U.S. patent application number 10/749308 was filed with the patent office on 2005-05-26 for reciprocating piston drive mechanism.
This patent application is currently assigned to LEYBOLD VAKUUM GmbH, a Corporation of Germany. Invention is credited to Bahnen, Rudolf, Hodapp, Josef, Knoll, Gunter.
Application Number | 20050112001 10/749308 |
Document ID | / |
Family ID | 26005357 |
Filed Date | 2005-05-26 |
United States Patent
Application |
20050112001 |
Kind Code |
A1 |
Bahnen, Rudolf ; et
al. |
May 26, 2005 |
Reciprocating piston drive mechanism
Abstract
A reciprocating piston drive mechanism, especially for a
reciprocating piston vacuum pump, includes a cylinder (3) embodied
in a housing (12). A piston (4) is moved back and forth in the
cylinder by an electromagnetic drive that has an electromagnet (11)
on the stator side and at least one permanent magnet (18, 19) on
the piston side. In order to increase service life of said drive
mechanism, permanent magnets (15, 16) are also provided on the
stator side. The piston permanent magnet(s) (18, 19) and the stator
permanent magnets (15, 16) are configured and disposed in such a
way that the piston (4) is magnetically biased to a substantially
central axial position in the idle state.
Inventors: |
Bahnen, Rudolf; (Roetgen,
DE) ; Hodapp, Josef; (Koln-Sulz, DE) ; Knoll,
Gunter; (Aachen, DE) |
Correspondence
Address: |
Thomas E. Kocovsky, Jr.
FAY, SHARPE, FAGAN, MINNICH & McKEE, LLP
Seventh Floor
1100 Superior Avenue
Cleveland
OH
44114-2518
US
|
Assignee: |
LEYBOLD VAKUUM GmbH, a Corporation
of Germany
Koln
DE
|
Family ID: |
26005357 |
Appl. No.: |
10/749308 |
Filed: |
December 31, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10749308 |
Dec 31, 2003 |
|
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|
09959218 |
Feb 4, 2002 |
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6736614 |
|
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09959218 |
Feb 4, 2002 |
|
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PCT/EP00/03528 |
Apr 19, 2000 |
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Current U.S.
Class: |
417/418 ;
417/415; 417/416; 417/417 |
Current CPC
Class: |
F04B 35/045 20130101;
F04B 2201/0201 20130101; H02K 33/16 20130101; H02K 7/09
20130101 |
Class at
Publication: |
417/418 ;
417/415; 417/416; 417/417 |
International
Class: |
F04B 017/00; F04B
035/04 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 19, 1999 |
DE |
DE 199 17 560.8 |
Apr 18, 2000 |
DE |
DE 100 19 108.8 |
Claims
1. (canceled)
2. The drive mechanism according to claim 3, wherein: the piston is
equipped on each of its face sides with the piston permanent
magnet; and the stator permanent magnets are located in the area of
face sides of the cylinder.
3. A reciprocating piston drive mechanism, comprising: a housing, a
cylinder defined in said housing, stator permanent magnets disposed
in the cylinder, a piston mounted for back and forth movement in
the cylinder, face sides of the piston being equipped with
recesses, which correspond to the dimensions of the stator
permanent magnets, an electromagnetic drive for the piston
including an electromagnet on a stator side and at least one
permanent magnet on the piston, the stator permanent magnets being
disposed relative to the permanent magnet of the piston in such a
way that the piston adopts a substantially centered axial position
in an idle state.
4. A reciprocating piston drive mechanism comprising: a housing, a
cylinder defined in said housing, a piston mounted for back and
forth movement in the cylinder, an electromagnetic drive for the
piston including an electromagnet on a stator side and at least one
permanent magnet on the piston, stator permanent magnets disposed
on the stator side and disposed relative to the permanent magnet of
the piston in such a way that the piston adopts a substantially
centered axial position in an idle state, a pole component with a
cross section having a U-shape and U-limbs which end at a level of
the permanent magnets on the stator side.
