WO2014017163A1

WO2014017163A1 - Position detection device

Info

Publication number: WO2014017163A1
Application number: PCT/JP2013/064756
Authority: WO
Inventors: 茂川瀬
Original assignee: アズビル株式会社
Priority date: 2012-07-25
Filing date: 2013-05-28
Publication date: 2014-01-30
Also published as: JP2014025756A

Abstract

This position detection device comprises: a light projection means that has a light projection window (11) having a predetermined width (W) and a predetermined length (L) greater than said width (W), and that projects a parallel light beam having a constant width from the light projection window (11); a light reception means that has a light reception window (21) having the predetermined width (W) and the predetermined length (L), and that receives the parallel light beam with the light reception window (21); a light amount detection means that outputs a position signal having a magnitude proportional to the amount of light received by the light reception means; and a shielding means that is held so as to be horizontally movable in the length direction of the light reception window (21), and that, in accordance with the position of the object being measured, shields a portion or all of the parallel light beam that enters the light reception window (21). A mask unit is provided on the inner side of the light reception window (21), the mask unit having a form that is thick in the vicinity of the central section of the light reception window (21) in the length direction and that is thin in the vicinity of each end in the length direction and changing the width of the light reception window depending on the position in the length direction such that the intensity of the received light becomes constant irrespective of the position in the length direction of the light reception window (21).

Description

Position detection device

The present invention relates to a position detection device that detects the position of an actuator, for example.

In recent years, various types of linear actuators have been used in production sites depending on the application. For example, a linear actuator having a relatively high response speed is used in operations such as assembly and mounting of electronic parts and pick and place. The movable range is about 1 cm to 10 cm, and high-speed and precise work is realized by performing position feedback control using a position detection device suitable for position accuracy and response speed required for work.

The position detection device is based on the analog type and digital encoder type from the system, the light, magnetism, eddy current, differential transformer, potentiometer type, etc. from the detection principle, and the contact type, transmission type, reflection type, etc. Each can be classified.

As a digital type position detection device using light, there are a laser displacement meter and a digital scale. Digital type position detectors using light have high minimum resolution, good linearity as long as the scale is not deformed, and many advantages such as long stroke measurement. It is often used for high precision devices. However, the sensor itself is expensive, and there is a problem that a complicated and expensive dedicated IC is required as a peripheral circuit.

Some digital scales use magnetism, but are similarly expensive, and are more susceptible to noise generated when the actuator is driven with a large current compared to the optical system.
On the other hand, analog type position detection devices that use light include transmissive photointerrupters, reflective photoreflectors, and those that use magnetism as Hall elements and magnetoresistive elements (AMRs), giant magnetism. There is a resistance element (GMR: Giant Magneto Resistance), an element using an eddy current or a principle of a differential transformer.

The analog type position detection device is more susceptible to noise generated when the actuator is driven with a large current than the digital type. However, the method using light is relatively insensitive to current noise generated by passing a current through the coil of the actuator.

In particular, a fiber unit consisting of a projector and a receiver and an amplifier unit with a built-in light emitting unit and light intensity detector are separated, and an optical fiber type position detection device (hereinafter referred to as “fiber type optical sensor”) in which the fiber unit and amplifier unit are connected by an optical fiber. Is advantageous in that it is not affected by actuator drive current noise at all because the optical sensor and the amplifier can be installed at a location away from the actuator coil.

The fiber unit of the fiber type optical sensor has a transmission type and a reflection type. As an example of the transmission type, as shown in FIG. 1, the light from the optical fiber emitting end 14 installed inside is converted into a parallel light beam by the lens 13, There is a configuration in which the light is changed to the direction of the lens 23 through the

mirror arrays

12 and 22 in which small mirrors are arranged, and the light receiver 2 that condenses the parallel light flux on the fiber incident end 24 by the lens 23.

Particularly, a fiber unit of the type using the

mirror arrays

12 and 22 can produce a parallel light beam having a constant width with a simple configuration including only the

lenses

13 and 23 and the

mirror arrays

12 and 22. As shown in FIG. 2, the light projector 1 and the light receiver 2 are opposed to each other, and the shielding plate 3 is moved in the longitudinal direction of the parallel light flux, whereby the light amount of the light amount detection unit changes in proportion to the position of the shielding plate 3. For this reason, the output of the amplifier unit can also be used as a position detection device by moving the shielding plate 3 to change the light quantity of the light quantity detection unit according to the position.

