JPH03280405A - Electromagnet and knitting machine using same - Google Patents

Abstract

PURPOSE:To make it possible to obtain the required strength only when it is required by a method wherein a first magnetic circuit is composed of a semi-hardened magnetic member, equipped with an excitation coil, a magnet and a magnetic material to be attracted, a second magnetic circuit is composed of the above-mentioned magnet and a soft magnetical material, an excitation coil is excited by the magnet for a short period in the same direction as the magnetic field, and the attraction force of the material to be attracted is controlled through switching of forces between strong/weak. CONSTITUTION:A first magnetic circuit A is composed of semi-hardened magnetic bodies 2 and 3, equipped with excitation coils 5 and 6, and a magnet 1 in such a manner that a magnetic body 4 to be attracted will be attracted, and another second magnetic circuit B is composed of a magnet 1 and a soft magnetic soft material 7. In this magnet 1, its magnetic force can be maintained either in strong and weak states even when a current is interrupted. In this knitting machine, a device, with which the mechanism such as stitch cams 22b and 22d, a cam 25 and the like are switched according to the progressing direction of a carriage 21, is constituted by the above-mentioned electromagnet 41, the attraction force of the electromagnet is intensified only when the carriage 21 is inverted, and the attraction force is weakened when the electromagnet is travelling performing a knitting operation, thereby enabling the electromagnet to travel smoothly.

Description

[Detailed description of the invention] [　Industrial application field　]

TECHNICAL FIELD The present invention relates to an electromagnet that can increase or decrease attraction force with less electric power by combining with a permanent magnet.

[Conventional technology]

In the past, there were electromagnets that were configured in combination with magnets. This was configured to weakly control the magnetic force by exciting an electromagnet in a direction that canceled out the magnetic field of the magnet. In addition, the means for switching mechanisms such as the threads of conventional knitting machines is constituted by a magnet, and when the direction of movement of the carry/strip is reversed, the magnet is moved by the attractive force between the sliding bar and the magnet. A force is generated that tries to hold it back. This force is configured to switch the mechanism from the outbound trip state to the return trip state to prepare for the return trip formation.

[Problem to be solved by the invention]

However, with conventional electromagnets combined with the magnets described above, in order to keep the magnetic force weak, it is necessary to continuously supply current to the electromagnet to excite it, which poses a problem in that it consumes a large amount of energy. In the switching means of the knitting machine using magnets as described above, even when the carriage is running on the sliding bar after reversing and not knitting, there is a strong attraction force between the magnet and the sliding bar. This not only creates a load for carriage travel and requires wasted driving energy, but also
Because the carriage travels while being strongly pressed against the sliding groove due to the above-mentioned attractive force, a problem arises in that the sliding contact portion is likely to wear out. In order to solve this problem, it may be possible to use electromagnets instead of the magnets mentioned above.With conventional electromagnets, it is necessary to make them large to obtain sufficient adsorption force, so It was inappropriate to attach it to the carriage. Even if the magnet is attached, a large amount of power must be continuously supplied during the excitation time, resulting in a problem of increased heat generation. In particular, the smaller the electromagnet is, the worse the heat dissipation effect becomes, so it has been inappropriate to use an ordinary electromagnet as a means for switching the carriage. Therefore, the present invention was made with the aim of solving these various problems and realizing an electromagnet that can obtain the necessary magnetic force only when necessary.

[Means to solve the problem]

In the electromagnet according to the present invention, the semi-hard magnetic member provided with the excitation coil, the magnet, and the attracted magnetic body constitute a first magnetic circuit, and the magnet and the soft magnetic member constitute the first magnetic circuit. configuring a second magnetic circuit different from the magnetic circuit,
By providing an excitation coil driving means that excites the excitation coil for a short time in the same direction or in the opposite direction to the direction of the magnetic field generated by the magnet, the attraction force of the attracted magnetic body in the first magnetic circuit is controlled by switching the strength or weakness. We took measures to configure it as follows. In the knitting machine according to the present invention, when the direction of movement of the carriage traveling along the sliding bar made of magnetic material is reversed at both ends of the knitting width, the switching means switches the knitting mechanism such as the stitches and cams. A knitting machine comprising: a first magnetic circuit comprising a semi-hard magnetic member having an excitation coil, a magnet, and the sliding bar; and a first magnetic circuit comprising the magnet and the soft magnetic member. An electromagnet having a second magnetic circuit different from the first magnetic circuit is disposed on the carriage at a position facing the sliding bar, and a carriage reversal start signal is sent at the reversal position at the end of the knitting width. means for outputting a carriage reversal completion signal at a position slightly inside the reversal position or at a timing slightly delayed from the carriage reversal start signal; excitation coil driving means that excites the excitation coil for a short time in the same direction as the magnetic field generated by the magnet, and excite the excitation coil for a short time in the opposite direction to the magnetic field generated by the magnet in response to the carriage reversal completion signal, When reversing, the magnetic flux density of the first magnetic circuit of the electromagnet is increased only between the carriage reversal start signal and the carriage reversal completion signal, thereby increasing the attraction force between the electromagnet and the sliding bar. Steps were taken to configure the means to operate.

