Generally in order to do that, you need an initial mechanical design concept.
If using a rack & pinion then you need to chose a rack of a certain pitch and pinion with a diametric pitch together with the estimated weight of moving parts and from there you should get an idea of the effort required to move the load.
You can usually find helpful mechanical design from the sites such as Boston Gear, Martin Sheave, also Misumi who have a huge catalogue which they send out free that also has engineering designs, as well as stocking a very wide range of mechanical components together with online selection guides.
Max.

 

You may also be able to achieve that rate with a linear actuator, have you looked at this approach?
https://www.servocity.com/html/12v_linear_actuators.html
Max.

 

Hi,
Thank you very much for the great support. I will go through the details and get back to you later

 

hai,
i foud that the structure similar to the one i attached here can meet my requirement.But how to calculate the torque needed? the diameter of the gear can be a reasonable one,say 2inch and 3inch.
Thanks and regards

 

If gears X and Y have the same 4mm tooth pitch and a diameter ratio of N:1, the motor torque required will be 9.8 x 5 x R/N Newton-metres, where R is the radius of gear Z in metres. However, gears X and Y will make just over one rotation to move the load 4", so your motor will not be rotating much! I think you'd be better off using a worm-drive or ball-screw mechanism, having a much higher reduction gearing ratio and consequently lower torque requirement.

 

If gears X and Y have the same 4mm tooth pitch and a diameter ratio of N:1, the motor torque required will be 9.8 x 5 x R/N Newton-metres, where R is the radius of gear Z in metres. However, gears X and Y will make just over one rotation to move the load 4", so your motor will not be rotating much! I think you'd be better off using a worm-drive or ball-screw mechanism, having a much higher reduction gearing ratio and consequently lower torque requirement.

Not to mention much lower friction and efficiency too. Spur gears have a number called pressure angle, and the force transmitted from one gear to the next is proportional to the cos function of that angle. I'd say a ball screw actuator would be a far better choice for this application.

 

You need to know the diametric pitch of the relevant pinion you intend using, as well as the rack pitch.
Max.

 

This seems like a situation where they should just buy an off the shelf system or hire a proper Engineering firm to complete the work..
There are many Engineering aspects involved in this and its clear that the TS can't even handle the most basic of them..
And I don't think its fair at all to expect us to give any meaningful information with the limited information provided..

There could be many safety aspects that aren't even given/known to us..

There has been plenty of great information given by the members here but the TS keeps coming back to his original basic question and has not provided anywhere near what I would require to answer and feel safe.

 

Hi,
I have searched about the diametric pitch of pinion as well as rack pitch. But i couldn't find a reasonable theory to select a particular value for the same. If you have any suggestions please let me know. This thread gave me chance to learn many things about mechanical design. Thank you to all the people who is responding to my doubts. If it is possible let me know a reasonable diametric pitch of pinion as well as rack pitch and how to estimate a rough torque value for the motor. Any link to good document to learn more about the rack and pinion system and gear system will be much helpful

Thanks.

 

Here is a few that may help.
http://www.atlantadrives.com/pdf/ads_racksel.pdf
http://www.cnc-arena.com/en/forum/rack-pinion-calculations--171040.html
http://www.mecco.com.au/racksgears.html
Max.