JPH02231607A - Magnetic guidance system for vehicle - Google Patents

Abstract

PURPOSE:To easily miniaturize a magnetic sensor and to facilitate the assembling and control jobs by detecting the change of a short circuit space magnetic flux which varies in accordance with the position error of a vehicle to a magnetic mark and detecting the position error of the vehicle to the mark. CONSTITUTION:A part of a space magnetic flux produced by an exciting signal generating means 4 with an exciting signal via a magnetic field generating means 5 short-circuits the both ends of the means 5 with no intervention of a magnetic mark 2. Furthermore a short circuit space magnetic flux varies in accordance with the position error of a vehicle 1 to the mark 2 and has an electromagnetic interlinkage with a short circuit magnetic flux detection coil 6. Thus a short circuit magnetic flux detecting signal is induced to the coil 6. As a result, the position of the vehicle 1 is electrically detected to the mark 2 as the short circuit magnetic flux detection signal. Thus a magnetic sensor 3 is miniaturized and the assembling and control jobs are facilitated for the sensor 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to a magnetic guidance system that enables vehicles to automatically travel along magnetic markings placed on vehicle travel routes. [Prior Art] Recently, in factories, warehouses, hospitals, golf courses, etc., magnetic signs are installed on the travel paths of transport vehicles, tractors, pallets, etc. (hereinafter referred to as vehicles), and vehicles are equipped with magnetic sensors. As a result, the importance of magnetic guidance systems for vehicles that allow vehicles to automatically travel unmanned along driving routes is increasing.

Hereinafter, typical examples of conventional magnetic guidance systems using such magnetic labels will be explained.

Magnetic signs such as ferrite sheets and amorphous magnetic sheets will be installed on the driving route, and magnetic sensors will be installed in the vehicles. The magnetic sensor is equipped with an excitation coil and a pair of misalignment detection coils arranged symmetrically in the width direction of the magnetic label with the excitation coil at the center, and the excitation coil is excited by an excitation signal of about 100 KHz to generate a spatial magnetic flux. do. This spatial magnetic flux interlinks with the pair of misalignment detection coils and focuses on the magnetic label. When the vehicle deviates from the center of the magnetic sign, the amount of spatial magnetic flux that interlinks with each misalignment detection coil in the pair becomes unbalanced, causing each misalignment detection coil to detect Between the signals,
It makes a big difference. In this way, the detection signals from the pair of positional deviation detection coils are used to detect the positional deviation of the vehicle to the left and right with respect to the magnetic sign, thereby controlling the running direction of the vehicle and allowing the vehicle to automatically travel along the magnetic sign. be.

(Refer to Japanese Patent Application Laid-Open No. 62-49409).

[Problems to be Solved by the Invention] However, according to the above-mentioned conventional technology, the magnetic sensor must be equipped with a pair of positional deviation detection coils each individually interlinked with the spatial magnetic flux passing through the magnetic label. Moreover,
Since the running of a vehicle is controlled based on detection signals generated by each pair of misalignment detection coils, there have been various unresolved problems as described below.

That is, in general, it is difficult to completely align the electromagnetic characteristics of each pair of misalignment detection coils, and furthermore, it is extremely difficult to make them electromagnetically equally coupled to the spatial magnetic flux and the excitation coil. Moreover, not only the magnetic sensor becomes larger and has a more complicated structure, but also the assembly and adjustment work of the magnetic sensor is extremely cumbersome.

Additionally, since the pair of misalignment detection coils are usually placed on the vehicle in the width direction of the magnetic sign,
If the floor of the vehicle is tilted due to rolling or unbalanced loading, it may be mistaken as a misalignment of the vehicle and cause the vehicle to drive out of control.

Moreover, not only when the vehicle is located in the center of the magnetic sign and driving normally, but also when the vehicle completely deviates from the magnetic sign and goes off the rails, the pair of positional deviation detection coils generates an equal detection signal. In order to distinguish between a normal running condition and a completely derailed condition, a special judgment method was required.

[Means for Solving the Problems] This invention solves the unsolved problems of the above-mentioned prior art. J
In order to solve these problems, the magnetic sensor attached to the vehicle includes a magnetic field generating means that receives an excitation signal D and generates a spatial magnetic flux φ, and a magnetic field generator that generates a spatial magnetic flux φ from the magnetic sensor. A short-circuit magnetic flux detection coil is provided which generates a short-circuit magnetic flux detection signal E by interlinking with the short-circuit space magnetic flux φ' connecting both ends of the magnetic field generating means.