[Effect]

FIGS. 1 and 2 show the action of the electromagnet according to the present invention. This will be explained with reference to FIG. In the electromagnet of the present invention, the semi-hard magnetic bodies 2 and 3 provided with excitation coils 5 and 6 and the magnet 1 constitute a first magnetic circuit A to attract the magnetic body 4 to be attracted, and
A second magnetic circuit B, different from the magnetic circuit described above, was formed by a magnet l and a soft magnetic member 7. That is, in the magnet l, the semi-hard magnetic member 2,
A first magnetic circuit A made up of magnets 3 and a second magnetic circuit B made of magnets 1 and soft magnetic material members 7 are formed in parallel. In the electromagnet 1, when the excitation coils 5 and 6 are not excited, the lines of magnetic force of the magnet 1 mainly pass through the second magnetic circuit B of the soft magnetic member 7, which has a higher magnetic permeability. Only a small amount of leakage magnetic flux passes through the first magnetic circuit A, which is smaller than , and the force (
Fl) is weak. The semi-hard magnetic bodies 2 and 3 are not saturated with this leakage magnetic flux. However, when the excitation coil 5 is energized and excited in the same direction X as the magnetic field Z by the magnet l to provide a magnetic field Hs, the semi-hard magnetic members 2 and 3 forming the first magnetic circuit A become saturated. As the magnetization Ms is obtained, the magnetic permeability increases, the magnetic flux density increases, and the magnetic body 4 to be attracted is strongly attracted. At this time, even if the current to the excitation coil 5 is cut off, residual magnetization Mr remains in the semi-hard magnetic members 2 and 3 due to their residual magnetization characteristics, and the magnetic flux density to the first magnetic circuit remains high. The strong adsorption force (F2) is maintained. Here, the excitation coil 6 is energized to be excited in the direction Y opposite to the direction Z of the magnetic lines of force caused by the magnet l, and the first magnetic circuit A
The coercive magnetic field (-He
) When a reverse magnetic field of more than
The residual magnetization of the magnet becomes less than zero, and this state is maintained even when the current is turned off. Therefore, the second magnetic circuit B has a higher magnetic permeability and a higher magnetic flux density, and the first magnetic circuit A has a lower magnetic flux density, which increases the force (Fl) for attracting the magnetic body 4 to be attracted. becomes weaker. That is, the semi-hard magnetic material member in the present invention is a magnetic material that can obtain residual magnetization. In this way, the magnetic force can be maintained in either the strong or weak state even if the current is turned off by simply applying current to excite in the opposite direction only at the moment when the magnetic force is switched to strong or weak. According to the knitting machine according to the present invention, the means for switching mechanisms such as the stitches and cams depending on the direction of movement of the carriage is constituted by the electromagnet having the above structure. When the excitation coil is energized to excite it in the same direction as the magnetic flux generated by the built-in magnet, the magnetic flux density of the first magnetic circuit A' remains high even if the current supply is stopped. Therefore, the sliding bar as the magnetic body to be attracted is strongly attracted, and a resistance force in a direction opposite to the traveling direction of the carriage acts on the switching means,
Switch the mechanism. When the switching of the mechanism such as the cam is completed, when the excitation coil of this electromagnet is energized in the opposite direction, the magnetic flux density of the first magnetic circuit A' decreases, and the current Even if the supply is stopped, the first magnetic circuit A
The magnetic flux density at ′ is kept low. Therefore, the attraction force against the sliding bar as a magnetic body to be attracted becomes weaker.
The resistance force that tries to prevent the carriage from moving is weakened, and the carriage runs smoothly.

