BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a linear pump or compressor, comprising a reciprocating linear motor, a compressing or pumping head, a rod connecting the head and the motor and a support structure connecting the motor and the head.

2. Description of the Prior Art

Usually, linear pumps and compressors as mentioned above comprise an actuator/stator configuration with an E-shaped magnetic coil/core arrangement. The actuator comprises several permanent magnets and reciprocates over the E-shaped magnetic core. The actua tor is mounted by elastic elements like diaphragms or leaf springs for an oscillating move ment. A coil is placed over the inner leg of the E-shaped magnetic core.

Without applying voltage, the initial position of each of the permanent magnets is over one part of the coil and partially over the sides of the E-shaped magnetic core. The mag nets are attached to the actuator with a relatively large distance between them, which is usually bigger than the width of the side leg of the E-shaped magnetic core.

Figure 1 shows in a cross-sectional view an example of a known linear pump 1 with two diaphragm units 3, 5. The linear pump 1 comprises a linear motor 7 having a stator and an actuator. The stator comprises two E-shaped magnetic cores 9, 10 having outer legs 11 and a middle leg 12. Along each middle leg 12 of the E-shaped magnetic cores 9, 10 coils 13, 15 are mounted. The E-shaped magnetic cores 9, 11 and the coils 13, 15 are forming a stator 17. The actuator 19 comprises a plunger 21 having permanent magnets 23, 25 at tached thereto. The plunger 21 is connected via two rod units 27, 29 with diaphragm units 3, 5. The plunger 21 can move a certain distance along its longitudinal axis A. The two permanent magnets 23, 25 are arranged along the longitudinal direction A with a gap between them. The polarity axis of the permanent magnets 23, 25 is perpendicular to the longitudinal axis A and the polarity of the first permanent magnet 23 is in opposite di rection to the second permanent magnet 25. The center of each permanent magnet 23, 25 is above the E-shaped magnetic core between an outer leg 11 and the middle leg 12.

The two coils 13, 15 are connected such that the magnetic poles in the E-shaped magnetic cores 9, 10 are mirrored regarding the longitudinal axis A.

When an alternating current is applied to the coils 13, 15, the actuator 19 moves recipro cally along the longitudinal axis A. In the described design as well as in most electric drives it is a major goal to increase the effectiveness and the efficiency of the drive.

In the linear motor 1 of Figure 1 having an E-shaped magnetic core 9, 10 only the inner leg 12 is surrounded by a coil 13, 15 and therefore nearly all of the created magnetic flux is going through it, whereas some of the magnetic flux is lost due to leakage flux for both outer legs 11 and is therefore less usable.

During a phase when the actuator 19 is nearly fully deflected in one direction, the oppos ing outer leg 11 of the E-shaped magnetic core 9, 10 is conducting minimal useable mag netic flux, since it is too far away from the permanent magnets 23, 25.

SUMMARY OF THE INVENTION

It is an object of the present invention is to provide a linear pump or compressor having a higher effectiveness and efficiency compared to the known design.

This object is achieved by a linear pump or compressor according to claim 1. Further em bodiments of the invention are described in the dependent claims. A linear pump or compressor according to the invention comprises a reciprocating linear motor, a compressing or pumping head, a rod connecting the head and the linear motor, a support structure connecting the motor and the head.

The linear motor comprises a stator, an actuator, and at least two leaf springs, wherein the stator and the leaf springs are connected to the support structure, and the two leaf springs support the actuator such that it can oscillate relative to the stator in the linear movement direction. In certain embodiments, the leaf springs are arranged on the opposite sides of the actuator, where the movement of the actuator is reversed.

The stator comprises a magnetic core having a U-shape and at least two coils, wherein each one of the coils is arranged on one of the legs of the U-shape. The actuator com prises at least one permanent magnet and a bridge arranged along the moving direction of the actuator, wherein the magnetic core, the coils, the bridge, and the permanent mag net are forming a magnetic circuit.

The coils are electrically connected such that the magnetic poles created at the end of the legs differ from each other, when an electrical current is applied to the coils, and the poles of the permanent magnets are arranged such that the polarity axis, i.e., the north/south pole orientation, is along the orientation of the coils.

The inventive linear pump or compressor has the advantage that the orientation of the poles of the permanent magnet along the orientation of the coils results in a better over- lap of the magnetic fields. The main part of the magnetic field of the permanent magnet is arranged parallel or antiparallel to the magnetic field of the coils and thus has a much bet ter interaction. Further, the use of two coils provides a much higher interaction of the magnetic fields in particular at the reversing points of the actuator. During all positions of the actuator, the magnetic fields of the permanent magnet and of the respective coil over- lap to a great extent. Thus, the full magnetic force can be exerted between the actuator and the stator at nearly all times. This results in a much higher force (or efficiency) applied to the actuator. Also, in the position in which both leaf springs are not loaded (i.e., the rest position) both coils exert a magnetic force upon the permanent magnet. Thus, the force exerted on the actuator is evenly distributed.

