Market Research: Linear Actuators
idbruce
Posts: 6,197
Hello Everyone
As many of you know, I have had a CNC PCB Drilling Machine in the works for quite some time, and I just recently started working on it again. This machine is going to be built with three stepper and screw driven linear actuators, which were designed by yours truly. When I began designing the PCB Drilling Machine, my goal was to make the linear actuators as cheap and as accurate as possible, so that I could offer them seperately as a reasonable solution to the hobbyist needing linear actuators. To be perfectly honest, I believe I have a pretty good solution. Within the next several days, I should have three prototypes ready for testing. After testing, I will determine the price, and start promoting them on my web site.
At this point in time, I am kind of curious to what is in the marketplace and the going rate. Of course I have links to various linear actuators and their prices, but I am looking for the lowest priced product with similar features. Until I get finished with my testing, this is what I know so far about my first model:
Bruce
As many of you know, I have had a CNC PCB Drilling Machine in the works for quite some time, and I just recently started working on it again. This machine is going to be built with three stepper and screw driven linear actuators, which were designed by yours truly. When I began designing the PCB Drilling Machine, my goal was to make the linear actuators as cheap and as accurate as possible, so that I could offer them seperately as a reasonable solution to the hobbyist needing linear actuators. To be perfectly honest, I believe I have a pretty good solution. Within the next several days, I should have three prototypes ready for testing. After testing, I will determine the price, and start promoting them on my web site.
At this point in time, I am kind of curious to what is in the marketplace and the going rate. Of course I have links to various linear actuators and their prices, but I am looking for the lowest priced product with similar features. Until I get finished with my testing, this is what I know so far about my first model:
- 4-1/16 of linear travel
- 1/4-20 lead screw
- (2) Silicone bronze lead nuts that can be shimmed for adjusting backlash
- NEMA 17 high torque stepper motor (optional motors)
- UHMWPE bearings
- (4) 0.125" diameter mounting holes for fixturing to the carriage
- (4) 4-40 threaded holes for mounting the actuator
Bruce
Comments
http://blog.makezine.com/maker/bart-dring/
Are the UHMWPE bearings sliding as you showed earlier? Do you improve the accuracy by making the slide part longer?
Are 1/4-20 lead screws very expensive, or are these the same as 1/4-20 screws? Where did you get them?
This is a completely different design then what you seen, so the UHMWPE bearings are completely different and being used in a different manner. As for the lead screws, yes they can be pretty darn expensive, which drives the cost up, as well as the nuts. Whenever you get into ACME or ball threads, the price jumps drastically. So my design is still based on common 1/4-20 threaded rod. The accuracy and movement won't be anywhere near the equivalency of ball threads, but I think I have a pretty good design to provide a fair amount of accuracy.
One of the major problems associated with standard threaded rod is backlash, and I believe I have that pretty well solved from earlier experiments.
Bruce
I only use ball-screws where I have no other option.
Mickster
Pertaining to the Z-axis, gravity and the load would cause the carriage to move. So instead of designing both screw driven and belt driven assemblies, I concentrated my design on a screw driven assembly because of the Z-axis. Additionally, belts are much faster, but I believe screws offer greater precision and reliability.
In a commercial high precision setting, I would tend to agree, however my goal is to target the hobbyist market, like for the maker bots and such.
Bruce
What is the basis for this belief?
Mickster
Don't misunderstand me, because I know that belts are very accurate, and my beliefs are not based upon any solid facts. But I believe that belts will stretch faster than a lead screw wears, both of which cause inaccuracies. Additionally, considering that belts are much faster, particular attention must be paid to the load and ramping speeds, otherwise it may shoot past the desired position, because their is nothing to stop the linear motion, whereas with a leadscrew, the threads stop linear motion.
Bruce
York Industries is a high quality supplier of timing pulleys, timing belts, idler pulleys, and belt tensioners. By visiting their web site, you can download their configuration software, which can be a helpful aid in designing belt drives.
http://www.york-ind.com/
Bruce
http://www.nookindustries.com/home.cfm
I'd guess half "Industrial" price would intrigue the hobbyist, but then that's still out of most people's price range for three units. Heck, that's $100 in parts on that little actuator and the price isn't related to the stroke really.
Nook
Misumi
THK
LM76
PCB Linear
Howa
IKO
LinMot http://www.linmot.com/?gclid=CL6ljtq3368CFQOFnQodhEw3iw
Parker https://www.motionusa.com/catalog/parker-hannifin?gclid=CKPn9-a3368CFcyb7QodOQsfAw
Oriental Motor http://www.orientalmotor.com/products/rotary-linear-actuators/motorized-linear-slides.html
Thanks for the input.