JP-A-6-258139 JP-A-1-26730

However, there is a problem that the light intensity distribution of the parallel light flux having a constant width produced by the projector 1 is not necessarily uniform.
In particular, in order to increase the width of the parallel light beam produced by the projector 1, it is necessary to increase the width of the mirror array 12, and the aperture of the lens 13 inevitably increases, so that the amount of peripheral light further decreases.
When the amount of light around the lens 13 is reduced, the light intensity distribution of the parallel light beam produced by the projector 1 is maximized at the center in the longitudinal direction of the parallel light beam and decreases as the distance from both ends increases.

The light receiver 2 changes the direction of the parallel light beam produced by the projector 1 by the mirror array 22 to the direction of the lens 23, and the parallel light beam is condensed on the optical fiber incident end 24 by the lens 23, but around the lens of the light receiver 2. The light intensity further decreases due to the influence of the decrease in the amount of ambient light.
Accordingly, the amount of light received by the light quantity detector changes by moving the light projector 1 and the light receiver 2 facing each other and moving the shielding plate 3 in the longitudinal direction of the parallel light flux. However, as described above, the light intensity distribution is not uniform. The amount of light received by the light quantity detection unit is not proportional to the position of the shielding plate 3.
Therefore, since the output of the amplifier unit does not change in proportion to the position of the shielding plate 3, the linearity of the position detection device is lowered, and there is a problem that accurate position detection cannot be performed.

The present invention has been made to solve the above-described problems, and provides a position detection device that can improve the linearity of the position detection device at low cost and detect an accurate position. Objective.

In order to achieve the above object, a position detection device according to the present invention has a projection window having a predetermined width and a predetermined length larger than the width, and projects a parallel luminous flux having a predetermined width from the projection window. A light receiving window having a light receiving window having a predetermined width and a predetermined length, and receiving a parallel light beam by the light receiving window; and a light amount detecting means for outputting a position signal having a magnitude proportional to the amount of light received by the light receiving means. And a shielding means for shielding part or all of the parallel light flux that enters the light receiving window according to the position of the measurement object, and is held inside the light receiving window. The width of the light receiving window, which is thick near the center in the length direction of the light receiving window and thin near the end in the length direction, is long so that the received light intensity is constant regardless of the position in the length direction. A mask portion that is changed according to the position in the vertical direction is provided.

According to this invention, since it is configured as described above, even if there is a variation in light intensity with a simple optical system, the light intensity received is constant regardless of the position in the length direction of the light receiving window. The position of the plate and the output of the optical sensor are proportional, and the linearity of the position detection device can be improved at low cost, thereby enabling accurate position detection. In addition, when determining the width of the light receiving window, it can be easily obtained by changing the light sensor output of the light amount detection unit when the shielding plate is moved in the length direction of the light receiving window without performing complicated calculations. Can do.

It is a side view which shows schematic structure of the position detection apparatus which concerns on Embodiment 1 of this invention. It is explanatory drawing which shows schematic structure of the state by which the shielding board is arrange | positioned between the light projector and light receiver which are shown in FIG. It is a block diagram which shows the whole structure of the position detection apparatus which concerns on Embodiment 1 of this invention. It is explanatory drawing shown about the fall of the peripheral light amount of a lens. It is explanatory drawing shown about the fall of the light intensity by the fall of the peripheral light amount of a lens. It is explanatory drawing shown about the linearity of the optical sensor output of a light quantity detection part. It is explanatory drawing shown about correction | amendment of the light intensity in the position detection apparatus which concerns on Embodiment 1 of this invention. It is explanatory drawing which shows the linearity of the optical sensor output by correction | amendment of the light intensity in the position detection apparatus which concerns on Embodiment 1 of this invention. It is explanatory drawing which shows the mask part of the position detection apparatus which concerns on Embodiment 1 of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Embodiment 1 FIG.
1 is a side view showing a schematic configuration of a position detection apparatus according to Embodiment 1 of the present invention. 2 is an explanatory view showing a schematic configuration showing a state in which the shielding plate 3 is arranged between the projector 1 and the light receiver 2 shown in FIG. 1, and FIG. 2 (a) is a side view similar to FIG. FIG. 2 (b) is a partial top view of the light receiver 2 of FIG. 2 (a). FIG. 3 is a block diagram showing the overall configuration of the position detection apparatus according to Embodiment 1 of the present invention.
This position detection device includes a fiber unit 41 including a light projector 1 and a light receiver 2, a light emitting unit 5, an amplifier unit 42 incorporating a light amount detection unit 6, and a shield that blocks light projected from the light projector 1 to the light receiver 2. The plate 3 is provided, and the fiber unit 41 and the amplifier unit 42 are connected by the optical fiber 4.

