Height adjustable table

The top of a table such as a drafting table which may be adjustable in its elevation, is counterbalanced by counterbalancing elements exerting an approximately constant balancing force. The counterbalancing elements comprise at least one leaf spring forming a bow inserted between the table top and a counter abutment below the table top so that the leaf spring or springs is biassed to form said bow, whereby the load on the bow has a tendency to cause a lateral flexure of the bow. The arrangement is such, that the downwardly directed force component caused by the weight of the table top and the pressure exerted by the bent leaf spring or springs, are directed opposite to each other.

BACKGROUND OF THE INVENTION 
The present invention relates to tables, especially tables the top of which 
is adjustable in its elevational position, particularly drafting tables or 
boards or work tables, wherein the table top is supported by weight 
balancing devices exerting a force of at least substantially constant 
effect. 
Gas springs are frequently used for weight balancing table tops which are 
adjustable in their elevation. The gas springs are provided with a 
discharge valve for the purpose of controlling the force exerted by the 
gas spring. However, if, for example, as a result of controlling the gas 
spring too much gas is released, it becomes necessary to demount the gas 
spring and to refill the gas spring to the desired pressure for the 
further use. Further, the supporting force of gas springs may become 
weaker with the lapse of time due to leakage. Besides, an increase of the 
supporting force of a gas spring always makes it necessary to change or 
demount the spring and to insert a new spring. Gas springs also have a 
relatively high friction of their own and cause disturbing friction noises 
when the table top is adjusted in its elevational position. 
Other types of weight compensating systems such as tension or pressure 
springs are not suitable for use in connection with table tops adjustable 
in their elevational position, because such other devices do not exert a 
constant force throughout their adjustment range. Such a force is 
necessary to counteract the weight of the table top. 
OBJECTS OF THE INVENTION 
In view of the above it is the aim of the invention to achieve the 
following objects singly or in combination: 
TO AVOID THE DISADVANTAGES OF THE PRIOR ART, SPECIFICALLY, TO AVOID THE USE 
OF GAS CYLINDERS FOR THE COUNTERBALANCING OF A TABLE TOP; 
TO COUNTER BALANCE THE WEIGHT OF A TABLE TOP WHICH IS ADJUSTABLE IN ITS 
POSITION BY RELATIVELY SIMPLE MEANS WHICH PROVIDE A BALANCING SPRING FORCE 
WHICH IS CONSTANT OVER A SUBSTANTIALLY WIDE RANGE OF ADJUSTMENT; 
TO PROVIDE A COUNTERBALANCING DEVICE WHICH IS EASILY EXCHANGEABLE, FOR 
EXAMPLE, IF A TABLE TOP OF DIFFERENT SIZE OR WEIGHT IS TO BE USED; AND 
TO USE A LEAF SPRING OR A SET OF LEAF SPRINGS FOR THE COUNTERBALANCING IN 
SUCH A MANNER THAT THE LEAF SPRING MEANS ARE SECURED SO AS TO PROVIDE FOR 
THEIR LATERAL FLEXING. 
SUMMARY OF THE INVENTION 
According to the invention there is provided an apparatus for 
counterbalancing the top of a table, which table top is adjustable in its 
elevational position, comprising leaf spring means, first abutment means 
secured to said table top at its downwardly facing surface, second 
abutment means secured to said table below said table top, holding means 
loosely holding said leaf spring means relative to said abutment means, 
said first and second abutment means being spaced from each other so as to 
bend said leaf spring means to form a bow loaded for lateral flexure 
sufficiently to provide a support pressure effective in a direction 
substantially opposite to the downward force component exerted by the 
weight of said table top, whereby the table top is supported by a 
substantially constant force. The features of the invention provide a 
relatively simple balancing mechanism for the weight of the table top and 
such mechanism is not trouble prone at all. The spring force of such a 
leaf spring bow loaded for lateral flexing or buckling is surprisingly 
constant over a relatively large adjustment range which is sufficient for 
normally occurring requirements. In addition, the exchange of the leaf 
springs is very simple, for example, if a table top having another weight 
is to be used on the same table base.

DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS 
FIG. 1 shows a plate shaped base 2 for the upright post 1 which may be a 
hollow column extending vertically upwardly and having, for example, a 
rectangular cross section. The column 1 forms an outer pipe within which 
an inner pipe 4 having a corresponding cross section fitting into the 
outer column 1 for vertically adjusting the elevational position of the 
inner pipe core relative to the outer column 1. A table top 3 is secured 
to the top of the pipe 4 by conventional means. For example, the lower 
surface of the table top 3 may be secured to carrier sectional rails 5 of 
which at least 2 are spaced from each other. A supporting plate 12 is 
arranged below the carrier sectional rails 5. The table top 3, the carrier 
sectional rails 5 and the support plate 12 may be tiltably secured to a 
bearing tubular member 13 for angularly adjusting the position of the 
table top 3 relative to the horizontal as is conventional in connection 
with drafting tables. However, it is also possible to rigidly secure the 
support plate 12 to the top of the inner tubular member 4 as shown, for 
example, in FIG. 3. 
A foot pedal 8 serves to release a conventional brake which is effective on 
the inner pipe 4. The brake is released when the pedal 8 is pushed in the 
direction of the arrow A. 
FIG. 2 shows that according to the invention an abutment block 41 is 
rotatably secured to the downwardly facing surface of the support plate 12 
by means of a vertically extending bolt 42 forming a rotational axis. 
Preferably, a washer 40 is secured to the support plate 12 between the 
latter and the abutment block 41. A further abutment member 44 is 
arranged, or rather, rotatably secured to the base plate 2 by means of an 
axial bolt 45 which is located substantially in vertical alignment below 
the abutment member 41 and thus substantially in axial alignment with the 
bolt 42. Preferably, a further washer 43 is positioned between the base 
plate 2 and the second abutment member 45. 
According to the invention there are arranged leaf spring means, for 
example, two leaf springs 46 and 47, the ends of which are held in 
position by the abutment blocks 41 and 44. The length of the leaf springs 
46, 47 is such that the springs are loaded to laterally flex or buckle as 
illustrated especially in FIG. 3. In order to define the contact position 
between the abutment blocks 41 and 44 on the one hand and the ends of the 
leaf springs, the abutment blocks 41, 44 are provided with grooves 48 
having a serrated cross section wherein the ends of the leaf springs rest. 
Holding means in the form of bails 49 and 50 are secured to the abutment 
blocks 41 and 44 respectively. These bails extend with play through slots 
or elongated holes 41, 52 in the ends of the leaf springs 46, 47, whereby 
the bails 49, 50 hold the ends of the springs in the grooves 48, thereby 
preventing that the biassed leaf spring bows jump out of the grooves 48. 
The bails 49, 50 are held in position by means of set screws 53. 
Due to the just described holding of the spring bows 46, 47, the ends of 
the springs are not tightly clamped but the biassing force of the springs 
presses the ends of the springs loosely against the grooves 48. The 
individual leaf springs 46, 47 are not connected to each other. The ends 
of the leaf springs 46, 47 are tapered in the manner of a cutting edge to 
properly fit into the respective groove 48. It is advantageous that the 
spring bow is formed by two metal leaf springs 46, 47 which will be 
satisfactory for many purposes. However, in order to make it possible that 
drafting machines of different weigths may be used on the drafting table 
or to use table tops of different weights, it is possible to use springs 
arranged in a package and comprising a plurality of springs, preferably of 
different thicknesses. Such springs may be exchangeable one against 
another. Preferably, the spring packages or sets of springs comprise 
several springs having different buckling strengths adjusted relative to 
each other in accordance with a geometric progression or sequence. Thus, 
for example, a set of four springs may be assembled of which the first 
spring has a buckling strength of 20 kg, whereas the second spring has a 
buckling strength of 10 kg, and the third spring has a buckling strength 
of 5 kg while the fourth spring has a buckling strength of 2.5 kg. 
Due to the fact that the abutment blocks 41 and 44 are rotatable about the 
respective axle bolts 42, 45, it is possible to tilt the spring bow from 
the position shown in FIG. 1 in one or the other direction through an 
angle of about 120.degree.. This has the advantage that the table support 
may be adapted to the available space. Thus, in FIG. 3 the spring bow is 
shown in the tilted position, whereby it does not extend beyond the base 2 
as shown in FIG. 1. In FIG. 3 the spring bow 46, 47 is tilted by about 
90.degree. relative to the position shown in FIG. 1. 
It has been found, that it is possible to provide a relatively large 
adjustment range throughout of which the supporting force is constant by 
using a spring bow 46, 47 the springs of which are loaded for lateral 
flexure or buckling. Thus, it is possible to move or adjust the table top 
3 after releasing the brake by actuating the pedal 8. Such adjustment of 
the table top may be accomplished within the adjustment range by exerting 
a very small force. The maximum elevational position or range of the inner 
pipe 4 is so selected that even in this maximum position of the talbe top 
the spring bow is never totally stretched out. On the other hand, when the 
table top is in its lower elevational position, the elasticity limit of 
the springs must not be exceeded. 
A specific example embodiment of apparatus according to the invention 
comprises leaf springs having a stretched out length of 1200 mm. The 
spacing between the abutment blocks 41 and 44 in the topmost position of 
the table top 1150 mm for the just mentioned length of springs. The 
spacing between the abutment blocks in the lowermost position of the table 
top is 700 mm thus providing for a stroke of 450 mm. 
Although the invention has been described with reference to specific 
example embodiments, it will be appreciated, that it is intended to cover 
all modifications and equivalents within the scope of the appended claims.