【 Example 】

Embodiments of the electromagnet according to the present invention will be explained in detail below based on the drawings. FIG. 1 is a side sectional view of an embodiment of the electromagnet of the present invention, and FIG. 2 is a timing chart for switching the strength of the electromagnet. In the drawings, 1 is a magnet in which a hard magnetic material is magnetized to form a south pole IA and a north pole IB, 2 is a semi-hard magnetic member whose end 2A is joined to the north pole IB of the magnet 1, and 3 is a semi-hard magnetic member. The end portion 3A is the magnet 1
4 is a magnetic member to be attracted, and 5 and 6 are the semi-hard magnetic members 2 and 3, respectively, which are joined to the S pole IA.
It is an excitation coil wound around. 8 and 9 are switches that connect the excitation coils 5 and 6 to the DC power supply 10 for a short time; when the switch 8 is turned on, a downward magnetic field X is generated in the excitation coil 5, and when the switch 9 is turned on, the excitation is coil 6
It is configured to generate a downward magnetic field Y. 7 has both ends 2A and 3A of the semi-hard magnetic member 2.3.
It is a soft magnetic material member joined to. In this case, the magnet 1 is 3.5 mm x 11.9
The semi-hard magnetic members 2 and 3 are made of carbon steel (S450) with a thickness of 44mm, and the excitation coils 5 and 6 are made of Diameter 0
．． 18" 9 turns 550 times, length 11mm, resistance value 15
A coil of Ω was used, and a 3 mm thick electromagnetic soft iron (SUYP) was used as the soft magnetic member 7. Magnet 1 mentioned above. Semi-hard magnetic member 2. Adsorbed magnetic material 4
．． The first magnetic circuit A is composed of the semi-hard magnetic member 3, and includes the magnet l, the end portion 2A of the semi-hard magnetic member 2, and the soft magnetic member 7.
．． The end portion 3A of the semi-hard magnetic member 3 constitutes a second magnetic circuit B. In the electromagnet 11 having the above configuration, in the initial state,
The magnetic flux generated by the magnet 1 mainly flows toward the second magnetic circuit B made of a softer magnetic material, and the magnetic flux density of the semi-hard magnetic members 2 and 3 constituting the first magnetic circuit A increases. is only the leakage flux from the magnet 1, so it is low. Therefore, the force for attracting the magnetic body 4 to be attracted is weak (Fl). Therefore, when the switch 8 is turned on, the excitation coil 5
The downward magnetic field X is generated in the first magnetic circuit A.
A strong clockwise magnetic field is generated. Therefore, the magnetic body 4 to be attracted is attracted with a strong force. Next, when the switch 8 is turned off, the excitation current in the excitation coil 5 disappears, but residual magnetization remains in the semi-hard magnetic members 2 and 3 due to their hysteresis characteristics. A strong clockwise magnetic flux continues to exist. Therefore, the magnetic body 4 to be attracted continues to be attracted with a strong force (F2). That is, in this state, the strong attraction force (F2) continues even though no power is supplied to the excitation coil 5.6. At this time, the measured sliding force was 1.0 kgf. Note that this sliding force is the force required to cause the electromagnet to slide between the attracted member and the electromagnet. Next, when the switch 9 is turned on, the downward magnetic field Y is generated in the excitation coil 6, and a strong magnetic field that exceeds the coercive magnetic field of the semi-hard magnetic material at the half-hour hand is generated in the first magnetic circuit A. However, due to this magnetic field, the residual magnetization of the semi-hard magnetic members 2 and 3 becomes zero or less, and in the first magnetic circuit A, only a slight leakage magnetic flux due to the magnet 1 exists, and the magnetic body to be attracted 4 The force to attract the magnet is weak (Fl).Next, when the switch 9 is turned off, the excitation coil 6 is not excited, and the semi-hard magnetic member of the first magnetic circuit A is 2.3 cannot be given a high residual magnetization, and the first magnetic circuit A remains in a state where only a small amount of leakage magnetic flux exists.Therefore, the force that attracts the magnetic body 4 to be attracted continues to be weak. is maintained (Fl
). At this time, the measured sliding force was 0.3 kgf. Therefore, by switching the attraction force of the electromagnet to strong and weak, the
It was possible to obtain a change in the sliding force of f. It is sufficient that the excitation coil 5.6 is energized for several m5 ec. Note that the material composition of this electromagnet 11 is not limited to that shown in FIG. For example, if the magnet 1 is a single magnet measuring 3.5 mm x 11.9" (845C) reduces the sliding force by 0.4 kg.