The light projector 1 and the light receiver 2 have a light projection window 11 and a light reception window 21 having the same shape. The light projection window 11 and the light reception window 21 have a predetermined width W and a predetermined width larger than the width W. It is the rectangular shape comprised by length L (refer FIG.2 (b)). And the light projection window 11 of these light projectors 1 and the light reception window 21 of the light receiver 2 are arrange | positioned facing each other so that it may correspond, seeing from a light beam direction.
The projector 1 converts the light from the optical fiber output end 14 guided by the optical fiber 4 into a parallel light beam by the lens 13 and changes the direction of the parallel light beam to the direction of the light receiver 2 by a mirror array 12 in which small mirrors are arranged. Shine.

The light receiver 2 receives the parallel light beam from the projector 1, reflects the direction of the light toward the lens 23 by the mirror array 22 in which small mirrors are arranged, and the parallel light beam is transmitted to the optical fiber incident end 24 by the lens 23. Condensate.
In addition, the amplifier unit 42 receives light from a light source such as an LED, which is guided to the projector 1 by the optical fiber 4, and receives the light that is condensed and guided to the optical fiber 4 by the light receiver 2 by the optical sensor. And a light amount detector 6 for outputting a value proportional to.

The shielding plate 3 has a surface that is perpendicular to the parallel light flux and has a width direction of the light receiving window 21 larger than W, and is held so as to be horizontally movable in the length direction (x direction) of the light receiving window 21. The shielding plate 3 moves horizontally according to the position of the measurement target, and shields part or all of the parallel light flux that enters the light receiving window. From the point (x = 0) at which the shielding plate 3 reaches one end of the light receiving window 21 and begins to block the parallel light beam, the point at which the shielding plate 3 reaches the other end of the light receiving window 21 and blocks all the parallel light beam (x = L) By the time, the amount of light reaching the light amount detector 6 changes from the maximum value (Pmax) to zero.

Accordingly, in the optical path from the lens 13 to the lens 23 via the mirror array 12 and the mirror array 22, if the light intensity distribution of these elements is uniform, the light receiver is proportional to the amount of movement of the shielding plate 3. The amount of received light 2 changes, and the amount of light detected by the light amount detector 6 has good linearity and can be used as a highly accurate position detection device.

However, the light intensity distribution of the constant-width parallel light beam produced by the projector 1 is not necessarily uniform due to the following factors.
1. 1. Lens aberration and decrease in peripheral light quantity 2. Uneven reflectance of mirror array Assembly accuracy of parts

Here, with respect to “2. Reflector unevenness of mirror array”, it is possible to make the reflectance uniform and improve by depositing aluminum on a resin that is less deformed by heat and has high molding accuracy. In addition, “3. Assembly accuracy of parts” can be improved by managing the assembly accuracy.

However, it is difficult to satisfactorily correct the above-mentioned “1. Aberration of lens 13 and decrease in peripheral light amount” with an inexpensive single lens. FIG. 4 is an explanatory diagram showing the aberration of the lens and the decrease in the amount of peripheral light. As shown in FIG. 4, the amount of light at the end (periphery) portion of the lens 13 is lower than the light transmitted through the central portion of the lens 13. In particular, in order to widen the width of the parallel light beam produced by the projector 1, it is necessary to widen the width of the mirror array 12, and the aperture of the lens 13 inevitably increases, so that the amount of peripheral light further decreases.

