Linear motor

A linear motor comprises a stator including a stator yoke and a plurality of permanent magnets arranged side by side on the stator yoke along a motor running direction in alternately reversed directions to produce alternating polarities, and a moving part including a plurality of magnetic teeth arranged along the motor running direction and coils wound around the individual magnetic teeth. Cutouts formed in end surfaces of yoke portions of the individual magnetic teeth opposite to their side facing the stator line up to form a groove-shaped channel running through the yoke portions of the successive magnetic teeth, and the multiple magnetic teeth are joined together into a single structure by fitting a connecting bar in the groove-shaped channel.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a linear motor. More particularly, the invention pertains to a linear motor used in a table feed mechanism of a machine tool.

2. Description of the Background Art

FIG. 20is a cross-sectional diagram showing the construction of a conventional linear motor disclosed in Japanese Laid-open Patent Publication No. 2000-217334.

Referring toFIG. 20, a stator1includes a plurality of permanent magnets3a,3barranged in a line at regular intervals on a stator yoke2in alternately reversed directions to produce alternating polarities. A moving part4moves along the stator1as if sliding over the stator1with a specific distance (gap) therefrom.

The moving part4includes a moving yoke5, connecting parts7each having a trapezoidal cross section which are held at specific intervals on one side of the moving yoke5facing the stator1by bolts6fitted in the moving yoke5, a plurality of magnetic teeth (poles)8generally T-shaped in cross section and joined to the individual connecting parts7which are fitted into dovetail grooves8aformed in a central part of each tooth end, each magnetic tooth8having a recess8band a protrusion8cformed on opposite sides, and a plurality of magnetic teeth (poles)9generally I-shaped in cross section and fitted between the successive magnetic teeth8as a recess9aand a protrusion9bformed on opposite sides of each magnetic tooth9fit over and into the protrusion8cand the recess8bof the adjoining magnetic teeth8, respectively. Also included in the moving part4are coils10individually wound around the magnetic teeth8,9and a resin molding11surrounding the magnetic teeth8,9and the coils10to join them together into a single structure.

In the conventional linear motor thus constructed, the moving part4is assembled by first winding the coils10around the individual magnetic teeth8,9. Next, the dovetail grooves8aformed in the individual magnetic teeth8are fitted over the respective connecting parts7held by the bolts6fitted in the moving yoke5by sliding the magnetic teeth8in a direction perpendicular to the plane of the paper (FIG. 20) and, when the magnetic teeth8have been set into position, they are fixed to the moving yoke5by tightening the bolts6. Then, the individual magnetic teeth9are slid between the successive magnetic teeth8with the recess9aand the protrusion9bformed on each magnetic tooth9meshed with the protrusion8cand the recess8bof the adjoining magnetic teeth8, respectively. Finally, the alternately arranged magnetic teeth8,9and the coils10are joined together into a single structure by the resin molding11.

Since the conventional linear motor is assembled by inserting the magnetic teeth9between the successive magnetic teeth8as stated above, the coils10wound around the magnetic teeth9slide over the coils10wound around the magnetic teeth8with friction. This assembly process could cause damages to the coils10, such as an insulation failure or a wire breakage, resulting in a reduction in reliability.

Furthermore, the conventional linear motor is associated with a poor labor efficiency problem. This is because its assembly involves rather complicated procedures including fitting and sliding the dovetail grooves8aformed in the individual magnetic teeth8over the respective connecting parts7, tightening the bolts6to fix the magnetic teeth8to the moving yoke5, mating the recess9aand the protrusion9bformed on each magnetic tooth9with the protrusion8cand the recess8bof the adjoining magnetic teeth8and sliding them to fit the magnetic teeth9between the successive magnetic teeth8.

Generally, magnetic teeth are manufactured by stacking press-cut electromagnetic steel sheets. Accordingly, the stacking thickness of the electromagnetic steel sheets should be increased if it is necessary to increase the width of the individual magnetic teeth due to an increase in motor capacity. An increase in the stacking thickness tends to cause an inclination of the stacked electromagnetic steel sheets due to stacking errors as well as a deterioration in assembling efficiency. In addition, it is necessary to increase the thickness of a lower press die if the stacking thickness increases. This would lead to an increase in cost for making the die and an eventual rise in manufacturing cost of the magnetic teeth.