5. The drive mechanism according to claim 4, wherein the U-shaped
pole component encompasses at least one coil from three sides.
6. The drive mechanism according to claim 5, wherein a further
cylindrical pole component is located between the coil and the
cylinder.
7. The drive mechanism according to claim 4, wherein axially
arranged pole components are assigned to the permanent magnets at
the piston.
8. A reciprocating piston drive mechanism comprising: a housing, a
piston mounted for back and forth movement in a cylinder, the
piston being equipped only with a single permanent magnet situated
approximately centrally in an axial directions, an electromagnet on
a stator which interacts with the permanent magnet on the piston to
drive the piston, stator permanent magnets disposed on the stator
and disposed relative to the permanent magnet of the piston in such
a way that the piston is biased toward a substantially centered
axial position in an idle state.
9. The drive mechanism according to claim 8, wherein permanent
magnets on the stator are located on opposite sides of the
permanent magnet of the piston, a distance between the permanent
magnets on the stator corresponds to an amplitude of the piston's
motion.
10. The drive mechanism according to claim 8, wherein: two coils
are provided next to each other along the axial direction, a yoke
encompasses the coils, a face side of a central yoke component
encompasses the permanent magnet of the piston, and face sides of
inner axially extending yoke components rest against the permanent
magnets on the stator.
11. A reciprocating piston drive mechanism comprising: a housing, a
cylinder defined in said housing, a piston mounted for back and
forth movement in the cylinder, a rotationally symmetrical
electromagnetic drive for the piston including an electromagnet on
a stator and at least one ring-shaped permanent magnet on the
piston, stator permanent magnets disposed on the stator and
disposed relative to the ring-shaped permanent magnet of the piston
in such a way that the piston is biased to a preselected axial
position in an idle state.
12. The drive mechanism according to claim 11, wherein the stator
includes axially symmetrical sole components.
13. A reciprocating piston drive mechanism comprising: a housing in
which a cylinder is defined, a stator surrounding the cylinder, a
piston mounted for back and forth movement in the cylinder, an
electromagnetic drive for the piston including an electromagnet,
permanent magnets, and pole components in the stator and at least
one permanent magnet on the piston, at least one of the pole
components interacting with the stator magnets such that resultant
magnetic forces are axially asymmetrical, the stator permanent
magnets being disposed relative to the piston permanent magnet to
bias the piston toward a substantially centered axial position in
an idle state.
14. A reciprocating piston drive mechanism comprising: a housing, a
cylinder defined in said housing, a piston mounted for back and
forth movement in the cylinder, an electromagnetic drive for the
piston including an electromagnet on a stator and at least one
permanent magnet on the piston, sensors for detecting the piston's
position, stator permanent magnets disposed on the stator relative
to the piston permanent magnet to urge the piston to adopt a
substantially centered axial position in an idle state.
15. A reciprocating piston drive mechanism comprising: a housing, a
cylinder defined in said housing, a piston mounted in the cylinder
for back and forth movement, the piston and the cylinder defining
two chambers, at least one of two chambers created by the piston
and the cylinder being equipped with an inlet valve and a discharge
valve, an electromagnetic drive for the piston including a stator
electromagnet and at least one piston permanent magnet, stator
permanent magnets disposed relative to the piston permanent magnet
for biasing the piston to a substantially center axial
position.
16. A reciprocating piston vacuum pump comprising: a housing; a
cylinder defined in the housing; a piston mounted in the cylinder,
the piston and cylinder defining a pair of chambers on opposite
sides of the piston, the piston mounted for reciprocating movement
in the cylinder, which reciprocating movement expands one of the
chambers as it contracts the other; an inlet line opening into at
least one of the chambers, the opening of said inlet line forming
together with the piston an inlet valve, at least one permanent
magnet mounted on the piston; permanent magnets mounted on a stator
such that magnetic forces between the stator permanent magnets and
the piston permanent magnet urge the piston toward a substantially
central axial position; and, an electromagnet on the stator for
selectively urging the permanent magnet on the piston to move the
piston along the cylinder.
