JPS6124907B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a brushless DC linear motor in which a commutator and brushes are removed and the drive current flowing through a moving coil is switched by detecting the position of the moving coil.

Linear motors that generate linear driving force have fewer types and uses than rotary motors. In particular, in order to realize a linear motor in which force generation is linear over a wide range, there are greater restrictions on the mechanical structure than in rotary motors. As shown in FIG. 1, the conventional device of this type has permanent magnets 1 ₁ , 1 ₂ , coils 6 , yokes 2 , 3 , and brushes 5 ₁ , 5 ₂ , 5 , similar to a rotary DC motor developed. ₃ , etc., the brush supplies power to the coil, and the coil 6
The method used was to move the This resulted in drawbacks such as wear of the brush portion and maintenance work such as brush replacement. Furthermore, when using this as a servo motor, fluctuations (ripples) in the driving force occur at the drive current switching position, and one way to improve this is to increase the number of coil terminals in contact with the brush, but this is not possible. The coils were connected in parallel, which was disadvantageous in terms of coil efficiency.

The present invention aims to eliminate the above-mentioned drawbacks and provide a stable and reliable DC linear motor for servo use.The present invention will be described in detail below with reference to the drawings.

First, in Figure 2, 1 ₁ , 1 ₂ , 1 ₃ ,...
... is a permanent magnet for the field, 2 and 3 are yoke, 4
₁ , 4 ₂ , 4 ₃ , ...... and 5 ₁ , 5 ₂ , 5
₃ , ...... are magnetic pole gaps, 6 ₁ and 6 ₂ are moving coils, 7 and 8 are yokes that constitute a magnetic circuit together with the yokes 2 and 3, and 9 is a fixed stand of a permanent magnet, which is a non-magnetic material. . Also 10 ₁ , 10 ₂ , 10 ₃ ......
indicates the magnetic path created by a permanent magnet.

The above-mentioned linear motor uses one or two magnetic gaps formed by one field permanent magnet and a yoke as a unit, and a moving coil is inserted into two sets of magnetic circuit units with different magnetization directions. Configure.
Since this type of linear motor has a plurality of magnetic circuit units arranged depending on the length of the motor, the magnetic circuit formed by the permanent magnets ₁₁ , ₁₂ , and ₁₃ in the figure will be described as an example. The permanent magnet 1 ₁ is magnetized in the direction from the air gap 5 ₁ to the air gap 4 ₁ , and the permanent magnets 1 ₂ , 1
₃ are magnetized in the direction from the air gap 4 ₂ to the air gap 5 ₂ and from the air gap 5 ₃ to the air gap 4 ₃ , respectively, and the magnetization directions of the permanent magnets 1 ₁ and 1 ₂ and 1 ₂ and 1 ₃ are mutually opposite. It goes in the opposite direction. The moving coils 6 ₁ and 6 ₂ are each air-core coils wound into a flat rectangular shape. Compared to the conventional configuration in which the coil is housed in a slotted iron core, this configuration of moving coils reduces the weight of the moving parts and helps improve the responsiveness of the motor, and also improves heat dissipation because the coil is exposed to direct air flow during operation. It is possible to improve the motor rating. The moving coils 6 ₁ and 6 ₂ are the third
As shown in the figure, relative to the magnetic pole pitch P,
Shift it by 2 bits and insert it into the magnetic pole gap. rectangle 4
Two of the sides are arranged so as to be inserted between the magnetic poles. In this case, as shown in Figure 4, they are 1/2 each other.
Even if two coils with different pitches are inserted into the same gap, the effect is exactly the same. Also, the permanent magnets described above may be replaced by field coils. In FIG. 3, 35 ₁ and 35 ₂ are detection elements of a coil position detector to be described later, W is the winding width of the coil, and P _c is the coil pitch. The coil pitch P _c and the magnetic pole pitch P are approximately equal in length.

