LINEAR SYNCHRONOUS MOTOR

Abstract

LINEAR SYNCHRONOUS MOTOR Abstract Aspects of the present disclosure relate to a linear synchronous motor, LSM. Further aspects of the present disclosure relate to an LSM system comprising such a motor. The present disclosure particularly relates to linear permanent magnet synchronous motors. According to an aspect of the present disclosure, the LSM comprises a primary part with a plurality of coils, and a secondary part comprising a plurality of separate secondary units that are adj acently arranged in a first direction. Each secondary unit comprises a magnetic member that comprises at least one closing plate and a plurality of permanent magnets adj acently arranged on the at least one closing plate. According to an aspect of the present disclosure, both the at least one closing plate and the permanent magnets are skewed, wherein a skewing angle of the at least one closing plate is different from o and different from a skewing angle of the permanent magnets.

Description

Aspects ofthe present disclosure relate to a , LSM. Further aspects of the present disclosure relate to anLSM system comprising such a motor. The present disclosure particularly relates to linear permanent magnet synchronous motors. LSMs are known in the art. An exemplaryLSM comprises a primary part and a secondary part. The primary part comprises a plurality of coils that are adjacently arranged in a first direction. The secondary part comprises a plurality of separate secondary units that are adjacently arranged in the first direction. Each secondary unit comprises a magnetic member that comprises at least one closing plate and a plurality ofpermanent magnets adjacently arranged on the at least one closing plate in the first direction. Each of the at least one closing plate comprises a first edge and opposing second edge that both extend in the first direction, and a third edge and opposing fourth edge that connect the first edge and second edge. Upon energizing the coils, for example by feeding each coil with a different phase, a mutual movement can be induced between the primary part and the secondary part. Typically, the secondary part is positionally fixed, whereas the primary part is able to perform a linear motion back and forth along the first direction. Now referring to figures 1A and 1B, several different types ofLSM are known in the art. Figure 1A illustrates anLSM 100 of the so-called iron-less type, whereas figure 1B illustrates an LSM 200 of the so-called iron core type. As shown in figure 1C, inLSM 200 of the iron core type, primary part 210 comprises a magnetic core 212 from which a plurality ofmagnetic teeth 213 extends toward secondary part 220. Coils 214 ofprimary part 210 are wound around teeth 213. Secondary part 220 ofLSM 200 comprises a plurality of secondary units 221. For example, secondary part 220 comprises n secondary units 221. Each secondary unit 221 comprises a magnetic closing plate 222 on which a plurality ofmagnets 223 are adjacently arranged in first direction D1. In order to couple a plurality of secondary units 221 for realizing a long path of permanent magnets 223, a supportmember (not shown) can be used on which closing plates 222 of secondary units 221 are mounted. Now referring back to figure 1A, primary part 110 ofLSM 100 comprises a plurality of coils that are not mutually fixed using a magnetic core. Instead, other, non-magnetic means are used to mutually fix the coils. These means could for example comprise a solidified molding compound. InLSM 100, secondary part 120 comprises a plurality of secondary units 121. Each secondary unit 121 comprises a pair ofoppositely arranged closing plates 122A, 122B, each holding a respective plurality ofpermanent magnets 123A, 123B. As shown, closing plates 122A, 122B are coupled to a supportmember 124. Similar to secondary parts 221, closing plates 122A, 122B can be coupled to a support member 124 that is shared by a plurality of secondary units 121. Alternatively, each secondary unit 120 may have a respective support member, and a separate common supportmember is used to which support members 124 and / or closing plates 122A, 122B of secondary units 121 are coupled. Figures 1A and 1B further illustrate electrical wiring 111, 211 through which an electronic drivermay provide electronic signals for driving the coils ofprimary part 110, 210 ofLMS 100, 200. Such electronic driver, when combined with an LSM, is referred to as anLSM system and is illustrated in figure 2. An important parameter ofanLSM is the force that can be generated. It is known that the force generated by theLSM depends on the mutual positioning of the primary part and secondary part. More in particular, the force as a function of the mutual position of the primary part and secondary part displays a periodic behavior ofwhich a representative period is defined by the distance Lp in the first direction in which the pattern ofpermanent magnets repeats itself. For example, if the permanent magnets are arranged