17. A reciprocating piston pump comprising: a housing; a cylinder
defined in the housing; a piston mounted in the cylinder, the
piston and cylinder defining a pair of chambers on opposite sides
of the piston, the piston mounted for reciprocating movement in the
cylinder, which reciprocating movement expands one of the chambers
as it contracts the other; discharge valves which are controlled by
one of pressure and the piston, at least one permanent magnet
mounted toga piston; permanent magnets mounted on a stator such
that magnetic forces between the stator permanent magnets and the
piston permanent magnet bias the piston toward a substantially
centered position axially; and, an electromagnet on the stator for
selectively urging the permanent magnet on the piston to
reciprocate the piston in the cylinder.
18. The sums according to claim 17 wherein the discharge valves
include closure pieces which extend substantially over the entire
cross section of the cylinder.
19. The pump according to claim 18, wherein closing motion of the
closure pieces is assisted by the resilient forces of springs.
20. The sums according to claim 18, wherein closing motion of the
closure pieces is assisted by the magnetic forces.
21. The pump according to claim 20, wherein: the closure pieces
include discs made at least partly of a ferromagnetic material; and
an outer face side of one of the permanent magnets on the stator
forms a discharge valve seat.
22. A reciprocating piston drive mechanism comprising: a housing;
several cylinders accommodated in the housing, a piston mounted in
each of the cylinders, the pistons and cylinders defining pairs of
chambers on opposite sides of each piston, each piston being
mounted for reciprocating movement in a corresponding one of the
cylinders, which reciprocating movement expands one of the chambers
as it contracts the other; at least one permanent magnet mounted on
each piston; permanent magnets mounted on a stator such that
magnetic forces between the stator permanent magnets and the piston
permanent magnets urge the pistons toward selected axial positions;
and, an electromagnet on the stator for selectively reciprocating
each piston along the corresponding cylinder.
23. A drive mechanism comprising: a housing; a cylinder defined in
the housing; a piston mounted in the cylinder, the piston and
cylinder defining a pair of chambers on opposite sides of the
piston, the piston mounted for reciprocating movement in the
cylinder, which reciprocating movement expands one of the chambers
as it contracts the other; at least one permanent magnet mounted on
the piston; permanent magnets mounted on a stator such that
magnetic forces between the stator permanent magnets and the piston
permanent magnet bias the piston; an electromagnet on the stator
for selectively urging the permanent magnet on the piston to move
the piston along the cylinder; and, a switching means for driving
the electromagnet coil, said switching means being driven by
signals dependent on the piston's position.
24. A method for operating a drive mechanism according to claim 13,
wherein at least one of a frequency of the piston's motion and a
maximum current flow in the electromagnet is pre-set.
25. The method according to claim 24 wherein the piston motion is
reversed before reaching an end of travel.
26. A method for operating a drive mechanism according to claim 22,
wherein pairs of the pistons are controlled to reciprocate in
opposite directions.
27. A piston for a reciprocating piston drive mechanism according
to claim 15, the piston including: two pot components which in an
area of their open face sides are equipped with joining means.
28. The piston according to claim 27, wherein the pot components
are equipped in the area of their open face sides with rims which
in the assembled state form a ring groove for accepting a single
permanent magnet ring.
Description
[0001] The present invention relates to a reciprocating piston
drive mechanism, especially for a reciprocating piston vacuum pump,
comprising a housing, a cylinder embodied in said housing, a piston
moving back and forth in the cylinder and an electromagnetic drive
for the piston that has an electromagnet on the stator side and at
least one permanent magnet on the piston side.
[0002] A reciprocating piston drive mechanism having such
characteristics is known from DE-A-41 02 710. In this reciprocating
piston drive mechanism according to the state-of-the-art there are
located in the cylinder two springs, of which one each extends
between one of the face sides of the piston and the related face
side of the cylinder. Through this, the piston adopts a
substantially central axial position in the idle state. When
continually stressing the helical springs, fatigue affecting the
material of the springs is unavoidable. For this reason, the
service life of reciprocating piston drive mechanisms according to
the state-of-the-art is thus limited to the service life of the
material employed for the springs.