To further explain the operation of the present invention, as shown in FIG. 5, when a current is passed through the coil ₆₁ in a direction perpendicular to the plane of the paper, magnetic fluxes 10 ₁ and 1 pass through the magnetic pole gaps 4 ₁ and 4 ₂ .
A force 12 interlinked with 0 ₂ and according to Fleming's left hand rule is generated in the moving coil. The direction of the force depends on the direction of the current flowing through the moving coil, and it is necessary to switch the current according to the direction of the magnetic flux in the air gap. On the other hand, the magnitude of force is generally expressed as F= _Bli [Newton]. Here, B: Air gap magnetic flux density [wb/m ² ] l: Coil wavelength interlinking with the magnetic flux in the air gap [m] i: Current flowing through the movable coil [A]. In order for this force F to be constant over a long range, the effective components of B and l must not vary from place to place. In order to widen the moving range of the moving coil, it is sufficient to simply arrange the permanent magnets shown in FIGS. 2 and 4 in the longitudinal direction, and the magnetic circuit structure is extremely simple. On the other hand, the moving coil
When moving from the position shown in the figure to the right in the figure under the action of force 12 and moving in parallel to the position shown in Figure 6, the direction of the magnetic flux changes from the gap 4 ₂ to 4 ₁ and from the gap 4 ₃ to 4 ₂ . is reversed, so if the polarity of the coil current remains the same, when the movable coil 6 enters the gaps 4 ₂ and 4 ₃ , the direction of the force moves in the opposite direction. Therefore, in order to advance the movable coil further to the right, it is necessary to change the direction of the current flowing through the movable coil. Conventionally, this method uses a combination of brushes and commutators to reverse the polarity of the voltage applied to the coil terminals depending on the position of the moving coil, but as already mentioned, sliding wear and contact failure occur. This may not necessarily be the best method. An alternative method is to detect the relative position of the moving coil with respect to the magnetic pole in some way, operate a transistor switch using the detection signal, and gradually switch the polarity of the current flowing through the moving coil. To achieve this, the method of changing the polarity of the coil current and at the same time switching to another coil 6 ₁ or 6 ₂ , which is placed 1/2 apart in order to maintain output linearity, is shown in the block in Figure 7. This will be explained with a diagram. In the figure, 30 is a position deviation calculation circuit, 31 is a current switching position change circuit, 32 is a coil current polarity switching signal generation circuit, 3
3 is a drive circuit, 34 is a linear motor, 35 is a coil position detector, 36 is a servo position detector, 37
is a comparison circuit, 40 is a positioning target value, 41 is a position deviation obtained by subtracting the movement of the coil,
44 is a coil selection and current polarity switching signal, 45 is a coil current, 46 and 47 are coil position information, 48 is a current polarity switching signal, 49 is a coil position signal, 42
43 indicates a signal that compares the target position and the current switching position and indicates whether they match, and 43 indicates a switching position change signal when the target position and the current switching position match with a positional deviation of 0. The characteristics of the system shown in Figure 7 compared to general servo systems are not only switching the polarity of the coil current, but also simultaneously switching the coil to 1/2 pitch in order to maintain output linearity, and Switching of coil and current polarity is stopped in the vicinity. It has a switching position change function. In the figure, the position detectors 35 and 36 can be used as one detector, and in that case, the signal line is shown by a broken line 50 in the figure. In FIG. 7, the amount of movement of the linear motor 34 is determined by the magnitude of the target value 40. In FIG. That is, the amount of movement is detected by the servo position detector 36, and the linear motor 34 moves until the position deviation signal 41 representing the difference between the target value calculated by the position deviation calculation circuit 30 and the amount of movement becomes zero.

On the other hand, the current switching of the coil as it moves is performed by the coil current polarity switching signal 48 obtained from the coil position detector 35, but when the servo stop position (position deviation = 0) and the current switching position match, is the signal 48 to stabilize the positioning characteristics.
Processing is being performed to change the switching position defined by . The polarity switching signal generating circuit 32 outputs a current polarity and a selection signal for the coil to be switched based on the signals 41, 48, and 43 to operate the drive circuit 33. Note that a position signal for servo control is used to change the switching position, and a preset current switching position and a servo stop position are compared, and if they match, a switching position change signal 43 is output.

Next, the relationship between the coil and magnetic pole dimensions and the current switching position will be explained with reference to FIG. The dimensions of the coil and magnetic pole are such that the motor output does not vary depending on the coil position even if the polarity of the coil current is changed, and current switching is difficult to control if the servo stop position and the coil current switching position overlap. It solves the following problem. First, to simplify the explanation, the winding width of the coil and the distance g between the permanent magnets are made equal, and the coil pitch is equal to the sum of the permanent magnet length l and the distance g between the permanent magnets. The relationship between the coil pitch and l and g is not the only dimensional relationship in the structure of the present invention). Here, an important condition in the present invention is that the output ranges of the coil ₆₁ and the coil ₆₂ , which are arranged 1/2 magnetic pole pitch apart, overlap. The constant output range of the coil is approximately _30o , 30o ₊₁ , ...... (coil 6
₁ ) and 31 _o , 31 _o+1 , ...... in Figure 8C.
(coil 6 ₂ ). That is, the constant output range is defined as the length l of the magnetic poles minus the distance g between the magnets. Here constant power range 30 _o and 3
Section that overlaps with section 1 _o , Figure 8D
_40o , similarly 40o ₊₁ , 40o ₊₂ , etc., indicate the zone in which the polarity of the coil current should be switched within this section, and the polarity switching position of the coil current has a width. This is to avoid the servo stop position and the current polarity switching position from coinciding. For example, current switching zones 40o _-1 , _40o , 40o ₊₁ ,...
The left end of ..., that is, 5 in E of Figure 8, which falls within the constant output range.
If current switching is to be performed at the positions shown as 0 _o , 50 _{o +1} , ......, the current switching positions 50 _o , 50 _{o +
1.} If we focus on one coil, the coil current is switched on and off in order, and when this switching position and the servo stop position match, the current is switched due to the hysteresis of the current switching position detector, etc. A dead zone occurs, and the stability of positioning control deteriorates.
This adversely affects positioning accuracy. Therefore, in the present invention, the constant output ranges of the two coils are overlapped,
When switching is performed at the left end position 50 _o of the switching zone shown as 40 _o , 40 _o+1 , ......, if the positioning stop positions match exactly, the coil switching position is changed to 51 _o in Figure 8F. This is to remove discontinuous points in the stop position caused by servo control. To change this current switching position, a signal from a precision position detector for servo control is used.The current switching position is memorized in advance in a memory such as a preset counter, and a logical comparison with the positioning stop position is performed to find a match. It is only necessary to temporarily change the current switching position when this occurs. The amount of displacement to be changed in this current switching position may be set to be greater than or equal to the maximum displacement amplitude from the target position with reference to the transient vibration characteristics of the position control system. In the above example, the distance between magnets = coil winding width It is set equal to .

