"Vesna" coplanar doors. Construction

I hope you will be able to see a core idea of the project behind this particular realization. Sometimes it seems that idea is unfeasible, so I decided to illustrate not an abstraction but a real prototype.

Figure 1. "Vesna" closed and opened.

In figure 1 a door 1 is depicted in closed (on the left) and closed (on the right) states, mounted on "Vesna" mechanism. The door frame, that can be, for example, a wardrobe body or an built-in cupboard frame, is not shown.

Rail 14 is screwed to the door. All the door weight is transferred to bottom carriage via this rail.

Figure 2. The carriages.

This carriage is shown in details in figure 2b. The carriage is connected to a shaft 2 (which destination will be explained below) via a barrel hinge with an axis of rotation denoted as B. Rail 14 rests upon rollers 22 and 23 which roll inside a special groove in it. The rollers are connected with the carriage by a rocker 21, which ensures an equal distribution of the door weight between the rollers. The roller shape and the rail groove shape are designed in such a way that the roller’s plane of rotation and rail’s symmetry plane tend to coincide. This way the carriage can’t rotate around a vertical axis, it only can roll along the rail.

Top carriage is shown in figure 2a. It inflexibly connected to a body 10 (an external part) of a full extension telescopic rail. It is also connected via a barrel hinge to the shaft 2. An axis of rotation of this hinge is B (see the bottom carriage).

In figure 1 you can see that a slider 9 (an internal part) of the full extension telescopic rail is inflexibly connected to the door. From the essence of a full extension rail operation it is clear that the body 10 and top carriage, connected to it, can slide along the door.

The shaft 2 is connected to the pivot plates 12 and 13 via levers 5 and 6. The connection is a pivot hinge with an axis of rotation A. Pivot plates are screwed to the door frame.

The shaft

If you track the route "frame — pivot — plates — shaft — carriages — door" you will note that the frame and the door are actually interconnected with two (on the top and bottom) floating hinges . This allows the door to move away from the frame being parallel to it. An important thing is that rotation of both hinges is always equal because they are synchronized by the shaft 2.

The shaft experiences torsional load. It will be to verbose and unnecessary to explain the reason of this and to show a calculations of a required minimal cross-section of the shaft. I just say: there will be no problems with the shaft diameter for all reasonable weights of the door.

The equalizer

Top and bottom carriages can move along horizontal edges of the door. If their offsets are not equal to each other, the door will rotate around an axis perpendicular to its plane. Simply put, the door will be crooked in the frame. To avoid this the carriages offsets must be equalized. To accomplish this different approaches can be used. The simplest and cheapest (in my opinion) is a cable equalizer.

Figure 3. Cable equalizer.

In figure 3 you can see "Vesna" mechanism with some parts hidden so the equalizer is visible. It consists of four anchors 16 which connect cables 17 and 18 to the door. The cables pass over pulleys 3 and 4, which are connected to carriages. In figure 3 a detailed views of how the cables are placed inside the pulleys grooves are shown. From these views one can conclude that the cable 17 prevents the door from a clockwise rotation and the cable 18 prevents a counterclockwise rotation of the door.

You can doubt about reliability of the equalizer. In addition to persuasive (in my opinion) video here I’ll show a simple calculation of the cable require strength.

Lets designate the door mass as m, vertical distance between pulleys as a and the door width as b. Then a maximum tensile force F, which acts on the cable, will be:

, where g is standard gravity.

Wardrobe and built-in cupboard doors usually have height to width ratio more than 2. Their mass varies from 10 to 80 kilos.

Lets calculate F for a door 1 m wide, 2.2 m high and weighting 20 kilos. Vertical distance between rollers is 2 m because "Vesna" mechanism decreases this distance by approximately 0.2 m relative to a door height. Then we have a=2 m, b=1 m and m=20 kg, which gives us F=49 N. An ordinary steel cable DIN 3055 with diameter of 1 mm has workload of 470 N. This means that for selected door the cable workload almost 10 times greater than we need. Even 100-kilo door will not exceed the cable strength. For doors up to 40 kg a cable of 1 mm diameter (workload 117 N) is enough. It is also possible to replace the steel cable with something modern like an aramid cable.

The parallelogram linkage and the door trajectory controller

All the parts of "Vesna" described above still allows the door to rotate around a vertical axis. To remove this unnecessary degree of freedom the body 10 of the full extension telescopic rail must be connected to the frame with parallelogram linkage.

Figure 4. The parallelogram linkage and the door trajectory controller in motion

Four stages of the door opening (top view) are shown in figure 4. The pivot plates 11 and 12 are screwed to the frame, levers 7 and 8 are movable connected with the body 10 and the pivot plates. These parts form a parallelogram linkage with the levers 7 and 8, the body 10 and the frame being its sides. The parallelogram makes the door plane parallel to the frame plane.

Rod 15 is added to the parallelogram mechanism to overcome its dead point.

The door trajectory controller is also shown in figure 4. It is actually a couple of small parts in addition to the parallelogram. The controller is indispensable to create the door opening (and closage, of course) trajectory. The door will have undefined trajectory, it will collide with door frame without the controller. This situation you can see in prototype video when the door depicted #1 is being moved.

In figure 4a you can see a figured groove A shown with dash line. It is on a back side of the lever 8. A pin 24 is engaged with the groove. The pin 24 is mounted on the slider 9 which in turn is connected to the door. When turning, the lever 8 controls relative position between the slider 9 and the body 10 via the pin 24. In other words, rotation of the parallelogram levers and linear movement of the door along its guide systems become linked. The type of this linkage is solely determined by the shape of the groove A. By changing this shape, one can "program" the door trajectory. By comparing figures 4a and 4b you can see that when being dragged out the door moves along a normal to its plane. Then it gradually moves to the right along arched trajectory and after all slides along a straight line.

The shaft 2 have to stop its rotation near a point where the arched trajectory is changed by the straight line trajectory. It have to stay blocked during all the time the door moves along the staright trajectory.

"Vesna" is designed in such a way that rotation of the levers 7 and 8 and rotation of the shaft are synchronous. So when the lever 7 is block the shaft is blocked too.

There is a locking plate 25. It has a hook B, that can capture a pin attached to the lever 7 (on its back side). This pin is coaxial to the screw 27 as you can see in figure 4d. When the pin is captured by the hook B, the lever 7 becomes blocked.

The locking plate rotation is controlled by a pin 26, which is connected to the slider 9 and is engaged with figured cut in the locking plate.

At certain moment during the door opening the pin 26 forces the locking plate to block the lever 7. Then the pin 24 leaves the groove A and almost at the same moment the pin 26 leaves the locking plate cut. Unwanted rotation of locking plate is avoided by a friction or a small spring. When you close the door, both pins can return to their grooves and cuts without any problems. The pins 24 and 26 can be made cylindrical rollers to reduce wear.

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