Linear pulse motor with magnetic armature lock

In a planar linear pulse motor, the relative movement between the stator and the armature is positively restricted when no electric current is supplied to the drive coils by means of a lock member provided on either the armature or the stator. This lock member is attracted to a permanent magnet by its biasing magentic flux so as to be brought into contact with whichever of the armature or stator does not have the lock member on it. As a result, the armature may be locked up without consuming any electric power. If the lock member is attached to the stator or armature by means of an elastic member, the vertical dimension of the member attaching the lock member to the stator or armature can be reduced. Furthermore, the mechanical strength and the security of the engagement of the lock member to the stator or armature can be increased. As a result, the planar linear pulse motor disclosed is compact and highly reliable. In those cases when the lock member is mounted on the stator, there is no increase in the moving mass of the motor, resulting in no impairment of the rate of response of the pulse motor.

TECHNICAL FIELD 
The present invention relates to linear pulse motors, and in particular to 
planar linear pulse motors for such applications as the magnetic head 
drives of floppy disk drives for personal computers and word processors. 
BACKGROUND OF THE INVENTION 
A conventional planar linear pulse motor typically has a stator and an 
armature carrying mutually opposing magnetic pole teeth and is controlled 
so that some of the magnetic pole teeth of the stator may oppose the 
corresponding magnetic pole teeth of the armature. By appropriately 
energizing the drive coils provided in the magnetic pole teeth of the 
stator in a prescribed order, the opposing pairs of the magnetic pole 
teeth are made to shift in such a manner that the armature is moved by one 
fourth of the pitch of the magnetic pole teeth by each shifting of the 
energized state of the drive coils. To prevent inadvertent movement of the 
armature when the drive coils are not energized, a permanent magnet may be 
provided to produce a biasing magnetic flux in such a manner that a 
closed-loop magnetic flux may be produced across the magnetic pole teeth 
of the stator and the armature (refer to Japanese patent laid-open 
publication No. 62-64252). In other words, in such a linear pulse motor, 
when the drive coils are not energized, the armature is kept stationary 
and fixedly engaged by the force (which is called a cogging force) acting 
between the magnetic pole teeth of the stator and the armature which are 
magnetized by the biasing magnetic flux produced from the permanent 
magnet. 
However, since this cogging force is not very strong, the armature could 
move and its stationary position could change when impacts, vibrations or 
other external forces were applied to the armature. Therefore, there was a 
possibility when such a planar linear pulse motor was used for the head 
drive of a floppy disk drive that its head would move abruptly, thereby 
causing not only faulty operation of the (read/write) head, but also 
damage to the linear pulse motor or to the head. 
On the other hand, in order to more securely hold the armature, a large 
electric current must be supplied to some of the drive coils to increase 
their attractive forces, but this leads to an increase in power 
consumption. 
BRIEF SUMMARY OF THE INVENTION 
A primary object of the present invention is therefore to provide a planar 
linear pulse motor which can positively engage an armature at an arbitrary 
position with a simple structure and without consuming much electric 
power. 
A second object of the present invention is to provide a planar linear 
pulse motor which can positively engage an armature at an arbitrary 
position without impairing the response property of the motor during 
normal operation. 
A third object of the present invention is to provide a planar linear pulse 
motor which can positively engage an armature at an arbitrary position 
without increasing the thickness (or vertical dimension) of the motor. 
These and other objects of the present invention can be accomplished by 
providing a planar linear pulse motor, comprising: which includes a stator 
having a yoke provided with magnetic pole pieces defining a plurality of 
magnetic pole teeth; an armature having a plurality of magnetic pole teeth 
opposing the magnetic pole teeth of the stator and slidably supported by 
the stator; a plurality of drive coils provided in the associated magnetic 
pole pieces of the stator yoke so as to be sequentially energized to 
produce a magnetic flux for moving the armature relative to the stator; a 
permanent magnet provided in the stator to form a closed loop of a biasing 
magnetic flux passing through the magnetic pole teeth of the stator and 
the magnetic pole teeth of the armature; and a lock member consisting of a 
magnetic member supported by the armature or the stator by way of a spring 
or elastic member to urge the lock member against the other of the 
armature or the stator; the permanent magnet being disposed in a part of 
the stator in such a manner that the biasing magnetic flux produced from 
the permanent magnet urges the lock member toward the other of the 
armature or the stator, against the biasing force of the spring member in 
order to restrict the movement of the armature relative to the stator when 
the drive coils are not energized, and releases the lock member away from 
the other of the armature or the stator under the biasing force of the 
spring member to permit movement of the armature relative to the stator 
when the drive coils are energized with a part of a magnetic flux produced 
from the drive coils canceling in the lock member the biasing magnetic 
flux produced from the permanent magnet. 
