linear guide action

[Gioan]

Bye to all,
I have a little generic question about precise linear movements.
wanting to deepen my knowledge about the handling of skates on linear guides (I will have to do a job in the near future using them) I see that you usually use the following systems:
- ball recirculation screw
- rack and pinion (usually tilted teeth)
- dentate straps
what I would like to understand is how the choice of a system is made rather than another (the following variables surely come into play: performance, translation speed, positioning accuracy, costs etc.).
is there a network of detailed documentation explaining these concepts? or better, can you recommend me a textbook to buy to deepen these concepts and the sizing of these systems?
Thank you.

 

[Iena]

Bye to all,
I have a little generic question about precise linear movements.
wanting to deepen my knowledge about the handling of skates on linear guides (I will have to do a job in the near future using them) I see that you usually use the following systems:
- ball recirculation screw
- rack and pinion (usually tilted teeth)
- dentate straps
what I would like to understand is how the choice of a system is made rather than another (the following variables surely come into play: performance, translation speed, positioning accuracy, costs etc.).
is there a network of detailed documentation explaining these concepts? or better, can you recommend me a textbook to buy to deepen these concepts and the sizing of these systems?
Thank you.

I don't know, but I might be wrong.
cmq to the question about what system you have already given the answer, that is: precision costs etc. etc. I personally prefer not to use them in favor of straps, maybe those with steel wires. there is also another alternative for moving rowing screws: motor-reducer epicycloidal- joint and screw.
cmq linear is a vast mooooolto argument

 

[Pastorman75]

There is no way I know any text. only imagination, theory and experience can help you.

I can suggest this to you:

1) Define positioning and repeatability accuracy.
2) define whether translation is also associated with the technological process (laser, plasma, etc.) or is a simple +/- precise positioning.
3) define whether external forces (process or not) are involved in motion in addition to inertia.
4) define positioning speed and acceleration.

already define these parameters excludes many of the design possibilities, for example:

- machine in which the bike is associated with the process with forces during the movement (fresher) - it implies - surely no toothed belt.

- high accelerations and precision thrust on short runs - it implies - linear engines could do to your case.

and this only to talk about the actuators; if we switch to linear translation components then find everything:

ball recirculation guides in different precision and precarious classes; They are usually rectified but are also drawn (less precise but cheaper).
to limit weight, when it's a problem, thk makes of quarries inside (I'm cool).

then there is the problem of the replacement, the guides do it in length max 3-4 meters and you can have in precision such that as you put the "they are good" in junction (no steps between one and the other) or there are those that you have to mount in the sequence set by the manufacturer.
for the latter, if after 2 years you have to change one, it is not said that the joint returns as before.

we can talk about wheel guides or ball sleeves, crawling etc.
Recently, the technopolymer (plastic) guides have made good progress. igus offers different models.

As they told you, the subject is vast!

if you add some info, maybe we narrow the field of possible solutions.

Hi.

 

[Gioan]

Thank you for answering me, especially pastorman for explanations.
I want to build a machine tool for light work with the three classic movements x y z.
seeing what is on the market I noticed that the alternative is usually between the handling with pinion-crew or recirculation screw; I would therefore be more interested in understanding the merits and defects in comparison between these two systems.
But there is no text that deepens these arguments.

 

[Pastorman75]

for a small cutter, then I would say:

- traslation on recirculation skates (if they find very cheap)
- movement with screw (better to recirculation of spheres - a little care if rectified, less saddled)

What are you thinking?

 

[Gioan]

I thought of a repeat positioning accuracy of +-0,02.
Can I ask you, in general, what do you prefer handling with recirculation screw rather than the lazy-cremagliera system?
Thanks again.

 

[MFT]

I thought of a repeat positioning accuracy of +-0,02.
Can I ask you, in general, what do you prefer handling with recirculation screw rather than the lazy-cremagliera system?
Thanks again.

that precision you can also obtain with a pinion-cremagliera provided that they are of good quality (returned and inclined) and its reducer also at reduced play.
to my client I made a cnc for wood with this method and the precise one gets it, I put a kit reducer with pinion and its tempered and rectified rack of alpha.

Hi.

Mar

 

[Pastorman75]

lazy racks are excellent.
It depends on the race you have to do on the axis.

for short runs (minimum of about 3 meters) I prefer the screw while for long the screw becomes unpractical if not even not feasible.

another advantage of the screw is the intrinsic reduction ratio that sometimes allows you to sew the motor shaft directly on it without interposing any gearbox.
this has a relapse also on the relationship between the motor and reflected inertias that you have to keep under control for the design of the axis.

pinion/cremagliera (unless to use couple engines) practically always needs a reducer (more cost).

a further advantage of the screw is the ease with which then "preload" the system and avoid "backlash" phenomena (play in reverse).

in the advanced rack systems are used 2 pinions with a motor (preloaded double output reducer) or even adopt the so-called "electric charge" by fitting two engines on the same axis and leaving the preload to the motor drivers (top solution for performance and precision but very expensive)
You can get an idea of these systems on the redex-andantex website.

greetings

 

[Gioan]

Thanks again for the explanations, pastorman I see you are very prepared on the subject.
I will try on the weekend to consult the sites you have indicated to me.
However, there are no texts with these concepts explained.

