Sovella table - 06 Updated 01-07-12

Last crawled date: 1 year, 10 months ago

LIFTING MECHANISM

Two models uploaded:
Sovella_06 = solution with torsion spring
Sovella_07 = solution with gas spring

The first solution is based on two pairs of reduction and a shift by chain sprockets.
The main element is the worm type gear reducer "Motovario", commercial type box shaped with machined sides, complete of bearings, gaskets, and lubrication for life.
The presence of this reducer is useful for the irreversibility of the motion. It is well known that the couple screw-worm becomes irreversible if its efficeincy is less than 0.5.
I expected to recover efficiency with a sprocket chain generously sized so that a small rotation corresponds to a good vertical displacement.
Another small gearbox reduces the effort applied to the crank.
The handle is removable and fixable with quick device (little sphere with spring).

TABLE SUPPORT

Just as it was designed this lifting mechanism can be fitted in the existing legs and secured under the table top. But I still wanted to rethink the shape of the legs to get a more "high tech" look using some extruded aluminum best suited to environments where cleaning is needed .
Instead of a closed-shell profile which depends extrusion matrix more complicated, I considered three modular elements that are joined with a tail like puzzles. I saw this solution applied in the construction of a large blades of axial fans.
There are thus two types of the curved elements for the inner and outer leg, and a straight element identical to connect both.
Faced with a higher initial cost for extrusion matrix, the profiles would be advantageous to decrease the processing. It would need only a few drilling and cutting instead of cutting, folding, painting necessary for other metal legs .
The sliding pads are polymer such as "Peek" suitable for high surface pressures.
Depending on the location of the centroid of the applied loads over the table, you can have different balance legs over foot, so the legs can located in more central positrion to reduce the overturning moment on the slide rails.

PERFORMANCE

To approach the required performance of speed and energy, it is necessary an energy storage device aid maneuvering.
It 'clear that the more efficient devices are gas springs,
but however, I have studied the possibility of applying the normal mechanical compression springs.
Unfortunately, the performance demands are too high. The springs become very large and you can not obtain an affordable housing in the legs. Any counterbalancing masses are too large and expensive to transport. I tried so the torsion springs whose contribution is low, however, are easier to assemble. I then added to the main shaft.
So for this type of conformation to not increase the effort of the operator, it is necessary to accept a reduction in travel speed.

CALCULATION WITH TORSION SPRING

From spreadsheets of the torsion spring:
Torque: from 27000 to 73300 Nmm, average 50000 Nmm.
sprocket diameter = 114.6 mm
Resultant force 50000/57.3 / 9.81 = 89 kg
Force varies between about 130 kg at start of travel course, to 50 kg at the end.
500-89 = 411 kg to be lifted
Worm gear reducer, ratio = 1:30
Efficiency from Motovario catalog = 0.45 (irreversible)
gear pair z1 / z2 = 25/60
crank radius = 200 mm
We can obtain:
(411 * 57.3) / 30 * (25/60) / 200 = 1,635 kg to apply at the handle
Performance of the system about 0.45
1.635/0.45 = 3.63 kg = 35.65 N
1 revolution = 360 ° crank
360 / (60/25) / 30 = 5 ° of rotation of the pinion.
Vertical path of the pinion shaft = 114.6 * Pi / 360 * 5 = 5 mm
need to do the entire race:
400 / 5 = 80 revolutions of the crank
Choosing a travel speed of 5 mm / sec,
revolution speed of the crank = 1 turn/sec
time = 400/5 = 80 sec
W = (35.65 * 1) = 35 Watts
Consider that the effort applied to the handle is very low, and applicable from weaker persons, strongest people can increase the number of revolutions of the crank and reduce travel times.

Alternatives without torsion springs:
- Increase handle lenght until about 300-350 mm (poor ergonomics and unaesthetic)

ALTERNATIVE WITH GAS SPRING

By inserting a pair of gas springs that have a thrust of about 1200N (IGS has a model with suitable performance)
we obtain the following values​​:
The load to be lifted becomes: 500 kg - (1200/9.81x2) = 255.35 kg
The worm gear must have a ratio of at least 1:30 to ensure the irreversibility of the motion.
chain pitch= 9.53, and diameter of the sprocket Dp = 114.6 mm
Effort on the crank of radius 250 mm
((57.3 x 255.35) / 30/250 = 1,951 kg
Applying an efficiency of about 0.45
Effort = 1.951/0.45 = 4.33 kg = 42.53 N
For a = 360 ° turn of the handle the chain sprocket wheel rotates:
360 / 30 = 12 °
along a vertical space:
(114.6 x Pi / 360 ° x 12 °) = 12 mm
assuming to make one turn of the handle in one second
speed = 12 mm / sec
Required speed 15 mm / sec
15/12 = 1.25 RPSec
W = 42.53 x 1.25 = 56.9 Watt