[0003] The reciprocating piston drive mechanism according to
DE-A-41 02 710 is a component of a reciprocating piston pump, in
which at least one of the two chambers created by piston and
cylinder has the function of a compression chamber. Located in this
chamber or these chambers are the helical springs. This gives rise
to unwanted clearance volumes, this impairing the pumping
effect.
[0004] It is the task of the present invention to improve a
reciprocating piston drive mechanism of the aforementioned kind in
such a manner that it no longer offers the disadvantage of spring
materials being subjected to fatigue. Moreover, the design goal is
such that the drive mechanism be particularly well suited for
reciprocating piston vacuum pumps.
[0005] This task is solved by the present invention in that
permanent magnets are provided on the stator side and where the
stator magnet(s) is/are so configured and disposed that the piston
adopts a substantially central axial position in the idle state. In
the idle state, i.e. with the electromagnets de-energised, the
superimposed magnetic fields being generated by the permanent
magnets affixed to the piston and in the stator, generate forces
affecting the piston holding it in a central axial position. Thus
in the idle state a defined, for example, central piston position
results which is solely effected by the effect of magnetic forces
and does not require any additional facility of a mechanical kind,
like springs.
[0006] It is expedient that the piston be equipped with two
permanent magnets, of which one each is located in the area of the
two face sides of the piston. Assigned to each of these permanent
magnets on the side of the piston is one each permanent magnet on
the stator side, specifically in the area of the face sides of the
cylinder at an approximately equal radial position.
[0007] In a particularly simple solution, the piston is only
equipped with a permanent magnet ring arranged approximately
centrally in the axial direction. Located to the side of this ring,
there is located one each permanent magnet on the stator side, the
distances of which with respect to the magnet ring of the piston
define the amplitude of the piston's stroke and the desired amount
of piston delay as soon as it approaches one of the dead
centers.
[0008] If the permanent magnets of the stator are magnetised in the
axial direction with reversed polarity with respect to the
corresponding permanent magnets of the piston, then their magnetic
fields will generate repelling forces. These forces then have the
effect that the velocity of the piston, as it approaches the face
side of the cylinder, is reduced, and finally the movement of the
piston in the reverse direction is initiated. If this arrangement
is designed to be in all symmetrical, specifically with respect to
its dimensions and also with respect to the strength of the
magnetic fields, then the piston will, in the de-energised state of
the electromagnet's coil, assume a central axial position.
[0009] When employing the drive mechanism in accordance with the
present invention in a reciprocating piston vacuum pump, an
asymmetrical arrangement in the axial direction may be expedient,
since the symmetry conditions determine the force characteristic.
If the load on the two compression chambers of the pump located at
the two face sides is asymmetric during the pumping process, the
force characteristic can be adapted by an axially asymmetric drive
mechanism.
[0010] Further advantages and details of the present invention
shall be explained with reference to the schematically depicted
design examples of drawing FIGS. 1 to 8.
[0011] Depicted are in
[0012] drawing FIGS. 1 and 2 sectional views through two
implementations of a reciprocating piston drive mechanism according
to the present invention,
[0013] drawing FIG. 3 a reciprocating piston vacuum pump with a
drive mechanism according to the present invention,
[0014] drawing FIGS. 4 and 5 design implementations for
reciprocating piston vacuum pumps each with two pistons,
[0015] drawing FIGS. 6 and 7 examples of circuits and,
[0016] drawing FIG. 8 a further implementation example for a
reciprocating piston vacuum pump according to the present
invention.
[0017] In the drawing figures in each case the outer housing is
designated as 2, the cylinder embodied in the housing 2 as 3, the
piston located in cylinder 3 as 4 and its sleeve as 5.