Yea, motion products are quite pricey.
I figure I will offer up my little units for about $150.
Bruce
We evaluated a THK linear motor here at work, as we're a distributor of THK... regardless: http://www.thk.com/us/NEWS/products/20090430.html
That baby will absolutely haul ...!! We had it set to creep across the 1m stroke, index a couple times then beyond a blur, zzzzzzzzZIP to the other side, all 4m/s. I think it's built like a rail gun with the linear magnet segments.
I wanna build a CNC with two of those
$150 doesn't sound too bad honestly Bruce, if your specs hold true. It's still outa' my poor boy budget range but for a linear actuator, that's good. I had some "Linear actuators" bookmarked that cost less, but they were more electric thrusters than anything and not very position-able with poor radial load support (meaning it needs external bearings) and backlash.
That said, in a pure drilling app, there won't be any side load, except for an inertial one. So a spring-loaded backlash take-up mechanism may suffice. I would never advocate a jam-nut approach, like the Sherline mill used, though. It's just too fussy to maintain in adjustment. (But, due to side-loading in a milling operation, a spring-loaded take-up would not have worked.) And, if you do persist in using machine threads, by all means don't just buy cheap zinc-plated threaded rod from the hardware store. Get something that's precision-threaded and is -- or can be -- hardened, in order to minimize premature wear.
-Phil
http://www.use-enco.com/CGI/INSRAR?PMSECT=0000000451
From my understanding, stay away from stainless screws with bronze bushings and nuts.... but I do not have experience to back that up
1/4 x 16 aren't too bad. I think standard 1/4x20 threads may not be accurate enough.
I am not a big fan of machine threads for this type of application, however as previously stated, ball and acme threads drive the price way up. ACME threaded rod is not that costly, but the nuts are way out there, and to buy a tap and make the nuts, well I suppose that is within reason, but still costly and time consuming. If the available ACME products were a little more in reason, then I would go ACME all the way.
When it came to selecting the lead screw material, I checked and weighed all options. Unless a person has a lathe to cut their own threads, 1/4-20 threaded rod with machine threads comes in one basic formula (CHEAP) I forget the grade. I checked McMasters, Graingers, etc.... One common thread.
To save the threads from wear on the CHEAP lead screws, as you can see above, I will be using silicone bronze nuts. Replacement of the lead screws should be cheap and easy to replace. Simply loosen the two set screws on the coupler to the motor, unscrew the lead screw from the carriage, and loosen the two set screws on the other end within a journal that runs within a bearing. I will probably supply replacement lead screws for about $4-5 plus shipping. The bronze nuts are a little more costly and labor intensive, so I will probably sell replacements of those for around $15. Between the bronze nuts, proper lubrication, and properly adjusted backlash, these CHEAP lead screws should be able to get a fair amount of use before requiring replacement, but of course they will wear fast.
As for the subject of backlash, you never want zero backlash, because then the threads are locked, unless of course you are using spring loaded nuts as you mentioned. Once again, I considered all options and looked at many designs. There are some pretty interesting designs out there, that would probably work well, but then it becomes labor intensive. Backlash on these units should be able to be adjusted quite easily with different thicknesses of paper or metal shims. Simply remove any upper stages (4 screws), loosen the two set screws on the coupler to the motor, unscrew the lead screw from the carriage, loosen two screws for one of the lead nuts, slide in shim, tighten the two screws, reinstall lead screw and upper stage assemblies.
To be perfectly honest, it won't be anything to fancy, but I think it should provide a fair amount of precision at an affordable cost. I would estimate that 90% of these linear actuators will be constructed from extruded aluminum.
Bruce
The even have spring-loaded anti-backlash nuts.
-Phil
Thanks for the link.
I have visited that page before, but I must have lost the link.
Keep in mind that I am not disagreeing with you, because I totally agree.
However, consider this...
Each assembly uses approximately 1 foot of threaded rod and two bronze nuts. At the bare minimum, that is $54 per stage * 3 stages equals $162. The price of the lead screw and nut assemblies quickly raise the price bracket, thus making it less obtainable for many people.
However, if I do realize any sales from the promotion of this product, I could always offer an ACME version for those willing to pay the upcharge.
Bruce
Don't EVEN say rail gun around these parts! I have too many projects already!