in anN S N pattern, withN referring to the north pole of the magnet that is directed towards the primary part, and S the south pole, the abovementioned distance is twice the pitch between adjacent magnets. When observing the force as a function of the mutual position of the primary part and secondary part, it displays an average force value in combination with a force ripple. Such force ripples are unwanted as they complicate the position tracking of the primary part relative to the secondary part. To compensate for these force ripples, the positioning system, given its finite bandwidth, will need to reduce the speed of the motion. This is undesirable and, ultimately, economically unattractive for a commercial system. Alternatively, if the requirements on position tracking are relaxed, vibrations will enter the system with generally deleterious effects. Aknown approach for reducing the force ripple is shown in figure 3. In this figure, a skewed orientation is shown ofpermanent magnets 223 relative to underlying closing plate 222. It is noted that this arrangement can be applied in bothLSMs of the iron-core type andLSMs of the iron-less type. Figure 3 illustrates the underlying principle as to why the skewed orientation reduces the force ripple. The secondary part can be regarded as a combination of separate secondary parts that are shifted in second direction D2. For each individual part, amaximum force exerted on the primary part can be observed for different mutual positions of the primary part and secondary part. Each individual part generates a force ripple. As shown in figure 3, the combination of these force ripples results in a reduced overall force ripple. Figure 4 shows twoknown but different secondary parts that can be used for mitigating the force ripple effect. In the configuration shown on top, a rectangular closing plate 222 is used in combination with skewed permanent magnets 223. More in particular, a longitudinal axis of permanent magnets 223 makes an angle with direction D2. This angle is referred to as first angle al. The angle between edges E3, E4 and direction D2, referred to as second angle az, equals 0 degrees in this configuration. In the configuration shown on the bottom, a non-rectangular closing plate 222 is used. Here, closing plate 222 comprises a first edge E1, a second edge E2, a third edge E3, and a fourth edge E4. First edge E1 and second edge E2 are straight edges and extend in first direction D1, whereas opposing edges E3 and E4 connect edges E1 and E2 and are also straight. In this configuration, angle azbetween edges E3 andE4 and directionD2 is identical to first angle al that describes the orientation ofpermanent magnets 223 relative to second direction D2. The closing plate shown on the bottom in figure 4 offers many advantages during manufacturing of theLSM and during commissioning, i.e. when the end user mounts primary and secondary parts in their final positions, compared to the closing plate shown on the top in figure 3. When handling the secondary part, a small collision between a magnet and something from the surrounding equipmentmay degrade the adhesive with which the magnet is attached to the closing plate. These collisions are more likely because the magnets strongly attract ferrous material in the vicinity. This is a reason why the available space between any magnet corner and the edge of the closing plate must be maximized. In addition, permanent magnets are often encased in casting resin after being glued in place. The casting mold for this resin sets requirements on the distance of any permanent magnet corner to the edge ofthe closing plate. In the art, the abovementioned requirements are met by using al = az. This maximizes the available space between any magnet corner and the edge of the closing plate. The distance that can be covered by the primary part is defined by the length of the secondary part in the first direction. To this end, the secondary part can be realized using a plurality of secondary units that are adjacently arranged in the first direction. At the boundary between adjacent secondary units, a discontinuitymay therefore exist in magnetic reluctance. For example, small air gaps may exist between adjacent secondary units. The Applicant has found that the force ripple of existingLSMs that use multiple secondary units, even if the skewed arrangements of figure 4 are used, may still be unsatisfactory for some applications. Any additional methods to further reduce the ripple, such as using a priori knowledge of the ripple to improve position tracking by using feedforward control, a method that is known in the art, must perforce still operate on the principle that the best results are obtained by first reducing the force ripple as much as is feasible, and then compensating for what is left. It is therefore an object of the present disclosure to provide anLSM having multiple secondary units that displays a reduced force ripple. According to an aspect ofthe present disclosure, this object is achieved