[0001] The present invention is concerned with an improved structure of a linear electric
motor for electromechanical actuators of weaving machines, and more particularly of
metering weft-suppliers for fluid jet looms.
[0002] More precisely, the invention relates to linear electric motors comprising a driving
shaft, usually made of a ceramic material, to which are coupled cylindrical, radial-polarity
permanent magnets which form a movable core for the motor. The core linearly slides
within a cavity of a stator housing bearing excitation coils and guide/supporting
bushes for said driving shaft.
[0003] As well known to persons skilled in the art, the movable core in a linear motor of
the above-specified kind moves at a high speed. Due to this circumstance, on the one
hand, such motors are particularly suitable to operate as electromechanical actuators
because of their quick action, but, on the other hand, because of the high accelerations
and decelerations to which the core is subjected, the core suffers to high mechanical
stresses, and the parts of the motor must therefore be oversized, with unfavorable
dynamical and economical consequences, including a limitation of the life of the motor.
[0004] It is the main object of this invention to overcome the above mentioned drawbacks
of known linear motors and, more particularly, to provide a linear motor having a
considerably improved structure, with a high mechanical resistance, with a simple
and compact construction, with a limited mass and inertia, and free from welded and
bonded joints and from moulded polymeric components, so that the structure will be
easy to assemble and able to operate under severe conditions for a long time and at
high frequencies, e. g. in the range of 1300 to 1600 cycles/minute.
[0005] According to the invention, the above and other objects, such as will appear from
the following detailed description, are achieved by means of a structure of a linear
electric motor having the features recited in the attached claims.
[0006] Substantially, the invention is based on the innovative concept of providing the
driving shaft with a central salient collar integral with the shaft and onto which
the entire movable core of the motor is firmly crimped. To such purpose, the movable
core consists of two substantially cylindrical, identical core portions made of a
non-magnetic material, provided with respective terminal flanges and mounted on the
driving shaft on opposite sides of said collar, from which they are separated by means
of at least one elastomeric ring. Said core portions have respective threaded areas
which are screwed into corresponding threaded areas of a cylindrical central case.
The threaded engagement, by deforming said elastomeric ring, pushes the terminal flanges
of said core portions axially into abutment with corresponding, radial-polarity, magnetic
rings, thereby locking said magnetic rings onto said driving shaft.
[0007] The features, purposes and advantages of the improved motor structure according to
the present invention will appear from the following detailed description and with
reference to the attached explicatory drawings, wherein:
Fig. 1 is an axial section of an improved linear electric motor according to the present
invention,
Fig. 2 is a detail of the movable core of the motor shown in Fig. 1,
Fig. 3 is an exploded perspective view of the movable core of Fig. 2.
[0008] Fig. 1 shows a known linear motor 1 of a known kind, comprising a hollow stator 2
having at least two pole pieces 3, 4 and preferably a third pole piece 5 (intended
to considerably improve the performance of the motor) and two excitation coils 6,
7. A movable core of the motor, referenced generally as 8, is slidable with rectilinear
motion within the stator cavity and is firmly crimped onto a driving shaft 9, typically
of a ceramic material, and which is also slidable, being supported and guided by bushes
10 carried by stator 2.
[0009] According to the invention, driving shaft 9 is provided with a projecting central
collar 9a integral with the shaft, onto which movable core 8 is firmly crimped. To
such purpose, core 8 consists of two identical, substantially cylindrical core portions
11a, 11b, made of a non-magnetic material such as aluminum, and provided with respective
terminal flanges 110a, 110b. Said portions are mounted on driving shaft 9 on opposite
sides of collar 9a, and they are separated from the collar by at least one elastomeric
O-ring 12. Core portions 11a, 11b have respective threaded areas 13-14 that are screwed
into a correspondingly threaded cylindrical central case 15. The threaded engagement,
by deforming elastomeric ring 12, pushes terminal flanges 110a-b of said core portions
axially into abutment with corresponding, radial-polarity, magnetic rings 16a, 16b,
thereby locking said magnetic rings onto said driving shaft 9.
1. A structure of a linear electric motor (1), particularly for electromechanical actuators
of weaving machines, comprising a driving shaft (9) and an associated movable core
(8) linearly moving within a corresponding cavity of a stator housing (2) bearing
excitation coils (6-7) and guide/supporting bushes (10) for the driving shaft, characterized in that said driving shaft (9) is provided with a projecting central collar (9a), integral
with the shaft, and onto which the whole movable core (8) of the motor is firmly crimped.
2. Structure of a linear electric motor according to claim 1, characterized in that said movable core (8) consists of two identical core portions (11a, 11b), made of
a non-magnetic material, provided with respective terminal flanges (110a, 110b) and
mounted on driving shaft (9) on opposite sides of the projecting collar (9a), from
which they are separated by at least one elastomeric ring (12), and in that said core portions (11a, 11b) are substantially cylindrical and have respective threaded
areas (13-14), engaging a correspondingly threaded, cylindrical central case (15),
the threaded engagement deforming said elastomeric ring (12), to axially pushes the
terminal flanges (110a-b) of the core portions into abutment with corresponding, radial-polarity
magnetic rings (16a, 16b), thereby locking said magnetic rings onto said driving shaft
(9).
3. Structure of a linear electric motor according to claim 2, characterized in that said driving shaft (9) is made of a ceramic material and said substantially cylindrical
core portions (11a-11b) are made of aluminum.
