Stand

A stand for movable equipment has a first stand part and a second stand part that is movable relative to the first stand part and includes a pivot arm hinged to the first stand part and pivotable around a pivot axis. An energy storer provides weight equalization. The energy storer exerts a force on the pivot arm, by means of a deflecting element that is directed towards an abutment point on the first stand part. The pivot axis and the abutment point always define a vertical plane. The deflecting element is arranged on the second stand part.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a stand, and more particularly, to a stand for 
movable equipment. 
2. Description of Relevant Art 
Such a stand is known, for example, from German Laid-Open Patent document 
DE 37 39 080 A1. This stand has a stand column and a pivot arm jointed to 
the stand column. To equalize the weight or torque acting on the pivot 
arm, a spring is provided that is attached at one end to the stand column 
and the other end, via a cord, to the pivot arm, the cord being reversed 
in its direction between the spring and the pivot arm. As a result, the 
spring exerts force on the pivot arm that is directed toward an abutment 
point, and the abutment point is displaced depending upon the respective 
position of the pivot arm. 
The theory of this stand is also described in the article, "Weight 
Equalization in Precision Equipments" by H. Hilpert in Feingeratetechnik 
[Precision Equipment Technology], Vol. 2/1965 (see FIG. 7 on page 63 of 
this article). In the first paragraph of the left-hand column on page 63 
of this article, it is explained that in the known stand, because of the 
finite curvature of the deflecting roller, i.e., because of the 
displacement of the abutment point when the pivot arm pivots, only an 
approximate weight equalization can be attained. 
Such a stand is also known from East German Patent DD 221 571 A1, and is 
constructed according to the principles in the article by H. Hilpert. The 
abutment point in this stand also moves depending upon the respective 
position of the pivot arm because the deflecting element that deflects the 
cord connecting the end of the spring to the pivot arm is formed by an 
inclined surface with a finite curvature. 
Furthermore, in both of these known stands, a separate constructional space 
is required for the arrangement of the deflecting element and the spring. 
As a result, the operability and possible pivoting region of the pivot arm 
may become restricted. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide a stand of the kind 
described, with the weight equalization improved as far as possible, and 
with an improved arrangement of the energy storer. 
This object is attained by a stand having a first stand part and a second 
stand part that is movable relative to the first stand part. The second 
stand part has a pivot arm that is pivotable around a pivot axis and 
hinged to the first stand part and an energy storer that exerts a force 
directed toward an abutment point on the first stand part via a deflecting 
element. The pivot axis and the abutment point always define a vertical 
plane, and the deflecting element is arranged on the second stand part. 
When the deflecting element is arranged on the second stand part and the 
pivot axis and the abutment point always define a vertical plane, an 
improved weight equalization is possible in relation to the point of 
action of the weight equalization force on the first, unpivoted, stand 
part, and a bulky deflecting arrangement that restricts the pivoting 
region is dispensed with. 
In an embodiment in which the abutment point is arranged to be displaceable 
orthogonal to the pivot axis by means of a screw spindle, the optimum 
weight equalization can be restored by suitable displacement of the 
abutment point, even when there is a change in the torque acting on the 
pivot arm. 
In a further, particularly compact embodiment, the energy storer includes a 
spring arranged on the pivot arm, the deflecting element being a 
deflecting roller arranged on the pivot arm. 
When the spring is a compression spring, in particular a flattened wire 
spring, which at the pivot axis side is supported on the pivot arm, and 
whose end remote from the pivot axis acts on a flexible force-transmitting 
element passing about the deflecting roller to the abutment point, the 
possible fall path of the pivot arm in the case of a broken spring is 
limited. In addition, the flexible force-transmitting element that 
transmits the spring force provides good vibration damping properties. 
In order to prevent bending or deflection of the spring from its 
longitudinal direction, thus providing further safety measures in case of 
a broken spring, the spring is guided on a tube that is displaceable in 
the pivot arm and whose end remote from the pivot axis is connected to the 
flexible force-transmitting element. 
With a view to a spring that is guided precisely on the pivot arm and as 
free from play as possible, it is advantageous if the tube is guided by 
the deflecting roller and a pressing roller and also by means of a sliding 
bearing on the pivot arm. 
When the tube has a friction-reducing coating on its spring side, that is, 
on its side facing the energy storing spring, the frictional forces of the 
spring on the tube can be minimized in the sense of a minimum resistance 
to movement of the pivot arm and minimum noise related to the friction of 
the spring on the tube. 
In the embodiment in which the flexible force-transmitting element is 
constructed as a toothed belt that engages with teeth of the deflecting 
roller, slippage on the deflecting roller can be largely prevented. 
However, it is also possible to provide a chain wheel or a cord that wraps 
around a cord roller, instead of a toothed belt. 
It is particularly advantageous in connection with a flexible 
force-transmitting element constructed as a toothed belt if the rotary 
mobility of the deflecting roller arranged on the pivot arm can be locked. 
The pivot arm can thereby be fixed in its position at any given time by 
rendering the deflecting roller stationary. 
In a further embodiment, the pivot arm is constructed as a substantially 
closed hollow body that receives the spring in its interior. In this 
embodiment, the energy storer is largely protected from external 
influences. The pivot arm furthermore has a high torsional stiffness 
because it has only to permit passage of the flexible force-transmitting 
element through it in the region between the deflecting roller and the 
pivot axis.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
A stand (1) according to the invention is shown in FIG. 1, and carries an 
operation microscope (3). The stand (1) has a base part (5) mounted on 
rollers (6) and a stand part (7) that is movable relative to the base part 
(5). 