In the planar linear pulse motor of the present invention, a lock member 
consisting of a magnetic member is supported by or the armature and the 
stator, and this lock member applies a pressure to the other of the 
armature or the stator by means of an attractive force produced by the 
permanent magnet when the drive coils are not energized. This pressure 
prevents relative movement between the armature and the stator. Since this 
attractive force is produced by the permanent magnet, no electric power is 
consumed. When the motor is activated and electric current is supplied to 
the drive coils, the resulting magnetic flux passes through the lock 
member and cancels the magnetic flux which was the cause of the attractive 
force, so that the attractive force is lost and the armature can move 
freely relative to the stator. The motor otherwise operates in the same 
way as a conventional planar linear pulse motor in that the drive coils 
are sequentially energized to move the armature by the increment of P/4, 
where P is the pitch of the magnetic pole teeth. 
According to a preferred embodiment of the present invention the lock 
member is supported by the stator by way of the spring member so that the 
moving mass attached to the armature may be minimized, and the response 
property of the motor may not be impaired. 
According to a structurally advantageous embodiment of the present 
invention, the permanent magnet is disposed adjacent to the yoke thus 
defining an opening between the permanent magnet and the yoke, and the 
lock member is disposed adjacent an end of the opening remote from the 
armature, the lock member being provided with a projection which extends 
through the opening so as to come into contact with a part of the armature 
when the lock member is actuated by the biasing magnetic flux of the 
permanent magnet. This acts to minimize the overall vertical dimension of 
the motor. Alternatively, the armature is provided with a frictional rail 
element extending along the direction of movement of the armature and 
comprising a depending portion depending from the armature and a lateral 
extension extending laterally from a lower end of the depending portion, 
and the lock member is disposed above the lateral extension so as to be 
pressed upon the lateral extension when actuated by the biasing magnetic 
flux of the permanent magnet. A similar result can be achieved if the lock 
member is provided with a lateral arm which is adapted to engage with the 
armature when the lock member is actuated by the biasing magnetic flux of 
the permanent magnet. 
To achieve a secure and stable engagement between the armature and the 
stator, the spring member should consist of a sheet spring carrying the 
lock member in a central part thereof and fixedly secured to the stator at 
two ends thereof. 
If the lock member is supported by the armature by way of the spring 
member, the moving mass of the armature may be increased but the overall 
height of the motor may be reduced. 
Alternatively, the lock member may consist of a magnetic member supported 
on the stator by way of a sheet spring member, the spring member 
comprising a central part carrying the lock member, a pair of intermediate 
parts on either side of the central part supported by parts of the stator 
in the manner of fulcrums, and free ends extending beyond the intermediate 
parts and carrying frictional members. In this case, the pressure applied 
to the armature may be amplified by the lever action of the sheet spring 
member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1 through 8 are drawings illustrating a first embodiment of the 
planar linear pulse motor according to the present invention. 
FIGS. 1 through 5 illustrates its structure: FIG. 1 is a perspective view 
of the planar linear pulse motor showing its armature in a detached state; 
FIGS. 2 and 3 are cross sectional views of the planar linear pulse motor 
in its assembled state; FIG. 4 is an exploded perspective view of the 
planar linear pulse motor; and FIG. 5 is a perspective view of stator of 
the planar magnetic pole teeth. 
The stator 15 has a base 11. A central part of the base 11 is provided with 
a rectangular opening 11a. The two side portions of the upper surface of 
the base 11 serve as roller guide surfaces (rail surfaces). The 
rectangular central opening 11a receives a pair of yokes 12 made of 
magnetic material and a pair of permanent magnets 13. The prismatic 
permanent magnets 13 are interposed between the laterally arranged pair of 
yokes 12 and the yokes 12 are integrally attached not only to one another 
but also to the front and rear fringes of the lower surface of the base 11 
adjoining the rectangular opening 11a. Gaps are defined between the yokes 
12 and the lateral ends of the rectangular opening 11a. Each of the yokes 
12 is provided with a pair of coil cores 12a integrally projecting 
therefrom, and magnetic pole teeth 10a, 10b, 10c and 10d are formed on the 
upper surfaces of the coil cores 12a either by etching or by machining. 
The permanent magnets 13 are each provided with N and S poles on their 
side surfaces adjoining the yokes 12. 
The magnetic pole teeth 10a through 10d are formed as ridges and grooves of 
rectangular cross-section which alternate at a fixed pitch P as shown in 
FIG. 5 in enlarged scale. As described hereinafter, they are called as 
magnetic pole teeth because the rectangular ridges serve as N or S poles. 
It is also possible to use magnetic pole teeth made of permanent magnets. 
The magnetic pole teeth 10a and 10c are arranged at equal pitch and in the 
same phase relationship, and the same is true with the magnetic pole teeth 
10b and 10d. The magnetic pole teeth 10a and 10b are arranged at the same 
pitch but at a phase relationship which is shifted by P/2. The four coil 
cores 12a or the magnetic pole teeth 10a through 10d are provided with 
drive coils 5a, 5b, 5c and 5d wound around spools 4 fitted thereon. 
To the lower surface of the base 11 is secured a pre-pressure spring frame 
2 which is substantially conformal (annular frame) to the base 11 and is 
provided with various tab pieces along its periphery. The pre-pressure 
spring frame 2 serves both as a motor mount and a member for preventing 
the armature 1 from coming off. To the lower surface of the pre-pressure 
spring frame 2 is fixedly secured a circuit board 14 for the drive coils 
5a through 5d. To the upper surface of a side end of the pre-pressure 
spring frame 2 are fixedly secured a sensor 25 for detecting the reference 
position of the motor and a circuit board 26 for this sensor. 