[0018] The stator components of the electromagnetic drive mechanism
accommodated in the housing in accordance with drawing FIGS. 1 to
5, are at least one coil 8 as well as a pole component 11 (yoke)
with a U-shaped cross section open towards the inside encompassing
the coil(s) 8 from three sides. Moreover, a pole component 12
(guiding yoke) shaped like a pipe section is provided which is
located between coil 8 and sleeve 5. Finally, two permanent magnets
15, 16 which are located in the areas of the face sides of cylinder
3 belong to the stator system. The U-limbs of the yoke 11 terminate
at the level of these permanent magnets 15, 16.
[0019] Two permanent magnets 18, 19 which are located in the areas
of the face sides of the piston 4 are components of the
electromagnetic drive mechanism on the side of the piston. In the
radial direction, pole components 21 to 24 (drawing FIGS. 1, 2) are
assigned to the permanent magnets 18, 19. Expediently, they are
covered by these pole components, whereby the covers 21, 24 located
on the face side may be components of piston covering disks 25, 26
which in their central areas consist of non-ferromagnetic material.
The remaining part of the piston 4 is made of non-ferromagnetic
material.
[0020] The design of the drive mechanisms depicted in drawing FIGS.
1 to 5 is preferably rotationally symmetrical. Expedient here is
the configuration of ring-shaped permanent magnets, both at the
stator (15, 16) and also at the piston (18,19). Non-rotationally
symmetrical solutions would be more involved as to their
manufacture.
[0021] In all design examples depicted in drawing FIGS. 1 to 5 in
each instance two permanent magnets 18, 19 are provided at the
piston substantially at the face side. These might also be replaced
by a single piece permanent magnet which, for example, when shaped
like a tube encompasses the piston 4.
[0022] Expediently reciprocating piston drive mechanisms according
to all drawing figures are equipped with sensor components; only in
drawing FIGS. 1 and 2 are such sensor components 31, 32 depicted.
They are also configured to be ring-shaped. One is arranged in the
area of the two face sides of the electromagnetic drive mechanism.
These sensors 31, 32 serve to detect the piston's position, chiefly
in the area of its dead centers. Preferably the sensors 31, 32 are
designed as ring-shaped coils. The voltage induced in these
ring-shaped coils depends on the position of the piston, so that
the generated signals can be employed to drive the coil(s) 8.
Instead of the ring-shaped coils also Hall elements, optical
sensors or eddy current sensors may be utilised.
[0023] The reciprocating piston drive mechanisms in accordance with
drawing FIGS. 1 and 2 differ only with respect to the way in which
the guiding yoke 12 is designed. In the design example in
accordance with drawing FIG. 1 it is designed to be symmetrical in
the axial direction. The driving forces exerted on the piston 4 are
for this reason also symmetrical. In the design example in
accordance with drawing FIG. 2 the guiding yoke 12 is asymmetrical
in the axial direction. Its distance to sensor coil 32 is less than
its distance to sensor coil 31. For this reason, the driving forces
exerted in the area of the sensor coil 32 on the permanent magnet
19 of the piston 4 are greater than the corresponding driving
forces in the area of permanent magnet 18. This effect may also be
attained by an axially unsymmetrical design of other pole
components, for example, the covering disks 21 to 24, the design of
the limb ends of yoke 11 or alike. Moreover, the reciprocating
piston drive mechanisms in accordance with drawing FIGS. 1 and 2
are depicted in a highly schematic manner. Drive components linked
to the piston 4 have been omitted.
[0024] Drawing FIG. 3 depicts a reciprocating piston vacuum pump
equipped with a reciprocating piston drive mechanism according to
the present invention. In this example of an implementation the
cylinder 3, the face sides of the piston 4 and the sleeve 5 form
partial volumes 34, 35, having the function of compression
chambers. Each of these pump stages has each an inlet 36, 37 which
at the side opens out into the compression chamber 34 and 35
respectively. Thus the piston and the openings have, in a basically
known manner, the function of inlet control valves.
