Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K19/00—Synchronous motors or generators
  • H02K19/02—Synchronous motors
  • H02K19/10—Synchronous motors for multi-phase current
  • H02K19/103—Motors having windings on the stator and a variable reluctance soft-iron rotor without windings
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K41/00—Propulsion systems in which a rigid body is moved along a path due to dynamo-electric interaction between the body and a magnetic field travelling along the path
  • H02K41/02—Linear motors; Sectional motors
  • H02K41/03—Synchronous motors; Motors moving step by step; Reluctance motors

Definitions

• the invention relates to a motor according to the introductory part of claim 1.
• each of these types of motor may be "opened out” and extended in a plane to form a linear motor.
• the force parallel to the flux (attractive force) is:
• Fp s * B * B / (2 * ⁇ O)
• Fp the attractive force in newtons
• s is the y surface in m
• B is the magnetic induction in teslas
• ⁇ O is the permeability of the gap.
• the ratio t/p may be optimal to generate the maximum torque.
• Electric motors may be grouped into two major categories: motors with one elementary pole for each winding; - motors with more than one elementary pole for each winding.
• the second category includes stepping motors, while the first category includes all other motors: it is now clearer why stepping motors provide higher torques on average for the same dimensions.
• the working force is always directly proportional to the dimension of the air gap traversed by the lines of force of the magnetic field.
• the moving part of the motor is also subject to a force (Fp) parallel to the lines of flux of the magnetic field in the air gap and not participating in the generation of the torque (in a rotary motor) or of the total working force in a linear motor.
• Fp force parallel to the lines of flux of the magnetic field in the air gap and not participating in the generation of the torque (in a rotary motor) or of the total working force in a linear motor.
• the forces Fp generated at each pole provide a theoretically zero resultant and one which can in any case be easily discharged onto the rotation bearing of the rotor
• the force Fp forms an attractive stress between the inductor and the armature which has to be discharged internally onto the supports which hold the armature. This represents a considerable technical problem which is difficult to solve and which drastically limits the working force which can be generated by a linear motor.
• the object of the present invention is to propose a new structure for an electric motor, whether rotary or linear, by means of which it is possible to obtain greater torque (in the case of rotary motors) or greater force (in the case of linear motors), without the problems stated above.
• a further object of the present invention consists in the provision of a linear electric motor with which it is possible to obtain high working forces while simultaneously eliminating the attractive stresses between the inductor and armature.
• a further object of the present invention consists in the provision of an electric motor with which it is possible to obtain higher torque or forces than those provided by conventional motors for the same excitation current, and consequently without increasing the dimensions of the motor.
• FIG. 1 to 3 are simplified diagrams relating to the state of the art as described previously;
• Fig. 4 is a plan view of a theoretical system on which the structure of the motor according to the present invention is based;
• Fig. 5 is a transverse section through V-V in Fig. 4;
• Fig. 6 is an enlargement of Fig. 4;
• Fig. 7 is the graph of the force acting on the armature shown in Figs. 4 and 5 as a function of the displacement between the armature and inductor, when the inductor winding is supplied with direct current;
• Fig. 7a is a series of diagrams showing the variation of the forces on the armature in a multiple- phase power supply
• Fig. 8 is a plan view of an embodiment of a linear motor with three-phase supply
• Fig. 9 is a section through IX-IX in Fig. 8;
• Fig. 10 is a plan view of a further development of the structure shown in Fig. 8;
• Fig. 11 is a section through XI-XI in Fig. 10;
• Fig. 12 shows a further development of the embodiment shown in Fig. 11;
• Fig. 13 shows a particular embodiment of one pole or phase of the motor
• Fig. 14 shows a possible method of inserting a position transducer into the motor shown in Fig. 4
• Figs. 15a, 15b and 15c show three geometrical views of a possible embodiment of an armature.
• Figs. 15b and 15c being views through XVb-XVb and XVc-XVc in Fig. 15a
• Figs. 16a and 16b show respectively a plan view and a section through XVI-XVI of a motor with a structure of the type shown in Fig. 10, with an armature made according to Fig. 15;
