JP3124897B2 - Magnetic screw - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic screw used for machine tools and other various devices.

[0002]

2. Description of the Related Art For example, feeders for machine tools and other various precision instruments include those using a sliding screw or a ball screw and those using a magnetic screw. A feed device using a sliding screw or a ball screw is disclosed in Japanese Utility Model Publication No. 58-40.
No. 377, Japanese Utility Model Publication No. Sho 30-30511, etc., a screw shaft and a nut are provided, and a screw contact is made between the screw shaft and the nut by sliding contact of a screw raceway surface or rolling contact by a ball. It adopts a structure that converts the rotation of the shaft into the linear movement of the nut.

[0003] A feeding device using a magnetic screw is disclosed in JP-A-49-101771, JP-A-54-15695.
As disclosed in Japanese Patent Application Laid-Open No. 9-205, etc., a screw shaft and a cylindrical body fitted with a gap around the outer periphery of the screw shaft are made of a magnetic material, and at least one of the screw shaft and the cylindrical body has a spiral. A magnetic pole is provided, and the rotary motion of the screw shaft is converted into a linear motion of the cylindrical body by the magnetic force of the magnetic pole.

[0004]

In any of the conventional feeders using a sliding screw or the like, a screw shaft, a nut or the like makes metal contact, and one of the motions is transmitted to the other via the metal contact. However, there are the following problems. That is, since a feed device using a sliding screw or the like always has frictional resistance due to metal contact of the screw raceway surface, it is necessary to cover the screw raceway surface with a wear-resistant material and lubricate it with a solid lubricant, grease or lubricating oil. There is.

Moreover, even if such measures are taken, there is a natural limit in reducing the frictional resistance, and the heat generated by the frictional resistance causes the screw shaft to expand linearly, and the mechanical accuracy is reduced. There is a problem that leads to a decrease in the target accuracy, a decrease in the durability, and the like. Furthermore, there are drawbacks of causing environmental pollution due to use of a lubricant, grease, etc., environmental pollution due to abrasion powder generated due to abrasion of the metal contact portion, and noise problem generated due to vibration of the metal contact portion. .

[0006] The feeder using a magnetic screw converts the rotational movement of the screw shaft into a linear movement of the cylinder by the magnetic force of the magnetic pole, and there is no need to directly contact the screw shaft with the cylinder. It can be used without lubrication, and can prevent environmental pollution and noise due to wear, improve durability, etc., and have the advantage of completely eliminating the problems of the feeder using a sliding screw or ball screw. .

On the other hand, in this type of magnetic screw, the magnetic force generated by the magnetic pole between the screw shaft and the cylinder, particularly the attraction force, is used, so that the screw shaft and the cylinder are always concentrically held. Then, it is necessary to ensure a predetermined minute gap over the entire circumference so that they do not directly contact each other, even if it is local,
If the two come into contact with each other and become in a suction state, the cylinder may not move even if the screw shaft is rotated.

However, the conventional magnetic screw merely covers the cylinder with a gap around the outer periphery of the screw shaft.
Since the magnetic screw unit itself does not have a means for holding the screw shaft and the cylinder concentrically with a predetermined gap therebetween, when mounting this magnetic screw on a machine tool or other device, the screw shaft and the cylinder must be connected to the device side. It must be assembled so that a predetermined minute gap can be secured with the cylinder, and extremely high processing accuracy and assembly accuracy are required on the device side. In addition, even if the accuracy on the equipment side is increased, it is very difficult to manufacture in consideration of all of these, because there are variations in shape and poor accuracy on the magnetic screw side such as the screw shaft and cylindrical body in reality. is there.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, the present invention can reliably hold a shaft and a cylinder in a non-contact state with a simple structure, and can make the gap between the shaft and the cylinder a minute gap. It is an object of the present invention to provide a magnetic screw capable of smoothly and reliably converting one rotational or linear motion into the other linear or rotational motion by an action.

[0010]

According to the first aspect of the present invention, there is provided a screw comprising a magnetic material and having a thread formed on an outer periphery.
A shaft, at a gap and the outer periphery of the screw shaft made of a magnetic material and a fitted around in-cylinder body, the inner circumferential surface of the cylindrical body thereof
The cylindrical body has the same diameter over the entire length in the axial direction.
Helical magnetic poles corresponding to the threads are magnetized on the inner peripheral surface of
And, on both sides in the axial direction of the cylinder, the screw shaft held substantially concentrically relative to the tubular member provided slidably guided guide ring, at least one of said guide ring, before
A protrusion for preventing loss of synchronization that slidably fits into the thread groove of the threaded shaft.
It is provided with an origin .

