DE102006019491A1 - Optical encoder has light source, a main scale, which has a first grid, and a second grid, which has a 4N group of slots arranged in a sample matrix, whereby each group of slot has several slots - Google Patents

Abstract

Optical encoder has a light source, a main scale, which has a first grid, and a second grid, which has a 4N group of slots arranged in a sample matrix, whereby each group of slot has several slots. Optical encoder also has a light receiving element which is designed to produce four types of periodically displaced signals. Each of the columns of the second grid has types of four of slots, which corresponds four types of displaced signals. Any combination of four groups of slot, which are arranged in a sample matrix consists of 2 rows and 2 columns.

Description

The The invention relates to an optical encoder that is robust against disorders, how a fouling or build-up bead is on a scale.

5 Fig. 16 is a perspective view showing an example of an optical system used in a conventional optical encoder. A light-emitting element 1 generates light through a collimator lens 2 happens. After the light through the collimator lens 2 happened, the light spreads in a focused parallel beam towards a main scale 3 out. The light passes successively the main scale 3 and an index scale 4 before it is on a light-receiving surface of a light-receiving element 5 arrives. The light receiving element 5 can convert the received light into an electrical signal. The main scale 3 may be formed of a metallic film deposited on a glass substrate and partially removed by etching. The main scale 3 is an optical grating (hereinafter referred to as a first grating) having a regular pattern of alternating transmissive regions (ie slits) and non-transmissive regions. The grid line or lines of the main scale 3 is / are perpendicular to the longitudinal direction of the main scale 3 , The index scale 4 can be formed by applying a metallic film on a glass substrate and then partially removing the film by etching. The index scale 4 is an optical grating (a second grating) which has a regular pattern of alternating transmission areas (slits) and non-transmission areas.

In such an optical system, the main scale 3 be moved or moved along its longitudinal direction. The positional relationship between the optical grating, which is on the main scale 3 is formed, and the optical grating which is on the index scale 4 is formed, varies depending on any shift of the main scale 3 , The quantity of the transmitted light changes periodically, and accordingly, the light receiving element generates 5 a periodically changing displacement signal. The shift signal has a period equal to a pitch P of the optical grating which is on the main scale 3 is trained.

Generally For example, an optical encoder may have such a periodic displacement signal, which is available is when the main scale shifts, electrically interpolate and divide to ensure high resolution. To this end For example, the optical system can generate four types of displacement signals. which have mutual phase differences of 90 degrees. In In the following description, "a", "b", "a /", and "b /" represent the four types of Displacement signals of related or similar optical systems The displacement signals "b", "a /" and "b /" have a phase difference, in electrical angles, of 90 degrees, 180 degrees and 270 degrees with respect to the Shift signal "a".

The displacement signals of an optical encoder can be considered sine waves. Represents "x" a shift of the main scale 3 in its longitudinal direction, four kinds of shift signals can be expressed by K + M × sinX, K + M × cosX, K-M × sinX and K-M × cosX, respectively. "K" represents an offset component and "M" represents the amplitude. In the following description, the four types of shift signals are referred to as signals Sa, Sb, Sa / and Sb /, respectively. According to a general interpolation and division method, a difference signal SA based on a subtraction of two signals Sa and Sa / which have opposite phases can be obtained. The difference signal SA can be expressed by 2M · sinX as a result of the cancellation of the offset components. In a similar manner, a difference signal SB, as 2M · cosX, can be obtained as a result of subtracting the signals Sb and Sb / having opposite phases. A ratio of the two difference signals SA and SB can be expressed by sinX / cosX. By calculating an arctangent or by using a reference table, the position can be obtained in a period of a shift signal.

For example, when the four types of displacement signals are the same in causing a change in the offset component or the amplitude as a result of a change in the quantity of light that is emitted from the light-generating element 1 is generated, the offset component based on the difference values are removed in the interpolation and division method. Furthermore, the change in the amplitude has no effect on the ratio of the differential signals SA and SB. Accordingly, no interpolation error is generated.

If however, the four types of shift signals are mutually independent the change the offset component or the amplitude are, can the interpolation and the division will not be executed accurately, and there will be interpolation errors arise.