• Fig. 17 shows an axial section of a rotary motor according to the invention
• Figs. 17a, 17b, and 17c show the disposition of the windings of the motor shown in Fig. 17; and Figs. 18 and 19 show a further embodiment.
• the two polar expansions 9, which form the inductor, are excited by the winding 10 and are shaped so that they concentrate the flux generated in a multiplicity of elementary poles 9A provided on both expansions 9 and corresponding to each other.
• a housing within which an armature 12 is disposed slidably as shown by the arrow X is formed ' between the two polar expansions 9 of the inductor.
• a first air gap tl is formed between the armature 12 and the first polar expansion 9, while a second air gap t2 is formed between the armature and the second polar expansion 9.
• the armature 12 is subject to a force which tends to bring it to the minimum energy configuration, which is that in which the elementary poles 13 of the armature 12 are aligned with the elementary poles 9A of the inductor 9.
• a major advantage of this structure in the case of a linear motor, is that only lateral working forces, and not attractive forces, are generated between the moving part 9 and the fixed part 12, since the attractive forces are cancelled out on the moving part 12 because they are equal and opposing in the two air gaps tl and t2 traversed by the lines of flux 11.
• the attractive force is exerted only between the opposing poles of the inductor 9 and is easily withstood by the rigidity of the inductor.
• the resultant working force in the direction X is an alternating cyclical function of the relative positions of the armature 12 and inductor 9, as shown in Fig. 7.
• the function shown in Fig. 7 should preferably be as nearly rinusoidal as possible.
• the poles as shown in Fig. 6: the elementary pole 9A of the inductor 9 is half of the pole pitch p, while the elementary pole 13 of the armature (or the keeper 13) is one third of the pole pitch p.
• the second harmonic and all the even harmonics in the force diagram in Fig. 7 are canceled out, together with the third harmonic and all its multiples, resulting in a closer approximation to the sinusoid.
• An advantageous number of poles is three, since this simplifies the construction of the motor, minimizes the power supply and provides a theoretical force which is completely constant in all relative positions of the inductor and armature.
• the structure of the motor may become that shown in Figs. 8 and 9.
• the three-phase inductor consists of a ferromagnetic core 27 which terminates in three poles 17, 18 and 19, suitably shaped to concentrate the flux in the elementary poles 28 of pitch p.
• the force produced by a single phase is of the sinusoidal type as a function of the displacement and is proportional to the square of magnetic induction B.
• the graph Gl in Fig. 7A shows the variation of the force fl generated by the first phase or pole 17 as a function of the relative displacement x for a constant excitation current related to the value of the current il.
• the graphs G6 and G9 show these forces, again in the case of constant excitation currents, again related to the corresponding values of i2 and i3.
• the excitation currents must not be constant, but for each phase the excitation current must be dependent on the relative position x of the armature and inductor as indicated in Fig. 7A in graphs G2, G5 and G8.
• phase 1 For example, if phase 1 is analyzed, it will be seen that the absolute value of the current il is maximum (points A and B) when the force produced in the positive direction is maximum, and is zero (points C and D) when the force produced in the negative direction is maximum.
• graph G3 shows, for phase 1, the square of the excitation current il, represented by graph G2.
• Graph G4 obtained by multiplying graphs G3 and Gl point by point, represents the force produced by phase 1.
• the three-phase power supply system provides a constant force perfectly smoothed with the variation of the relative position of the inductor and armature, at the cost of a modest 25% of loss with respect to the maximum force developed by a single phase.
• Another source of modulation of the force is the fact that the excitation current is not perfectly sinusoidal: with the three-phase system, the third harmonic is advantageously canceled from the current waveform.
• Figs. 8 and 9 show a motor which, for the sake of constructional simplicity, has excitation windings on side 27 of the inductor only, the opposite side 23 being a simple passive encloser of the flux.
• the excitation windings may be distributed on both sides of the motor, the 1-eeper 23 being replaced by an active inductor identical to 27.