If carbon steel (S450) is used as the soft magnetic member 7 and electromagnetic soft iron (SUYP) is used as the semi-hard magnetic members 2 and 3, the sliding force can be changed to 0. I was able to switch between .45kgf and 0.7kgf. Therefore, the soft magnetic member 7 also has the semi-hard magnetic member 2,
3 also used electromagnetic soft iron (SUYP), and the sliding force hardly changed. In order to obtain a change in sliding force of 0.5 kg f or more in this way, it is inconvenient to use electromagnetic soft iron as the semi-hard magnetic members 2 and 3, and it can be said that hard carbon steel of about 345C or more is suitable. In addition, instead of two excitation coils with different winding directions,
- The polarity of the current supplied to the excitation coils may be changed, and the winding method is not limited to the above embodiment, and it goes without saying that, for example, a bifilar or unifier coil may be used. Next, embodiments of the knitting machine according to the present invention will be explained in detail based on the drawings. Fig. 3 is a plan view structural diagram with a part of the carriage of the knitting machine according to the present invention cut away, Fig. 4 is a partially enlarged sectional view of the magnetic attraction member of the carriage, and Fig. 5 is a diagram of the knitting machine. FIG. 6 is a block diagram of the control circuit and a timing chart for changing the suction force of the knitting machine. 3 to 6, a raised crest 24 is fixed to the base plate 23 of the carriage 21, and raised ridges 22a, 22b supported so as to be movable up and down are provided facing the cam surfaces 24a, 24b. Toyama 22a
, 22b is a spring 31a. 31b, it is urged to move diagonally downward along the groove. The rollers 12a and 12b provided on the upper surface of the guide plates 13a and 13b are connected to the guide member 26 of the main plate 23.
a and 26 b are in contact with a cam plate 25 supported so as to be slidable in parallel to the direction of movement of the carriage 21 . The cam plate 25 has a concave portion 32 formed in the center thereof, and the concave portion 3
The rollers 12a, 1 near the inclined surfaces 32a, 32b of 2
I am receiving 2b. Further, step portions 27a and 27b are formed near both ends of the cam plate 25, and when the cam plate 25 moves from side to side, the step portions 27a and 27b move toward the guide member 26a,
26b and prevents further movement of the cam plate 25. A magnetic attraction member 28 is provided on the cam plate 25, felt is fitted and fixed in the recesses provided at both ends of the magnetic attraction member 28, and an electromagnet 4 whose attraction force can be switched between strong and weak is provided in the middle part.
1 was established. As shown in FIG. 4, this magnetic adsorption member 28
2. Soft magnetic member 43, semi-hard magnetic member 44a, 44b
, and an electromagnet 41 composed of excitation coils 45a and 45b. And magnet 42. Semi-hard magnetic member 44a, sliding bar 29°, and semi-hard magnetic member 44b
The magnet 42 and the soft magnetic member 43 constitute a second magnetic circuit B'. When the attraction force of this electromagnet 41 is made strong, this magnetic attraction member 28 strongly attracts the sliding bar 29 extending in the moving direction of the carriage 21, and when the attraction force of this electromagnet 41 is made weak, the attraction force is was configured to be weak. The control unit 51 constantly obtains the pulse signal γ indicating the position of the carriage 21 from the encoder 56 that scans a pattern such as a magnetic or optical stripe provided along the sliding bar 29. When the carriage 21 reaches the end of the knitting width after knitting one course,
In the processing circuit 55, the count value of the pulse signal ゛γ, the left end setting device 53 of the knitting width, and the right end setting device 5 of the knitting width are processed.
4, and when they match, a carriage reversal start signal α is output, and the carriage reversal is performed after a predetermined time of this carriage reversal start signal α (or after counting a predetermined number of pulse signals γ). Outputs a completion signal β. The electromagnet drive circuit 52 receives this carriage reversal start signal α
In response to the input, an excitation current that generates a magnetic field in the same direction as the magnetic field of the magnet 42 is supplied to the excitation coil 45a of the electromagnet 41 for a short time of several m5ec. Then, the first
The magnetic flux density of the magnetic circuit A' becomes high (and strongly attracts the sliding bar 29. When the carriage reversal start signal α is input to the carriage drive device 57, the carriage 21
The direction of travel is reversed. Then, upon input of the carriage reversal completion signal β, the electromagnet drive circuit 52 causes the excitation coil 4 of the electromagnet 41 to