According to a second aspect of the present invention, in the first aspect, a material having wear resistance and slipperiness is used for each of the guide rings.

According to a third aspect of the present invention, in accordance with the first or second aspect of the present invention, there are provided two threads on the outer periphery of the screw shaft.
A thread is provided, and one of the two threads has an N pole, and the other has a thread.
At the inner peripheral side of the cylindrical body, the S poles correspond to the
An N pole and an S pole are provided.

[0013]

According to the present invention, the screw shaft and the cylinder are held concentrically by the guide rings on both sides of the cylinder, and both are kept in a non-contact state with a minute gap. In operation, the screw shaft is slidably guided by the respective guide rings in a state where they are kept in a non-contact state with a minute gap. Guide in thread groove
Slide out the step-out prevention projection provided on at least one of the rings.
Movably fits the screw shaft and cylinder
Prevent step-out. The inner peripheral surface of the cylindrical body is configured to be smooth,
Since the inner peripheral surface of the body is magnetized according to the thread,
Simple structure, easy to manufacture, magnetic powder for screw shaft
Can also be prevented from adhering.

According to the second aspect of the present invention, a material having wear resistance and slipperiness is used for each guide ring.
This ensures the durability of the guide ring and the slidability of the screw shaft, and suppresses or prevents the entry of dust and the like into the cylinder.

According to the third aspect of the present invention, the outside of the screw shaft is provided.
Two threads on the circumference and N pole on the inner circumference of the cylinder
And S pole respectively correspond, and the magnetic circuit between them
Be composed. For this reason, the magnetic force of each magnetic pole on the cylinder
Effectively works on the side thread.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings. 1 and 2 illustrate a first embodiment of a magnetic screw according to the present invention. As shown in FIG. 1, the magnetic screw includes a screw shaft 1, a cylinder 2 fitted around the outer periphery of the screw shaft 1, and a pair of guides provided on both sides of the cylinder 2 in the axial direction. Rings 3 and 4, cylinder 2 and guide rings 3 and 4
And a housing 5 for holding the

The housing 5 is formed in a cylindrical shape from a stainless material or the like, and a flange 6 for mounting is integrally formed on the outer periphery of one end side in the axial direction of the housing 5. Inside the housing 5, a cylindrical fitting recess 7 is formed at the center in the axial direction, and a female screw hole 8 is formed at one end of the cylindrical fitting recess 7 and a partition wall 9 is formed at the other end. The guide fitting concave portions 10 are respectively formed through the guide holes.

The cylindrical body 2 is fitted in the cylindrical body fitting recess 7, and the cylindrical body 2 is fixed by a partition 11 and a nut 11 which is detachably screwed into the female screw hole 8. Nut 11 has cylindrical body 2
On the side, a guide fitting recess 13 is formed so as to form a partition 12 corresponding to the partition 9. Each of the guide rings 3 and 4 is fitted concentrically with the cylindrical body 2 in each of the guide fitting recesses 13 and 10 of the nut 11 and the housing 5, and a plurality of screws 14 and 1 are arranged in the circumferential direction.
5, it is detachably fixed to the partition walls 12, 9 from the outside in the axial direction.

The screw shaft 1 is made of a magnetic material such as an iron-based metal material or a manganese-aluminum magnetic material containing manganese, aluminum, carbon or the like as a main component. Are formed in a spiral shape. The threads 16, 17 have a rectangular cross section.

The cylindrical body 2 is made of a magnetic material such as an iron-based metal material or a rare-earth magnetic material, and has a cylindrical shape. The inner peripheral surface of the cylindrical body 2 has the same diameter over its entire length in the axial direction. Is formed. As shown in FIG. 2, each of the magnetic poles 1 of the N pole 18 and the S pole 19 is disposed on the inner periphery of the cylindrical body 2 in the axial direction.
8,19 are helically magnetized so that they can be alternated at regular intervals. Each N-pole 18 and S-pole 19 is a screw thread of the screw shaft 1.
In order to correspond to the threads 16 and 17, respectively, they are provided spirally and continuously at the same lead angle and the same pitch as the threads 16 and 17.