Even when the structure of magnetic teeth does not adopt the aforementioned steel sheet stacking design, it is still necessary to vary the width of the individual magnetic teeth with changes in motor capacity, and this makes it difficult to attain desirable levels of efficiency with respect to the control of production and inventory of various components.

SUMMARY OF THE INVENTION

In light of the aforementioned problems of the prior art, it is an object of the invention to provide a novel structure for joining a plurality of magnetic teeth into a single structure. More specifically, it is an object of the invention to provide a linear motor adopting a magnetic tooth joining structure which permits improvements in reliability of a magnetic tooth assembly and in assembling efficiency. It is also an object of the invention to enable a cost reduction by improving the efficiency of controlling the production and inventory of components regardless of changes in motor capacity.

According to a principal feature of the invention, a linear motor comprises a stator including a stator yoke extending in a motor running direction and a plurality of permanent magnets arranged on the stator yoke at regular intervals along the motor running direction in alternately reversed directions to produce alternating polarities, and a moving part positioned generally parallel to the permanent magnets of the stator and separated therefrom by a specific gap, the moving part including a plurality of magnetic teeth arranged side by side along the motor running direction and coils wound around the individual magnetic teeth. In this linear motor, each of the magnetic teeth has a yoke portion located opposite to a side facing the stator, the yoke portion of each magnetic tooth being held in contact with the yoke portion of each adjoining magnetic tooth, and a tooth portion around which the coil is wound, the tooth portion extending from the yoke portion toward the stator. Cutouts formed in end surfaces of the yoke portions of the individual magnetic teeth opposite to their side facing the stator line up to form a groove-shaped channel running through the yoke portions of the successive magnetic teeth, and the multiple magnetic teeth are joined together into a single structure by fitting a connecting member in the groove-shaped channel.

The linear motor thus constructed offers enhanced reliability and greater assembling efficiency.

These and other objects, features and advantages of the invention will become more apparent upon reading the following detailed description along with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the invention are now described with reference to the appended drawings.

First Embodiment

FIGS. 1A-1Bare diagrams showing the construction of a linear motor according to a first embodiment of the invention, in whichFIG. 1Ais a plan view andFIG. 1Bis a cross-sectional side view.FIG. 2is a front view of the linear motor ofFIGS. 1A-1B,FIG. 3is a plan view showing how magnetic teeth25of the linear motor are successively arranged,FIG. 4is a front view showing how the magnetic teeth25are joined into a single structure by means of connecting bars27,FIG. 5is a front view showing how the connecting bars27are welded to the magnetic teeth25,FIG. 6is a plan view showing an assembly of the magnetic teeth25upon completion of a welding process shown inFIG. 5, andFIG. 7is a diagram showing details of how each connecting bar27is welded to the magnetic teeth25.

Referring to these Figures, a stator21includes a platelike stator yoke22extending in a motor running direction shown by double arrows (FIGS. 1A-1B) and a plurality of permanent magnets23,24arranged on the stator yoke22at regular intervals along the motor running direction in alternately reversed directions to produce alternating polarities. Separated by a specific distance from the permanent magnets23,24arranged on the stator yoke22, a moving part29includes the aforementioned multiple magnetic teeth25arranged along the motor running direction, coils28individually wound around the magnetic teeth25and the aforementioned connecting bars27joining together the magnetic teeth25into a single structure.

As illustrated inFIG. 1B, upper parts of the individual magnetic teeth25(that are opposite to ends of the magnetic teeth25facing the stator21) constitute yoke portions25c, from which tooth portions25dextend downward toward the stator21. The coils28are wound around the individual tooth portions25dand the multiple magnetic teeth25are arranged side by side with side faces of their yoke portions25cheld in contact with one another.