Due to the symmetric design, with one coil over each leg, the leakage flux is minimal and the flux density of the two magnetic poles, which are created at the end of the legs, is the same.

The U-shaped magnetic core preferably comprises laminated electrical steel but may also comprise other magnetic material like ferrite or powder metals.

The coils may comprise preferably a copper winding wrapped around a bobbin but may also comprise any isolated conductor placed on a carrier or directly wrapped around the leg of the U-shaped magnetic core.

The permanent magnets may preferably comprise rare-earth magnets but may also com prise ceramic or ferrite magnets for low-cost versions.

According to a preferred embodiment, the actuator comprises a first set of permanent magnets comprising at least the two outer permanent magnets having the north/south poles oriented along the orientation of the coils in a first direction, and a second set of permanent magnets comprising at least one permanent magnet having the north/south poles oriented along the orientation of the coils in a second direction, wherein the second direction is in the opposite direction of the first direction.

In particular, the orientation of the permanent magnets of the actuator is perpendicular to the moving direction of the actuator.

The polarity of the inner two permanent magnets is in the same direction and opposite to the polarity of the two outer permanent magnets, therefore, in some cases the inner two permanent magnets can be replaced by one wider permanent magnet.

According to a further preferred embodiment, the permanent magnets are complemented by additional permanent magnets to form at least partially a Halbach array. In particular, the three or four magnets can further be extended by smaller magnets with a perpendicu lar polarity to form two parts of or two full Halbach arrays to focus the magnetic field in the direction of the U-shaped magnetic core.

In an embodiment, the stator comprises a magnetic material arranged, regarding the actu- ator, on the opposite side of the coils. Preferably, the stator may comprise a bridge closing the magnetic circuit of the side of the actuator that is opposite to the coils. The bridge or a part of the bridge may be a magnetic flux conductor. The bridge may be placed over the permanent magnet(s) to close the magnetic flux.

Alternatively, the stator comprises a second magnetic core having a U-shape and a corre- sponding second set of coils, wherein the second magnetic core with second coils is ar ranged such that the orientation of the second coils is antiparallel to the orientation of the first coils. The second U-shaped magnetic core with two coils mirrored along the longitu dinal axis can be arranged, e.g., over the permanent magnets.

According to an embodiment, the actuator comprises magnetic material adapted to assist in providing a magnetic return.

The linear pump or compressor may comprise two compressing or pumping heads, but it can also comprise a single pump or compressor unit.

The compressing or pumping head may comprise a piston/cylinder or a membrane ar rangement. The leaf springs can be shaped asymmetrical regarding a plane that includes the longitu dinal axis, i.e., to one side. Further, the leaf springs can be arranged so that the leaf spring on one side of the U-shaped magnetic core is mirrored at the plane including the longitu dinal axis, i.e., the axis of movement, to the spring on the other side of the U-shaped mag netic core. Multiple leaf springs on both sides can be used. BRIEF DESCRIPTION OF THE DRAWINGS

Various features and advantages of the present invention may be more readily understood with reference to the following detailed description taken in conjunction with the accom panying drawings in which:

Figure 1 is a longitudinal sectional view of a conventional linear motor with two dia phragm pumps;

Figure 2 is a perspective view illustrating an embodiment of a linear pump or com pressor in accordance with the present invention;

Figure 3 is a side view of the embodiment of Figure 2 with a longitudinal sectional view on the electrical part; Figure 4 is a detailed view of the embodiment shown in Figure 3;

Figure 5 is a further detailed view of one side of the linear motor of the embodiment shown in Figure 4;

Figures 6-12 are further detailed views of embodiments of the linear motor in a detailed view similar to Figure 4; Figures 13, 14 are a perspective view and a side view with a longitudinal sectional view of the electrical part of a further embodiment of a linear pump or compressor comprising a single pump/compressor unit;

Figures 15, 16 are perspective views of leaf springs of the embodiment of Figure 2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Figures 2 and 3 are views illustrating an embodiment of a linear pump or compressor 100. The linear pump or compressor 100 includes a reciprocating linear motor 102, a pair of compressing or pumping head 104, 105, a pair of rods 106, 107 connecting the heads 104, 105 and the linear motor 102. The linear motor 102 and the heads 104, 105 are further connected by a support structure 108.