The cylinder 2 is fitted around the outer periphery of the screw shaft 1 and has a small gap between the magnetic poles 18 and 19 on the inner periphery and the threads 16 and 17 on the outer periphery of the screw shaft 1. The body 2 is held concentrically with the screw shaft 1 in a non-contact state by guide rings 3 and 4 on both sides of the body 2. Therefore, the cylinder 2 and the screw shaft 1 are relatively movable in the axial direction and the circumferential direction.

The N pole 18 of the cylinder 2 is attached to the thread 16 of the screw shaft 1,
The S pole 19 corresponds to the thread 17 of the screw shaft 1, and between the screw shaft 1 side and the cylindrical body 2 side, the cylindrical body of the spiral magnetic poles 18, 19 extends over the entire range. 2 N pole 18 to thread of screw shaft 1
A magnetic circuit in the form of a closed loop is formed following the thread 17 and the S pole 19 of the cylinder 2 via the thread 17, and the N pole 18 and the S pole 19 of the cylinder 2 are respectively formed.
The screw shaft 1 is attracted to the outside around the entire circumference due to the magnetic force of.

Each of the guide rings 3 and 4 is made of a non-magnetic material such as a synthetic resin material having abrasion resistance and slipperiness such as MC nylon or Delrin.
The screw shaft 1 is slidably inserted in 3, 4 in the axial direction and the circumferential direction. When the magnetic screw is incorporated in a feeder of a machine tool, for example, the screw shaft 1 is connected to a drive source such as a motor, and the flange 6 of the housing 5 is fixed to a slide table or the like.

The screw shaft is driven by a driving source such as a motor.
When 1 is rotated in the forward or reverse direction around the axis, the cylinder
The magnetic force between the N pole 18 and S pole 19 on the 2 side is
7, the cylinder 2 moves in the axial direction with the rotation of the screw shaft 1 due to the magnetic force, and the slide table can be moved in the axial direction. At this time, each of the guide rings 3 and 4 slides on the outer periphery of the screw shaft 1 so that the screw shaft 1 and the cylinder 2
The cylindrical body 2 is guided in the axial direction along the screw shaft 1 while keeping the contact and the small gap in a non-contact state.

That is, the spiral N-pole 18 and S-pole 19 on the cylinder 2 side
The magnetic force of the screw shaft 1
This acts on the top surfaces of the cylinders 16 and 17 from the outside via a minute gap, and an attractive force acts between the magnetic poles 18 and 19 on the cylinder 2 side and the threads 16 and 17 of the screw shaft 1. The screw shaft 1 is constrained in the axial direction by the action.

Then, the screw shaft 1 is rotated so that the screw threads 16, 17
Is rotated in the circumferential direction, the magnetic poles 18, 19 on the cylinder 2 side corresponding to the threads 16, 17 try to follow the rotation,
It moves in the axial direction according to the lead angle of the threads 16,17.
For this reason, there is a small gap between the screw shaft 1 side and the cylinder 2 side.
The rotational motion of screw shaft 1 is applied to the cylinder 2
Can be converted to linear motion.

The magnetic screw has the following advantages. In this magnetic screw, the screw shaft 1 and the cylindrical body 2 are kept in a non-contact state, and there is no mechanical contact between the two, so that all the problems caused by the conventional frictional resistance can be solved. That is, since the screw shaft 1 and the cylindrical body 2 are held in a non-contact state and the magnetic force of the magnetic poles 18 and 19 on the inner peripheral side of the cylindrical body 2 is used, the conventional mechanical mechanism using friction is used. It can be used semi-permanently in a high-accuracy state without a decrease in target accuracy, durability, etc.

Since the screw shaft 1 and the cylinder 2 are not in contact with each other, there is essentially no need for lubrication, and long-term use without lubrication is possible. There is an advantage that all noise problems due to environmental pollution and vibration can be prevented. Therefore, it is very effective for use in places where a lubricant, abrasion powder and the like are disliked.

Further, in holding the screw shaft 1 and the cylinder 2 in a non-contact state, guide rings 3 and 4 are provided on both sides of the cylinder 2.
The guide rings 3 and 4 are used to
The screw shaft 1 and the cylinder 2 can be reliably prevented from coming into contact with each other because they are concentrically held and guided slidably. Can be held.