In order to obtain four types of signals, four slot groups are on the index scale in conventional optical encoders 4 , as in 5 or in 6A shown, provided. 6A represents a combination of four rectangular slit groups arranged in a matrix pattern consisting of 2 rows and 2 columns. Each slot group includes a plurality, for example, tens to hundreds of slots. The period of the slots on the index scale 4 corresponds to the period of the slits on the main scale 3 , In the following description, Ga, Gb, Ga / and Gb represent slit groups which can respectively generate the displacement signals Sa, Sb, Sa / and Sb /.

For example, in order to obtain shift signals having different phases, the slots belonging to the slot group Gb may be slightly inclined in the longitudinal direction of the main scale 3 with respect to the slots belonging to the slot group Ga. In this case, the amount of offset is P / 4, where P represents the period of the shift signal. The shift signal obtained from the slot group Gb / has a phase difference of 90 degrees, in electrical angles, with respect to the shift signal obtained from the slot group Ga. Similarly, the slots belonging to the slot group Ga / are offset with nP + P / 2 (n is an integer) relative to the slots belonging to the slot group Ga. The shift signal obtained from the slot group Ga / has a phase difference of 180 degrees in electrical angle with respect to the shift signal obtained from the slot group Ga.

The beam which has passed through these slot groups may enter the light receiving element 5 enter. The light receiving element 5 has four separate light receiving regions which are in the form of the respective slot groups Ga, Gb, Ga / and Gb / of the index scale 4 correspond. Each light receiving region has a photoelectric conversion function for converting the incoming beam into an electrical signal. So the light receiving element 5 generate four types of electrical signals corresponding to the four separate light-receiving regions.

6B Fig. 12 illustrates another combination of four rectangular slit groups Ga, Gb, Ga / and Gb / which are lined up in the longitudinal direction so that the four slit groups can generate displacement signals having mutual phase differences of 90 degrees.

It is now assumed that a pollution or the like on the main scale 3 is available. 7A shows pollution on the main scale 3 , Shifts the Haupka-la 3 relative to the index scale 4 , blocks pollution on the main scale 3 partially a jet, which has the slots on the main scale 3 happens so that the light receiving element 5 within the shadow of pollution no light is received. As a result, the shift signals are disturbed. 8A shows a displacement movement of pollution on the main scale 3 (with reference to a hatched area in 7A ) relative to the slot groups Ga, Gb, Ga / and Gb /, which are on the index scale 4 (out 6A ), which is observed when the main scale 3 relative to the index scale 4 emotional. For simplicity shows 8th the main scale 3 Not.

Moves the main scale 3 from left to right in the drawing, the fouling first affects the slot group Ga, and accordingly, the displacement signal Sa is largely attenuated. Next, the pollution affects the slit group Gb /, and accordingly, the shift signal Sb / is largely attenuated. In this way, the displacement signals are successively attenuated. As described above, the corresponding displacement signals independently generate variations in the offset component or the amplitude. Thus, the contamination can generate large interpolation errors.

Furthermore, in case of using an index scale, which slot groups, as in 6B As shown in FIG. 1, the fouling first affects the slot group Ga as shown in FIG 8B and accordingly, the displacement signal Sa is largely attenuated. Then, the contamination sequentially deteriorates the slit groups Gb, Ga / and Gb /, and the shift signals Sb, Sa / and Sb / are largely attenuated in this order. Similar to the index scale, which in 6A is shown, the pollution can cause large interpolation errors.

A joint (that is, a joint area) of the main scale can also produce interpolation errors. Mostly the main scale is made of a glass material. Due to intrinsic limitations, the length of a glass section is rarely more or greater than 2 m to 3 m. Therefore, to locate a long distance or stroke, it is necessary to join a plurality of sections together to form a main scale of sufficient length. When this is done, the main scale has at least one construction line along a line that is perpendicular to the longitudinal direction. 7B shows an example of a main scale, which is composed of a plurality of components. In a region corresponding to the joint (that is, the hatched region), no slit may be provided on the main scale become.

