e6/1b/f4/72/7a/43/81/CD00200596.pdf/files/CD00200596.pdf/jcr:content/translations/en.CD00200596.pdfhttp://datasheet.octopart.com/MD7120K6-G-Supertex-datasheet-11966372.pdfhttps://cdn.anaren.com/product-documents/MSK/DiscontinuedProducts/bridges-gate-drive/MSK4227_DataSheet(Rev_E).pdfhttp://www.ti.com/lit/ds/symlink/ucc27714.pdfhttps://www.infineon.com/dgdl/irs2110.pdf?fileId=5546d462533600a40153567660ff27b0https://www.infineon.com/dgdl/an-978.pdf?fileId=5546d462533600a40153559f7cf21200

author: Dumpsterholic
author_rank: Regular Contributor
timestamp: January 11, 2018, 02:30:03 pm
content: Wow, I just glanced over those application notes and data sheets, and I feel like the snake who swallowed the rabbit! Operative word here: "steep learning curve". I probably will not get around to tinkering with the linear actuator for awhile, but it's good to have some idea what kind of control circuitry is out there. Thanks for sourcing these documents.I should note that the "10A @ 110VDC" I came up with above is a wild guess. As it happens, in the place where I scored the LA I also grabbed a pair of motors made by Shanghai Jugong Industry Co, Ltd. which have about the same size and heft but which came equipped with pulleys for driving belts. Grabbing one at random, I read this from the label:6ZY10002 DC MOTOR100VDC P0809040.58A 31W 1500 r/minI suspect the motor on the LA has similar specs, so maybe the monster bridge rectifier I bought off of eBay was overkill. No matter. At least it didn't burst into flames when the LA was under test! Living in a part of Florida where nursing homes are about as common as liquor stores, I imagine that I will be finding more of these motors and linear actuators.... And at the very least, I now know how to safely test them for functionality.

author: arw
author_rank: Newbie
timestamp: August 22, 2019, 04:48:15 pm
content: By coincidence I found one the same DTG 110-92.. I tested the motor at 24 volts DC thinking it would not be sufficient however it did move slowly taking about 50 mAmps. Even worked down to 10volts. Almost certainly 110volts nevertheless seems to work OK at lower voltages. I did not test under load though so it might stall at the lower voltages. Armature resistance 95 ohms, possibly what the -92 means. I did not try the control wires but reversing the voltage changes direction.

author: arw
author_rank: Newbie
timestamp: August 22, 2019, 05:13:36 pm
content: Stall current at 24 volts would be around 250 mA so about 6 watts power required, which is probably enough to drive light loads, given the high gearing . Stall current at 100 volts would be over 1 Amp so 100 watts and enough for some serious motive force. A reasonable compromise might be to drive at 50 volts so stall current about 500mA or 25 watts depending on the load required.