FIG. 5 is an explanatory diagram showing a decrease in light intensity due to a decrease in the amount of light around the lens. As shown in FIG. 5, the light intensity of the parallel light beam produced by the projector 1 when the peripheral light amount of the lens 13 is reduced is the center (x = L / 2) in the longitudinal direction (length direction of the window) of the parallel light beam. It becomes maximum and decreases as it approaches both ends (x = 0, L).
The light receiver 2 changes the direction of the parallel light beam produced by the projector 1 by the mirror array 22 to the direction of the lens 23, and the parallel light beam is condensed on the optical fiber incident end 24 by the lens 23. The light intensity further decreases due to the influence of the decrease in the amount of light.

Therefore, the amount of light received by the light quantity detector 6 is also changed by making the projector 1 and the light receiver 2 face each other and moving the shielding plate 3 in the longitudinal direction of the parallel light flux, but the light intensity distribution is the length of the light receiving window 21 as described above. Since each position in the vertical direction is not uniform, as shown in FIG. 6, the light sensor output e (x) of the light quantity detection unit 6 is not proportional to the position of the shielding plate 3, and the light intensity is uneven, so that the output is output. Also decreases. The upper one-dot chain line shown in FIG. 6 indicates the optical sensor output when the light intensity at the displacement x (x = 0 to L) of the light receiving window 21 is all Pmax, and the lower one-dot chain line. Is an auxiliary line for indicating that the linearity is deteriorated.
Therefore, since the output of the amplifier unit 42 does not change in proportion to the position of the shielding plate 3, the linearity of the position detection device is lowered, and accurate position detection cannot be performed.

Therefore, a method for improving the linearity degradation of the position detection device due to the unevenness of the light intensity distribution in the present invention will be described below.
The light intensity at the optical fiber incident end 24 of the light beam passing through the displacement x of the light receiving window 21 of the light receiver 2 shown in FIG. The change of the light intensity p (x) can be obtained by differentiating the optical sensor output e (x) when the shielding plate 3 is at the displacement x of the light receiving window 21, and the displacement x and the light intensity p (x). FIG. 5 shows the relationship.
As shown in FIG. 5, the light intensity p (x) at the optical fiber incident end 24 obtained in this way is the maximum (maximum value Pmax) when the displacement x is near L / 2 (near the central portion in the length direction of the window). ), And the vicinity of the end in the length direction (x = 0, L) is the minimum (Pmin). Therefore, in order to make the light intensity constant regardless of the position of the displacement x, correction is made so that the light intensity becomes Pmin at all positions in the length direction (x = 0 to L) as shown in FIG. To do.

As a result, the optical sensor output e (x) obtained by integrating the light intensity p (x) with the displacement x is proportional to the displacement x, so that the output value is slightly lowered as a whole, but the position detection device as shown in FIG. Can improve the linearity. 8 indicates the case where the light intensity at the displacement x (x = 0 to L) of the light receiving window 21 is all Pmax, and the lower dashed line indicates the light receiving window. It is shown that the linearity is improved although the light output is slightly lowered by correcting all the light intensities at 21 displacement x (x = 0 to L) to be Pmin.

Next, a specific method for making the light intensity p (x) at the optical fiber incident end 24 constant regardless of the displacement x will be described below.
The light intensity p (x) at the optical fiber incident end 24 of the light beam at the displacement x of the light receiving window 21 is proportional to the width of the light receiving window 21. Therefore, as shown in FIG. 9, the original width of the light receiving window 21 is W, and the window width w (x) to be set in the displacement x of the light receiving window 21 is set as follows using the value of the light intensity p (x). Calculated according to equation (1).
w (x) = W × Pmin / p (x) (1)
The mask portion 25 is provided inside the light receiving window 21 so that the window width at the displacement x becomes the calculated window width w (x) to be set.