Moves out the main scale 7B relative to an underlying index scale, a light beam blocked by the junction on the main scale does not reach the light receiving element via the slit groups of the index scale, and accordingly the displacement signals will be disturbed. For example, if an index scale is used, the slot groups as in 6A 1, the groove first obscures the slit groups Ga and Gb with respect to the movement of the main scale, which shifts from left to right. The displacement signals Sa and Sb are attenuated. Next, the groove affects the slit groups Ga / and Gb /, and accordingly, the displacement signals Sa / and Sb / are attenuated. In this case, the displacement signals are successively attenuated. As described above, corresponding shift signals independently cause variations in the offset component and the amplitude. This allows the joint to generate large interpolation errors.

Furthermore, if an index scale with slot groups as in 6B As shown, the gap first influences the slit group Ga, and accordingly, the displacement signal Sa is attenuated. Then, the groove sequentially affects the slit groups Gb, Ga / and Gb / and, accordingly, the shift signals Sb, Sa / and Sb / are decreased in this order. Again, the joint can produce large interpolation errors.

Of Further, as described in international patent application WO 01/031292, several light receiving areas for each signal must be provided to average out faults due to contamination. However, the polling effect is in this publication is revealed, insufficient, if the scale is a joint, a partial pollution or a another type of defective or broken slot has.

As From the foregoing description, the layout becomes from conventional slot groups disadvantageous due to contamination or a joint on the main scale affected. This generates interpolation errors.

The The present invention relates to an optical encoder, includes slot groups arranged in such a pattern, that adverse effects or effects of pollution or a groove on the main scale evenly between respective displacement signals can be distributed.

The accompanying drawings, which form a part of the description and to which the description refers, embodiments of the invention and, together with the description, serve the principles to explain the invention. In these show:

1A and 1B an index scale and a light receiving element according to a first embodiment of the present invention;

2A and 2 B the function of the index scale, according to the first embodiment of the invention;

3 a perspective view of an optical system, according to a second and third embodiment of the invention;

4A and 4B Slot groups, according to a fourth embodiment of the invention;

5 a perspective view of a conventional optical system;

6A and 6B Examples of an index scale used in a conventional optical system;

7A and 7B Examples of a main scale used in a conventional optical system; and

8A and 8B the function of an index scale used in a conventional optical system.

in the Below are exemplary embodiments of the invention described with reference to the figures.

Embodiment 1

The optical system of a first embodiment of the invention, except for the arrangement of the index scale and the light receiving element, is substantially the same as the conventional optical system as shown in FIG 5 is shown.

1A FIG. 11 shows an example of an index scale used in the optical encoder according to the first embodiment. An optical grating (that is, a second grating) is formed on the index scale. In the embodiment is a set of 16 slit groups arranged in a matrix pattern consisting of 4 lines (in the vertical direction) and 4 columns (in the lateral direction). Each slot group includes a plurality of slots. The slit groups Ga1, Ga2, Ga3 and Ga4 can respectively generate shift signals having the same phase.

1B shows a light receiving element which is disposed behind the index scale in the optical direction of the light emitted from the light source. A total of 16 light-receiving surfaces corresponding to the 16 slot groups of the index scale are formed on the light-receiving element. The light entering each light receiving surface can be converted into a displacement signal. 1B shows displacement signals Sa1, Sa2 Sa3, Sa4, ... obtained from the 16 light receiving surfaces. The sum of the signals Sa1, Sa2, Sa3 and Sa4 is equal to, for example, the conventional offset signal Sa, and the sum of the signals Sb / 1, Sb / 2, Sb / 3 and Sb / 4 is equal to the conventional deviation signal Sb ,

On similar Way you can the slot groups Gb1, Gb2, Gb3 and Gb4 each have deviation signals generate that have the same phase. The displacement signals, the are obtained from the slit groups Gb1 to Gb4 have phase differences of 90 degrees with respect to the displacement signals coming from the slot groups Ga1 to Ga4 are obtained. The shift signals coming from the slot groups Ga / 1 to Ga / 4 have phase differences of 180 degrees with respect to the displacement signals coming from the slot groups Ga1 to Ga4 are obtained. The displacement signals used by the Slot groups Gb / 1 to Gb / 4 are obtained, have phase differences of 270 degrees with respect to the displacement signals coming from the slot groups Ga1 to Ga4 are obtained. In other words, the slot groups, which are labeled with different letters (for example a or a /), displacement signals with mutually different phases produce. The slot groups, which are denoted by the same letters are, can, too if they are labeled with different numbers, shift signals generate, which have the same phases.