The linear motor 102 further comprises a stator 110, an actuator 112, and two leaf springs 114, 115. The stator 110 and the leaf springs 114, 115 are connected to the support struc- ture 108.

The two leaf springs 114, 115 support the actuator 112 such that it can oscillate relative to the stator 110 in a linear moving direction along its longitudinal axis A.

The stator 110 comprises a magnetic core 116 having a U-shape and two coils 118, 119. Each one of the coils 118, 119 is arranged on one of the legs 120, 121 of the U-shaped magnetic core 116. In the embodiment of Figures 2 and 3, the coils 118, 119 are arranged such that the longitudinal axis of each coil is perpendicular to the longitudinal axis A of the actuator 112.

The actuator 112 comprises a bridge 132 and at least one permanent magnet. In the pre sent embodiment of Figures 2 and 3 the actuator 112 comprises four permanent magnets 122-128 arranged along the bridge 132 in the moving direction A of the actuator 112.

The magnetic core 116, the coils 118, 119, the bridge 132, and the permanent magnets 122-128 form a magnetic circuit.

The coils 118, 119 are electrically connected such that the magnetic poles created at the end of the legs 120, 121 differ from each other when an electrical current is applied to the coils 120, 121.

The poles of the permanent magnets 122-128 are arranged such that the north/south pole orientation is along the orientation of the coils 118, 119.

Each one of the coils 118, 119 is wrapped around a bobbin 130, 131 placed on the legs 120, 121 of the U-shaped magnetic core 116. The actuator 112 is mounted by the leaf springs 114, 115 and is movable for a certain dis tance along the longitudinal axis A in Figure 3. The actuator 112 includes, as already men tioned, four permanent magnets 122-128. Further, the actuator 112 comprises the bridge 132, whereas the bridge 132 is connected to each of the pump or compressor units 104, 105. The bridge 132 may comprise a material having a high magnetic permeability such as iron, or ferromagnetic compounds such as ferrites.

The four permanent magnets 122-128 are arranged along the longitudinal axis A having a small gap in between each permanent magnet 122-128. As already mentioned, the polar ity axis of all four permanent magnets is oriented along the longitudinal axis of the coils 118, 119. Further, the polarities of the two outer permanent magnets 122, 128 are oriented in the opposite direction of the two inner permanent magnets 124, 126. One of each of the outer permanent magnets 122, 128 and one of each of the adjacent inner permanent magnets 124, 126 form a pair above the center of each of the legs 120, 121 of the U- shaped magnetic core 116. The leaf springs 114, 115 are attached to the support structure 108 and to the actuator 112 allowing a longitudinal movement of the actuator 112 close to the poles of the U- shaped magnetic core 116.

The two coils 118, 119 are connected such that two opposing poles are created at the end of each of the legs 120, 121 of the U-shaped magnetic core 116. When an alternating current is applied to the coils 118, 119, an alternating magnetic flux interacts with the magnetic field of the permanent magnets 122-128, alternately attracting and repelling the outer 122, 128 and inner permanent magnets 124, 126. Since the poles at the end of the legs 120, 121 of the U-shaped magnetic core 116 are opposing, each pole is attracting and repelling each of the pairs of the permanent magnets 122-128 in the same direction, creating forces which add up.

A resulting force created by these forces reciprocally moves the actuator 112 and a part of the pump or compressor units 104, 105 along the axial direction A. Figure 4 is an enlarged part of Figure 3, showing the central part of the bridge 132, the permanent magnets 122-128 attached thereto, parts of the coils 118, 119, and parts of the magnetic core 116, in particular parts of the legs 120, 121 thereof.

As can be seen in Figure 4, a pair of one outer permanent magnet 122, 128 and one inner magnet 124, 126 is centered in the rest position of the actuator 112 - here in particular the bridge 132 - around the longitudinal axis B of the corresponding coil 118, 119. This is shown in Figure 4 for the coil 118. An air gap 133 is formed between the ends of the legs 120, 121 of the magnetic core 116 and the permanent magnets 122-128.

Figure 5 is an enlarged view of Figure 4 and shows the orientation of the magnetic poles. Referring to Figure 5, the end of the left leg 120 of the U-shaped magnetic core 116 is shown. When current runs through the coils 118, 119 in such a direction that the magnetic field at the end of the leg 120 is orientated as a north pole, the outer permanent magnet 122 is attracted and the inner magnet 124 is repelled, therefore the actuator 112 is pushed to the right. When the current is reversed, a south pole is created and similarly the plunger actuator 112 is pushed to the left.

