Patent Application
20190280582
The invention relates to an electromagnetic actuator for a surgical or medical instrument according to the preamble of claim 1.
Surgical or medical instruments, such as endoscopes with an elongate shaft, can have an objective arranged distally in the same. This objective serves the purpose of viewing an object inside a body. When an operator views this object, the image generated by the objective is conveyed electronically or by means of an image guide via a camera through the shaft. In this case, the objective can have an optical element, such as a lens or a group of lenses, which are mounted so as to be movable by means of an actuator in the direction of an optical axis of the objective to focus and/or to change the focal length. This electromagnetically driveable actuator is arranged in the shaft of the endoscope and is therefore only a few millimeters in size.
An essential component of the actuator is a cylindrical stator in which an element is arranged which is movable along the optical axis. The stator has at least two annular, axially magnetized permanent magnets, and at least two coils for generating an electromagnetic field. The movable element is designed as a rotor arranged in a sliding tube. The sliding tube is surrounded by the annular permanent magnets and the coils.
The movable rotor in the sliding tube serves to accommodate the objective—in particular, the lens or the lens group—and consists of a magnetizable material. The sliding tube has a stop at each of its ends, which limits the axial movement of the rotor in the sliding tube. Due to the arrangement of the permanent magnets around the sliding tube, the rotors on each of the ends of the sliding tube are positioned in a bistable orientation. Energizing the coils moves the rotor from one end position to the other end position, as a result of the magnetic field induced in the coil. If no magnetic field is induced by the coil, the rotor, together with the lenses, remains in one of its end positions.
Since the space available in the shaft of an endoscope is very limited, the actuator and the lenses must be miniaturized accordingly. This not only places particularly high demands on the precision of the coils and the rotor, and the arrangement of the lenses, but also on the shape of the permanent magnets. Even the smallest variations in the sizing of the permanent magnets, resulting from manufacturing processes, have a negative effect on the field line pattern of the magnets and thus on the switching behavior of the rotor. A consequence of a slightly too large or too small permanent magnet can be that the end positions of the rotor are no longer bistable, and thus the lens cannot focus properly.
The object of the invention is therefore to provide an electromagnetic actuator for a surgical or medical instrument which can be switched in a particularly reliable manner.
An actuator for achieving this object has the features of claim 1. In the same, the permanent magnets are arranged around the sliding tube in such a manner that a magnetic south pole of the one permanent magnet faces a magnetic north pole of the other permanent magnet. In this complementary pole arrangement of the permanent magnets, the two magnetic fields overlap at least partially, and accordingly interact. As a result of the identical orientation of the magnetic field vectors, slight deviations in the dimensioning of the magnets have a less-pronounced effect on the magnetic field than an arrangement in which the field lines are oriented opposite each other. As such, the permanent magnets having the same polarity allows a greater tolerance range in the manufacture of the permanent magnets. Since slight differences in length and/or diameter of the permanent magnets can therefore be compensated for by the interaction of the two permanent magnets, the positioning of the rotor in the two end positions in the sliding tube becomes particularly stable. This makes it possible to achieve a particularly reliable switching of the actuator—specifically, the rotor.
In a further preferred embodiment of the present invention, the two coils can have opposing winding directions. With the opposing winding directions, the magnetic field lines of the magnetic field generated in the coils by a current of the same sign run opposite each other. However, if only one coil is energized by a current of that sign, magnetic fields are induced with field vectors which alternately have different orientations along the optical axis. Accordingly, by appropriately switching the coils, the rotor can be moved from a stable end position in the sliding tube into the other stable end position. The decisive factor in this case is that the magnetic force induced by the coil in the rotor is at least momentarily greater than that of a permanent magnet. This arrangement of the two coils and/or their opposite winding makes it possible to achieve a particularly simple contacting of the coils with short leads.
In particular, each coil can also be preceded by a diode oriented differently from the other, such that the conducting directions of the diodes are reversed with respect to the coils. Therefore, according to the current applied to the coils, only one of the coils is activated as a function of the conducting direction of the diode, such that a magnetic field is always induced only in one coil. The arrangement of the diodes creates a circuit which functions with as few electrical lines as possible. Since, in particular, the space in the shaft is very limited, this is a particular advantage of the present invention. Since the interior of the shaft is a hermetically sealed space, the reduction in the number of electrical lines which are necessary has a particularly advantageous effect—since fewer lines are required which could otherwise hinder a hermetic seal.
Furthermore, it can be particularly preferred that the coils can be separately activated, wherein the coils are operable with an alternating pulse of electromagnetic energy. These pulses are only a few—particularly ten to twenty—milliseconds long, and periodically change their sign. Moreover, according to the invention, the coils can be arranged on the sliding tube between the permanent magnets, wherein the permanent magnets are functionally assigned to end regions of the sliding tube. As a result of this arrangement of the coils between the permanent magnets, the magnetic fields—and particularly the induced magnetic fields—couple together particularly effectively. As a result, on the one hand, the rotor rests in its stable end positions, while on the other hand it can be moved in a reliable manner from one position into the other position.