To one side of the base 11 is fixedly secured a travel reference guide 7a 
by screws or with a bonding agent. The inner side surface of this guide 7a 
defines an exact right angle with respect to the direction in which the 
rectangular ridges (grooves) of the magnetic pole teeth 10a through 10d 
extend. On the other side of the base 11 is disposed a pre-pressure guide 
7b in a slightly laterally moveable manner. The pre-pressure springs 2a 
provided as tabs extending from the peripheral edges of the pre-pressure 
spring frame 2 urge the pre-pressure guide 7b inwardly. 
A travel support mechanism 6 for the armature 1 is provided between the 
guide 7a and the pre-pressure guide 7b, and this mechanism comprises a 
retainer 6a. This retainer 6a is rectangular in shape and is provided with 
vertical portions on either side end thereof, as well as a rectangular 
central opening conformal to the base 11. The side fringes and the 
vertical portions of the retainer 6a are provided with a plurality of 
small openings for rotatably receiving roller pins 6b therein. 
The armature 1 consists of a planar magnetic member, and its lower surface 
is provided with two rows of magnetic pole teeth 1a and 1b. The magnetic 
pole teeth 1a and 1b also consist of a plurality of alternating ridges and 
grooves of rectangular cross-section, and their pitch and phase 
relationship are the same as those of the magnetic pole teeth 10a through 
10d. The magnetic pole teeth 1a and 1b are provided with a relative phase 
shift of P/4. A light shield 17 is attached to a side end of the upper 
surface of the armature 1 to detect the position of the armature 1 by 
shielding light from the sensor 25 for detecting the reference position of 
the motor. This armature 1 is received in the retainer 6a, and is 
supported by the roller pins 6b in a freely slidable manner. The vertical 
roller pins 6a contact the side surfaces of the armature 1 and the guides 
7a and 7b, while the horizontal roller pins 6b are interposed between the 
lower surface of the armature 1 and the upper surface of the base 11 and 
are in contact with them. The magnetic pole teeth 1a of the armature 1 
oppose the magnetic pole teeth 10a and 10b, and the magnetic pole teeth 1b 
oppose the magnetic pole teeth 10c and 10d, defining a predetermined gap 
therebetween in each case. 
The lock member 3 consists of a base portion 3a consisting of magnetic 
material and a projection 3b projecting upwardly from a central part of 
the base portion 3a. The projection 3b may consist of non-magnetic 
material. This lock member 3 is fixedly secured to a central part of the 
upper surface of a sheet spring 16 which is secured to front and rear end 
portions of the base 11. As described hereinafter, the lock member 3 is 
attracted by the permanent magnet against the elastic force of the sheet 
spring 16, and the base portion 3a is thereby brought into contact with 
the reverse surface of the yokes 12. 
As shown in FIG. 4(B), the free end of the lock member 3 and the associated 
lower surface portion of the armature 1 may be provided with irregular 
surfaces so as to achieve secure engagement therebetween. 
The operation of the planar linear pulse motor described above is now 
described in the following with reference to FIG. 6. FIG. 6 shows the 
positional relationship between the magnetic pole teeth 1a and 1b of the 
armature 1 and the magnetic pole teeth 10a through 10d of the stator 15. 
The drive principle of this planar linear pulse motor is based on the 
unipolar drive method. The biasing magnetic flux produced from the 
permanent magnet 13 acts upon the magnetic pole teeth 1a, 1b, and 10a 
through 10d, and the rectangular ridges thereof are magnetized as 
illustrated in FIG. 6. 
When the magnetic pole teeth 10a and 1a are shifted by P/4 from each other, 
electric current is supplied to the drive coil 5a corresponding to the 
magnetic pole teeth 10a so that a magnetic flux of the same direction as 
the biasing magnetic flux is produced in the magnetic pole teeth 10a. This 
produces a strong attractive force between the magnetic pole teeth 10a and 
the magnetic pole teeth 1a of the armature 1, and the armature 1 is moved 
by P/4 or until it reaches a stable state in which the rectangular ridges 
(of different polarities) of the magnetic pole teeth 10a and 1a squarely 
oppose each other. This state is illustrated in FIG. 6. By this time, the 
magnetic pole teeth 1b, and 10c and 10d have shifted by P/4 from each 
other. 
Then the supply of electric current to the drive coil 5a is terminated, and 
electric current is supplied to the drive coil 5c so as to produce a 
magnetic flux in the magnetic pole teeth 10c which is directed in the same 
direction as the biasing magnetic flux produced from the permanent magnet 
13. A strong attractive force acts between the magnetic pole teeth 10c and 
the armature 1, and the armature 1 is moved until the magnetic pole teeth 
1b and 10b oppose each other and a stable state is reached. Likewise, by 
conducting electric current to the drive coils 5b and 5d in that order, 
the armature is moved by P/4 each time. 
When electric current is supplied to none of the drive coils, the stator 1 
reaches a stable position (for instance the position illustrated in FIG. 