• 1. Es gibt vier (das heißt a, b, a/ und b/) Arten von Schlitzgruppen und jede Art beinhaltet dieselbe Anzahl von Schlitzgruppen (das heißt vier Schlitzgruppen);
• 2. Jede Spalte beinhaltet vier (a, b, a/ und b/) Arten von Schlitzgruppen; und
• 3. Jede Kombination von vier Schlitzgruppen, die in einer rechteckigen Form angeordnet ist, wie eine Matrix, welche aus 2 Zeilen × 2 Spalten besteht, beinhaltet jede der vier Arten der Schlitzgruppen.

As in 1A and 1B In this embodiment, a plurality of slit groups are arranged in a matrix pattern consisting of 4 vertical columns or lines x 4 lateral rows or rows satisfying the following three conditions:

• 1. There are four (ie a, b, a / and b /) types of slot groups and each type contains the same number of slot groups (ie four slot groups);
• 2. Each column contains four (a, b, a / and b /) types of slot groups; and
• 3. Each combination of four slot groups arranged in a rectangular shape, such as a matrix consisting of 2 rows × 2 columns, includes each of the four types of slot groups.

For example, in an optical encoder using the slit groups arranged as described above, soiling on the main scale 3 (please refer 7A ), a projected fouling region shifts as indicated by arrows in FIG 2A displayed, according to a movement of the main scale relative to the index scale. A slot group blocked by the fouling region will not receive light and thus generate a shift signal which is reduced or attenuated in the offset component or the amplitude. However, according to this embodiment, four slit groups are substantially uniformly affected by the scum, unlike the conventional optical system described above in which only one slit group is affected by the scumming.

There the four types of slot groups close to each other, as described above, can be arranged (for example as a matrix), can continue to ensure be that any region on the index scale regularly or respectively in principle four (a, b, a / and b /) may include types of slot groups. In other words, independent from the position of pollution becomes the impact that this Effect on each of the four types of slot groups will have in the Be essentially the same.

In the equations containing the four types of displacement signals express (that's Sa = K + M · sinX, Sb = K + M × cosX, Sa / = K - M · sinX and Sb / = K - M · cosX), more precisely, the offset component K as a result of a Subtraction between Sa and Sa / and as a result of a subtraction between Sb and Sb / extinguished when the offset component K in the corresponding signals enlarged or at the same rate reduced. Furthermore, the amplitude M has no effect on the result of calculation, when the amplitude M coincides with the same Rate in the corresponding signals increased or decreased, as the final Position, based on the ratio 2M · sinX / 2M · cosX calculated becomes. In practice you can the corresponding signals change independently of each other. Compared with the conventional one described above Technique, however, this embodiment Mostly Reduce interpolation error.

If further, a gap on the main scale 3 is present as in 7B As shown by arrows, a projected joint region moves as shown by arrows 2 B displayed, in accordance with a movement of the main scale 3 relative to the index scale 4 , The slot group, when blocked by the joint region, can not receive the light and accordingly generates a shift signal that is reduced or attenuated in the offset component or the amplitude. However, according to this embodiment, each column includes four types of slot groups corresponding to four kinds of shift signals, whereas according to the above-described conventional technique, only one slot group is affected by the joint. According to this embodiment, the four kinds of slit groups are uniformly affected by the joint. Thus, this embodiment can greatly reduce interpolation errors.

The Index scale used by this embodiment includes a total of 16 slot groups, which are arranged in a matrix pattern of 4 rows × 4 columns. However, any index scale containing the above three Conditions fulfilled, be used. For example, the index scale of this embodiment have a total of 64 slot groups, which in one Matrix pattern of 8 lines × 8 Columns are arranged, or may have more slot groups. The formation of as many slot groups as possible is advantageous with respect to on improving the effect of extinguishing or balancing the adverse effect of pollution on the four types of slit regions, since every pollution a unique shape and size.

