# Linear actuators in a cartesian robots

I would like to make a Cartesian robot with maximum speed of up to $1ms^{-1}$ in x/y plane, acceleration $2ms^{-2}$ and accuracy at least 0.1mm. Expected loads: 3kg on Y axis, 4kg on X axis. Expected reliability: 5000 work hours. From what I have seen in 3D printers, belt drive seems not precise enough (too much backlash), while screw drive is rather too slow.

What other types of linear actuators are available? What is used in commercial grade robots, i.e. http://www.janomeie.com/products/desktop_robot/jr-v2000_series/index.html

• @Chuck Well it's not. I'm not asking for a specific models (although examples are welcome). I just want to see answers like "rack and pinion would be good because..." or "belt drive would be ok, you just need to..." etc. Oct 13 '15 at 11:47
• What is a velocity of $1\,m^{-1}$, or an acceleration of $2\,m^{-2}$? Also, you have to specify loads, and other things that are important for you. These include weight, price, precision/accuracy/backlash, reliability and durability. What, for instance, is "precise enough"? Oct 13 '15 at 12:34
• @JJMDriessen these were from edit by other user. I have already fixed it. I've also added some additional info. Oct 13 '15 at 13:12
• Thanks mactro, you might want to mention the total working envelope you are looking at too. Oct 13 '15 at 13:14
• @mactro - I see; you're asking for other methods of actuation. You asked for types of "linear actuators", perhaps not realizing that an (implied electric) linear actuator refers to a specific style of actuation. Oct 13 '15 at 13:15

## 1 Answer

I have worked on a cartesian robot with similar requirements as your own, and we selected direct drive synchronous linear motors for our x/y stages. In our case, both axes were around 2m in length, but magnet the tracks have the potential to be as long as you need to build them.

† Less than an order of magnitude higher at $2/5ms^{-1}$ velocity & $10/20ms^{-2}$ acceleration for x & y stages respectively.

In our case, we used an exposed magnet track linear motor from aerotech, but for most applications a u-shaped track is more convenient as it contains the high magnetic fields within a more enclosed space. Our cartesain robot had large exposed magnet track surfaces which meant that we had to post warnings regarding letting pacemakers and metal tools getting too close (a screwdriver could be attracted to the magnet track with sufficient force to damage both and anything which got in between, such as your fingers).

There are a number of manufacturers making direct drive linear motors (as a google search will show), and in addition to flat and U-shaped tracks, manufacturers such as Nippon Pulse and LinMot do cylindrical shaft motors, which might be easier to retrofit to a robot which currently uses a lead-screw linear actuator.

The accuracy of these direct drive systems can be very much dependent on tuning. They often suffer from significant cogging effects, though some manufacturers claim to include patented zero and anti-cogging techniques and often maximum and minimum speeds can be related to how smooth you want the movement to be at those speeds.

As an aside, we also used air-bearings on our X track, which is how we managed high speed and acceleration with a relatively small motor. They were really difficult to tune however and this was complicated by the fact that we had 6 X-carriages on each Y beam (of which there were two, so 14 x/y axes and 16 motors in total).