6) and is retained at this position by the attractive force acting between 
the magnetic pole teeth 1a, 1b and 10a through 10d and the permanent 
magnet 13. The force acting on the armature is the cogging force. 
Now the locking action of the lock member 3 is described. FIG. 7 shows the 
state in which the armature 1 is locked up, and FIG. 8 shows the state in 
which the armature 1 is moved as described above. These drawings are 
enlarged views of a part of FIG. 2, but are given as views of a different 
cross-section from that of FIG. 2. In other words, for convenience of 
description, the drive coils 5a and 5c are illustrated instead of the 
drive coils 5b and 5d, and the magnetic pole teeth 10a and 10c are 
illustrated instead of the magnetic pole teeth 10c and 10d. Further, only 
the base portion 3a of the lock member 3 is illustrated, and the 
projection 3b is omitted from the drawings. In the following disclosure, 
the term "lock member" means the base portion 3a. 
In FIG. 7, when electric current is supplied to none of the drive coils 5a 
through 5d, the biasing magnetic flux .PHI..sub.B of the permanent magnet 
13 forms a closed loop passing through the yoke 12, the magnetic pole 
teeth 10a and 10b, the magnetic pole teeth 1a, the armature 1, the 
magnetic pole teeth 1b, the magnetic pole teeth 10c and 10d, and finally 
the yoke 12 again. This induces magnetic poles in the magnetic pole teeth 
and, hence, the cogging force. A leak magnetic flux .PHI..sub.BL of the 
biasing magnetic flux .PHI..sub.B passes through the lock member 3a, and 
attracts the lock member 3a toward the parts of the yokes 12 located on 
either side of the permanent magnet 13 against the restoring force of the 
sheet spring 16 so as to apply pressure to the armature 1 through the 
projection 3b. Since the pressure of the projection 3b is produced in 
addition to the cogging force, the armature 1 is very securely engaged. As 
there is no electric current involved, the armature may be fixedly engaged 
without consuming any electric power. 
Now is described how the armature 1 is moved with reference to FIG. 8. When 
electric current is supplied to the drive coil 5a to produce a magnetic 
flux .PHI..sub.C directed in the same direction as the biasing magnetic 
flux .PHI..sub.B in the main magnetic circuit of the motor, this magnetic 
flux passes through the magnetic pole teeth 10a, the magnetic pole teeth 
1a, the armature 1, the magnetic pole teeth 1b, the magnetic pole teeth 
10c, the yoke 12, the lock member 3a, and the yoke 12. Since this magnetic 
flux in the lock member 3a is opposite in direction to the leak magnetic 
flux .PHI..sub.BL produced from the permanent magnet 13, the attractive 
force acting on the lock member 3a is sufficiently weakened for the lock 
member 3a to be moved away from the yoke 12 under the restoring force of 
the sheet spring 16, and the locking action is removed. The movement of 
the armature resulting from P/4 by supplying electric current to the drive 
coil 5 a occurs in the way described above. 
This action takes place in the same way when electric current is supplied 
to the drive coils 5b, 5c and 5d. 
The locking action can be removed even when the projection 3b is not 
completely moved away from the yoke 12 as long as the attractive force 
acting between the lock member 3a and the yoke 12 is weakened. For 
instance, by appropriately selecting the restoring force of the sheet 
spring 16, it is possible to move the armature 1 even while the projection 
3b is still in contact with the yoke 12. In this case, if a suitable 
amount of frictional resistance is applied to the armature, the distance 
required for the armature 1 to travel before coming to a complete stop can 
be reduced. 
FIG. 9 shows a second embodiment of the planar linear pulse motor according 
to the present invention. The permanent magnet 13 of the first embodiment 
extends in the direction of the movement of the armature 1 and the N and S 
poles thereof are located laterally with respect to the direction of the 
movement of the armature 1 in the first embodiment, but this second 
embodiment makes use of a pair of permanent magnets 13 extending 
perpendicularly to the direction of the movement of the armature 1 so as 
to define the N and S poles along the direction of the movement of the 
armature 1 and an opening between the two permanent magnets 13. The yokes 
12 are disposed to the front and rear of the permanent magnets 13. The 
biasing magnetic flux of the permanent magnets 13 passes through the yoke 
12, the magnetic pole teeth 10 and 10c, the magnetic pole teeth 1a and 1b 
of the armature, the magnetic pole teeth 10b and 10d, and the yoke 12, in 
the same direction as the movement of the armature 1. 
According to this linear pulse motor, the lock member 3a is elongated in 
the direction perpendicular to the direction of the movement of the 
armature 1, and achieves its locking action by being attracted to the 
yokes 12. A spring not shown in the drawing is fixedly secured to the 
lower surface of a pre-pressure spring frame 2. Its action of locking and 
releasing the armature 1 is the same as that of the first embodiment. 
This linear pulse motor operates in the same way as the first embodiment, 
and the phase relationship of the magnetic pole teeth are determined as 
summarized in the following: 
______________________________________ 
armature magnetic pole teeth 1a-1b 
same 
phase 
stator magnetic pole teeth 10a-10c 
P/2 
magnetic pole teeth 10a-10b 
+P/4 
magnetic pole teeth 10a-10d 
-P/2 
______________________________________ 
Energization of the drive coils is conducted in the order of the coils 5a, 
5b, 5c and 5d. 