• An important variant of the motor, which may multiply the force generated, requires the presence of a plurality of movable armatures (carrying elementary poles, in other words keepers) aligned with each other and having inserted between them fixed armatures carrying keepers, in other words elementary poles aligned with the elementary poles of the inductor.
• Figs. 10 and 11 show a possible non-restrictive embodiment of this variant.
• the two parts of the inductor 31 and 32 are identical to the preceding parts 27 and 23 in Fig. 8. However, there are two movable armatures 33 and 34, separated by a fixed armature 35.
• the armatures 33 and 34 are movable in the longitudinal direction X and are integral with each other, being secured in a common support 41.
• the fixed armature 35 is integral with the inductor, being secured in the support 40 which links the two parts 31 and 32 of the inductor.
• the force acting on the movable armature in the direction X is, for a given flux, double that of the motor shown in Fig. 8, since there are twice as many air gaps: the line of flux 42 in Fig. 10 passes through four air gaps tl, t2, t3, and t4, and therefore generates a force four times greater than that which could be generated by a conventional motor in the same conditions.
• the number of movable armatures (each of which generates force) may be increased until a magnetizing force is available to generate the desired magnetic induction through the sum of the air gaps. With a high number of movable armatures there may be an unfavourable reduction of the flux in the movable armatures farthest from the excitation winding, as indicated in Fig. 12.
• a pair (movable armature) + (fixed armature) has a total width of 2h, which must be proportional to the pitch p of the elementary poles.
• h — p the pitch of the elementary poles.
• the total volume of the space between the poles is the total volume of the space between the poles.
• the operating frequency to which the magnetic materials are subjected differs substantially between linear and rotary motors.
• sheet iron is optimal for linear motors and slow rotary motors, but not suitable for fast rotary motors.
• Ferrite is unsuitable for making elementary poles, ov. ⁇ ng to the low saturation induction; since the force is proportional to the square of induction on the poles, the force would be approximately 25 times lower than that obtainable with sheet iron or pressed powder.
• Pressed ferromagnetic powder has a low relative permeability and therefore requires a higher excitation current.
• the percentage increase of magnetizing force is minimal and therefore tolerable, while for the inductor and the opposing keeper there may be a significant percentage increase.
• the section of the pole inside the winding should not be greater than the active terminal section, to obtain a distribution of the flux over a greater section and consequently a further reduction of the mean induction.
• a variant of the invention provides for the poles to be shaped as shown in Fig. 13.
• the mean induction inside the pole 48 is therefore equal to the maximum induction on the ends of the elementary poles multiplied by the ratio between the overall surface of the elementary poles and the surface of the pole 48. If the inductor 49 is made from magnetic powder, its greater section proportionally reduces the magnetic reluctance and consequently the greater magnetizing current required.
• a differential use of materials is also possible, with pressed magnetic powder being used for the concentrator 49 and armatures 50, and ferrite for the inductor 48.
• fast rotary motors By using ferrite or pressed powder or a combination of the two, fast rotary motors, with electrical supply frequencies possibly exceeding 20 kHz, may be made according to the invention.
• the invention therefore also provides a possible form of construction which provides optimal geometrical repeatability, strength, and economy of production.
• This form of construction is shown in Fig. 15, in which three orthogonal sections of an armature are shown by way of example.
• the armature basically consists of an insulating non-magnetic support 55, which contains a series of transverse apertures 54 which have the exact dimensions of the elementary poles of the motor; the apertures will therefore have different dimensions and positions according to what has been disclosed above, depending on whether there is a movable armature or a fixed armature.
• Packs of plates 56 formed from magnetic sheet iron of the type normally used for motors and transformers, are fitted precisely inside these apertures. These packs form the transverse keepers. Two thin sheets 57 of insulating non-magnetic material are fixed laterally to the armature and keep the plates in position.
• This structure may be formed with the techniques and materials normally used for making printed circuits; the insulating material may be resin-glass fibre laminate, and the two thin lateral sheets, also made of resin-glass fibre laminate, may be glued as in the case of a multiple-layer circuit.