Referring now toFIG. 2, a pair of cutouts25a(width W1, depth H2) having a rectangular cross section are formed at specific locations in an upper end surface of the yoke portion25cof each magnetic tooth25in such a manner that the cutouts25ain the successive yoke portions25cline up along the motor running direction (which is perpendicular to the plane of the paper in FIG.2). At both upper corners (left and right as illustrated inFIG. 2) of the yoke portion25cof each magnetic tooth25, there are formed cutouts25beach having a width equal to one half the width W1of each cutout25a(i.e., W1/2). When the magnetic teeth25are assembled, the cutouts25aformed in the individual yoke portions25cline up in double straight lines and together form a pair of groove-shaped channels26running through the successive magnetic teeth25(refer to FIGS.1A-1B).

The aforementioned connecting bars27are fitted in the individual groove-shaped channels26all the way along their length to join together the magnetic teeth25. There are formed screw holes27ain the connecting bars27at specific positions for fixing them to an unillustrated driven part.

Assembly processes of the moving part29of the linear motor of the first embodiment thus constructed are specifically described below referring to the drawings.

First, the coils28are wound around the individual magnetic teeth25. The individual magnetic teeth25are then aligned with the side faces of the yoke portions25cplaced in contact with one another as shown in FIG.3. As a result, the cutouts25ain the individual yoke portions25cline up in double straight lines, together forming the two groove-shaped channels26. Then, the connecting bars27are fitted in the groove-shaped channels26as shown in FIG.4and welded as shown inFIG. 5, so that the connecting bars27are firmly fixed to the yoke portions25cof the individual magnetic teeth25as shown in FIG.6. The magnetic teeth25are joined together by the connecting bars27into a single structure, whereby assembly of the moving part29is completed.

The aforementioned welding process is explained in further detail referring to FIG.7. What is important in this welding process is the relationship between the height H1of the connecting bars27and the depth H2of the groove-shaped channels26(cutouts25a) as can be recognized from FIG.7. If either of the connecting bars27warps due to thermal shrinkage occurring at welding points P, there arises a problem that an array of the magnetic teeth25joined by the connecting bars27, particularly a bottom surface of the moving part29facing the stator21, would become deformed.

It is therefore desirable that the depth H2of the groove-shaped channels26be made slightly smaller than half the height H1of the connecting bars27(i.e., H1/2) so that the welding points P are located generally at the middle of the height H1of the connecting bars27.

It will be recognized that if there is established a relationship H2<H1/2, the welding points P might be located slightly below the middle of the height H1of the connecting bars27depending on performance of welding operation. In this case, the connecting bars27tend to warp, swelling upward at central parts, as a result of the welding operation. Even if this situation occurs, however, deformation of the bottom surface of the moving part29facing the stator21is made sufficiently small as compared to a case where the welding points P are located above the middle of the height H1of the connecting bars27. This is because side surfaces of the successive magnetic teeth25joined by the connecting bars27are in direct contact with one another in the above-described structure of the first embodiment.

As can be seen from the foregoing discussion, the cutouts25aformed in the upper end surfaces of the yoke portions25cof the individual magnetic teeth25line up in double straight lines, together forming the two groove-shaped channels26, and the connecting bars27are fitted into these groove-shaped channels26to join together the magnetic teeth25into a single structure in the aforementioned first embodiment. This structure of the embodiment facilitates assembly of the moving part29and helps improve assembling efficiency. In addition, the individual magnetic teeth25can be assembled without causing the adjacent coils28to slide over each other with friction, and this serves to prevent insulation failures and wire breakage and improve reliability.

Furthermore, it is possible to prevent warpage of the connecting bars27or reduce the influence of their warpage by making the depth H2of the groove-shaped channels26smaller than half the height H1of the connecting bars27(H2<H1/2) when fixing the connecting bars27into the groove-shaped channels26by welding. This makes it unnecessary to carry out operation for removing the effect of warpage of the connecting bars27and thereby improve assembling efficiency.

Second Embodiment

FIG. 8is a plan view showing the construction of a linear motor according to a second embodiment of the invention,FIG. 9is a front view of the linear motor ofFIG. 8, andFIG. 10is a perspective view showing a process of winding a coil33around one of magnetic teeth25shown in FIG.8. In these Figures, elements identical to those of the foregoing first embodiment are designated by the same reference numerals and a description of such elements is omitted.