The present invention also provides vehicle position control means for generating a vehicle position control signal H in accordance with the positional deviation of the vehicle with respect to the magnetic sign, based on the excitation signal D and the short-circuit magnetic flux detection signal E of the short-circuit magnetic east detection coil. It is something to be prepared for.

Furthermore, in the present invention, the magnetic sensor is provided with a displacement direction detection coil that interlinks with the spatial magnetic flux φ" of the spatial magnetic flux φ passing through the magnetic marker.

[Function] The structure of the present invention is such that the excitation signal generation means shorts both ends of the magnetic field generation means without passing through the magnetic label, so that a part of the spatial magnetic flux φ generated by the excitation signal D through the magnetic field generation means. , Moreover, a short-circuit space magnetic flux φ′ that changes in response to the positional deviation of the vehicle with respect to the magnetic sign is formed, and is electromagnetically linked with the short-circuit magnetic flux detection coil to induce a short-circuit magnetic flux detection signal E in the short-circuit magnetic flux detection coil. As a result,
The position of the vehicle relative to the magnetic sign serves to be electrically detected as a short-circuit magnetic flux detection signal E.

Further, in another configuration of the present invention, the excitation signal D of the excitation signal generation means is an electric signal for generating a steady spatial magnetic east φ via the magnetic field generation means, and on the other hand, the excitation signal D of the excitation signal generation means is an electric signal for generating a steady spatial magnetic field The short-circuit magnetic flux detection signal E is an electrical signal that changes slightly depending on the position of the vehicle with respect to the magnetic sign, but has a low rate of change.It is difficult to detect accurate positional deviation of the vehicle by itself, but the vehicle position control means , based on the excitation signal D and the short-circuit magnetic flux detection signal E, generates a vehicle position control signal H that changes significantly depending on the position of the vehicle, thereby enabling automatic driving control of the vehicle along the magnetic sign. It works like this.

Furthermore, in another configuration of the present invention, of the spatial magnetic flux φ, the spatial magnetic flux φ'' that passes through the magnetic marker changes in response to the positional deviation of the vehicle with respect to the magnetic marker, and moreover, the spatial magnetic flux φ'' that passes through the magnetic marker changes in response to the positional deviation of the vehicle with respect to the magnetic marker, and is linked to the positional deviation detection coil. Due to the electromagnetic action of the misalignment detection coil,
It functions to generate a detection signal G corresponding to the position of the vehicle, and to enable the vehicle to reliably automatically travel along the magnetic marker based on the positional deviation signal G and the short-circuit magnetic flux detection signal E.

[Embodiments] Hereinafter, the configuration and operation of several embodiments of the present invention will be explained based on FIGS. 1 to 6.

In the figure, the spatial magnetic fluxes φ, φ', and φ"° are shown by broken lines for ease of understanding.

FIG. 1 is a perspective view showing the overall configuration of a magnetic guidance system for an unmanned vehicle, which is a first embodiment of the present invention.

A magnetic marker 3J2 is laid on the travel path of the unmanned vehicle 1, and at a predetermined height position on the magnetic marker 2 of the unmanned vehicle 1.
A magnetic sensor 3 is provided.

The magnetic sensor 3 includes an excitation coil 5 and a short-circuit magnetic flux detection coil 6 as magnetic field generating means. The excitation coil 5 is
It has a rod-shaped ferrite core with a diameter of 12Ilm and a length of 60a+m that is parallel to the magnetic label 2 and oriented in the width direction of the magnetic label 2, and a wire diameter of 0.2Im is provided in the middle of the core. 3 2m+
An insulated copper wire of n is wound 130 times, and excitation signal generating stages 4 are connected to both ends of the winding.

The short-circuit magnetic flux detection coil 6 is located between both ends of the excitation coil 5,
Moreover, it is arranged directly above it with a gap of about 5llI1 left. Insulated wire with a wire diameter of 0.32mm+ has a diameter of 2 times.
The coil is an air-core coil wound 40 times with the winding wire 20110, and the vehicle position control means 7 is connected to both ends of the winding.