In a particularly advantageous embodiment of the present invention, a cylindrical back iron can also be arranged around the coils between the permanent magnets, wherein, in particular, this back iron has pole shoes which are arranged between the coils and/or between the permanent magnets and the coils. By means of these pole shoes, the magnetic field density can be redirected or concentrated in some places such that the switching process of the rotor is improved even more. In particular, the arrangement of a pole shoe between the coils has a particularly advantageous effect for smooth switching between the two end positions of the rotor.
Furthermore, in the invention, the coils can be energized in such a way that a magnetic flux forms in the back iron with the same orientation as the magnetic flux of the permanent magnets. The purpose of the back iron is therefore to form a homogeneous magnetic field around the sliding tube and/or in the sliding tube—at least during the energization of the coils.
Particularly preferably, in the present invention, a stop can be functionally assigned to each of the end regions of the sliding tube in order to limit the stroke of the movable rotor. These stops can be located inside and/or outside the sliding tube and can define the length over which the objective and/or lens group can be focused.
In particular, in the invention, the rotor can be designed as a hollow cylinder made of a soft magnetic material—preferably for receiving at least one lens. The lower the energy required to magnetize the rotor, the less magnetic energy has to be applied by the coils, and/or generated by the permanent magnets, to switch the rotor. Steel alloys have been found to be particularly suitable.
As a further advantageous embodiment of the present invention, the rotor can have two pole shoes which are functionally assigned to the end regions of the rotor. Due to the design of the pole shoes, the rotor particularly preferably couples to the magnetic fields, enabling a faster and more reliable switching process of the actuator.
A preferred embodiment of the invention is explained in more detail below with reference to the drawing, wherein:
The present invention is directed to an actuator 10 for a surgical or medical instrument. This surgical or medical instrument may, for example, be an endoscope 11. However, it should be expressly pointed out that the actuator 10 described here can also be used in other instruments, and the endoscope 11 shown in
The endoscope 11 shown in
In the shaft 13 of the endoscope 11, an optics is installed which makes it possible to image the interior of a body (not shown) during an operation. For this purpose, an image is captured—for example, via a sensor unit (not shown) which is located in the distal end 16 of the endoscope—and is fed via the conductor 18 to an external image display device, such as a monitor. However, it can also be contemplated that the image is fed via optical fibers or rod lenses to the proximal end 17 of the endoscope 10.
In order to image the object in the interior of the body in sharp focus, an objective and/or at least one lens, which is movably mounted for focusing and for setting the focal length, is functionally assigned to the distal end 16 in the interior of the shaft 13. This movable mounting of the lens (not shown) is realized by an electromagnetic actuator 10 in the interior of the shaft 13.
In the embodiment of an endoscope illustrated in
The electromagnetic actuator 10 substantially consists of a cylindrical stator 19 and a movable element arranged in the stator 19 (
In the embodiment of the actuator 10 shown in
The movable element in the interior of the stator 19 is formed by a rotor 28. This rotor is a hollow cylinder made of a magnetically soft material. When the actuator 10 is used in an endoscope 11, the objective and/or the at least one lens is positioned inside this rotor 28.
The rotor 28 is movably mounted inside a sliding tube 29. The previously described permanent magnets 20, 21 and the two coils 26, 27 are arranged in an annular fashion around this sliding tube 29. In order to limit the movement of the rotor 28 in the sliding tube 29, stops 30 are functionally assigned to each of the end regions 22, 23. These stops 30 can likewise be annular or simply designed as cuboid stops to prevent the rotor 28 from leaving the sliding tube 29.
The rotor 28 is movably mounted in the sliding tube 29 in such a manner that it can be moved parallel to an optical axis 31. This optical axis 31 also corresponds to the optical axis of the at least one lens. All elements of the actuator 10—such as the stator 19, the permanent magnets 20, 21 and the coils 26, 27, are arranged symmetrically about this optical axis 31.
In order to guide and/or to amplify the magnetic field generated by the coils 26, 27 and the permanent magnets 20, 21 toward the optical axis 31, in the embodiment of the present invention shown in
In a further embodiment of the actuator 10, the back iron 32 has pole shoes 34, which can be arranged, for example, between the permanent magnets 20, 21 and the coils 26, 27, and between the two coils 26, 27 (
The pole shoes 38 act on the rotor 28 (
In
The arrangement of the permanent magnets 20, 21 and the coils 26, 27 shown here generates a particularly suitable magnetic field with which the rotor 28 in the sliding tube 29 can be switched in a particularly simple and reliable manner. The arrangement of these elements can compensate for manufacturing-related deviations in the dimensioning of the permanent magnets 20, 21 which affect their magnetic fields, such that these variations have no influence on the switching of the rotor 28 and/or on the focusing of the optics.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2016 122 951.2 | Nov 2016 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2017/080060 | 11/22/2017 | WO | 00 |
