Encoder device

Abstract

An encoder device comprising a readhead for reading a reflective scale located adjacent to the readhead, the readhead comprising a circuit board having mounted thereon a sensor including one or more photodiodes for detecting light reflected from the scale located adjacent to the readhead, and at least one light emitting element, the light emitting element being mounted to the circuit board via a light emitting element support structure that holds the light emitting element away from the circuit board and a sensing surface of the sensor, at least a portion of the light emitting element support structure extending over the sensor.

Description

Technical Field

[0001] The present invention also relates to an encoder device, known as a position measurement encoder, a position encoder, or simply an "encoder". In particular, the present invention relates to a so-called absolute encoder device.

Background Art

[0002] Encoder devices / position measurement devices for measuring the relative position between two movable objects are well known. Usually, a series of scale markings are provided on one object, and a read head for reading the scale markings is provided on another object. The scale markings can be formed integrally with the object or provided on a scale that can be fixed to the object.

[0003] Encoder devices are generally classified as either incremental encoder devices or absolute encoder devices. In an incremental encoder device, the scale has a plurality of periodic markings that can be detected by a read head to provide an incremental up / down count. For example, such a scale is described in Patent Document 1. A reference mark can be provided adjacent to or embedded in the periodic markings to define a reference point. For example, such a scale is disclosed in Patent Document 2. An absolute position encoder device typically measures the relative displacement by a read head that detects a unique series of marks, such as a code, and converts those codes into an absolute position. Such a scale is disclosed in Patent Document 3, and such an encoder is described in detail in Patent Document 4.

[0004] An absolute encoder differs from an incremental encoder in that, at startup, it can determine the absolute position of the read head relative to the scale without requiring relative motion of the read head within the scale. In contrast, in an incremental encoder, the read head must move to a reference mark to determine the zero position.

[0005] Encoder devices can also be classified based on their primary means of detecting scale features, such as optical, magnetic, inductive, and capacitive. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] European Patent Application Publication No. 0207121 [Patent Document 2] International Publication No. 2005 / 124282 [Patent Document 3] International Patent Application No. PCT / GB2002 / 001629 (International Publication No. 2002 / 08423) [Patent Document 4] International Publication No. 2010 / 116144 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] This invention relates to an improved optical encoder device. [Means for solving the problem]

[0008] According to a first aspect of the present invention, an encoder device is provided comprising a read head for reading a reflective scale positioned adjacent to a read head, the read head comprising a circuit board to which a sensor comprising one or more photodiodes for detecting light reflected from the scale positioned adjacent to the read head is mounted, and at least one light-emitting element, the light-emitting element being mounted to the circuit board via a light-emitting element support structure that holds the light-emitting element away from the sensing surface of the sensor. At least a portion of the light-emitting element support structure, and optionally the light-emitting element(s), may also extend over the sensor. In other words, the light-emitting element support structure can overhang the sensor or be "vertically aligned" with the sensor. In particular, the light-emitting element support structure may be configured such that a line extending perpendicular to the plane of the circuit board (or the sensing surface of the sensor) can pass through both a portion of the light-emitting element support structure and the sensor chip.

[0009] Typically, light-emitting elements (or more) for a readhead are mounted directly next to the sensor on the same circuit board as the sensor. The inventors have adopted a novel approach in which the light-emitting elements are mounted (physically / structurally) on the same circuit board as the sensor via a light-emitting element support structure that holds the light-emitting elements substantially away from the circuit board and the sensing surface of the sensor, such that, for example, at least a portion of the light-emitting element support structure may extend over the sensor. Such a support configuration opens up a new range of optical configurations for the readhead. In particular, it allows the light-emitting elements to be positioned substantially longitudinally (e.g., between them) the sensor and other optical components, such as lenses and / or diffracting elements. This helps reduce the total number of optical components required, thereby helping to reduce the size and / or cost of the readhead.

[0010] The light-emitting element support structure holds the light-emitting element away from the circuit board and the sensing surface of the sensor. In other words, the light-emitting element may be positioned away from the circuit board and the sensor chip in a dimension that extends perpendicular to the plane of the circuit board (or the sensing plane of the sensor). In other words, the light-emitting element is positioned off-plane (e.g., in an "elevated position") relative to the sensor on the circuit board. In other words, the light-emitting element support structure suspends the light-emitting element away from the circuit board and the sensor. For example, the distance between the light-emitting element and the sensor, measured perpendicular to the plane of the sensor, may be at least 1 mm, e.g., at least 1.5 mm, e.g., at least 2 mm. More specifically, the distance between the center of the emission surface (or emission point) of the light-emitting element and the sensing surface of the sensor, perpendicular to the sensing surface of the sensor, may be at least 1 mm, e.g., at least 1.5 mm, preferably at least 2 mm, e.g., about 2.5 mm. The said distance may be between 2 mm and 3 mm, e.g., about 2.5 mm.