[0025] The discharge valves 41, 42 are each arranged on the face
side. Preferably the discharge opening substantially extends over
the entire cross sectional area of the cylinder 3 (basically known
from DE-A-196 34 517). The closure components are designed as
flexible discs 43, 44 extending across the entire cross section of
cylinder 3, said discs being centrally affixed at housing 2 and
being actuated peripherally by the pressure created or by the face
sides of the piston. In the example of a design implementation in
accordance with drawing FIG. 3, the face sides of the piston have a
concave contour. The face sides of the cylinder wall or--as
depicted in drawing FIG. 3--the outer face sides of the permanent
magnets 15, 16 on the stator side form the valve seats. The gases
emerging from the valves 41, 42 first enter into the discharging
chambers 45, 46 to which outlets 47, 48 are linked.
[0026] In the implementation in accordance with drawing FIG. 3, the
stator permanent magnets 15, 16 are located in cylinder 3. The face
sides of the pistons are equipped with outer recesses 10, 20
corresponding to the size of these magnets. These measures serve
the purpose of avoiding clearance volumes while the pump is
operating.
[0027] Depicted in drawing FIGS. 4 and 5 are examples of
implementations for reciprocating piston vacuum pumps where in a
housing 2 having a joint center housing plate 50, two each pistons
4, 4' of the same design are accommodated. The drive mechanisms are
so designed and controlled that the two pistons 4, 4' reciprocate
in opposing directions. Owing to the thus effected balancing of
masses, the pumps are free of vibrations.
[0028] In the example of the implementation depicted in drawing
FIG. 4, the two pumping stages of the two pistons 4 and 4' are
connected in parallel. From the paths for the gases, in each case
schematically represented by lines, it is apparent that the gas
which is to be pumped is fed from the gas inlet 51 to the
compression chambers 35 and 34'. They exit these compression
chambers through discharge valves 42, 41'. From there they are in
each instance supplied to the compression chambers 34 and 35'
respectively. The two gas outlets are designated as 52 and 53.
[0029] The depicted discharge valves 41, 42 and 41', 42' are
similarly designed as depicted for the design example in accordance
with drawing FIG. 3. The difference is, that the face sides of the
pistons 4, 4' do not exhibit a concave contour; instead they are
equipped with tappets which actuate the related valves discs. Other
embodiments for discharge valves of this kind are known from
DE-A-196 34 517.
[0030] Moreover, also different compared to the solution in
accordance with drawing FIG. 3 is that both drive mechanisms for
the pistons 4 and 4' are in each instance designed to be
asymmetrical in the axial direction. The yoke components 12, 12'
are extended towards the respective gas discharge side (outlets 52,
53). The permanent magnets on the outlet side 18 and 19' of the
pistons 4 and 4' are covered on both sides by the pole components
21, 22 and 21', 22' respectively whereas to the inner permanent
magnets 19, 18' in each instance only one pole component 23 and 23'
respectively is assigned. Through these measures the force
characteristics of the drive mechanisms take account of the fact
that the outer pumping stages are pumping against atmospheric
pressure.
[0031] In the example of the design implementation in accordance
with drawing FIG. 5 the four pumping stages are series connected.
The gases pumped from the inlet 51 to the outlet 54 pass through
compression chambers 34', 34, 35, 35' one after the other. The
solution in accordance with drawing FIG. 5 is particular, in that
the closure motion of the valves 41, 42, 41', 42' is effected
magnetically. The disc-shaped closure elements consist at least in
part (outer wall, for example) of ferromagnetic material, so that
the permanent magnets 15, 16, 15' 16' of the stator exercise an
attracting force. The discs are opened under pressure control or
under piston control (via the tappets depicted), whereas the
closure motion is effected by magnetic forces.
[0032] Depicted in drawing FIGS. 6 and 7 are examples of circuits
for reciprocating piston drive mechanisms equipped with sensor
components. The components of the drive mechanism are in each
instance accommodated in block 61, and the components of the
electronics in block 62.