The excitation signal generating means 4 sends a frequency of 100κH to the excitation coil 5.
An excitation signal D having a sine wave of z is supplied, and the excitation coil 5 generates a spatial magnetic flux φ directed in the width direction of the magnetic label 2 from both ends thereof.

Next, the operation of the above configuration will be explained with reference to FIG.

FIG. 2A shows the positional relationship among the magnetic sign 2, the excitation coil 5, and the short-circuit magnetic flux detection coil 6 corresponding to the position of the vehicle with respect to the magnetic sign 2. The figure (8) is
Excitation signal D and short circuit magnetic flux detection signal E corresponding to (A) in the same figure
The waveforms of each are shown. In the following description of the drawings, <<A>> to (N) each indicate the positional relationship during movement of the vehicle from one end of the magnetic sign to the other end.

First, the vehicle deviates from the road, and the magnetic sensor detects magnetic sign 2.
In the case of a complete derailment in which the wheel completely comes off from one end, the spatial magnetic flux φ of the excitation coil 5 is distributed almost in the same way as when there is no magnetic material around, and the excitation coil 5 does not pass through the magnetic marker 2. The short-circuit space magnetic flux φ′ connecting both ends of the short-circuit magnetic flux φ′ increases, the magnetic flux density interlinking with the short-circuit magnetic flux detection coil 6 increases, and the short-circuit magnetic flux detection coil 6 outputs a large short-circuit magnetic flux detection signal E (
(See Figure 2 (a)).

In the waveform diagrams below, the short-circuit magnetic flux detection signal E shown in FIG. 2(a) is shown by a broken line for ease of understanding.

Next, in the process of the vehicle returning to the driving route, the magnetic sensor approaches one end of the magnetic sign 2, and a part of the spatial magnetic flux φ of the excitation coil 5 is collected on the magnetic sign 2, and the spatial magnetic flux φ' via the magnetic sign 2 is increase. On the other hand, the short-circuit space magnetic flux φ' that does not pass through the magnetic marker 2 decreases, and the short-circuit magnetic flux detection signal E also decreases (see FIG. 2 (0)).

When the vehicle returns to the driving path and the magnetic sensor is located directly above the center of the magnetic sign 2, most of the spatial magnetic flux φ is transferred to the magnetic sign 2.
Since the short-circuit space magnetic flux φ' linked to the short-circuit magnetic flux detection coil 6 becomes the minimum, the short-circuit magnetic flux detection signal E also becomes the minimum (see FIG. 2(A)).

Thereafter, when the magnetic sensor is removed from directly above the center of the magnetic marker 2 again, the short-circuit space magnetic flux φ' increases and the short-circuit magnetic flux detection signal E also increases (see FIG. 2 (2)). When the vehicle completely derails again, the magnetic sensor comes off from the magnetic marker 2, and most of the spatial magnetic flux φ does not pass through the magnetic marker 2, but rather the short-circuit spatial magnetic flux φ′ interlinks with the short-circuit magnetic flux detection coil 6. The magnetic flux density reaches its maximum, and the short-circuit magnetic flux detection signal E also reaches its maximum (Fig. 2 (
(See ).

Next, the configuration of a second embodiment of the present invention will be explained with reference to the circuit diagram of FIG. 3.

The excitation signal generation means 4 has a normal sine wave generation circuit and a buffer amplifier, and its output terminal is connected to the excitation coil 5, and an integral circuit consisting of a variable resistor 72 and a capacitor 73 of 1,000 stages for vehicle position control. It is connected to an operational amplifier 74 via a circuit, and further connected to an operational amplifier 75 via an operational amplifier 74.
It has reached the non-inverting input terminal of . Short circuit magnetic flux detection coil 6
is connected to an inverting input terminal of an operational amplifier 75 through an operational amplifier 71 of the vehicle position control means 7 whose amplification factor is variable.

The output terminal of the operational amplifier 75 is connected to the capacitor 76.
1! 1,000 stages of driving direction correction and driving road deviation identification means 10
are commonly connected.

The operation of the above configuration will be described below with reference to the waveform diagram of each part in FIG. In addition, (A) to (N) in the same figure
2 correspond to the position of the vehicle with respect to the magnetic sign, as in FIGS. 2(a) to 2(n).