FIGS. 10 and 11 show a third embodiment of the present invention, in which 
FIG. 10 is a perspective view, and FIG. 11 is a longitudinal sectional 
view. In this embodiment, the parts corresponding to those of the first 
and second embodiments are denoted with like numerals. In this embodiment, 
the lock member 3 made of magnetic material is fixedly secured to the 
lower surface of a central part of a sheet spring 16 (elastic member), and 
the two ends of the sheet spring 16 are bent upwards and are provided with 
pressure rubber pieces 18 on their upper surfaces. This sheet spring 16 is 
placed in the space between the magnetic pole teeth 10a and 10b, and 10c 
and 10d in the opening of the base 11 from above. By thus placing the 
sheet spring 16, the lock member 2 is attracted to the yokes 12 and this 
causes upward movements of the two ends of the sheet spring until the 
rubber pressure pieces 18 come into contact with the armature 1. The 
armature 1 can be fixedly engaged in this way. According to this 
structure, the lock mechanism including the lock member 3 would not 
increase the overall height of the motor, and the pressure upon the 
armature 1 is amplified by the lever action with the base 11 serving as 
the fulcrum for the sheet spring 16 whose tow arms serve as levers so as 
to increase the effective force keeping the armature stationary. 
FIGS. 12, 13 and 14 show a fourth embodiment of the present invention. FIG. 
12 is a perspective view, FIG. 13 is a cross-sectional view, and FIG. 14 
is an exploded perspective view. In this embodiment, the parts 
corresponding to those of the first, second and third embodiments are 
denoted with the same numerals. 
This embodiment makes use of a pair of separate retainers 6a which are 
provided with tabs. The armature 1 is received in these retainers 6a, and 
is slidably supported thereby by way of balls 6c and roller pins 6b. To a 
central part of the lower surface of the armature 1 is fixedly secured a 
pressure receiving rail 20 having a rectangular C-shaped cross section and 
extending along the direction of the movement of the armature 1. The 
pressure receiving rail 20 thus comprises a depending portion 20a 
depending perpendicularly from the lower surface of the armature 1 and a 
lateral extension 20b extending laterally from the lower end of the 
depending portion 20a. The balls 6c are in contact with the side surfaces 
of the armature 1 and the guides 7a and 7b, and the roller pins 6b are 
disposed between the lower surface of the armature 1 and the upper surface 
of the retainers 6a and is in contact with them. The base 11 is provided 
with notches 11b at central portions of its front and rear ends for 
avoiding interference between the pressure rail 20 and the base 11. 
The magnetic pole teeth 1a oppose the magnetic pole teeth 10a and 10b, and 
the magnetic pole teeth 1b oppose the magnetic pole teeth 10c and 10d, 
defining a certain gap therebetween. The magnetic pole teeth 10a, 10b, 10c 
and 10d are integrally fabricated as denoted by numeral 10 in FIG. 14, and 
are cut apart after the entire assembly is fixedly secured to the yokes 
12. By doing so, an accurate alignment of the pitch of the magnetic pole 
teeth can be attained. 
A lock member 3 made of magnetic material is fixedly secured to a central 
part of the lower surface of a sheet spring 16 whose two extreme ends are 
fixedly secured to a fixing portions 11a provided in central portions of 
the front and rear ends of the base 11 by suitable fixing means such as 
screws. The lock member 3 and the sheet spring 16 oppose the yokes 12 (the 
permanent magnets 13) with the pressure receiving rail 20 being interposed 
therebetween. Normally, the lock member 3 is attracted to the yokes 12 
with the pressure receiving rail 20 interposed therebetween, and the 
armature 1 is fixedly engaged by fixedly engaging the pressure receiving 
rail 20 to the stator 15. The lock releasing action is the same as the 
previous embodiments described above. In other words, when the attractive 
force of the permanent magnets 13 is released, the lock member 3 moves 
upwards under the restoring force of the sheet spring 16, and releases the 
application of pressure to the pressure receiving rail 20. 
FIGS. 15 and 16 show a fifth embodiment of the planar linear pulse motor 
according to the present invention. FIG. 15 is an exploded perspective 
view of only a part of the stator, and FIG. 16 is an overall 
cross-sectional view. In this embodiment also, the parts corresponding to 
those of the first embodiment are denoted with like numerals. 
This embodiment makes use of a planar permanent magnet 13 having an N pole 
and an S pole above and below on one side of a central boundary 13a, and 
an S pole and an N pole above and below on the other side of the central 
boundary 13a, respectively. The boundary 13a corresponds to the position 
where the "prismatic permanent magnets 13" were disposed in the previously 
described embodiments. To define a passage for the magnetic flux produced 
from this permanent magnet 13, a planar and conformal back yoke 17 is 
fixedly secured to the lower surface of the permanent magnet 13. 