Referring to the Figures, a stator31includes a stator yoke22and permanent magnets23and24alternately arranged in a double row on the stator yoke22. Each of the magnetic teeth25constituting a moving part37is formed of a pair of magnetic tooth elements32aligned in a direction perpendicular to a motor running direction. As depicted inFIG. 10, each pair of magnetic tooth elements32is held by a wire-winding jig34and turned in a direction shown by an arrow, whereby the two magnetic tooth elements32are securely joined together by the coil33form by a magnet wire35wound around them.

In this embodiment, a plurality of magnetic teeth25individually would by the coils33as described above are arranged side by side with side faces of their yoke portions25cheld in contact with one another in the same manner as in the first embodiment. When the magnetic teeth25are arranged in this fashion, cutouts25aformed in the individual magnetic teeth25line up and together form four parallel groove-shaped channels26in a top surface of the moving part37, and cutouts25bformed at both upper corners of the individual magnetic tooth elements32also line up and together form a groove-shaped channel36bridging the inside upper corners of the double rows of the magnetic tooth elements32. Three connecting bars27are then fitted in the individual groove-shaped channels26,36as shown in FIG.9and fixed therein by welding them at specific points as shown in FIG.8. Consequently, the individual magnetic teeth25are securely joined together by the connecting bars27into a single structure, whereby assembly of the moving part37is completed.

As seen above, each magnetic tooth25is formed by winding the coil33around a pair of magnetic tooth elements32arranged in tandem in a direction perpendicular to the motor running direction in the aforementioned second embodiment. This structure of the embodiment makes it possible to flexibly increase (or decrease) in accordance with changes in required power of the linear motor (motor capacity) by a combination of the magnetic tooth elements32. The embodiment not only serves to improve assembling efficiency but enables the use of the same components for different purposes, facilitates the control of inventory of various components and helps achieve an eventual cost reduction.

Particularly when the magnetic teeth are formed by stacking electromagnetic steel sheets, they can be produced by combining the magnetic tooth elements32having a standardized shape and dimensions. Consequently, even when the required motor capacity increases, the stacking thickness of the electromagnetic steel sheets can be held within specific limits. This serves to reduce the cost of a press die, decrease an inclination of the stacked electromagnetic steel sheets due to stacking errors and improve productivity. If multiple magnetic tooth elements32are stacked while reversing their directions as necessary, it would be possible to further decrease the inclination of the entire assembly of the magnetic teeth25.

Furthermore, since the groove-shaped channel36formed in the top surface of the moving part37bridges the double rows of the magnetic tooth elements32and the connecting bar27is fitted in the groove-shaped channel36, the magnetic tooth elements32are joined even more securely, this serves to further improve the reliability.

While the magnetic tooth25of the second embodiment is formed by arranging two magnetic tooth elements32in tandem in a direction perpendicular to the motor running direction and uniting them by winding the coil33, the number of magnetic tooth elements32to be united into a single structure is not necessarily limited to two, but three or more magnetic tooth elements32may be jointed together to form a larger magnetic tooth.

The aforementioned method of forming a magnetic tooth by arranging multiple magnetic tooth elements in tandem in a direction perpendicular to the motor running direction and uniting them into a single structure by a coil wound around them is not necessarily limited to the linear motor described above employing a structure in which the a plurality of magnetic teeth25are joined together by the connecting bars27. The novel method of the present embodiment can also be applied to other structures of linear motors, such as the earlier-mentioned conventional linear motor in which the moving yoke5and the magnetic teeth8,9are separately produced and joined together by a dovetail joint structure, facilitating the control of inventory of components and enabling a cost reduction. In a case where the magnetic teeth are formed by stacking electromagnetic steel sheets, the aforementioned method of the present embodiment serves to reduce the inclination of the stacked electromagnetic steel sheets due to stacking errors, improve productivity and reduce the cost of the press die.

Third Embodiment

FIG. 11is a plan view showing the construction of a linear motor according to a third embodiment of the invention,FIG. 12is a side view of the linear motor ofFIG. 11,FIG. 13is a front view of the linear motor ofFIG. 11,FIGS. 14A-14Bare front views showing how connecting bars27are welded to individual magnetic teeth41shown inFIG. 11, andFIG. 15is a plan view showing an assembly of the magnetic teeth41upon completion of a welding process shown in FIG.14. In these Figures, elements identical to those of the foregoing second embodiment are designated by the same reference numerals and a description of such elements is omitted.