5b, an excitation current that generates a magnetic field in the opposite direction to the magnetic field of the magnet 41a is supplied for a short time of about several m5ec. Then, the semi-hard magnetic member 44a of the electromagnet 41. The residual magnetization of 44b disappears, and the magnetic flux density of the second magnetic circuit B' becomes high, but the magnetic flux density of the first magnetic circuit A' becomes low, and the force that attracts the sliding bar 29 becomes weak. In the knitting machine having the above configuration, the carriage 21 is now moving to the concave portion 32 of the cam plate 25.
It is assumed that the carriage is moved while being knitted in the direction of the arrow in FIG. 3, with the step part 27b being in contact with the guide member 26b with the carriage being positioned on the rear side in the direction of carriage movement. At this time, the roller 12a of the leading arm 22a is moving up the inclined surface 32a of the cam plate 25 against the elastic force of the spring 31a, so the arm 22a is in the raised position. On the other hand, the roller 12b on the trailing side of the dowel 22b moves down the inclined surface 32b of the cam plate 25 to be located in the recessed portion 32 due to the elastic force of the spring 31b, so the dowel 22b is at a predetermined lowered position. Next, when the carriage 21 finishes knitting a predetermined width and reverses, the control section 51 outputs a carriage reversal start signal α. The electromagnet drive circuit 52 strengthens the attraction force of the electromagnet 41 based on the carriage reversal start signal α, and the magnetic attraction member 28 strongly attracts the sliding bar 29. If the carriage 21 continues to reverse and starts moving leftward, the magnetic attraction member 28 is attracted to the sliding bar 29, so the cam plate 25 cannot start moving to the left and tries to remain stationary, causing the main plate 21 of the carriage 21 to Slide to the right relative to. At this time, the roller 12a on the side of the thread 22a moves down the slope 32a of the cam plate 25 due to the elastic force of the spring 31a and is located in the recessed part 32, and the roller 1 on the side of the thread 22b
2b moves up the inclined surface 32b of the cam plate 25 against the elastic force of the spring 31b. Then, as the stepped portion 27a of the cam plate 25 comes into contact with the guide member 26a, the cam plate 25 can no longer remain stationary and starts moving leftward as the carriage 21 moves leftward. Subsequently, the carriage reversal completion signal β is sent to the electromagnet drive circuit 5.
2, the attraction force of the electromagnet 41 becomes weaker, and the carriage 21 moves to the left while knitting smoothly. When the carriage is moving to the left while forming one course in this manner, the attraction force of the electromagnet is weakened as described above to prevent it from becoming a load on the carriage travel. Further, when the carriage 21 is reversed from the left row to the right row at the left end of the knitting width, the control section 51 again outputs the carriage reversal start signal α, strengthens the attraction force of the electromagnet 41, and 25 to the left heslite relative to the main plate 23 to form a dowel 22a. When the position of the carriage 22b is switched and the carriage reversal completion signal β is output from the control section 51, the attraction force of the electromagnet 41 is weakened to make the traveling smooth. Of course, the structure of the knitting machine is not limited to the above structure, but is a knitting machine with a structure in which a carriage runs along a sliding bar made of magnetic material, and mechanisms such as stitches are switched at both ends of the knitting width. It's good to have. Furthermore, the structure of the electromagnet 41 is not limited to the structure shown in FIG. 4, and the carriage reversal start signal α may be obtained not only from the encoder but also from position detection means such as a limit switch. . As described above, according to the knitting machine according to the present invention, only when reversing the carriage 21, the attraction force of the electromagnet is strengthened and the cam plate 25 is slid to switch the positions of the threads 22a and 22b, so that the carriage knits. While the vehicle is running, the attraction force of the electromagnet 41 is weakened so that the vehicle can run smoothly. Therefore, the energization time is short, which has an energy saving effect, and it also generates less heat and allows the electromagnet to be made smaller, making it possible to install it in a carriage with limited space. Therefore, it is possible to provide a knitting machine that is compact and consumes less energy.