The cylindrical body 2 and each of the guide rings 3 and 4 are fitted in a housing 5, and each of the guide rings 3 and 4 is screwed with a screw shaft.
Since 1 and the cylindrical body 2 are concentrically held with a minute gap, the whole magnetic screw can be handled as one unit, and handling when incorporated in a feeder or the like is very easy.

In particular, when the magnetic screw is incorporated into a machine tool or the like, there is no need to maintain the screw shaft 1 and the cylindrical body 2 concentrically to secure a minute gap on the machine side. It is not necessary to pay attention to the gap between the screw shaft 1 and the cylinder 2, and it is sufficient to install it so that the magnetic screw side will not be twisted. The mechanism is simplified and the precision is not particularly required.

Further, the screw shaft 1 and the cylindrical body are
2 is kept out of contact with the screw shaft 1
It is possible to make the gap between the cylinder body 2 and the cylinder 2 a minimum minute gap. Therefore, each magnetic pole 18, 19 of the cylinder 2 and the screw shaft
The magnetic action between the thread 16 and the first thread 16 and 17 is increased, and the torque transmitted from the screw shaft 1 to the cylinder 2 can be increased.

Moreover, since the screw shaft 1 and the cylindrical body 2 can be securely held in a non-contact state by the guide rings 3, 4, the screw shaft 1
The threads 16, 17 of the cylinder 2 do not directly contact the magnetic poles 18, 19 of the cylinder 2, and the cylinder 2 can be reliably moved in the axial direction in conjunction with the rotation of the screw shaft 1. Is in contact with the cylinder
There is no such thing as 2 becoming immobile.

Each of the guide rings 3 and 4 holds the screw shaft 1 and guides it slidably. The screw threads 16 and 17 of the screw shaft 1 are spirally continuous and the guide rings 3 and 4 are made of MC nylon. Since it is made of a non-magnetic material such as a synthetic resin material having abrasion resistance and slipperiness such as Delrin, each guide ring 3,
4, the screw shaft 1 can be smoothly guided, and the durability of the guide rings 3, 4 can be sufficiently ensured. Also, since each guide ring 3, 4 is made of a non-magnetic material such as a synthetic resin material, the guide rings 3, 4
The magnetic flux does not pass through the side and the guide rings 3 and 4 can also prevent dust such as iron powder from entering the cylinder 2 side.

Since the guide rings 3 and 4 are fitted in the guide fitting recesses 13 and 10 of the housing 5 and are removably fixed by the screws 14 and 15, when the inner peripheral side is worn due to long-term use, , Can be easily replaced by removing screws 14,15. Since the inner periphery of the cylinder 2 is formed in a smooth shape, and the inner periphery is magnetized to provide the N-pole 18 and the S-pole 19 in a spiral shape, the respective magnetic poles 18, 19 are provided on the cylinder 2 side. Nevertheless, the structure is simple and easy to manufacture.

The magnetic poles 18 and 19 are provided on the cylinder 2 side, and the screw shaft 1 is made of a magnetic material. The outer periphery of the screw shaft 1 is the same as the spiral magnetic poles 18 and 19 on the cylinder 2 side. Since the threads 16 and 17 are formed spirally at the same lead angle and pitch, machining of the screw shaft 1 side can be facilitated, and at the same time, other magnetic powder etc. adheres to the surface of the screw shaft 1 from the outside Not even.

Moreover, since the magnetic poles 18 and 19 are located on the inner periphery of the cylinder 2, no other magnetic powder or the like is directly attached to the magnetic poles 18 and 19 from the outside. Most of the magnetic flux of 19 passes through the internal screw shaft 1 side, so despite the use of the magnetic force of the magnetic poles 18 and 19, there is almost no leakage magnetic flux leaking from each of the magnetic poles 18 and 19 to the outside. Problems caused by the leakage magnetic flux can be less likely to occur.

Further, since the magnetic poles 18 and 19 are provided on the cylinder 2 side, regardless of the stroke when the cylinder 2 linearly moves, the magnetic pole 1
The range of the axial direction where 8,19
The range can be made smaller than when the magnetic poles 18 and 19 are provided on the side.