The stand part (7) includes a pivot arm (9) that is pivotably hinged to the 
base part (5) to pivot around a pivot axis (A1). The pivot axis (A1) is 
orthogonal to the plane of the drawing in FIG. 1, and also orthogonal to 
an equipment arm (11). The equipment arm (11) is rotatably supported by 
the pivot arm (9), to rotate around an axis (A2). An operation microscope 
(3) is arranged on the equipment arm (11), to be pivotable around an axis 
(A3) that is orthogonal to the plane of the drawing in FIG. 1. 
The operation microscope (3) is always held by the stand in an unstable 
equilibrium (i.e., any point of the trajectory of the microscope is a 
stationary equilibrium. The microscope stands still as soon as the moving 
forces are removed. Only frictional or inertial forces but not gravity may 
resist movement of the microscope.) by means of the weight equalizing 
mechanism on the stand (1). This allows the microscope to be moved by the 
operator during an operation with as little force as possible. 
For this purpose, an energy storer (12) is arranged within the pivot arm 
(9) (and therefore shown dashed in FIG. 1) and exerts force on the pivot 
arm (9) that is directed toward an abutment point (15) on the base part 
(5) by means of a flexible force-transmitting element (13) guided by a 
deflecting roller (14). 
A vertical plane (16), shown dashed in FIG. 1 and orthogonal to the plane 
of the drawing in FIG. 1, is defined by the abutment point (15) and the 
pivot axis (A1). The vertical plane is independent of the respective 
pivoting position of the pivot arm (9). Thus, the abutment point (15) does 
not move while the pivot arm (9) is pivoted. 
The abutment point (15) is displaceable, orthogonal to the pivot axis (A1), 
in a longitudinal slot (17) of the base part (5), in order to restore the 
desired unstable equilibrium when there is a change in the weight of the 
equipment (3) that is carried by the pivot arm (9). 
FIG. 2 shows the position of the abutment point (15) in detail, and a 
sectional view of the energy storer (12) arranged in the pivot arm (9). 
The flexible force-transmitting element (13) has a joint piece (19) on the 
side toward the base part (5) that is hinged about a joint axis (A4) 
parallel to the pivot axis (Al). The abutment point (15) thus lies at the 
point of intersection of the pivot axis (A4) and the tangent to the 
portion of the flexible force-transmitting element (13) between the joint 
piece (19) and the deflecting roller (14). 
The energy storer (12) includes a flattened wire spring (21) received in 
the interior of the pivot arm (9) that is constructed as a hollow body. 
The flattened wire spring (21) is guided on a tube (23), movable in the 
pivot arm (9), and is supported at its end nearer the pivot axis (A1) on 
an annular shoulder (25) within the pivot arm (9), and at its other end on 
a flange (27) of the tube (23). Furthermore, the flexible 
force-transmitting element, constructed as a toothed belt (13), is 
fastened to the flange (27), and is deflected into its direction toward 
the abutment point (15) by the deflecting roller (14). 
Since the shaft pin (20) is arranged on the runner of a vertically aligned 
screw spindle (49), the abutment point (15) can be displaced orthogonally 
of the pivot axis (A1) and within the vertical plane (16), by means of a 
spindle displacement screw (51) to restore the desired unstable 
equilibrium even when there is a change in the weight of the operation 
microscope (3). 
A stand which functionally corresponds to the stand with weight equalizing 
mechanism as shown in FIG. 7 of the article by H. Hilpert is embodied by 
the arrangement shown according to the invention, of the compression 
spring (21), toothed belt (13), abutment point (15) and pivot axis (A1). 
Herein, the distances between the pivot axis (A1) and the abutment point 
(15), and also between the pivot axis (A1) and the deflecting roller (14), 
are selected so that the condition (22) in the article by H. Hilpert is 
fulfilled. This sets a precondition that the point of action of the masses 
that exert a torque on the pivot arm (9) about the pivot axis (A1) lies on 
a tangent (47) to the deflecting roller (14) that intersects the pivot 
axis (A1), or can be displaced into this tangent (47) by the displacement 
devices known for example from European Patent EP 433 426. 
The tube (23) carrying the flattened wire spring (21) is guided without 
play, by means of its flange (27), by a sliding bearing (33) formed on the 
inner wall of the pivot arm (9) and by the deflecting roller (14) and a 
pressing roller (35). 
This guiding of the tube (23) on the pivot axis side is shown in FIG. 3 in 
a sectional view along the section line denoted by the arrows III--III. 
The deflecting roller (14) is mounted on the pivot arm (9), is rotatable 
about an axis (37) parallel to the pivot axis (A1), and has two flanges 
(39) that receive the tube (23) between them. The tube (23) is 
semi-cylindrical in the region of the deflecting roller (14). A pressing 
roller (35) arranged to be rotatable around a rotation axis (45) parallel 
to the rotation axis (37) presses the tube (23) against the deflecting 
roller (14). 
A locking element (46) that can be operated from outside the pivot arm (9), 
is installed on the rotation axis (37) and when operated prevents the 
deflecting roller (14) from rotating around the rotation axis (37). 
Because of the toothed belt (13) that meshes with teeth (44) of the 
deflecting roller (14), the position of the pivot arm (9) at any given 
time can be fixed by means of the locking element (46). 
FIG. 4 shows the pivot arm (9) together with a portion of the base part (5) 
in a different pivoted position from that shown in FIG. 2.