[0011] A light-emitting element support structure can be described as a “raised” light-emitting element support structure in that it is configured to extend and hold the light-emitting element away from the circuit board and sensor. As is understood, terms such as “raised” and “lifted” are used to help describe the relationships between various components, particularly their relative positions, but are not intended to restrict the orientation of the components being described. For example, the term “raised” can be used to describe a light-emitting element support structure being raised from the circuit board, regardless of its orientation. For example, in this case, the term “raised” can be used even when a readhead is used in an orientation where, relative to gravity / earth, the light-emitting element is held below the circuit board and sensor.

[0012] A sensor can be a sensor chip / component. Therefore, a sensor may include additional elements / components, such as a body / shell / casing / housing for the photodiode(s) and / or other electrical elements of the sensor, as well as the photodiode(s) of the sensor.

[0013] At least one light-emitting element and the sensing surface of the sensor can be separated by a dimension extending perpendicular to the sensing surface of the sensor. In particular, the light-emitting element may be held directly above the sensor. This means that a line extending perpendicular to the sensing surface of the sensor may pass through both the light-emitting element and the sensor.

[0014] The light-emitting element support structure may include a frame. The light-emitting element support structure, e.g., the frame, may be mounted on the circuit board separately from the sensor. In other words, optionally, the light-emitting element support structure, e.g., the frame, may be mounted directly to the circuit board rather than via the sensor. Therefore, the device may be configured such that the light-emitting element support structure (e.g., the frame) does not directly contact / engage with the sensor, for example, by having a gap between the light-emitting element support structure (e.g., the frame) and the sensor.

[0015] A light-emitting element support structure (e.g., a frame) may be seated across the sensor. For example, the light-emitting element support structure (e.g., a frame) may be attached to the circuit board on at least two (opposite) sides of the sensor, optionally three, for example, four / all sides of the sensor.

[0016] A light-emitting element may be mounted on the upper surface of a light-emitting element support structure (e.g., a frame). The upper surface may be fixed to the circuit board via one or more (side) supports extending between the circuit board and the upper surface. Thus, the frame may include a table-like structure.

[0017] The upper surface of the light-emitting element support structure (e.g., frame), and one or more (side) supports may comprise a single piece of material.

[0018] The light-emitting element support structure (e.g., frame) may include an opaque material. Thus, the light-emitting element support structure (e.g., frame) may be configured / arranged (e.g., molded, sized, and / or positioned) such that light returning from the scale can pass through the light-emitting element support structure (e.g., frame) and reach the sensor. For example, the light-emitting element support structure (e.g., frame) may include one or more holes / windows / openings / perforations through which light returning from the scale can pass and reach the sensor.

[0019] Optionally, the light-emitting element support structure may include a transparent material. Therefore, light returning from the scale will pass through the material of the light-emitting element support structure and reach the sensor.

[0020] The light-emitting element support structure (e.g., frame) may include a sheet material structure, e.g., a sheet-metal structure. The use of a sheet material structure may offer significant cost-effectiveness, reduce the mass of the readhead, be advantageous during assembly, for example when setting the height of the light source to be mounted, and provide a more deformable structure than other structures (e.g., machined, molded structures). Optionally, the sheet material is a bendable sheet material structure, i.e., the sheet material is bent to provide a structure / three-dimensional frame that supports the light-emitting element away from the circuit board, for example, to provide top and (side) supports. The sheet material / metal may include one or more defined fold lines (e.g., lines of reduced thickness). Such lines could have been etched into the sheet material. Suitable metal materials include brass, aluminum, tin, cadmium, gold, silver, etc. The light-emitting element support structure (e.g., frame) may be covered with another material. For example, the light-emitting element support structure (e.g., frame) may be coated with brass, aluminum, tin, cadmium, gold, silver, nickel-gold, etc. Preferably, the thickness of the sheet material is 2 mm or less, for example, 1 mm or less, for example, 0.5 mm or less.

[0021] The light-emitting element support structure can be attached to the circuit board via the sensor chip. The light-emitting element support structure can include a transparent material and can cover (or rather, "span across") one or more photodiodes. For example, the light-emitting element support structure can include a piece / block of a transparent material (such as glass, plastic, sapphire, quartz).

[0022] A plurality of light-emitting elements can be provided. In such a case, the plurality of light-emitting elements are preferably provided together so as to function as a single light source. Optionally, the lead head includes only one light-emitting element.

[0023] Optionally, the light-emitting element includes a semiconductor diode without a "cap", without a "package", or without a "lens", for example, a bare die semiconductor diode. The light-emitting element can include, for example, a light-emitting diode (LED), or a laser (such as a vertical cavity surface emitting laser (VCSEL)).

[0024] The light-emitting element support structure can include a conductive material. In this case, the light-emitting element support structure can include the anode and / or the cathode of the light-emitting element.