• the packs 56 may be made of ferrite or pressed powder as well as of plates of the transformer type. In the case of pressed powder, the powder may be pressed directly in the apertures present in the resin-glass fibre laminate, with higher economy and precision of mounting.
• the structure of a linear motor made by this technique is shown schematically in Fig. 16.
• the inductor 58, the windings 59 and the terminal keeper 60 are similar to the preceding ones, but the concentration of the flux in the multiplicity of the elementary poles is provided by the structures 61. These structures are similar to those of the fixed armatures 62, with the only difference that the protective sheet 63 is not present on the side of the inductor or its terminal short-circuit, to avoid an unnecessary air gap.
• keepers are housed precisely in the cut-outs formed in the insulating support, there is an optimal alignment, which becomes more important as the poles are brought closer together.
• the movable armatures are also constructed by the same technique.
• the precise mounting of the movable and fixed armatures is assisted by the spacers 65, which force the armatures into suitable positions to obtain the requisite air gap.
• the air gap is partly filled by the covering sheets, which also make the surfaces of the poles smooth and uniform.
• the reduced freedom of lateral oscillation is particularly useful in the case of thin armatures, which have lower rigidity. Furthermore, any occasional friction is less likely to cause damage.
• the armatures are in disk form: the fixed armatures have their keepers grouped in three poles (Fig. 17A) disposed at 120 degrees to each other, while the movable ones (Fig. 17B) have them disposed uniformly over their whole circumferences.
• the inductor (section in Fig. 17C) consists of three columns 68 on which the three windings 69 act, while the two terminal toroids 70 provide the magnetic circuit closure. To prevent parasitic currents and consequent electrical losses, these terminal toroids may consist of a winding of thin magnetic sheet.
• Possible variants of the rotary motor may have 6 or more poles (providing better distribution of the forces and consequently a smoother motion) or the closure of the pole flux in each pole (as in Fig. 5), or windings on both sides of the inductor.
• position sensing system which is used to keep the three-phase supply current correctly phased according to the position of the movable armatures, and which may also be used for position control.
• the passive scale of the sensing system consists of the movable armature itself, whose keepers repeated with a regular pitch are sensed by the inductive proximity sensor integral with the fixed part.
• Fig. 14 shows an example of a possible disposition of the proximity sensor 51, facing the movable armature 52, in the space available between the poles of the inductor 53.
• FIGs. 8 and 9 is an illustration of a motor in which are provided three poles, each consisting of a corresponding pole expansion 17, 18, 19, on which the corresponding winding is completely wound.
• Figs; 18 and 19 show schematically one embodiment of this type.
• the numerals 27 and 28 again indicate the elementary poles of the armature and of the inductor respectively.
• the elementary poles 27 are equidistant from each other, as are the elementary poles 28.
• the windings (only indicated in Fig. 18), distributed in a way similar to that provided, for example, in three-phase asynchronous motors, are disposed in the cavities formed between every two elementary poles 28 of the inductor.
• the armature has two elementary poles 27 less than the inductor (or vice versa) , to ensure the generation of a thrust on the armature at every instant.
• FIG. 19 shows highly schematically the distribution of the windings of the three phases in the case of a linear motor with three poles.
• the diagram in Fig. 19 shows that the distribution of the windings is not uniform, as in rotary three-phase asynchronous motors, owing to the fact that the armature and inductor are developed in a plane instead of being annular. This causes the occurrence of edge effects, the incidence of which may be reduced simply by elongating the inductor and then repeating the disposition illustrated in Figs. 18 and 19 a sufficient number of times.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Physics & Mathematics (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Electromagnetism (AREA)
• Linear Motors (AREA)

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Cited By (6)

Citations (7)

• 1993
  • 1993-11-03 IT ITFI930219A patent/IT1262572B/it active IP Right Grant
• 1994
  • 1994-10-26 WO PCT/IT1994/000180 patent/WO1995012914A1/en active Application Filing

Patent Citations (7)

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