using theLSM defined in claim 1 ofwhich the third edge and fourth edge extend under a second angle az relative to the second directionD2 that is different from the first angle a1 and that is different from 0 degrees. This configuration is shown in figure 5, which also shows coils 214 of the primary part. In figure 5, permanent magnets 223 are arranged according to a repetition of a pattern with length Lp in first direction D1, see the insert. More in particular, magnets are arranged in a pattern ofN S N S, etc., wherein North or South indicates the pole of the magnet that faces the primary part. In this configuration, Lp is twice the center-to-center distance of adjacent permanent magnets 223. Figure 5 further illustrates length Lm ofpermanent magnets 223 and distance dl representing the distance corners ofpermanent magnet 223 are shifted in first direction D1. This distance is related to angle al according to: . dl s1n(a1) = The ratio between distance dl and distance Lp is defined as the first electrical angle el, which when expressed in degrees, can be calculated using: e1 =360 x%: 360 ><Lm+n(al) p p First electrical angle e1 may lie within in a range between 10 and 120 degrees, and wherein 0.361 S ez S 0.861, or wherein 1.261 S ez S 361. More preferably, first electrical angle 61 may lie within in a range between 30 and 90 degrees, and wherein 0.561 S ez S 0.761, or wherein 1.5e1 S ez S 261. Features described in connection with figures 1A-1C, 2-4, which are subject ofdependent claims, and in so far as being consistent with the abovementioned requirement for angles al and az, may equally apply to theLSMs of the present disclosure. Next, embodiments of the present disclosure will be described in more detail referring to the appended drawings, wherein: Figures 1A-1C illustrate twoknown types ofLSMs in which aspects of the present disclosure can be implemented; Figure 2 illustrates anLSM system using theLSM in figures 1A-1C; Figure 3 illustrates the concept of using skewed permanent magnets for reducing force ripple; Figure 4 illustrates alternative embodiments of the secondary part according to the concept of figure 3; Figure 5 illustrates an orientation ofpermanent magnets relative to edges of the closing plate in accordance with aspects ofthe present disclosure; and Figures 6A and 6B illustrate a comparison between a) the force ripple of aknownLSM in accordance with theLSM shown on the bottom of figure 4, and b) anLSM in accordance with the present disclosure that is in accordance with figure 5. It is noted that embodiments of anLSM in accordance with the present disclosure may be substantially identical to the knownLSMs with the exception of the shape of the closing plate, more specifically the angle ofedges E3, E4 relative to second direction D2. The Applicant found the proposed solution, i.e. using az different from 0 and al, based on measurements of the effect of the magnetic reluctance of the transition between adjacent secondary units, TBASU. Because the effect of theTBASU is relatively small, it was anticipated that a Fourier Transform (FT) would be necessary in order to show it quantitatively. For this reason, three relatively long secondary units were produced in which az is different from al and different from 0. The secondary units were adjacently arranged in the first direction for forming a magnet track. Because the end of the magnet track has an effect on the measured motor performance, the primary part was positioned in the middle of the first secondary unit for the start of the measurement. It then drove towards the second secondary unit, traversed it, and stopped in the middle of the third secondary unit. Without being bound by theory, when transforming the resulting measured force ripple using FT, the assumption is made that the signal, in this case the measurements, are periodic. This is not actually the case for a linear motor. The resulting step that occurs between the last and the first measured value is represented in the Fourier transformed spectrum by a large number of high frequency harmonics. This is not considered a major problem, because the frequencies of interest are low. The spatial frequency corresponding to a single electric cycle is referred to here as the first harmonic. The major harmonics that dominate the force ripple are typically the first and the second harmonics. The first harmonic because the motor current repeats over that distance, and the second harmonic because the magnets repeat twice as fast as the electric cycle. Depending on the pole / slot ratio of the motor, the 6th harmonic might be important or, somewhat surprisingly, the 11 / 2th or the 1 / 2th harmonic. The secondary units used for this test had 16 magnets each which is 8 electrical cycles. By traveling over 16 electrical cycles, theTBASU is encountered twice, firstwhen moving from the first secondary unit to the second, next by traversing from the second secondary unit to the third secondary unit. The spatial frequency corresponding to theTBASU