The excitation signal D of the excitation signal generating means 4 is a steady electrical signal with a sinusoidal amplitude regardless of the positional relationship of the vehicle with respect to the magnetic sign, and generates a spatial magnetic flux φ via the excitation coil 5.
In addition, it is delayed by a variable resistor 72, a capacitor 73, and an operational amplifier 74 of the vehicle position control means 7, and is adjusted to be in phase with the phase of a short 13 magnetic flux detection signal E, which will be described later. 75 non-inverting input terminal. On the other hand, the short-circuit spatial magnetic flux φ′ is the magnetic label 2
The magnetic flux density changes depending on the position of the vehicle with respect to the short circuit magnetic flux detection coil 6, and generates a short circuit magnetic flux detection signal E that changes in height depending on the position of the vehicle. The short-circuit magnetic flux detection signal E is amplified to a predetermined value according to the amplitude of the delayed excitation signal D' by an operational amplifier 7l with a variable amplification factor, and is sent to the inverting input of the operational amplifier 75 as the amplified short-circuit magnetic flux detection signal E'. input to the terminal.

In the following explanation, for ease of understanding, when the vehicle is located directly above the center of the magnetic sign, the short-circuit magnetic flux detection signal is set such that the amplitude of the short-circuit magnetic flux detection signal E matches the width of the excitation signal D. It is assumed that an amplification factor of E is set.

The input amplifier 75 uses the excitation signal D', which constantly changes regardless of the position of the vehicle relative to the magnetic sign, as a reference signal, and uses the excitation signal D' as a reference signal. A short-circuit magnetic flux detection signal E' which increases and decreases is inputted, and these signals D' and E' are operationally amplified, and the difference between the two is made into an amplified vehicle position control signal H, which is output from the output terminal.

As a result, the vehicle position control signal H has a large amplitude when the vehicle deviates from the magnetic sign (see Figure 4 (a) and (ne)), and the vehicle position control signal H has a large amplitude when the vehicle deviates from the magnetic sign. If the 4th
(See Figure (8)). That is, the amplitude of the vehicle position control signal H is
Changes according to the amount of positional deviation of the vehicle from the magnetic sign (
(See Figure 4 (mouth), (2)).

Although the vehicle position control signal H also includes direction information regarding the direction of positional deviation of the vehicle with respect to the magnetic sign, the following description will focus on positional deviation amount information regarding the positional deviation amount.

Vehicle position control signal H is supplied to capacitor 7 shown in FIG.
6, the DC component is removed and distributed to the traveling direction correction stage 9 and the traveling road deviation identification means IO. The traveling direction correction step 9 corrects the traveling direction of the vehicle by sampling the vehicle position control signal H and, for example, operating a normal steering device according to the field of view. The road deviation identification means IO compares the amplitude of the vehicle position control signal H with a preset threshold value by manually applying the vehicle position control signal H to a normal window converter, for example. If the amplitude exceeds the threshold, it is assumed that the vehicle has deviated from the magnetic sign and the vehicle is stopped.
to prevent runaway behavior.

Next, a third embodiment of the present invention will be described with reference to FIG. 5, which shows the main structure of the magnetic sensor.

The magnetic sensor 3 includes an excitation coil 5 and a short-circuit magnetic flux detection coil 6 on a substrate 31, and further includes a single displacement detection coil 8 that generates a displacement detection signal G. The positional deviation detection coil 8 is an air-core coil that surrounds the excitation coil 5 on the same plane, and the plastic rectangular bobbin in which the excitation coil 5 is installed has a 0. The insulated wire I21'Ilm is wound 130 times, and the vehicle position control means 7 (not shown) is connected to the terminal of the winding.

The operation of the above embodiment will be explained below with reference to FIG. FIG. 6(A) shows the output characteristics of the positional deviation detection signal G, and shows the change in the positional deviation detection signal G when the vehicle moves from the left end to the right end of the magnetic sign. Similarly, FIG. 6B shows the output characteristics of the short-circuit magnetic flux detection signal E of the short-circuit magnetic flux detection coil 6.

In the figure, the distance h between the magnetic sensor 3 and the magnetic sign 2 (the height of the magnetic sensor above the running road) is set to 14 mm and 20n+m.