 

[Jeffcott]

Hello everyone, I take advantage of this discussion to ask for advice on a job that I am going to study. I was asked to design a lazy-cremagliera system that vertically shifts a small working platform. to be more precise I describe you in detail as you require. the platform (or operating machine) of base 260x430 mm and height 260 mm (unrelevant data) must move vertically for a height of 2400 mm making of stops of 1 secons every 600 mm. the speed that must possess this platform is 0.2 m/s and its weight is 30 kg. reached the fifth position will have to return to starting position, going down to the starting point, and resume its 5 phase cycle (the first at position 0 and the other every 600 mm). other specific will be the need to use, choosing it appropriately, an electric motor sites from 1400 rpm. who can give me suggestions on how to choose the different components to achieve such a system? I make your contribution. :smile: a catch!

 

[Pastorman75]

do you have electrical components on board or do you need to connect some pipe or cable to something on the platform?

I ask you to understand if you need to put the engine on board.

If, as I imagine, you have something to connect on the ground platform, then it is worth putting on the engine as well.

instead of the rack I recommend the chain with three pinions (2 follies and 1 motorized) put in ground to the top. if the positioning is not too precise is a valid and economical alternative to the rack.
better a toothed belt with the same principle; silent and almost maintenance free.
30 kg would hold them well.

for the stop I recommend a reducer with integrated brake or choose a reducer with a performance of less than 0.5 (motortrograde not allowed) and remove any problem.

If you do not put anything on the platform to connect to the ground with pipes or cables, then you may think of a system with fixed motor and transmission via belt, chain or screw (difficult due to speed).

greetings

 

[Jeffcott]

Thank you for the answering pastorman! :smile:
on board the platform I have a punching machine therefore I think it is appropriate to equip the platform also of the engine. but what do you mean by chain with three pinions? for now I have only had a guideline but I can very well get rid of something more suitable for the situation therefore every council properly multiplied is well accepted. I think it is appropriate to use an auto-frenating motor and I also ask for advice on this choice. What is your opinion?

 

[Pastorman75]

I mean a system where instead of the fixed rack you have a chain placed in "thyrus" between the ground and a higher attack, which in your case could be about 3000 mm from the ground.
the chain is not straight but passes between three pinions placed on the cart of which two are crazy, the external ones, while the third, central, is motorized.
If you want me to do you a sketch and place.

Since you have a puncher, however, I don't know if it's the best way since you have forces generated by the puncher itself.

It is worth understanding the intensity of such forces as if the machine or the motion system is not rigid enough it may feel the correct success of the process.

from this point of view the rack is usually more rigid than the pinion chain system.

So the punching machine basically what punching? steel, plastic or anything?
What form? massive (and therefore substantially fixed) or a sheet or tape (and therefore substantially yieldable)?
in which direction is the motion of the punch? parallel to the motion of the platform or orthogonal to the same?

Finally, by punching machine I mean a system consisting of matrix/punzone that performs a hole even not to circulate on a certain thickness.
Is this your case, or do you only have a punch that "decides" the surface without a matrix below?

Hi.

 

[Jeffcott]

do not consider the punching machine as it will certainly change the use of the platform, for now the only certain thing is the height it will have to reach and the weight of the same pairs to 30 kg. cmq would make me picere a scheme to better understand the solution with chain. but apart from this choice, how does it proceed for the balance of the structure seen the 30 kg placed almost 3 meters high? and finally need a motor, what power? is it appropriate to self-frenating?

 

[Pastorman75]

I'll sketch.

suitable self-frenating motor or reducer system that does not admix reverse motion (which is to say that transmission performance must be less than 0.5)

for the power you must see; There are several ways. the simplest and coarse is:

♪

pt= theoretical power (w)
f= force (weight in your case) in newton
v= speed (m/s)

to correct with various mechanical yields "n".
ipotizzo performance n=0.3 (30%) then:

pn=pt/n

pn= necessary power (w)

Hi.

 

[Jeffcott]

0.5 as for lifts
I understood the solution with chain but I think it doesn't like it very much
:smile: cmq thank you very much for the answer

See you soon!

 

[Jeffcott]

...cmq remains the problem relative to the balance of the structure, I will have to carry more than 30 kg to almost 3 meters height. How can I balance the structure?

 

[Pastorman75]

too generic.
post a drawing of what you have in mind would help all users to give you tips.

Let us know.