Servos & Steppers.

[tutichip]

if you want to give me 10.00 dollars , this is OK , if you want to give me 1,000 , this is better .

Foot pounds is a measure of torque . It can also be a measurement of kinetic or potential energy .

I suppose at some point we may have a unified system of measurement , whilst I have a certain affection for the old "english" system ,with its little quirks ( I am for instance a full bore rifle fan , and muzzle energy just has to be in footlbs) , there is no way that we can say that using a mish-mash of old units that have no relationship . Sure , I know what a CuFoot of water weighs , but it must be easier to work in KgF , Metres , Centigrade and untits that actually have some reference together .
My pet hate is to see drawings with "old" units interspersed with SI units .

Not in the least bit relevent to the guy who wants a servo drive , but there we go .

 

[elevmike]

Great, Thanks for all the help in advance.

Background:

We typically use these operators: http://www.gal.com/images/content/aboutus/news/20050713_NGDO/MOVFR2-01_LG.jpg

The large pully on the left has a swing arm that connects to a pivot point on the car door. We order the operator as per job specs, and the manufacture configures it approperately. A real turnkey operaton, hence I have no expierance figuring all this out.

The problem with the GAL operator is that the customer does not have the head room to mount the conventional operator on top of the cab like this:

Note the 16-1/2" dimension above the header. In this case the header will be aganst the showroom ceiling.

Possable solution:

Install a small motor behind the header (there is about 3-1/2" of space behind the header). The motor will have a timing pully that will drive a horizontal endless belt. The belt will be clamped to the door hanger rollers. The actual max force applied to the door cannot be more then 30lbs. This is a 42" opening so each door panel will travel only 21" Rule of thumb is that the door should close at the rate of no more then 1 ft opening per second. So if you have a 4 ft opening the doors should take about 4 seconds to close. However there is a kenetic energy limitation that may alter the actual speed depending on the moving mass. I have to look that up & I actually have to go and weigh the door panels, and make some drawings to show exactly what is what. Once I get that done I'll post better info to work with.

Mike.

 

[Steve Bailey]

Why are you considering a servo for this application? It looks to me like the actuator simply needs to move the doors between the open and closed positions.

 

[elevmike]

I'm looking for something small & mechanically simple to provide the power and control to move the doors with a degree of accuracy and repeatability. Actually I'm not entirely sure what the answer is yet. I got hit with this at a 3:30pm meeting yesterday, and have to provide an answer by Monday AM, so I've got some cramming to do.

 

[ndzied1]

Mike,

Correct me if I am wrong but it seems to me the 30 lb. figure has nothing to do with moving the doors but rather is the maximum force a door can impart to a person standing in the doorway when the doors are closing.

If this is the case, either a DC motor and dirve or servo should be the easiest to set up with a torque limit. What that limit is will depend on the mechanics of the and how the torque gets multiplied from the motor to the door.

 

[elevmike]

Mike,

Correct me if I am wrong but it seems to me the 30 lb. figure has nothing to do with moving the doors but rather is the maximum force a door can impart to a person standing in the doorway when the doors are closing.

That is correct!!!

 

[Rod]

Folks don't overlook the 'back-drivable' part!!
Safety!

Rod - scratching head

 

[LadderLogic]

So there is no 30 lb-in torque requirement after all?

That makes it much, much easier.

Mike, I know Hoerbiger-Origa in Chicago have been heavily involved into designing of similar type of applications for bus doors. Of course, all they do is pneumatics, not servos. However, you may want to contact them and see if anything could be cooked...

 

[Bob O]

Just a thought

Couldn’t you work backwards?

If you have similar door configuration already running, look at the motor and gearing and size backwards. This should eliminate working through the kinematics of the linkages.


Bob O

 

[Rod]

another wierd idea

Mike,

Since this is a demo unit:

Remember the hydraulic unit I turned you one to? Bet you bought a spare.

A small hydraulic vane-type motor can deliver both speed and torque in a quiet package. 24VDC controlled valve. (I have one here). Some JIC quick disconnects.

I'm thinking of being able to force the door(s) open. Gear reduction could prevent that, but a 'dump to tank' would allow it in power failure mode.

OOPS! you need a 'spring return valve' for that mode. The pump would have to provide continous flow for 'door(s) closed - darn!

Hmmm, I'm still thinking

Rod

 

[elevmike]

Rod,
I don’t recall that. I probably should but I cant remember....There was a manufacture that made a hydraulic door operator for elevators, but I think they went bust, or stopped making them.

Anyway the total moving mass is about 456.7256 lb. (not including the motor armature). With this figure I used a chart to look up the max closing speed for an average Kinetic energy of 7.37 ft lb. (ASME A17.1-2000). So the speed is actually .872 fps. (or there-abouts).

Luck shines my way...(I think...maybe)...I found a 90 VDC PM planetary gear motor in the graveyard. Output rated at 121 RPM & 115in lb. of torque. With a 2 inch dia timing pulley turning at 105 rpm I'll get the right speed.

Question is..... does it have the guts? So call me ignorant, how does one calculate HP & torque required for horizontal motion?

 

[Leadfoot]

Torque is rotational ONLY. You can have a certain amount of torque applied to cause an object to move in a linear direction. Then it is just force.

Torque is 2R x Force needed to move perpindicular to the arc of motion. Force being the linear aspect.

 

[elevmike]

Torque is rotational ONLY. You can have a certain amount of torque applied to cause an object to move in a linear direction. Then it is just force.

Yes you are correct, I miss-spoke that.

Anyway I'm pretty sure I stumbled accross the solution to my problem, however I'll have to stand the gear motor on end. I also have a PWM motor control that can be setup with digital (on-off) inputs to start accel-decel & stop the motor in a highly controlled fashon.

BTW, I also stumbled across this handy site here: http://www.engineersedge.com/Calulators_Online.shtml

Thanks for all the responses......

Off to do the fabercation drawings..

 

[rsdoran]

I get so tired of being corrected for something that does not require correcting.

Torque is rotational FORCE...use of the word force was applicable.
I was merely stating that in this case 30 ft-lbs was high for a stepper application and getting up there for a servo.

I dont care what kind of energy you have or use if motion is involved...make it do WORK without FORCE.

Servos usually are rated in (Nm) instead of ft-lbs, I was just trying to show the exchange AND that sometimes (even with SI) the use of a comma may signify a decimal, if you know the conversion then you will know the difference. I am not saying the use of the comma is right or wrong, just that it is done.

 

[tutichip]

"I get so tired of being corrected for something that does not require correcting"


With the greatest respect , short of holding a survey , I can guarantee that if you ask 100 engineers to define 12,345 nm or 12.345 nm , that 99 (that is 99.000 , not 99,000 ) of them will define the comma delimiter as indicating thousands , and the point delimiter as indicating a decimal fraction .
Its something that can be argued about all night , but if you don't want mistakes , use a ".".