Even though Furthermore, the description of this embodiment, as described above, on a transmission-type optical system or Durchlaß-type, which includes a light source, the sends out a beam that passes through the slits of a main scale can penetrate and reaches a light receiving element is appropriate this embodiment anyone not permeable or not transferring Area of the main scale is a metallic film, which has a higher reflectivity. The pattern of an alternating permeable area and a non-permeable Area can thus be replaced by a similar pattern, in the non-reflective areas and reflective areas change. Accordingly, this embodiment be applied to a reflection-type optical system, which has a light receiving element which is on the same side like a light source the main scale is arranged. An optical system of the reflection type may also be used in conjunction with any of the following embodiments become.

Embodiment 2

3 shows an optical system according to a second embodiment of the invention. In the second embodiment, no index scale is used. Instead, slots are directly on the light receiving element 105 intended.

More specifically, the light receiving element has 105 a variety of light receiving surfaces, as in 1B shown. First, a transparent insulating film is formed on the light receiving element 105 educated. Subsequently, a metallic film is formed on the transparent insulating film by evaporation or sputtering. Subsequently, the metallic film is partially removed by etching to form slit groups similar to those 1A train.

There formed the index scale and the light receiving element integrally can, the arrangement according to the second embodiment offer a more compact optical system compared to the first Embodiment. Furthermore needed the system according to the second embodiment No preparatory work to align the index scale in With respect to the light receiving element. Such alignment work be in the first embodiment needed because the light passing through the slit groups on the index scale occurs, exactly one corresponding light receiving surface of the Must reach Lichtempfangselementes. In this regard, the system can after the second embodiment easier a highly accurate positioning of the light receiving surfaces and realize the slot groups, since the positioning in the second embodiment as a semiconductor process.

More accurate said, each slot group will have a smaller area if the total number of slot groups is increased to those described above to increase the balancing effect. In such a case can with the second embodiment the slot groups are more accurately aligned with respect to the light receiving surfaces. Accordingly, the second embodiment may be preferable when the total number of slot groups is large.

Embodiment 3

According to a third embodiment, the invention provides a method of forming the light receiving surfaces having a slot arrangement on the light receiving element. In the manufacturing process of the light receiving element, each light receiving surface having a light receiving sensitivity can be arranged in a slot arrangement similar to that in FIG 1A shown, trained. Then, the total light receiving surface having a slot arrangement, for example, a light receiving surface corresponding to Ga1, be connected to a conductive pattern. With this arrangement, signals similar to those of the second embodiment can be obtained. The third embodiment is relatively simple as compared with the second embodiment because both the formation process of the metallic film and the etching process of the metallic film can be omitted.

Embodiment 4

Next, the above-described index scale or slit groups formed on the light-receiving element will be described in more detail. As the simplest example, as in 4A As shown, a slot group includes a plurality of slots. The period P of the plurality of slots is substantially equal to the period of the slots arranged on the main scale. By defining the positional relationship between the slits on the main scale and the slots of the slit groups, in this way, by changing the positional relationship between the opposing slits, the amount of transmitted light can be changed. With respect to a relative shift of the main scale, a shift signal having a substantially sine shape may be generated as described in the description of the conventional art.

however the current displacement signal has higher harmonic components whose periods are equal to 1/2 or 1/3 of the signal period. In general can be a displacement signal, which has higher harmonic components has, greater interpolation error produce. Furthermore, higher harmonic components tend to, depending from the distance or the gap between the main scale and the index scale or depending on Manufacturing errors of the slots to vary. Because of that, higher harmonious Components not by simply correcting them by interpolation calculations be removed.

The fourth embodiment of the invention proposes an effective layout of a plurality of slots in a slot group that can remove higher harmonics. 4B shows an example of a slot layout that is both higher harmonics 3 , Order as well as higher harmonics 5 , Can remove order. According to the in 4B As shown, the gap between the two slots SL1 and SL2 is smaller by the size P / 6 than the slot period P of the main scale (that is, the gap between SL1 and SL2 is P - P / 6). Similarly, a distance between two slots SL3 and SL4, a distance between SL5 and SL6, and a distance between SL7 and SL8 is P - P / 6. With this modified arrangement, the higher order harmonics having a period P / 3 can cancel each other out.