In this embodiment also, a pressure receiving rail 20 is fixedly secured to 
a central part of the lower surface of the armature 1, and this pressure 
receiving rail 20 is fixedly engaged by the lock member 3 which is fixedly 
secured to the sheet spring 16 and attracted to the vicinity of the 
central portion of the yokes 12. In this case, the pressure receiving rail 
20 is constructed as having a pair of depending portions 20a extending 
parallel to each other, and a pair of lateral extensions 20b extending 
laterally toward each other from the lower ends of the depending portions 
defining a gap between the free ends of the lateral extensions 20b. 
FIGS. 17, 18 and 19 show a sixth embodiment of the planar linear pulse 
motor according to the present invention. FIG. 17 is a perspective view of 
the planar linear pulse motor showing its armature in detached state, FIG. 
18 is a cross-sectional view of the same, and FIG. 19 is an exploded 
perspective view. In this embodiment also, the parts corresponding to 
those of the first embodiment are denoted with the same numerals. 
This embodiment makes use of yokes 12 which are separated into four pieces, 
each of the yokes 12 is provided with a projection 12a extending in the 
direction of the movement of the armature 1. Coils 5a through 5d are 
provided on these projections 12a, and the axial directions of these coils 
5a through 5d coincide with the direction of movement of the armature 1. 
The permanent magnets 13 and the yokes 12, which are integrally joined 
together, are fixedly secured by a frame 18. The frame 18, the coils 5a 
and 5d, the front and rear yokes 12, and a reference guide 7a are shown on 
the left hand side of the drawing as integrally joined together. Another 
guide 7b is provided on the right hand side so as to be able to move 
laterally, and the retainer 6a is disposed between these guides 7a and 7b. 
The retainer 6a supports the armature 1 in a moveable manner. Two ends of 
a pre-pressure spring 8 are fitted into holes 19a provided in the yokes 19 
so as to apply pressure to the guide 7b and one of the retainers 6a. 
According to this embodiment, since the thickness of the coils does not 
affect the height of the motor, the advantage of a low-profile design can 
be obtained. 
The lock member 3 is fabricated as a rod which is bridged across the front 
and rear yokes 12 defining a small gap with respect to the yokes 12. The 
front and rear yokes 19 oppose the leg portions 3a. A pressure member 3c 
for applying pressure to the armature 1 is provided in a central part of 
the upper surface of the lock member 3 so as to project toward a central 
part of the motor. This lock member 3 is mounted on a central part of the 
upper surface of a sheet spring 2 which is fixedly secured to a side end 
of yoke bases 19. As the leg portions 3a of the lock member 3 are 
attracted to the side portions 19a of the front and rear yoke bases 19, 
the pressure member 3c presses upon the armature, and fixedly engages with 
14. In this embodiment also, the direction of the magnetic flux 
.PHI..sub.c passing through the lock member 3 produced by the coils 5a 
through 5d is opposite to the direction of the magnetic flux .PHI..sub.B 
produced by the permanent magnet 13, as shown in FIG. 17. It is also 
possible to provide a pair of lock members on either side of the yoke 
bases 19. 
Thus, according to the planar linear pulse motor of the present invention, 
the stator is securely engaged when no electric current is supplied to the 
drive coils by means of a lock member provided in the stator which is 
attracted to a permanent magnet by its biasing magnetic flux. Therefore, 
the armature can be locked up without consuming any electric power. Thus, 
there is provided a linear pulse motor which consumes little electric 
power and is highly resistant to impact, vibration and other external 
forces. When this linear pulse motor is applied to the drive for a 
magnetic head, proper action of the head is ensured, and the possibility 
of damaging the motor or the head due to inadvertent external forces can 
be eliminated. 
Further, by providing the lock member on the stator, the mass of the 
armature is not increased, and the responsiveness of the armature is not 
impaired. 
In the planar linear pulse motor of the present invention, a lock member 
consisting of a magnetic member is supported on the armature by way of an 
elastic member whose two extreme ends are fixedly secured to the armature. 
When the drive coils are not energized, the lock member is attracted to 
the permanent magnets or the yokes to fixedly engage the armature to the 
stator by a magnetic attractive force. Since this attractive force is 
produced by the permanent magnet, no electric power is consumed. When the 
motor is activated and electric current is supplied to the drive coils, 
the resulting magnetic flux passes through the lock member and cancels the 
magnetic flux which was the cause of the attractive force so that the 
attractive force is lost and the armature can move freely. The motor 
otherwise operates in the same way as a conventional planar linear pulse 
motor in that the drive coils are sequentially energized to move the 
armature by the increment of P/4. 
The action resulting from fixedly securing the two extreme ends of the 
elastic member is described in the following with reference to FIGS. 25 
and 26. FIG. 25 shows an example in which the two extreme ends of an 
elastic member are fixedly secured according to the present invention, and 
FIG. 26 shows a case in which only one end of an elastic member (a coil 
spring) is fixedly secured. In FIGS. 25 and 26, numerals 101, 102, 103, 
104 and 105 denote armatures, an elastic member, lock members, permanent 
magnets (yokes) and a coil spring, respectively. The solid lines show the 
state in which the lock member is attracted to the permanent magnet 104 by 
its biasing magnetic flux. This attractive force fixedly engages the 
armature 101 and the stator (permanent magnets 104) to each other, and 
restricts their relative movement. When this attractive force is removed 
by energizing the drive coils, they move away from each other by a small 
distance d. This small distance d is so selected as to allow the movement 
of the armature and to permit the lock member 3 to be attracted back to 
the armature again when required. The gap between the armature 101 and the 
permanent magnet 104 required to ensure this distance d is h. On the other 
hand, when a coil spring 105 is used, the corresponding gap h' is larger 
than the gap h because of the height of the coil spring 105 itself, and 
this causes an increase in the vertical dimension. Furthermore, the 
elastic member 102 can achieve a stable locking state since it is secured 
to the armature at its two ends whereas the coil spring 105 can lock up 
only one point of the armature 102 and its locking action is therefore 
unstable. 