The positional deviation detection coil 8 surrounds the excitation coil 5 and interlinks with the spatial magnetic flux φ generated by the excitation coil 5, and when the vehicle is located directly above or in the vicinity of the magnetic sign 2, it It also interlinks with the spatial magnetic flux φ' passing through the magnetic label 2.

When the magnetic sensor is located directly above the center of the magnetic marker 2, the spatial magnetic flux φ' interlinks symmetrically with respect to the center of the displacement detection coil 8. As a result, the induced voltage in the winding of the positional deviation detection coil 8 is canceled out every turn, and the positional deviation detection signal G is not generated.

However, when the magnetic sensor is displaced from the center of the magnetic marker 2, the spatial magnetic flux φ'' interlinks asymmetrically with respect to the center within the displacement detection coil 8, and the displacement detection coil 8 At each turn of the winding, an induced Jl! voltage that is not canceled out is generated to generate a positional deviation detection signal G.Moreover, the amplitude of the positional deviation detection signal G corresponds to the amount of positional deviation of the vehicle with respect to the magnetic sign within a certain range. Moreover, its polarity corresponds to the direction of displacement of the vehicle with respect to the magnetic sign 2, and is either positive or negative (see FIG. 6(A)).

As a result, the positional deviation detection signal G of the positional deviation detection coil 8
Even if the magnetic sign 2 is used alone, the direction and amount of positional deviation of the vehicle with respect to the magnetic sign 2 can be detected based on the polarity and the amplitude of the magnetic sign 2, so that the vehicle can be driven automatically.

However, even with the above, once the vehicle deviates significantly from the magnetic sign 2, the positional deviation detection signal G is no longer generated, and the vehicle cannot run safely and stably automatically. . On the other hand, the short-circuit magnetic flux detection signal E of the short-circuit magnetic flux detection coil 6 does not disappear and maintains a large signal level even when the vehicle deviates significantly from the road and completely goes off the track, and the magnetic sensor moves away from the magnetic sign. maintain.

Therefore, the vehicle position control stage 7 manually inputs the short-circuit magnetic flux detection signal E of the short-circuit magnetic flux detection coil and the position deviation detection signal G of the position deviation detection coil 8, and, for example, detects the amount of position deviation of the vehicle and the amount of correction thereof. The setting is performed based on the positional deviation detection signal G, and the detection of the direction of positional deviation of the vehicle and the correction of the traveling direction are performed based on the short circuit magnetic flux detection signal E. By combining these signals E and G, the direction and amount of positional deviation of the vehicle can be reliably detected, and the vehicle can be optimally and safely controlled in accordance with the positional deviation situation.

According to this embodiment, it is possible to prevent the vehicle from running out of control even in the case of complete derailment, and furthermore, the positional deviation of the vehicle is detected by two different detection means, the short-circuit magnetic flux detection coil and the positional deviation detection coil. This makes automatic vehicle driving fail-safe. In addition, the amplitude of the short-circuit magnetic flux detection signal E increases and decreases gradually near the center of the magnetic marker 2, and changes sharply as it moves away from the center (see Figure 6 (b)).
, it becomes possible to optimally control the running of the vehicle depending on the degree of positional deviation of the vehicle. Furthermore, since the single position detection coil described above is smaller than a conventional pair of symmetrical detection coils, the magnetic sensor can be made smaller, and the configuration of the magnetic sensor and peripheral circuitry can be significantly reduced. It can be purified. Moreover,
There is no possibility of mistaking the inclination of the floor surface due to the rolling of the vehicle or the unevenness of the load as being located on the vehicle.

Furthermore, it is also possible to detect a change in the distance h between the magnetic sensor 3 and the magnetic label 2 using the short-circuit magnetic flux detection signal E. According to this, the normal automatic gain adjustment means (AG
C) etc. to adjust the amplitude of the excitation signal D, and the excitation coil 5
It is also possible to increase/decrease the amount of magnetic flux of the spatial magnetic flux φ by increasing/decreasing the value of the excitation current flowing into the magnetic flux φ, so that the positional deviation of the vehicle can always be detected accurately regardless of the change in the above-mentioned interval.

Although several embodiments of the present invention have been described above, the present invention is not limited to the explanation of the above embodiments, and the present invention is not limited to the explanation of the above embodiments, but can be applied to the excitation coil 5, the short-circuit magnetic flux detection coil 6, the positional deviation detection coil 8, etc. It is also possible to change the shape and mounting position, or to use multiple of these in combination.

