This section contain some basic information how the axis being controller was manufactured. The objective was to create a light weight but very robust structure so that a table could move at fast speeds (20 m/min) with a high acceleration (0.2 seconds to achieve the max speed). The desired travel is 1700mm (about 67 inches). The target accuracy is about 0.01mm and precision 0.02mm .
To obtain such a movement, we decided based on availability, price and easiness of construction.
- Base structure: Tubular 200x100mm with 5mm wall thickness
- Guides: Linear guides, size 25mm, standard
- Torque transmission: Rack and pinion
- Motor selection: 2.8Kw servo motor
- Reducer: Alpha size 90 with ratio 1:10
- Total weight: About 60Kg for the axis support (not taking in account the carriage)
Linear guides base
Since the linear guides had to be bolted and the tube is not straight enough to create a good support for the linear guides, a steel support was welded to the tubular structure in the area where the linear guides will be bolted and where the rack will be placed:
After welded, the steel supports give the necessary thickness to allow their machining. In order to have the best possible mechanical squareness, on the top of the structure the final support was welded and after machined. Since the axis will be supported by its ends when the axis is fully ready, we supported, in the machining phase, the axis by those points. This method avoids bending after machining when the part is tighten out from the machine bed where it will be machined, as we will tight the part on the same points where it will be fixed when finished.
Machining linear guides bases
Since the axis is very long (about 2 meters), machining it only fixed by its ends would result in a poor finish due to vibration. To avoid this, the axis was placed and leveled on a large milling machine only supported by its ends. After the axis was leveled enough (checked with a dial gauge), a vice was placed on the axis middle and fixed to the machine table. Note that only after the axis was leveled, the vice was tightened to the axis and then to the table. During leveling it was floating and therefor allowing the axis to be left free on a non stressing position.
On the following picture it can be seen the general fixing method of the axis. The ends are fixed by L shaped supports directly to the milling machine bed. The vice at the middle is still not fixed neither to the axis or to the machine bed so that the axis can be leveled freely on a non stressing situation.
On the following picture, the axis is ready to be machined. The vice was now 1st tight to the axis, then to the machine bed so that its tightening interfere the less possible with the axis normal standing position.
During machining. Both linear guides beds are almost finished.
Rack base machining
Finally the rack bed is machined. All was machining in one tightening, meaning that the squareness is the best possible.
After some sanding and primary painting, the axis support is ready for more work. We prefer to continue to work on an already painted area for a more clean work. Most of this primary will be sanded again before the painting stage. Now, the linear guides and rack will be placed on the beds (that are protected with painting tape).
While waiting for the linear guides, the carriage was created from 15mm aluminium plate. This plate will be bolted to the four carriages (2 per each guide) and the remaining carriage structure will be bolted to this.
This carriage suffered a few changes during the build process so that automatic, central, lubrication could be applied. It was a time consuming work to provide enough space for the lubrication channels and to keep the lubrication tubes without a tight bend. The following image also shows a complete length protection plate for the linear guides.
After drilling and threaded 66 holes:
after more 66 holdes, and with the carriage mounted, we now have a moving linear carriage.
After the axis was manually tested, and after double check the most important issues, the axis was totally dismounted and final paint was applied.
The following images shows the axis back view, with the cable carrier and support, and the front view, where the full length, linear guides protections visible, hiding the linear rails.
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