Control unit for a medical apparatus

A knob assembly is disclosed for a control unit of a medical apparatus with a front panel. In order to transfer a turning setting movement through the front panel, a feed-through sleeve is rotatably arranged in the front panel and a knob core is movably arranged in the feed-through sleeve. On the control side of the front panel the feed-through sleeve and the knob core are enclosed by a manipulable element which, through application of pressure, can axially move the knob core in the feed-through sleeve. The knob core on the back side of the front panel moves a resilient locking washer from a locking position to an unlocked position so that turning of the manipulable element also will turn the feed-through sleeve. To improve the sealing at the feed-through location, the front panel is provided with a protection plate which is beaded outwards and surrounding the feed-through sleeve, with the manipulable element tightly enclosing the beaded protection.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a control unit for a medical apparatus of the type 
having a front panel in which at least one setting knob and/or a switching 
knob is located. 
2. Description of the Prior Art 
A control unit is known through a service manual 10 for Servo Ventilator 
900B, Siemens-Elema AB, Publication No. S1080 Oct. 5, 1980 and having a 
front panel with setting knob assemblies that control potentiometers for 
setting of a number of different ventilator functions. A knob assembly 
includes a turning knob on the front of the front panel, which turning 
knob is screwed onto a feed-through shaft, which passes through a hole in 
the front panel to the potentiometer. The feed-through shaft is fastened 
axially in the front panel with a nut on the back side of the front panel 
and a locking nut on the front. To protect the control unit from the 
penetration of liquid, the front panel is covered with a thin protection 
plate of plastic. At the hole through the front panel, the locking nut 
prevents liquid from penetrating by its pressure against the front panel. 
The setting knobs of the control unit cannot, however, be fixed so as to 
remain precisely at the set positions, which means that a setting can be 
changed by mistake. There is also a risk that the potentiometer or the 
turning knobs may break, as the force applied to the turning knob is 
directly transferred to the potentiometer via the feed-through shaft. 
SUMMARY OF THE INVENTION 
An object of the invention is to provide a control unit that is easy to set 
in various positions without risking an accidental change of setting, and 
constructed in such a way that the potentiometer does not break from too 
much turning force applied to the setting knob, and wherein the front 
panel in an easy manner effectively seals off liquid, in particular in the 
area of the setting/switching knobs. 
This object is achieved in a control unit constructed in accordance with 
the principles of the present invention having a feed-through sleeve of 
the setting/switching knob rotatably arranged in the front panel, a knob 
core arranged in a movable and resilient manner in the feed-through 
sleeve, with the knob core being accessible from the front of the front 
panel. The setting/switching knob is locked in at least one direction of 
rotation by a stop when no force is applied to the knob core, and the 
setting/switching knob is turnable in both directions of rotation when 
force is applied to the knob core against the resilient arrangement. 
A setting/switching knob is thus obtained which is easy to handle by 
releasing the catch via the knob core and turning the knob to a desired 
setting with the feed-through sleeve. The knob can be locked either in 
both directions or in only one direction, to prevent a higher value than 
the desired to be set, for example. 
In connection with this embodiment of the invention, it is advantageous to 
have a manipulable element tightly enclose the feed-through sleeve and the 
knob core on the front of the front panel, and to provide a locking washer 
fastened to the knob core at the feed-through sleeve which locks the 
setting/switching knob against the stop. 
By having the manipulable element frictionally engage the feed-through 
sleeve, the force that can be transferred from the manipulable element via 
the feed-through sleeve to the potentiometer is limited and, before the 
force becomes great enough to damage the potentiometer, the manipulable 
element will start to slide in relation to the feed-through sleeve. By 
constructing the manipulable element with a region of increased diameter, 
preferably in the shape of a collar, the manipulation of the knob will be 
simplified as the collar works as a riveting head for the force applied to 
the knob core. 
By beading the front panel, or by beading a protection plate of the front 
panel at the feed-through sleeve, and by using a manipulable element that 
is elastic and encloses the beaded part, a liquid-proof front panel is 
obtained for the above embodiment. 
With an exchangeable protection plate it is also possible to quickly and 
easily adapt the front panel to a different language, to different 
settings, etc. 
The problem of sealing is solved in that a handling element of the 
setting/switching knob fits tightly against the front panel. Liquid is 
thus rejected directly at the interface between the manipulable element 
and the front panel. 
For this purpose, it is advantageous to make the front panel beaded at the 
setting/switching knob, with the manipulable element being elastic and 
formed to tightly enclose the beaded part of the front panel. This 
provides for a particularly tight interface, because liquid must pass 
through a long labyrinthine path to reach the feed-through sleeve. 
Alternatively, the front panel can be provided with a thin protection plate 
which is beaded at the setting/switching knob and the manipulable element 
can be elastic and formed to tightly enclose the beaded part of the 
protection plate. This provides a more simplified design for the front 
panel possible. 
For this embodiment of the invention, the setting/switching knob including 
a feed-through sleeve, rotatably arranged in the front panel, a knob core 
which is arranged in a movable and resilient manner in the feed-through 
sleeve and a locking washer arranged at the feed-through sleeve and 
fastened to the knob core. The locking washer locks the setting/switching 
knob against a stop in at least one direction of rotation and releases the 
setting/switching knob when the knob core is pushed against the resilient 
arrangement. The manipulable element tightly encloses the feed-through 
sleeve and the knob core. 
The problem of fixing the setting may alternatively be solved in accordance 
with the invention in another version wherein a resilient locking washer 
with at least one locking hook is fastened to a knob core of the 
setting/switching knob, the knob core being arranged in a movable manner 
in a rotatably arranged feed-through sleeve of the setting/switching knob. 
The locking washer prevents the rotatability in at least one direction 
against a stop, but the stop may be passed by applying force to the knob 
core against the resilient locking washer, causing the locking hook to be 
pressed making the setting/switching knob turnable. 
A functional and safe construction is thus obtained with a minimum of 
elements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A part of a front panel 1 of a control unit is shown in FIG. 1 together 
with a setting assembly knob 5. The front panel 1 is formed by a back 
panel plate 2 and a front panel plate 3, whereby the front panel plate 3 
is exchangeable and has a thin plastic plate 4 glued onto it. 
The setting knob assembly 5 includes a feed-through sleeve 6, a knob core 
10, and a resilient locking washer 11, a stop 12, a console 7 and a 
manipulable element 16. 
A potentiometer 8 is located in the console 7, which is connected to the 
feed-through sleeve 6. The console 7 is fastened to the back panel plate 2 
by two screws 9A and 9B thereby holding the potentiometer 8 and the 
setting knob assembly 5 in place on the front panel 1. 
As can be seen from FIG. 3, the feed-through sleeve 6 has two recesses, 
which thereby form two opposite branches 14 (only one is visible). A slot 
15 of the locking washer 11 (FIG. 2) fits over these branches 14. 
The knob core 10 in FIG. 1 has an annular groove 17 in which the locking 
washer 11 is to be fixed. In order to obtain a well-defined position for 
the locking washer 11 relative to the knob core 10, the slot 15 of the 
locking washer 11 is made narrower than the diameter of the annular groove 
17 of the knob core 10, except at a location which corresponds to the 
well-defined position for the locking washer 11. At this location, the 
slot 15 of the locking washer 11 is adapted to the annular groove 17. 
In FIG. 2, it is shown that the locking washer 11 further has two slots 13A 
and 13B, which are responsible for the resiliency of the locking washer 
11, which is necessary in order to make the knob assembly 5 function. Also 
necessary are two shoulders 18A and 18B which, when the locking washer 11 
is mounted, are in contact with the surface 19 (FIG. 3) of the 
feed-through sleeve 6. When the knob core 10 is pressed, the locking 
washer 11 will be forced apart at the two slots 13A and 13B and a locking 
hook 20 on the underside of the locking washer 11 (indicates with a broken 
line in FIG. 2) may be moved past the stop 12. In FIG. 1, the stop is 
formed as a projection on the back side of the front panel 1. The number 
of stops 12 depend on the number of settings made available to the setting 
knob assembly 5. The locking hook 20 may be formed rectangularly to enable 
locking in both direction, or have a slope on one side to be able to slide 
over the stop 12 in one direction. 
The manipulable element 16 is made of an elastic material and encloses the 
feed-through sleeve 6 and the knob core 10 at the front of the front panel 
1. In order to improve the sealing ability of the front panel 1 at the 
knob assembly 5, the plastic plate 4 is beaded 21 outwardly at the 
feed-through sleeve 6 and the manipulable element 16 tightly encloses the 
beaded part. To facilitate manipulation of the setting knob assembly 5, 
the manipulable element 16 is also provided with a collar 22. 
Although modifications and changes may be suggested by those skilled in the 
art, it is the intention of the inventors to embody within the patent 
warranted hereon all changes and modifications as reasonably and properly 
come within the scope of their contribution to the art.