FIGS. 3 and 4 illustrate a second embodiment of the magnetic screw according to the present invention, in which protrusions 20 for preventing loss of synchronism are spirally provided on the inner periphery of each of the guide rings 3 and 4. . The screw shaft 1 has a semi-circular thread groove (spiral groove) between its threads 16,17.
A projection 20 is formed integrally on the inner periphery of the guide rings 3 and 4 so as to slide in the screw groove 22.
The protrusion 20 is formed to be spirally long along the spiral direction of the screw groove 22.

As shown in FIG. 4A, the projections 20 correspond to the two thread grooves 22 on the screw shaft 1 side, respectively.
A threaded shaft may be provided, as shown in FIG.
One thread may be provided corresponding to one of the two thread grooves 22 on one side. In this embodiment, the projections 20 for preventing loss of synchronism are provided on each of the guide rings 3 and 4 in a helical manner. Therefore, even when an excessive load is temporarily applied in the thrust direction, the projections 20 allow the screw shaft to be rotated. The step-out phenomenon between 1 and the cylinder 2 can be prevented. Therefore, the screw shafts 16 and 17 of the screw shaft 1 and the magnetic poles 18 and 19 of the cylindrical body 2 always correspond to the screw shafts.
It is possible to transmit the torque from 1 to the cylinder 2 smoothly and reliably.

Moreover, since the projections 20 are spiral, damage to the projections 20 can be prevented as much as possible, and the durability is improved. The projection 20 is spiral, but the guide ring
When 3, 4 are made of synthetic resin, they can be easily and integrally molded at the time of molding. In the second embodiment, the projections 20 are provided on each of the guide rings 3, 4, but may be provided on either one of the guide rings 3, 4.

FIG. 5 illustrates a third embodiment of a magnetic screw according to the present invention, in which a protrusion 20 for preventing loss of synchronism is constituted by a pin. That is, the projection 20 is formed of a pin having a spherical tip, and after the guide ring 4 is fitted into the guide fitting recess 10 of the housing 5, the projection 20 is inserted into the guide ring 4 from outside the housing 5. Then, the spherical portion at the tip is fitted into the screw groove 22.

The projection 20 for preventing step-out is thus provided with the pin 31
May be used. In this case, the protrusion 20 and the screw groove
Since the contact area with the pin 22 can be reduced, the increase in frictional resistance due to the projection 20 can be prevented, and the pin 31
Since it penetrates through the guide ring 4, the guide ring 4 can be fixed by the pin 31 , and the screws 14 and 15 of the first embodiment can be omitted.

FIG . 6 illustrates a fourth embodiment of the present invention . Figure
6 (A), a trapezoidal thread 16 and a thread 17 corresponding to the N pole 18 and the S pole 19 of the cylindrical body 2 are respectively formed on the outer periphery of the screw shaft 1 side. A V-shaped screw groove 22 is provided between them. Figure 6 (B) on the outer periphery of the screw shaft 1 side, respectively corresponding trapezoidal threads N pole 18 and S pole 19 of the cylindrical body 2
A V-shaped inverted trapezoidal thread groove 22 is formed between the threads 16 and 17 by forming a thread 16 and a thread 17 respectively.

In these cases, the same effects as in the above embodiments can be obtained. Moreover, thread 1 of screw shaft 1
6, 17 are trapezoidal, and the wide top surface is cylindrical
Corresponding to the north pole 18 and the south pole 19 on the side, the magnetic flux of the north pole 18 and the south pole 19 passes perpendicularly to the top surface of the thread 16, and
A sufficient magnetic coupling state can be obtained. Further, since the threads 16 and 17 have a trapezoidal shape or a shape close thereto, and the guide rings 3 and 4 at both ends of the cylindrical body 2 slide on the top surface, the guide rings 3 and 4 have a cross section that is rectangular compared to the case where the cross section is square. , Ru can be less damage to the inner circumferential surface of 4.

[0046] have been described in detail for each example, the present invention is not limited to the embodiments. For example, a protective cylinder made of a non-magnetic material or a weak magnetic material may be used, and a small-diameter cylinder 2 made of a ferromagnetic material may be fitted around the inner periphery of the protective cylinder and magnetized . Further in each example, along with the movement of rotation, such as the screw shaft 1 has been described to be converted to linear movement of the cylindrical body 2, provided movably screw shaft 1 and the like in the axial direction, the cylindrical body 2 If it is rotatably provided, it is possible to convert the rotational movement of the cylinder 2 into a linear movement of the screw shaft 1 or the like. Also by increasing the lead angle, the screw shaft 1 or the cylindrical body 2
Can be converted into a rotational motion of the cylinder 2 or the screw shaft 1.