is therefore expected at the 1 / 8th harmonic. Figure 6A illustrates a comparison between a) the magnet track in accordance with the present invention for which the closing plate is skewed at an additional angle relative to the skewing angle of the permanent magnets, and b) a similar magnet track but for which a1 = az. As shown in figure 6A, the force ripple is very comparable between the different magnet tracks. This is because the force ripple is dominated by the 11 / 2th and 2nd harmonics for this motor type. The electrical cycle is 24 mm, so theTBASU occurs at 96 and 288 mm. Because theTBASU inuences the motor behavior while any part of the primary part is located over it, the effects are spread out and are not clearly visible in a direct plot of the ripple. Figure 6B illustrates the Fourier Transform of the data shown in figure 6A. From figure 6B, ripple components can be seen at and near the 1 / 8th harmonic that are considerably lower when skewing angle az of the closing plate is higher than the skewing angle al of the permanent magnets. It is known in the art that synchronous electric motors produce a force ripple in some relation to the base harmonic, which is itselfdetermined by the distance over which the motor travels when the rotating current rotates over exactly 360°. This characteristic distance is equal to the distance from magnetic north pole to the next magnetic north pole. Usually, the poles consist of only a single magnet, so that the magnets alternate north-south-north-south. This characteristic distance, known as the electric or magnetic cycle length, is therefore typically equal to twice the heart-heart distance from magnet to magnet, also known as the magnet pitch. As a practical matter, the cycle length is very well known for synchronous motors as it is impossible to control the motor without this knowledge. In the art, a method is known with which it is possible to predict the expected peaks in the Fourier Transform ofthe force ripple. The force ripple comprises one, two, or possibly more ripples that each have a different physical origin. For example, the bestknown of these is the so- called cogging which is caused by attraction between the magnets and ferromagnetic material associated with the phase coils. For this reason, it is present in iron-core motors but absent in iron- less motors. Several peaks in figure 6B can be accounted for given the design of the motor. For the motors shown in figures 6A and 6B, three phase coils repeat over a length equal to the distance over which four magnets repeat, which is equal to two magnetic cycle lengths. This is known as a 4-to-3 pole-to-slot ratio. Some of the harmonics are inherent to the design, such as the 2nd harmonic. This harmonic matches the distance from magnet to magnet. Some of the harmonics would not exist in an idealized motor of the same design. Only when manufacturing tolerances are considered, such as tolerances on magnet strength or position, the 11 / 2th harmonic appears. For a 4- to-3 pole-to-slot ratio, this harmonic corresponds to the distance from coil to coil. Somewhat counterintuitively, on the characteristic distance from coil to coil the motor will show variations in force based on individual magnet variability, just as on the characteristic distance from magnet to magnet, the motor will show variations in force based on individual coil variability. For this pole- to-slot ratio, the 6th harmonic is not very strong for cogging, but it is very strong for another type of ripple, sometimes known as linear ripple because it scales with current. Cogging, as is known in the art, does not. The most prominent peak in Figure 5 is of course the 0th harmonic which represents the average value ofthe motor force. Prior art remains silent about predicting harmonics below the 1 / 2th harmonic, or even below the 1st harmonic. These lower harmonics do not correspond to mechanical features that are present within the unit cell of the motor, which is either two magnets or three coils. Based on measuring over 16 magnetic cycles, where 2 transitions withTBASUs are present, one expects a 1 / 8th harmonic. The corresponding mechanical feature, in this case the length of the magnet track at 8 magnetic cycles, falls outside the unit cell of the motor. Every 8 magnetic cycles, some kind of effect is expected on the force, but it is difficult to predict what this effect will be, and therefore what the harmonic content of this effect will be. Figure 6B illustrates that there is an effect on the harmonics spaced around the 1 / 8th harmonic. Although shown for az > al, the Applicant has found that similar advantages can be obtained when angle a1 > az. In the above, detailed embodiments of the present disclosure have been described. However, the scope ofthe present disclosure is not limited to these embodiments. Rather, various modifications to the embodiments are possible without deviating from the scope of the present disclosure which is defined by the appended claims and their equivalents.