Referring to the Figures, each of the magnetic teeth41constituting a moving part42is formed of a pair of magnetic tooth elements43aligned in a direction perpendicular to a motor running direction. As described with reference to the aforementioned second embodiment, two magnetic tooth elements43are fastened and joined together into a single structure by a coil33wound around them. As shown inFIG. 13, two projecting parts41b,41care formed on an upper end surface of a yoke portion41aof each magnetic tooth element43, the two projecting parts41b,41cbeing separated by a distance W which is equal to the width of each connecting bar27. There is formed another projecting part41don the upper end surface of the yoke portion41aof each magnetic tooth element43. This projecting part41dis located such that when two magnetic tooth elements43are aligned to form one magnetic tooth41, the projecting parts41dof the magnetic tooth elements43face each other with their facing side surfaces positioned half the width W of the connecting bar27(W/2) apart from a side face of each yoke portion41a, creating an interval W between the facing side surfaces of the two projecting parts41d. Opposite side surfaces of the projecting parts41dare separated from the projecting parts41cof the respective magnetic tooth elements43by a distance equal to W.

Assembly processes of the moving part42of the linear motor of the third embodiment thus constructed are specifically described below referring to the drawings.

A pair of magnetic tooth elements43are arranged in tandem with their sides held in contact with each other in such a manner that the projecting parts41dformed on their yoke portions41aface each other and, then, the coil33is wound around the two magnetic tooth elements43to securely join them into a single structure, thereby forming each magnetic tooth41. The individual magnetic teeth41thus formed are arranged side by side along the motor running direction with the side faces of their yoke portions41aheld in contact with one another. When the magnetic teeth41are arranged in this fashion, there are formed parallel groovelike channels44due to the intervals W between the projecting parts41band41c. There is also formed another groovelike channel44between the projecting parts41dformed close to inner ends of the magnetic teeth41. Then, three connecting bars27are fitted in the groovelike channels44formed between the projecting parts41band41cand between the projecting parts41das shown in FIG.13. The connecting bars27are welded to the respective groovelike channels44as shown inFIGS. 14A-14B, whereby upper parts of side surfaces of the connecting bars27are fixed to upper edges of the individual projecting parts41b,41c,41dand lower parts of the side surfaces of the connecting bars27are fixed to upper ends of the yoke portions41a. As a result of this welding operation, the individual magnetic teeth41aligned as described above are securely joined together by the connecting bars27into a single structure, whereby assembly of the moving part42is completed.

As depicted in the foregoing discussion, the magnetic teeth41are joined into a single structure by fitting and fixing the connecting bars27between the projecting parts41band41cformed on the upper end surfaces of the yoke portions41aof the individual magnetic teeth41and between the facing projecting parts41din the third embodiment. This structure makes it possible to assemble the moving part42with least effort and thereby improve assembling efficiency. In addition, the magnetic teeth41can be assembled without causing the adjacent coils33to slide over each other with friction, and this serves to prevent insulation failures and wire breakage and improve reliability.

The connecting bar27in the middle bridges the two magnetic tooth elements43of each magnetic tooth41when fitted in the groovelike channel44formed between the facing projecting parts41dof the individual magnetic tooth elements43. This serves to reinforce the one-piece assembly of the magnetic teeth41, resulting in a further improvement of reliability. Furthermore, because the individual connecting bars27are fitted in the groovelike channels44formed between the projecting parts41band41cand between the projecting parts41d, their welding operation is quite easy, and this also serves to improve the assembling efficiency. Moreover, their welding points have an increased capability to withstand a moment of force applied thereupon as both upper and lower parts of the side surfaces of the connecting bars27are welded to the magnetic tooth elements43, resulting in an even further improvement in reliability.

As is apparent fromFIG. 13, there is formed a gap as wide as W between the projecting parts41cand41dof each magnetic tooth element43. Although three connecting bars27are fitted in the groovelike channels44formed between the projecting parts41band41cand between the projecting parts41din the third embodiment described heretofore, additional connecting bars27may be fitted in groovelike channels formed between the projecting parts41cand41dwhen needed to further reinforce the one-piece assembly of the magnetic teeth41.