Next, the linear guide structure of the moving coil and the lead wire of the moving coil will be explained with reference to FIG. The movable coils 6 ₁ and 6 ₂ are shaped into a planar shape and fixed to the carriage 11 with a 1/2 pitch offset to be integrated. The carriage 11 has linear ball bearings 16 and 17 inserted in two places, upper and lower, and can freely slide in the axial direction of the guide rails by the two guide rails 14 and 15. Also coil 6
The lead wires ₁ , 6, _{and 2} are guided from the side or lower surface of the carriage 11 (FIG. 9 shows an example from the lower surface) to the fixed terminal 22 by four flexible members 18, 19, 20, and 21. By making the flexible material sufficiently long compared to the range of movement of the carriage,
Care is taken to ensure that it does not place a burden on the carriage.

In addition to this guide structure, the structure shown in FIG. 10 using ball bearings may also be used. Ball bearings 16 are installed on the slopes of guide rails 14 and 15.
₁ , 16 ₂ , 16 ₃ , 16 ₄ respectively,
It enables only one-axis movement in the axial direction of the rail, and a total of 8 bearings are used, 4 bearings in 2 locations each in the axial direction of the rail. shaped coil 6
₁ and ₆₂ are inserted and fixed into the carriage 11.

As explained above, the brushless DC linear motor of the present invention can obtain a uniform output over the entire length of the motor by selectively using two sets of moving coils, and has extremely good linearity with respect to current. Additionally, since there is no iron core in the moving parts, it is lightweight, has excellent responsiveness, and has good heat dissipation.
In addition, there are no discontinuities in the positioning target position, which is essential for a servo motor, and there is no need for sliding parts or rectifying mechanisms to supply power to the moving parts, making operation and maintenance easy, and improving longevity and reliability. Excellent sex.

[Brief explanation of the drawing]

Fig. 1 is a structural diagram of a conventional DC linear motor, Fig. 2 is a perspective view of an embodiment of the linear motor of the present invention, Fig. 3 is a perspective view of the same part, and Fig. 4 is another embodiment of the present invention. 5 and 6 are diagrams for explaining the operation of the present invention, FIG. 7 is a control block diagram for driving and controlling the linear motor of the present invention, and FIG. 8 is a diagram for explaining the same operation.
FIGS. 9 and 10 are structural diagrams of application examples of the present invention, respectively. 1 ₁ ,1 ₂ ,1 ₃ ,1 _o-1 ,1 _o ,1 _o+1 ,1 _o+2
... Permanent magnet, 2, 3 ... Yoke, 4 ₁ , 4 ₂ , 4
₃ , 5 ₁ , 5 ₂ , 5 ₃ ... void, 6 ₁ , 6 ₂ ...
Moving coil, 7, 8... Yoke, 9... Permanent magnet holding plate, 10 ₁ , 10 ₂ , 10 ₃ ... Magnetic path, 11...
...Carriage, 14,15...Guide rail, 1
6 ₁ , 16 ₂ , 16 ₃ , 16 ₄ , 17 ... Ball bearing, 18, 19, 20, 21 ... Flexible material, 22 ... Fixed terminal, 30 ... Position deviation calculation circuit, 31 ... Current switching Position change circuit, 32
...Coil current polarity switching signal generation circuit, 33...
Drive circuit, 34... Linear motor, 35... Coil position detector, 36... Servo position detector, 3
7... Comparison circuit.

Claims (1)

[Claims] 1. In a brushless DC linear motor in which a moving coil is inserted into a magnetic gap between a plurality of equal-length magnet bodies and a yoke provided at a position facing each magnetic pole surface of the magnet bodies, the plurality of magnet bodies are arranged in parallel with alternating magnetization directions and at a certain distance in a direction perpendicular to the magnetization direction, with their magnetic pole surfaces aligned, and each of the magnets is placed on at least one side of the plurality of magnets facing the magnetic pole surfaces of the plurality of magnet bodies. Each of the movable coils is arranged integrally with the yoke so as to have a certain magnetic gap with the magnetic pole surface, and each of the movable coils has a pair of air-centered, flattened coils straddling the magnetic gaps of the adjacent magnet bodies. A brushless DC linear motor characterized in that the adjacent magnet bodies are integrally arranged so as to be shifted by 1/2 of the magnetic pole pitch, and the coil pitch of the movable coil is formed to be approximately equal to the magnetic pole pitch of the magnet bodies.