Claims

1. Linear synchronous motor (100; 200), LSM, comprising: a primary part (110; 210) comprising a multitude of coils (214) which are arranged adjacently in a first direction (Dl); a secondary part (120; 220) comprising a multitude of separate secondary units (121; 221) which are arranged adjacently in the first direction (Dl), each secondary unit (121; 221) comprising a magnetic component which has at least one strike plate (122A, 122B; 222) includes as well as a multitude of permanent magnets (123A, 123B; 223) arranged adjacent to at least one locking plate (122A, 122B; 222) in the first direction (Dl), where the permanent magnets (123A, 123B; 223) are elongated and each a have length Lm, where the permanent magnets (123A, 123B; 223) are arranged according to a repeat of a pattern of length Lp in the first direction (Dl); where each of the at least one locking plate (122A, 122B; 222) has a first rim (E1) and opposite second edge (E2) encompasses which both extend in the first direction (Dl), and a third edge (E3) and opposite fourth edge (E4) which the first edge (E) and the connect second edge (E2); where the permanent magnets (123A, 123B; 223) are arranged on the at least one strike plate (122A, 122B; 222) at an angle by means of a first angle already at with respect to a second direction (D2) which is perpendicular to the first direction (Dl); characterized by the fact that the third edge (E3) and fourth edge (E4) extend under a second book az with respect to the second direction (D2) which is different from the first angle al and which is different from 0 degrees.

2. LSM (100; 200) according to conclusion l, where a first electric angle el in degrees is defined according to: el = 360 X w p and where a second electric angle ez is defined in degrees according to: ez = 360 X %? where el lies within a range between 10 and 120 degrees, and where 0.361 S ez S 0.861 or 1.261 S ez S 391.

3. LSM (100; 200) according to claim 2, where el lies within a range between 30 and 90 degrees, and where 0.561 S ez S 0.761 or where 1.561 S ez S 231.

4. LSM (200) according to one of the preceding conclusions, where the primary part (210) a magnetic core (212) from which a multitude of magnetic teeth (213) extends towards the secondary part (220), and where the coils (214) around the teeth (213) his injured.

5. LSM (200) according to claim 4, further comprising an aid component on which the locking plates (222) of the secondary units (221) have been mounted.

6. LSM (100) according to one of claims 1-3, where at least one locking plate (121) of each secondary unit (120) includes a first magnetic locking plate (122A) on which a multitude of permanent magnets (123A) is arranged and an opposite second magnetic closing plate (122B) on which a corresponding second multiple of permanent magnets (123B) are arranged, where the primary part (110) is arranged to be between the first and move second magnetic locking plates (122A, 122B).

7. LSM (100) in accordance with claim 6, further comprising a support component (124) to which the first and second locking plates (122A, 122B) of the multiple of secondary units (121) are linked.

8. LSM (100; 200) according to one of the preceding conclusions, where the third margin (E3) and the fourth edge (E4) are straight edges.

9. LSM (100; 200) according to one of the preceding conclusions, where the coils (214) are designed to be individually electrically powered.

10. LSM (100; 200) according to one of the preceding conclusions, where the primary part (110; 210) is configured to move relative to the secondary part (120; 220) in the first direction (Dl) as soon as the coils (214) are energized.

11. Linear synchronous motor, LSM, system (300), comprising the LSM (100; 200) according to claim 10, and an electronic drive unit (330) for driving the coils (214) of the primary part (210) of the LSM (100; 200).

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