While the magnetic tooth41is formed by arranging two magnetic tooth elements43in tandem in the aforementioned third embodiment, it is needless to say that the same advantageous effect as described above can be achieved by fitting the connecting bars27in the groovelike channels44formed between the projecting parts41band41cand/or between the projecting parts41cand41deven when the assembly of the magnetic teeth is formed by a single row or more than two rows of the magnetic tooth elements43.

Fourth Embodiment

FIG. 16is a plan view showing the construction of a linear motor according to a fourth embodiment of the invention, in which elements identical to those of the foregoing third embodiment are designated by the same reference numerals and a description of such elements is omitted.

In this embodiment, each connecting bar51has a width W1larger than the distance W between projecting parts41band41c, and there are formed recesses51aand51bin both side surfaces of each connecting bar51in which the projecting parts41band41cfit, respectively.

Since the width W1of each connecting bar51is made larger than the distance W between the projecting parts41band41cand the recesses51aand51bin which the projecting parts41band41cfit are formed in both side surfaces of each connecting bar51in this fourth embodiment, movements of the connecting bars51in their longitudinal direction are restricted when the projecting parts41band41care fitted in the recesses51aand51b, respectively. This structure makes it possible to attach the connecting bars51in position more securely and further improve reliability.

Fifth Embodiment

A fifth embodiment of the invention provides an optimum construction of connecting bars applicable when individual magnetic teeth are formed by stacking electromagnetic steel sheets in a direction perpendicular to a motor running direction.

Although the connecting bars27(51) of the foregoing embodiments have a rectangular cross section, connecting bars61of the fifth embodiment each have a downward-directed ridgelike projection as shown in FIG.17.

In this embodiment, the direction of the width of each groove-shaped channel26formed by cutouts25ain yoke portions25cof individual magnetic teeth25matches the stacking direction of the electromagnetic steel sheets and, therefore, the width of each groove-shaped channel26could vary due to variations in the thickness of the individual electromagnetic steel sheets and fastening force of coils28wound around the magnetic teeth25. For this reason, there is a possibility that gaps will occur between the connecting bar61and the groove-shaped channel26, making it impossible to obtain a stable welding effect.

To cope with this problem, each connecting bar61has a downward-projecting mating part61a(i.e., the aforementioned ridgelike projection) which fits in the groove-shaped channel26with specific gaps between them and a flange portion61bwhich comes in contact with a top surface of the yoke portions25cof the magnetic teeth25along the groove-shaped channel26.

As shown inFIG. 18, width W3of the mating part61ais made smaller than width W2of the groove-shaped channel26. Given this relationship, W2>W3, gaps G are created between the mating part61aand the groove-shaped channel26as illustrated even when certain amounts of variations occur in the width W2of the groove-shaped channel26. In addition, the height H3of the mating part61ais made smaller than the depth H2of the groove-shaped channel26so that a gap G is created between the bottom of the mating part61aand the bottom of the groove-shaped channel26.

In the aforementioned structure, a bottom surface of the flange portion61bof each connecting bar61comes in close contact with the top surface of the yoke portions25cof the magnetic teeth25along each connecting bar61in a reliable fashion even when certain amounts of variations occur in the width W2of the groove-shaped channels26. This construction makes it possible to weld each connecting bar61to the corresponding groove-shaped channel26along their contact areas, enabling easy and stable welding operation as shown in FIG.19. As a result, the multiple magnetic teeth25can be reliably joined together into a single structure by the connecting bars61.

While the connecting bars61are fitted into the groove-shaped channels26formed by cutouts25amade in the yoke portions25cof the individual magnetic teeth25in the fifth embodiment, the aforementioned structure of the embodiment is also applicable to the structure of the earlier-mentioned third embodiment in which the connecting bars27are fitted in the groovelike channels44formed between the adjacent projecting parts41b,41c,41d, producing the same advantageous effect as described above.

Although not stated in the foregoing description of the individual embodiments, it is possible to enlarge magnetic paths and improve overall performance of the linear motor by forming the connecting bars27,51,61with magnetic material.