[0033] Drawing FIG. 6 depicts a solution having only one coil 8,
which is driven depending on the signals from the sensors 31, 32. A
bridge circuit 63 comprising four switches is employed for driving
purposes, where on the one hand the supply voltage U and on the
other hand the signals from the sensors 31, 32 processed by logic
circuitry 64 are supplied to said bridge. The four electronic power
switches are driven by the logic circuitry 64 in such a manner that
the two terminals of coil 8 are connected, depending on the desired
direction for the current flow, to the positive or the negative
terminal of the DC source 65.
[0034] In the arrangement in accordance with drawing FIG. 7, two
coils 8' and 8" wound in opposing directions are located in the
chamber accommodating the coils of the drive mechanism. They may be
arranged next to each other or concentrically with respect to each
other. In this case the current will need to flow only in one
direction through the two coils. For this reason one end of the
coil is permanently connected to the positive terminal of the DC
supply voltage U, whereas the other ends of the coil are connected
through two electronic power switches 66, 67 to the negative
terminal of the DC voltage U in alternating fashion. The two
switches are driven directly through the sensors 31, 32 at the top
and bottom dead center. This embodiment minimises the complexity of
the power electronic circuitry. However, it implies an inadequate
utilisation of the chamber accommodating the coils.
[0035] There exists the possibility of dispensing with sensor
components in the drive mechanism. In this instance the voltage
induced in the coil(s) in the stator may be utilised as information
for sensing the piston's position, and the subsequent current flow
through the same coil(s) may be derived therefrom.
[0036] As to the way in which the coil(s) is/are driven, several
embodiments are suited for implementation. In the first, an
oscillatory frequency is defined at a fixed frequency and the
current in the coil(s) is pre-set in such a manner that this
frequency is also attained. The motion is reversed at the end
position in each case. This approach is termed as "external
control". This principle offers the disadvantage that at very high
process loads the pump is prone to being overloaded.
[0037] In a second control law, the principle of "self-control" is
utilised. In this case the maximum current through the coil(s) is
pre-set, and in the event of too high a load the oscillatory
frequency is reduced. Here too, the motion is reversed as soon as
the piston reaches its end position in each case.
[0038] In a third control law, the second control law is varied
inasmuch as the motion is reversed already before the piston
attains its end position. Thus the reciprocating piston motor can
be protected during "pump up" or in the event of continuous and
excessively high loads, against being overloaded. In addition, the
system may be rated for smaller forces and its implementation can
be made to be more cost-effective. The same equally also applies to
the second control law.
[0039] The example of the implementation of a reciprocating piston
vacuum pump in line with the present invention in accordance with
drawing FIG. 8 differs from the implementation in accordance with
drawing FIG. 3, in that the piston 4 is only equipped with a
permanent magnet ring 20 arranged centrally in the axial direction.
It encompasses the jacket of the piston 4 so that the two permanent
magnets 15, 16 on the stator side can be spaced at the side at a
distance which corresponds to the amplitude of the piston. The
section of the linear drive mechanism on the stator side is adapted
to the arrangement of the permanent magnets 15, 16, 20. Two coils
8', 8" are provided being encompassed by a yoke 11 with a central
yoke component 11'. The face side of the central yoke component 11'
oriented radially towards the inside encompasses the permanent
magnet ring 20. The face sides of the inner, axially extending yoke
components rest flush from the outside against the permanent
magnets 15, 16 on the stator side.
[0040] Moreover, from drawing FIG. 8 an expedient embodiment for
piston 4 is apparent. For example, it consists of two pot
components 70, 71 which within the area of their open sides are
joined together by gluing, for example. For this purpose one each
axially directed protrusion 72 and 73 respectively which, in the
joined state meet concentrically against each together, may be
employed. Moreover, the pot components 70, 71 are equipped in the
area of their open sides each with a radially extending rim 74 and
75 respectively. The distance of these rims 74, 75 from the
corresponding open face side of the pot components 70, 71 is so
selected that these form, when joined, a circular groove 76, the
width of which corresponds to the width of the permanent magnet
ring 20. With this solution more reliable affixing of the ring 20
on the piston 4, as well as a piston mass which is as low as
possible, can be achieved.
* * * * *