[0047]

According to the present invention, according to the present invention, a magnetic material is used.
A screw shaft with a thread formed on the circumference, made of a magnetic material, and
A cylindrical body fitted with a gap around the outer periphery of the screw shaft ,
The inner peripheral surface of the cylindrical body has the same diameter over its entire length in the axial direction.
Helical shape corresponding to the thread on the inner peripheral surface of the cylindrical body
Magnetized poles on both sides in the axial direction of the cylinder, provided with a slidably guided to the guide ring to hold substantially concentrically the screw shaft relative to the tubular member, at least one of the guide ring
To prevent loss of synchronism, which is slidably fitted into the thread groove of the screw shaft.
Since the projections are provided , the screw shaft and the cylinder can be securely held in a non-contact state with a simple structure, and the gap between the screw shaft and the cylinder can be made a small gap. Rotation or linear motion can be smoothly and reliably converted to the other linear or rotary motion, and assembly to other devices or the like can be easily performed.

The inner peripheral surface of the cylindrical body extends over its entire length in the axial direction.
The cylindrical body is formed in a smooth shape with the same diameter.
Helical magnetic poles corresponding to
It is simple, easy to manufacture, and has a magnetic
Adhesion of powdery substances can also be prevented. And at least one guy
Step out to fit slidably into the thread groove of the screw shaft to the dring
The projection for prevention prevents the screw shaft from being overloaded.
There is no loss of synchronism with the cylinder, ensuring smooth and reliable operation
be able to.

According to the second aspect of the present invention, in the first aspect of the present invention, since each guide ring is made of a material having wear resistance and slipperiness, the durability of the guide ring and the shaft Slidability can be ensured, and the entry of dust and the like into the cylinder can be suppressed or prevented.

According to the third aspect of the present invention, a screw shaft
The outer periphery of is provided with two threads, one of the two threads
The cylinder is arranged so that the north pole corresponds to the other thread and the south pole respectively.
Since the N pole and the S pole are provided on the inner peripheral side of the body,
The magnetic force of each magnetic pole effectively acts on the thread on the screw shaft side
With a simple structure to reduce leakage flux and provide sufficient torque
Can be secured.

[Brief description of the drawings]

FIG. 1 is a partially cutaway front view showing a first embodiment of a magnetic screw according to the present invention.

FIG. 2 is an enlarged sectional view of a main part of FIG.

FIG. 3 is a partially cutaway front view showing a second embodiment of the magnetic screw according to the present invention.

FIG. 4 is a sectional view showing a second embodiment of the magnetic screw according to the present invention.

FIG. 5 is an enlarged sectional view of a guide ring showing a third embodiment of the magnetic screw according to the present invention.

FIG. 6 is an enlarged sectional view of a main part showing a fourth embodiment of the magnetic screw according to the present invention.

[Explanation of symbols]

 1 Screw shaft 2 Cylindrical body 3,4 Guide ring 5 Housing 9,12 Bulkhead section 10,13 Guide fitting recess 16,17 Thread 18 N pole 19 S pole 20 Protrusion 22 Screw groove

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F16H 25/20-25/24

Claims (3)

(57) [Claims] 1. A magnetic material and a thread formed on an outer periphery.
A screw shaft, and a cylindrical body made of a magnetic material and fitted over the outer periphery of the screw shaft with a gap therebetween , wherein
The peripheral surface has the same diameter and smooth shape over its entire length in the axial direction.
And a helical magnet corresponding to the thread on the inner peripheral surface of the cylindrical body.
Magnetized poles, on both sides in the axial direction of the cylinder, provided with a slidably guided to the guide ring to hold substantially concentrically with the screw shaft relative to the tubular member, at least one of the guide Rin
Step-out prevention fitting slidably into the screw groove of the screw shaft
A magnetic screw having a stop projection . 2. The magnetic screw according to claim 1, wherein a material having wear resistance and slipperiness is used for each of the guide rings. 3. A thread having two threads on an outer periphery of said screw shaft.
One of the two threads has an N pole and the other has an S pole.
The N pole and the S pole are provided on the inner peripheral side of the cylinder so that the poles correspond to each other.
The magnetic screw according to claim 1, further comprising a pole .