Re: [CAD_CAM_EDM_DRO] Re: Knee for z-axis control? pnuematic actuator

turbulatordude wrote:

>>I like this idea alot. Does anyone know how to calculate the size
>>
>>
>of
>
>
>>the accumulator that would be needed based on the different
>>
>>
>cylinder
>
>
>>diameters and strokes?
>>
>>Thanks
>>David
>>
>>
>
>If you figure your actuator (piston) diameter and stroke for your
>most rapid movements, ie: drilling lots of holes.
>
>and calculate the repetitive rate for drilling, you can easily
>calculate air volume. If your actuator is running at 80 PSI and
>your compressor tank is 120 psi.
>
>An example is a 4 inch dia actuator with 80 psi. That is 0.087 sq ft.
>
>Say your holes are 2 inches of travel. Each piston stroke would be
>0.174 cubic feet.
>
>10 holes a minute would use 1.74 cubic feet of air. An air
>compressor should have a duty cycle of less than 33%, so triple the
>air volume to 5.2 CFM.
>
>Since the air tank will not bleed dry, but go from 120 to 90 psi, all
>you need to know is how to calculate the volume of air at 120 psi and
>at 90 psi in a storage tank.
>
>Since we know 1 atmosphere is 14.7 psi and that at 2 atmospheres the
>volume is half and at 3, it is 1/3 and so on.
>
> 90 PSI is roughly 6 atmospheres and 120 psi is roughly 8
>atmospheres. So, you will lose 2 atmospheres in a pressure tank as
>it goes from 120 to 90 psi.
>
>Those two atmospheres should have a volume of 3 times your use, or as
>we figured 5.2 cubic feet.
>
>7.48 gallons is 1 cubic foot so 5.2 x 7.48 = 38.9 gallon tank.
>
>A typical commercial tank would be an 80 gallon tank so would be
>almost exactly 6 times the volume needed.
>
>Now, as for calculating hose sizes to meet your speed requirements,
>I'll leave that to another post.
>
>Dave
>

Are those calculations for a knee that's driven by air, or for one that
just has an air "spring" to reduce the load on a servo motor? In a
cylinder/accumulator system, do you lose the air from the piston when
it's moved? I would think that a sealed shock absorber-like system
would be best for the servo/spring combination. (I thought that was
what the question was)

- Steve