FIGS. 21 through 23 are drawings illustrating a seventh embodiment of the 
planar linear pulse motor according to the present invention. FIG. 21 is a 
perspective view of the planar linear pulse motor; FIG. 22 is a cross 
sectional view of the planar linear pulse motor in its assembled state; 
and FIG. 23 is an exploded perspective view of the planar linear pulse 
motor. 
This planar linear pulse motor comprises a stator 15 and an armature 1. The 
stator 15 comprises a base 11. A central part of the base 11 is provided 
with a rectangular opening 11a. The two side portions of the upper surface 
of the base 11 serves as roller guide surfaces (rail surfaces), and the 
rectangular central opening 11a accommodates various component parts 
therein. The accommodated component parts are fixedly secured to a 
pre-pressure frame 2 (which is described hereinafter). 
The rectangular opening 11a of the base 11 receives a pair of yokes 12 made 
of magnetic material and a permanent magnet 13. The laterally arranged 
pair of yokes 12 have the prismatic permanent magnet 13 interposed 
therebetween, and they are integrally attached not only to one another but 
also to the front and rear fringes of the lower surface of the base 11 
adjoining the rectangular opening 11a. Gaps are defined between the yokes 
12 and the lateral ends of the rectangular opening 11a. Each of the yokes 
12 is provided with a pair of coil cores 12a integrally projecting 
therefrom, and magnetic pole teeth 10a, 10b, 10c and 10d are formed on the 
upper surfaces of the coil cores 12a either by etching or by machining. 
The permanent magnet 13 is provided with N and S poles on its side 
surfaces adjoining the different yokes 12. 
The magnetic pole teeth 10a through 10d are formed as ridges and grooves of 
rectangular cross-section which alternate at a fixed pitch P in the same 
way as in the previously described embodiments. The four coil cores 12a or 
the magnetic pole teeth 10a through 10d are provided with drive coils 5a, 
5b, 5c and 5c wound around spools 4 fitted thereon. 
To the lower surface of the base 11 is secured a pre-pressure spring frame 
2 which is substantially conformal (annular frame) to the base 11 and is 
provided with various tab pieces along its periphery. The pre-pressure 
spring frame 2 serves both as a motor mount and a member for preventing 
the armature from coming off. Specifically, tabs 2b at its front and rear 
ends and the tabs 2d at its side ends constrain the horizontal movement of 
the armature 1 (play control), and mounting holes 2c permit it to be 
mounted on a main frame (such as a floppy disk drive). Pre-pressure 
springs 2a formed as curved tabs urge a pre-pressure guide 7b (which is 
described hereinafter) inwardly. To the lower surface of the pre-pressure 
spring frame 2 is fixedly secured a circuit board 14 for the drive coils 
5a through 5d. The circuit board 14 is also provided with a rectangular 
annular shape in the same way as the base 11. To the upper surface of the 
pre-pressure spring frame 2 are fixedly secured a sensor 25 for detecting 
the reference position of the motor and a circuit board 26 for this 
sensor. 
To one side of the base 11 is fixedly secured a travel reference guide 7a 
by screws or with a bonding agent. The inner side surface of this guide 7a 
defines an exact right angle with respect to the direction in which the 
rectangular ridges (grooves) of the magnetic pole teeth 10a through 10d 
extend. On the other side of the base 11 is disposed a pre-pressure guide 
7b in a slightly laterally moveable manner. The pre-pressure springs 2a 
provided as tabs extending from the peripheral edges of the pre-pressure 
spring frame 2 urge the pre-pressure guide 7b inwardly. 
A travel support mechanism 6 for the armature 1 is provided between the 
guide 7a and the pre-pressure guide 7b, and this mechanism comprises a 
retainer 6a. This retainer 6a is rectangular in shape and is provided with 
vertical portions on either side end thereof, as well as a rectangular 
central opening conformal to the base 11. The side fringes and the 
vertical portions of the retainer 6a are provided with a plurality of 
small openings for rotatably receiving roller pins 6b therein. 