Of Further, a space between two slots SL1 and SL3 is around P / 10 less than twice the slot scale P of the main scale (the is called the distance between SL1 and SL3 is 2P - P / 10). Similarly, there is a gap between two slots SL2 and SL4, a gap between SL5 and SL7 and a distance between SL6 and SL8 equals 2P - P / 10. With this modified Arrangement can the higher harmonics of the 5th order, which have a period of P / 5, are mutually canceled out.

On In this way, the method of the fourth embodiment, the higher harmonics the 3rd and the higher 5th order harmonics from the corresponding displacement signals remove and accurate sinusoidal signals that are not disturbed or distorted, preserved. By using a similar method, harmonics can be used of the 7th order and higher Order also extinguished become. Furthermore you can higher harmonic Components of 2nd order and other straight orders by one Subtraction of two displacement signals are removed, the one Phase difference of 180 degrees, for example Sa and Sa / or Sb and Sb /, as above in the interpolation and division method described. Will the slot layout of the fourth embodiment Applied to appropriate slot groups, interpolation errors can be reduced and a high accuracy of the position detection can be realized.

The Invention can also be applied to a rotary encoder, the one circular Main scale for detecting a rotation angle has. Furthermore the invention is not on encoders of the transmission type or transmission type limited, its optical system described in the above-mentioned embodiments is, but can also apply to an encoder of the reflection type be applied, which has a main scale of the reflection type.

As described above, without enlargement of the Number of essential components or components, detrimental Effects of soiling or fugue on the main scale resolved between the different displacement signals or be compensated, and interpolation errors can be largely reduced. Furthermore, suggests the invention before, the total number of slot groups on an index scale are arranged to increase and the slot groups accordingly order the rules described above, which means interpolation errors, that result from a fouling or fugue on the main scale, very clearly can reduce.

While the Invention has been described with reference to exemplary embodiments, is understandable, that the invention is not limited to the described exemplary embodiments is limited. The scope of the following claims should be construed broadly so that all modifications, equivalent versions and functions are included.

Claims (6)

Optical encoder with a light source, one Main scale, which has a first grid, a second grid, which 4N (N is an integer greater than or equal to equal to 2) has slot groups which are in a matrix pattern are arranged, each slot group having a plurality of slots, and a light receiving element which is arranged four To generate types of periodic displacement signals, which mutually different phases for detecting a relative Shift the main scale, wherein the second grid four Types of slit groups having four kinds of shift signals correspond and each type has the same number of slot groups; in which each column of the second grid contains the four types of slot groups which correspond to the four types of shift signals; and in which any combination of four slit groups, all in one Matrix patterns are arranged, which consists of 2 rows × 2 columns exists, each of the four types of slot groups, which with the four types of displacement signals correspond, has. Optical encoder according to claim 1, characterized that the second grid is a transmission type grid which a non-transparent film, which is on a transparent carrier is formed, wherein the non-transparent film has a Has area that is removed. Optical encoder according to claim 1, characterized that the second grid is a grid of the transmission type, the one has non-transparent film on the light receiving element and partially removed. Optical encoder according to one of claims 1 to 3, characterized in that each slot group has a plurality of slots arranged in a predetermined pattern are at least one higher Harmonic odd order cancel out in the shift signals is included. Optical encoder with a light source, one Main scale, which has a first grid, a light receiving element, which 4N (N is an integer greater than or equal to 2) has light-receiving region groups arranged in a matrix pattern are arranged, each light receiving region group of several slit Having light receiving regions, and set up the light receiving element is to generate four types of periodic displacement signals, have mutually different phases to a relative Detecting shift of the main scale, wherein the light receiving element has four types of light-receiving region groups associated with the four types of displacement signals correspond and each type having the same number of light-receiving region groups; in which each column of the light-receiving element has the four kinds of light-receiving region groups which correspond to the four types of shift signals; and wherein any combination of four light receiving region groups, arranged in a matrix pattern consisting of 2 rows x 2 columns are, each of the four types of light receiving region groups which correspond with the four types of shift signals. Optical encoder according to claim 5, characterized in that each of the light-receiving region groups has a plurality of light-receiving regions which are arranged in a predetermined pattern, at least one higher Harmonic odd order contained in the shift signals is included, extinguish.