【 effect 】

As described above, according to the electromagnet according to the present invention, the attraction force is maintained in either the strong or weak state even when the current is turned off by simply energizing it in the opposite direction only at the moment when the attraction force is switched to strong or weak. Therefore, it is possible to provide an electromagnet that consumes very little energy and whose strength can be switched. Since this electromagnet has a small amount of heat generation, it is also possible to obtain the effect that the electromagnet capable of achieving this effect can be made smaller. According to the knitting machine of the present invention, the attraction force of the electromagnet is strengthened only when reversing the carriage to switch mechanisms such as dowels, and when the carriage is traveling while knitting, the attraction force of the electromagnet is This makes it possible to run smoothly by weakening the adsorption force, so the adsorption force can be switched from strong to weak in a short period of time, resulting in the effect of reducing energy consumption. Since it consumes less energy and generates less heat, the electromagnet can be made smaller, and it can be installed in the limited space of the carriage of the knitting machine, making it possible to provide a compact knitting machine that consumes less energy.

[Brief explanation of drawings]

FIG. 1 is a side sectional view of an embodiment of an electromagnet according to the present invention;
FIG. 2 is a timing chart for switching the strength of the electromagnet, FIG. 3 is a plan view structural diagram of the carriage of the knitting machine according to the present invention with a part cut away, and FIG. 4 is a diagram of the magnetic attraction member of the carriage. A partially enlarged sectional view, Figure 5 is a block diagram of the control circuit used in the knitting machine, Figure 6 is a timing chart for switching the attraction force of the knitting machine, and Figure 7 is the magnetic hysteresis of the semi-hard magnetic member. It is a figure showing a curve. A: first magnetic circuit, B: second magnetic circuit, ■
...Magnet, 2...Semi-hard magnetic member, 3
... Semi-hard magnetic material member, 4... Magnetic material to be attracted, 7...
・Soft magnetic material member, lO... electromagnet drive circuit, 11
...Electromagnet, A'...First magnetic circuit, B'...Second magnetic circuit, α...Carriage reversal start signal, β...Carriage reversal completion signal, 21...Carriage , 25... cam plate (switching means), 29... sliding bar, 28... magnetic attraction member,
41... Electromagnet, 42... Magnet, 43... Soft magnetic member, 44a... Semi-hard magnetic member, 44b... Semi-hard magnetic member, 45a... Excitation coil, 45b.・・・
Excitation coil, 51...control circuit (means for outputting a carriage reversal start signal and a carriage reversal completion signal), 5
2...Electromagnet drive circuit.

Claims (2)

[Claims] (1) A first magnetic circuit is configured by a semi-hard magnetic member having an excitation coil, a magnet, and an attracted magnetic body, and the magnet and the soft magnetic member are different from the first magnetic circuit. By configuring a second magnetic circuit and providing an excitation coil driving means that excites the excitation coil for a short time in the same direction or in the opposite direction to the direction of the magnetic field generated by the magnet, the attracted magnetism in the first magnetic circuit can be reduced. An electromagnet characterized by being configured to control the adsorption force of the body by switching between strength and weakness. (2) In a knitting machine equipped with a switching means for switching knitting mechanisms such as stitches and cams when reversing the traveling direction of a carriage running along a sliding bar made of a magnetic material at both ends of the knitting width, excitation is applied. A first magnetic circuit composed of a semi-hard magnetic member with a coil, a magnet, and the sliding bar is different from the first magnetic circuit composed of the magnet and a soft magnetic member. means for disposing an electromagnet having a second magnetic circuit at a position facing the sliding bar on the carriage, and outputting a carriage reversal start signal at a reversal position at the end of the knitting width; means for outputting a carriage reversal completion signal at a position slightly inside the reversal position or at a timing slightly delayed from the carriage reversal start signal, and the excitation coil is moved in the same direction as the magnetic field by the magnet for a short time by the carriage reversal start signal. excitation coil drive means for exciting the excitation coil in a direction opposite to the magnetic field of the magnet for a short time in response to the carriage reversal completion signal, and when reversing the running direction of the carriage at both ends of the knitting width, Only between the start signal and the carriage reversal completion signal, the magnetic flux density of the first magnetic circuit of the electromagnet is increased to strengthen the attraction force between the electromagnet and the sliding bar, thereby operating the switching means. This knitting machine is characterized by: