Arrangement in a tunable magnetron

The invention relates to a tunable magnetron comprising a rotatable tuning element (10) projecting into a ring shaped interaction space between coaxially arranged cathode and anode systems. The tuning element (10) is driven by an electric motor (11) and produces upon rotation a periodic variation of the tuning. The tuning element (10) is situated within the evacuated space of the magnetron and the motor (11) in situated outside said space. The drive torque of the motor is then transferred to the tuning element via a coupling (12) having two active parts situated one on each side of the evacuated envelope (17) of the magnetron. Such a coupling can only transfer a limited torque. According to the invention the magnetron comprises means for limiting the torque which can be transferred to the coupling (12), both upon starting and stopping, for example a torque limiter (21-26) between the motor (11) and the coupling (12), whereby the start and stop procedures can be performed with optimum torque. Therefore starting and stopping of the tuning element (10), for example when switching between different fixed frequencies, can be made with maximum speed (FIG. 3).

The invention relates to an arrangement in a tunable magnetron. The 
magnetron comprises coaxial cathode and anode systems defining between 
themselves a ring shaped interaction space, which is evacuated during 
operation, and a rotatable tuning element with an active portion 
influencing the tuning of the magnetron by having around the circumference 
varying electric conductivity for producing a periodic variation of the 
tuning upon rotation of the turning element, The tuning element is 
situated within an evacuated space enclosed by a vacuum-tight envelope and 
driven by an electric motor situated outside the vacuum-tight envelope via 
a coupling having two active parts situated on each side of the 
vacuum-tight envelope. The magnetron furthermore comprises a brake or stop 
device influencing the motor shaft. 
Such a magnetron is for example described in SE-patent 191 373, to which 
U.S. Pat. No. 3,343,031 corresponds. It may for example be used for 
producing HF-pulses whose frequency varies from pulse to pulse but also, 
by means of the brake or stop device, for producing HF-pulses having a 
fixed frequency. 
In certain applications it is a great advantage if a transition from a mode 
with generation of pulses having varying frequency to a mode with 
generation of pulses having fixed frequency and vice versa can be effected 
as quickly as possible in a simple, reliable and cheap manner. 
In known constructions the time for the transition is in general relatively 
extended. 
The object of the invention is to achieve a very short time of transition 
from the generation of HF-pulses having varying frequency to the 
generation of pulses having fixed frequency and vice versa, or in other 
words a very short stopping or starting time for the tuning element in a 
tunable magnetron of the described kind. 
The difficulties in achieving short stop and start times depend upon the 
fact that the coupling, usually a magnetic coupling, between the tuning 
element and the drive motor only can transfer a limited torque. If this 
torque is exceeded, i.e. if the coupling loses its grip in a braking 
operation, there will be an uncontrolled brake action and a long stopping 
time. If the coupling loses its grip upon starting, the tuning element 
cannot be accelerated up to its operating speed. 
In constructions known until now small motors have been used, the driving 
torque of which is essentially below the torque which can be transferred 
by the magnetic coupling. With such an arrangement both the stopping time 
and the starting time will be unnecessarily extended. The stopping 
procedure is further complicated or extened by the necessity to 
electronically sense or wait for the stationary condition of the tuning 
element before a possible magnetic brake is made effective. 
The invention eliminates these disadvantages and offers the advantage to 
shorten the stopping and starting times radically. 
The characteristics for a magnetron according to the invention is that it 
comprises, in both directions effective, means for limiting the torque 
which can be transferred to that part of the coupling, which is situated 
outside the vacuum-tight envelope, and that the limited torque which can 
be transferred to the coupling is adjusted to a value lying just below the 
maximal torque which can be transferred by the coupling. 
In one embodiment of the invention, the means comprises a torque limiter 
arranged between the motor and the coupling. This embodiment has the 
advantage that both the brake or stop device and the motor can deliver 
unlimited torques during the stopping or starting procedure. 
The torque limiter can be a purely mechanical frictional coupling or the 
like. Alternatively it may be of electro-magnetic nature, in which case 
the torque is adjusted electrically. 
In another embodiment of the invention, the means consists therein that the 
magnetic brake influencing the motor has an adjustable brake torque. This 
solution can suitably be combined with the use of an electric motor 
delivering a maximum torque which is just below the maximum torque which 
can be transferred by the coupling.

In FIGS. 1 and 2 block 10 represents a tuning element which is embodied in 
a continuously tubable magnetron, block 11 is an electric motor for 
driving the tuning element 10, and block 12 is a magnetic coupling. The 
tuning element 10 is situated within an evacuated space communicating with 
the interaction space of the magnetron, while the drive motor 11 is 
situated outside the space, the magnetic coupling 12 being used to produce 
coupling between the motor 11 and the tuning element 10 via the 
vacuum-tight envelope of the magnetron. The magnetic coupling 12 is then 
only able to transfer a given maximum torque. 
The magnetron may be example be of a construction as described in SE-patent 
191 373 while the magnetic coupling may be constructed as described in 
SE-patent 199 364, which corresponds to U.S. Pat. No. 3,247,421. 
In the embodiment depicted in FIG. 1, a magnetic brake 13 is arranged on 
the drive shaft of the motor 11 and a torque limiter 14 is introduced 
between the motor 11 and the magnetic coupling 12. The magnetic brake 13 
in FIG. 1 can deliver an unlimited brake torque. 
The torque limiter 14 may be a frictional clutch of purely mechanical 
construction. Alternatively it may be an electro-mechanical or 
electro-magnetic device, in which case the transferable torque is 
controlled electrically. The torque which can be transferred by the torque 
limiter 14 is adjusted so that it is just below the maximum torque which 
can be transferred by the magnetic coupling 12. 
Such a torque limiter 14 is normally also active upon starting the motor, 
when the tuning element is accelerated to its final speed in the operating 
condition. The drive torque delivered by the motor therefore in this case 
does not need to be limited. 
In the embodiment depicted in FIG. 2, a magnetic brake 15 having an 
adjustable torque is arranged on the drive shaft of the motor 11, which in 
this case is rigidly connected to the magnetic coupling 12. The brake 
torque delivered by the magnetic brake 15 is then adjusted to a value 
which is just below the maximum transferable torque of the magnetic 
coupling 12. In this case the motor should be of a type allowing setting 
of a maximum torque, this maximum torque also being adjusted to a value 
just below the maximum transferable torque of the magnetic coupling 12. 
FIG. 3 shows a side view, partly in section, of that part of a tunable 
magnetron, where the magnetic coupling 12 and drive motor 11 with magnetic 
brake are situated, a mechanical frictional clutch used as a torque 
limiter in accordance with the invention being shown in detail. In FIG. 3 
the tuning element 10, the magnetic coupling 12, the drive motor 11 and 
the magnetic brake 13 are shown. The tuning element 10 is supported by 
ball bearings, one ball bearing 16 is visible in FIG. 3, and is situated 
within an evacuated envelope 17. The tuning element 10 is terminated by a 
part 18 cooperating with a part 19 of a yoke 20 situated outside the 
envelope; the parts 18 and 19 are made of magnetic material and together 
form the magnetic coupling 12. 
In according with the invention the yoke 20 of the magnetic coupling 12 is 
connected to the drive shaft of the motor 11 via a frictional coupling 
consisting of the following parts: pressure plate 21 with hub 22, washer 
23, compression spring 24, setting nut 25 and locking nut 26. The pressure 
plate 21 and hub 22 are rigidly connected to the drive shaft of the motor 
11, while the yoke 20 is free to rotate on the hub 22 and the washer 23 is 
axially displaceable on the hub but locked for rotation relative to the 
hub. The compression spring 24 acts between the setting nut 25 and the 
washer 23 and presses the central part of the yoke 20 between the washer 
23 and the pressure plate 21, whereby upon rotation of the motor shaft the 
yoke 20 will be carried along due to friction against surrounding parts. 
The maximum transferable torque of the frictional coupling can be set 
accurately by means of the setting nut 25, which is locked by means of the 
locking nut 26. 
A cooling element 27 with cooling flanges is in heat conductive contact 
with the envelope of the magnetron in order to lead away exessive heat. 
In another embodiment an electro-magnetic shaft-clutch is used as torque 
limiter, the maximum transferable torque of which can be controlled 
electrically. 
Other types of torque limiters can alternatively be used, for example 
hydro-mechanical or pneumatic devices.