The armature 1 consists of a planar magnetic member, and its lower surface 
is provided with two rows of magnetic pole teeth 1a and 1b. The magnetic 
pole teeth 1a and 1b also consist of a plurality of alternating ridges and 
grooves of rectangular cross-section, and their pitch and phase 
relationship are the same as those of the magnetic pole teeth 10a through 
10d. The magnetic pole teeth 1a and 1b are provided with a relative phase 
shift of P/4. A light shield 17 is attached to the upper surface of the 
armature 1 to detect the position of the armature 1 by shielding light 
from the sensor 25 for detecting the reference position of the motor. This 
armature 1 is received in the retainer 6a, and is supported by the roller 
pins 6b in a freely slidable manner. The vertical roller pins 6b contact 
the side surfaces of the armature 1 and the guides 7a and 7b, while the 
horizontal roller pins 6b are interposed between the lower surface of the 
armature 1 and the upper surface of the base 11 and are in contact with 
them. The magnetic pole teeth 1a of the armature 1 oppose the magnetic 
pole teeth 10a and 10b, and the magnetic pole teeth 1b oppose the magnetic 
pole teeth 10c and 10d, defining a certain gap therebetween in each case. 
The lock member 3 consists of an elongated rectangular block member made of 
magnetic material, and is provided with a pair of leg portions 3a 
extending from the lower surface thereof at either side end thereof. The 
spacing between the two leg portions 3a is selected so as to cause them to 
straddle the permanent magnet 13. The upper surface of the lock member 3 
is integrally attached, at its upper surface, to the lower surface of a 
central part of a strip of sheet spring 16. This sheet spring 16 is 
fixedly secured to the central parts of the longitudinal ends of the 
armature 1 by such fixing means as screws. As described hereinafter, the 
lock member 3 is attracted to the permanent magnet 13 against the elastic 
force of the sheet spring 16, and its leg portions 3a abuts the yoke 12 on 
either side of the permanent magnet 13. 
This planar linear pulse motor described above operates as a motor in the 
same way as the previously described embodiments. 
When electric current is supplied to none of the drive coils, the stator 1 
reaches a stable position and is retained at this position by the 
attractive force acting between the magnetic pole teeth 1a, 1b and 10a 
through 10d and produced by the permanent magnet 13. The force acting on 
the armature is the cogging force. 
Now the locking action of the lock member 3 is described. FIG. 23 shows the 
state in which the armature 1 is locked up, and FIG. 24 shows the state in 
which the armature 1 is permitted to move as described above. These 
drawings are enlarged views of a part of FIG. 21, but are given as views 
of a different cross-section from that of FIG. 21. In other words, for 
convenience of description, the drive coils 5a and 5c are illustrated 
instead of the drive coils 5b and 5d, and the magnetic pole teeth 10a and 
10c are illustrated instead of the magnetic pole teeth 10c and 10d. 
Referring to FIG. 23, when electric current is supplied to none of the 
drive coils 5a through 5d, the biasing magnetic flux .PHI..sub.B of the 
permanent magnet 13 forms a closed loop passing through the yoke 12, the 
magnetic pole teeth 10a and 10b, the magnetic pole teeth 1a, the armature 
1, the magnetic pole teeth 1b, the magnetic pole teeth 10c and finally 
back to 10d, and the yoke 12. This produces magnetic poles in the magnetic 
pole teeth and hence the cogging force. A leak magnetic flux .PHI..sub.BL 
of the biasing magnetic flux .PHI..sub.B passes through the lock member 3, 
and attracts the lock member 3 toward the parts of the yokes 12 located on 
either side of the permanent magnet 13 against the restoring force of the 
sheet spring 16. As there is no electric current involved, the armature 
may be fixedly engaged without consuming any electric power. 
Now is described how the armature 1 is moved with reference to FIG. 24. 
When electric current is supplied to the drive coil 5a to produce a 
magnetic flux .PHI..sub.C directed in the same direction as the biasing 
magnetic flux .PHI..sub.B in the main magnetic circuit of the motor, this 
magnetic flux passes through the magnetic pole teeth 10a, the magnetic 
pole teeth 1a, the armature 1, the magnetic pole teeth 1b, the magnetic 
pole teeth 10c, the yoke 12, the lock member 3, and the yoke 12. Since 
this magnetic flux in the lock member 3 is opposite in direction to the 
leak magnetic flux .PHI..sub.BL produced from the permanent magnet 13, the 
attractive force acting on the lock member 3 is sufficiently weakened for 
the lock member 3 to be moved away from the yokes 12 under the restoring 
force of the sheet spring 16, and the locking action is removed. The 
movement of the armature by P/4 by supplying electric current to the drive 
coil 5a occurs in the same way as described above. 
This action takes place in the same way also when electric current is 
supplied to the drive coils 5b, 5c and 5d. 
Thus, according to the planar linear pulse motor of the present invention, 
the stator is securely engaged when no electric current is supplied to the 
drive coils by means of a lock member provided in the armature which is 
attracted to a permanent magnet by its biasing magnetic flux. Therefore, 
the armature can be locked up without consuming any electric power. 
Further, by attaching the lock member to the armature by way of an elastic 
member whose two ends are fixedly secured to the armature, not only the 
vertical dimension required for the elastic member can be reduced but also 
the mechanical strength and the security of engagement can be ensured, 
thereby offering a planar linear pulse motor which is compact and highly 
reliable. 
Although the present invention has been shown and described with respect to 
detailed embodiments, it should be understood by those skilled in the art 
that various changes and omission in form and detail may be made therein 
without departing from the spirit or scope of this invention.