Here, if the window width w (x) to be set at the displacement x (x = 0, L) at which the light intensity p (x) is the minimum value Pmin is calculated using Expression (1), W is obtained. The mask portion 25 may not be provided.
Similarly, the window width w (x) to be set at the displacement x (x = L / 2) at which the light intensity p (x) is the maximum Pmax is W × Pmin / Pmax.
That is, as shown in FIG. 9, the mask portion 25 is formed so that the vicinity of the central portion in the length direction of the light receiving window 21 is thick and the vicinity of the end in the length direction is thin. The width of the light receiving window 21 becomes W × Pmin / Pmax near the displacement x = 0, L, and W × Pmin / Pmax near the displacement x = L / 2. The light intensity received by the light amount detection unit 6 becomes constant regardless of the position in the length direction of the light receiving window 21 by adjusting so as to satisfy the above formula.

Then, by providing the mask portion 25 so that the width W of the light receiving window 21 is set to the window width w (x) to be set calculated by the expression (1), the optical fiber incident on the light beam passing through the displacement x of the light receiving window 21. The light intensity p (x) at the end 24 can be set to a constant value Pmin regardless of the position of x, and the optical sensor output e (x) of the amplifier unit 42 obtained by integrating the light intensity p (x) with the displacement x. Since it changes in proportion to the displacement x, the linearity of the position detection device can be improved.

As described above, according to the first embodiment, the light projection window 11 having the predetermined width and the predetermined length larger than the width and projecting the parallel light flux having a constant width from the light projection window 11 is provided. A light receiving window 21 having a light receiving window 21 having a predetermined width and a predetermined length and receiving a parallel light beam by the light receiving window 21; and a position signal having a magnitude proportional to the amount of light received by the light receiving means 2. And a shielding means 3 that is held so as to be horizontally movable in the length direction of the light receiving window 21 and shields part or all of the parallel light flux that enters the light receiving window 21 according to the position of the measurement target. The light receiving window 21 is thick inside the light receiving window 21 so that the intensity of light received is constant regardless of the position of the light receiving window 21 in the length direction. A mask that changes the width of the light-receiving window, which is thin in the vicinity, according to the position in the length direction 5, even if there is a variation in light intensity with a simple optical system, the light intensity received is constant regardless of the position of the light receiving window 21 in the length direction. The output of the sensor is proportional, the linearity of the position detection device can be improved at low cost, and accurate position detection is possible. Further, when the width of the light receiving window 21 is determined, it can be easily obtained by a change in the light sensor output of the light amount detection unit 6 when the shielding plate 3 is moved in the length direction without performing a complicated calculation. it can.

In the present invention, any component of the embodiment can be modified or any component of the embodiment can be omitted within the scope of the invention.

The position detection apparatus according to the present invention includes shielding means for shielding part or all of the parallel light flux entering the light receiving window according to the position of the measurement target, and is located inside the light receiving window at a position in the length direction of the light receiving window. Regardless of this, a mask part that changes the width of the light-receiving window according to the position in the length direction is provided so that the light intensity received is constant, and the linearity can be improved at low cost and the accurate position can be detected. Therefore, it is suitable for use in detecting the position of a linear actuator or the like.

DESCRIPTION OF SYMBOLS 1 Light projector 11

Light projection window

12, 22

Mirror array

13, 23 Lens 14 Optical fiber output end 2 Light receiver 21 Light reception window 24 Optical fiber incident end 25 Mask part 3 Shielding plate 4 Optical fiber 41 Fiber unit 42 Amplifier unit 5 Light emission part 6 Light quantity detection part

Claims

A light projecting unit having a light projection window having a predetermined width and a predetermined length larger than the width, and projecting a parallel light flux having a constant width from the light projection window;
A light receiving means having a light receiving window of the predetermined width and the predetermined length, and receiving the parallel light flux by the light receiving window;
A light amount detecting means for outputting a position signal having a magnitude proportional to the amount of light received by the light receiving means;
A shielding unit that is held so as to be horizontally movable in the length direction of the light receiving window and shields part or all of the parallel light flux that enters the light receiving window according to the position of the measurement target;
Inside the light receiving window, the light receiving window has a thick central portion in the length direction and a length near the end so that the received light intensity is constant regardless of the position in the length direction of the light receiving window. A position detecting device characterized in that a mask portion is provided that changes the width of the light receiving window formed thinly according to the position in the length direction.