Figure 6 shows an alternative embodiment to Figure 4. Here and in the following, the same reference numbers are used for the same or for similar features already mentioned in one of the embodiments already described. In the alternative embodiment of Figure 6, the actuator 112 additionally comprises smaller permanent magnets 134 are added in between and enclosing the inner and outer perma nent magnets 122-128. By selecting the appropriate magnetic orientations and magnetic flux densities, the resulting configuration may operate as a Halbach array. The magnetic field of such a configuration may direct the magnetic field in direction of the coils 120, 121 and reduce the unusable magnetic field.

Figure 7 shows an alternative embodiment to Figures 4 and 6. In the alternative embodi ment of Figure 7, the inner permanent magnets 124, 126 are replaced by a single longer permanent magnet 136. The two inner permanent magnets 124, 126 may be replaced by a single permanent magnet 136, because the orientation of the polarity of the inner perma nent magnets 124, 126 is the same.

Figure 8 shows an alternative embodiment to Figures 4, 6, and 7. In the alternative em- bodiment of Figure 8 smaller permanent magnets 134 are added to the left and right of the outer permanent magnets 122, 128 and between the inner and outer permanent mag nets. This results in a Halbach array.

Figure 9 shows in an enlarged view a further alternative embodiment to Figures 4, 6-8. In this embodiment, the whole stator 110 of the linear motor 102 is vertically mirrored and placed over permanent magnets 142-148. The resulting four coils 118, 119, 150, 151 of the second stator 140 are connected in a way that the current, which flows when a voltage from a source is applied to all four coils 118, 119, 150, 151, excites a magnetic flux in the same direction in the U-shaped magnetic cores, creating opposing poles at the end of the legs facing towards each other and being next to each other. In this embodiment, the magnetic flux is running through both U-shaped magnetic cores instead being returned over the permanent magnets 142-148, therefore the actuator 152 is placed in the same level as the permanent magnets 142-148 instead of being placed on top, forming a sec ond air gap 154.

Figures 10 and 11 are enlarged views illustrating alternative embodiments of the actuator 112. In the embodiment of Figure 10, a flux conductor 160 is added to the bridge 132 to support the function of a magnetic return of the bridge 132. The flux conductor 160 is at tached to the top of the bridge 132 and thus also moves along with the bridge during os cillation movements. The permanent magnets are arranged in a threefold combination similar to the embodiment of Figure 7. In the embodiment of Figure 11, the flux conductor 160 is fully integrated with the bridge 132 and is thus in closer contact with the permanent magnets. The permanent magnets in this embodiment arranged in a fourfold combination similar to Figure 4. Figure 12 shows in an enlarged view a further alternative embodiment of the actuator 112 of Figs. 4, 6-11. In the embodiment of Figure 12, the flux conductor 162 is attached to the support structure (not explicitly shown in Figure 12), resulting in an air gap between the stationary flux conductor 162 and the moving actuator 112. The additional magnetic re- turn provided by the flux conductor 162 is included in the support structure and should be placed as close as possible to the permanent magnets 122-128 forming a second air gap 164. This embodiment has the advantage that the mass of the actuator 112 can be re duced substantially.

Figures 13 and 14 show a further alternative embodiment of a linear pump or compressor 200 having only a single pump or compressor unit. To avoid unnecessary repetitions, it is referred to the description regarding the embodiment of Figures 2 and 3. In Figures 13, 14, the reference signs already used in the embodiment of Figures 2 and 3 are used for the same features by adding 100.

Fig. 15 and 16 show different embodiments for the leaf springs of 114, 115 of Figures 2, 3 and 13, 14. In all embodiment of Figs. 15 and 16 the leaf springs are unsymmetrical to a plane comprising the longitudinal axis A of the actuator and the longitudinal axis B of each coil 118, 119 as indicated in Figs. 3 and 4.

Fig. 15 shows a first embodiment having two single leaf springs 114, 115, as used in the embodiments of Figs. 2 and 3 or 13 and 14. In the embodiment of Fig. 16, each leaf spring 314, 315 comprises at least two single leaf spring elements (here three elements per leaf spring 314, 315). In this embodiment, the individual elements are identical in shape and are arranged such that each element contacts directly the next one. Alternatively, the indi vidual spring elements could be separated by distance elements like washers or the like.

Each spring or spring elements on one side of the actuator is/are preferably mirrored to the spring or spring elements on the other side of the actuator regarding the above plane comprising both axis A and B . The leaf spring embodiments of Figs. 15 and 16 can be combined with the embodiments of Figs. 2-14 as described above.