[Effects of the Invention] As described above, according to the present invention, a short-circuit magnetic flux detection coil is attached to an excitation coil provided in a vehicle, and out of the spatial magnetic flux φ generated by the excitation coil, the short-circuit spatial magnetic flux that does not go through the magnetic marker is removed. By interlinking with φ' and detecting changes in the short-circuit space magnetic flux φ' that changes in response to the positional deviation of the vehicle with respect to the magnetic sign, the magnetic sensor detects the positional deviation of the vehicle with respect to the magnetic sign. This has the remarkable effect of not only making it possible to downsize and simplify the structure, but also making assembly and adjustment of the magnetic sensor extremely easy.

Moreover, even if the vehicle completely deviates from the magnetic sign,
It is possible to reliably detect stiffness, prevent the vehicle from running out of control, and allow the vehicle to travel safely and automatically.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the overall configuration of a first embodiment of the present invention, FIGS. 2(A) and (B) are explanatory views explaining the operation of the first embodiment, and FIG. is a circuit diagram showing the configuration of the second embodiment, FIGS. 4(^) and (B) are waveform diagrams explaining the operation of the second embodiment, and FIG. 5 is a circuit diagram of the third embodiment. The perspective view showing the configuration and FIGS. 6(A) and 6(8) are characteristic diagrams illustrating the operation of the third embodiment. 1-・Vehicle, 2-・Magnetic sign, 3-・Magnetic sensor, 4
. . . Excitation signal generation means, 5. Magnetic field generation means, 6. Short magnetic flux detection coil, 7. Vehicle position control means, 8.
...Positional deviation detection coil.

Claims (1)

[Claims] 1. A magnetic sign (2) is laid along the travel path of the vehicle (1), and a magnetic sensor (3) attached to the vehicle (1) detects the magnetic sign (2) when the vehicle (1) In a magnetic induction system for a vehicle that enables a vehicle (1) to automatically travel along a running path by detecting a relative positional deviation of a magnetic field generating means (5) that receives the signal (D) and generates a spatial magnetic flux (φ) directed in the width direction of the magnetic sign (2); A short-circuit space magnetic flux (φ') connecting both ends of the magnetic field generating means (5) without
A magnetic induction system for a vehicle, comprising a short-circuit magnetic flux detection coil (6) that interlinks with the short-circuit magnetic flux (φ') and generates a short-circuit magnetic flux detection signal (E) corresponding to a change in the magnetic flux density of the short-circuit space magnetic flux (φ'). . 2. The short-circuit magnetic flux detection coil (6) includes a magnetic field generating means (
2. The magnetic induction system for a vehicle according to claim 1, wherein the magnetic induction system is attached to the magnetic field generating means (5) at a predetermined distance between both ends of the magnetic field generating means (5). 3. A magnetic sign (2) is laid along the route of the vehicle (1), and the relative positional deviation of the vehicle (1) with respect to the magnetic sign (2) is detected by the magnetic sensor (3) attached to the vehicle (1). In a magnetic induction system for a vehicle that enables a vehicle (1) to automatically travel along a running route by detecting magnetic field generating means (5) for generating a spatial magnetic flux (φ) directed in the width direction of the magnetic label (2); (5) Short-circuit space magnetic flux (φ′) connecting both ends of
a short-circuit magnetic flux detection coil (6) that interlinks with the short-circuit magnetic flux (φ') and generates a short-circuit magnetic flux detection signal (E) corresponding to a change in the magnetic flux density of the short-circuit spatial magnetic flux (φ'); vehicle position control means (7) for generating a vehicle position control signal (H) corresponding to the position of the vehicle (1) with respect to the magnetic sign (2) based on E);
Magnetic induction system for vehicles equipped with. 4. The magnetic sensor (3) interlinks with the spatial magnetic flux (φ'') passing through the magnetic sign (2) among the spatial magnetic flux (φ), and detects the position of the vehicle (1) with respect to the magnetic sign (2). Claim 1, further comprising a positional deviation detection coil (8) that generates a positional deviation detection signal (G) corresponding to the deviation.
Magnetic induction system for a vehicle according to 2 or 3.