[0025] Optionally, the device includes a bond wire support structure extending from the circuit board. The bond wire can extend between it and the light-emitting element (to provide the anode and / or the cathode of the light-emitting element).

[0026] The bond wire support structure can include a frame. The bond wire support structure, such as the frame, can be attached to the circuit board separately from the sensor. In other words, optionally, the bond wire support structure, such as the frame, is not attached via the sensor, but rather, is directly attached to the circuit board. Thus, the device can be configured such that there is a gap, for example, between the bond wire support structure (such as the frame) and the sensor so that the bond wire support structure (such as the frame) does not directly contact / engage with the sensor.

[0027] A bond wire support structure (e.g., a frame) may be seated across the sensor. For example, the bond wire support structure (e.g., a frame) may be attached to the circuit board on at least two (opposite) sides of the sensor, optionally three, for example, four / all sides of the sensor.

[0028] Bond wires may be connected to the upper surface of a bond wire support structure (e.g., a frame). The upper surface may be fixed to the circuit board via one or more (side) supports extending between the circuit board and the upper surface. Thus, the bond wire support structure (e.g., a frame) may include a table-like structure.

[0029] The upper surface of the bond wire support structure (e.g., frame), and one or more (side) supports may comprise a single piece of material.

[0030] The bond wire support structure (e.g., frame) may include an opaque material. Thus, the bond wire support structure (e.g., frame) may be configured / arranged (e.g., molded, sized, and / or positioned) such that light returning from the scale can pass through the bond wire support structure (e.g., frame) and reach the sensor. For example, the bond wire support structure (e.g., frame) may include one or more holes / windows / openings / perforations through which light returning from the scale can pass and reach the sensor.

[0031] Optionally, the bond wire support structure may include a transparent material. Therefore, light returning from the scale may pass through the material of the bond wire support structure and reach the sensor.

[0032] The bond wire support structure (e.g., frame) may include a sheet material structure, e.g., a sheet-metal structure. Optionally, the sheet material is a folded sheet material structure, i.e., the sheet material is folded to provide a structure / three-dimensional frame that holds the bond wires away from the circuit board and provides, for example, top and (side) supports. The sheet material / metal may include one or more defined fold lines (e.g., lines of reduced thickness), for example, which could be formed by etching. Suitable metal materials include brass, aluminum, tin, cadmium, gold, silver, etc. The light-emitting element support structure (e.g., frame) may be covered with another material. For example, the light-emitting element support structure (e.g., frame) may be covered with brass, aluminum, tin, cadmium, gold, silver, nickel-gold, etc. Preferably, the thickness of the sheet material is 2 mm or less, e.g., 1 mm or less, e.g., 0.5 mm or less.

[0033] In this specification, the term "light" refers to electromagnetic radiation (EMR) in the range from ultraviolet to infrared. For example, light may be ultraviolet light, visible light, infrared light, or a combination thereof.

[0034] The readhead may include an optical device. The optical device may include a lens, for example, a singlet lens. Optionally, the optical device may include a diffractive optical element, such as a Fresnel zone plate. Optionally, the optical device may include a holographic optical element, such as a lens hologram. The light-emitting element may be held substantially at the focal plane of the optical device, while the sensor is held substantially away from the focal plane of the lens.

[0035] The encoder device could be an incremental encoder device. Therefore, the scale could include an incremental scale. An incremental encoder device could include one or more reference marks for defining one or more reference positions. Optionally, the encoder device could be an absolute encoder device. As understood, in contrast to an incremental encoder, an absolute encoder device can determine the absolute position of the readhead relative to the scale without requiring relative movement of the readhead and the scale. An absolute encoder includes an absolute scale, which includes a set of features defining a series of unique positions along its length. The series of unique absolute positions may be defined by features on multiple tracks, e.g., multiple adjacent tracks. Optionally, the series of unique absolute positions may be defined by features contained on only a single track. For example, absolute position information may be determined from a combination of features acquired along the measured length of the scale. Therefore, the encoder device could be configured to extract absolute position information from an image acquired by a sensor. Such extraction could be performed by the readhead or by a device external to the readhead.

[0036] Optionally, the readhead is configured to read the scale by acquiring at least one separate snapshot (i.e., a snapshot image) of the scale. This can be used, for example, as an alternative to continuously measuring and counting phase. Thus, an image of the scale can be acquired by a readhead that takes separate snapshots of the scale. The snapshot may be acquired at a single moment in time or formed by successively acquiring readings of a smaller range of consecutive sections of the scale. Snapshot reading of a scale can offer several advantages. For example, the maximum operating speed of the scale reader relative to the scale can be greater because it is not limited by the inherent frequency limitations of continuous phase measurement and counting systems. Furthermore, in an optical system that takes snapshots, only the light-emitting element must be on for a short time, which allows for increased light intensity compared to a continuous system without increasing average power consumption or limiting the lifetime of the light source. This increased light intensity may mean that more photons can be captured by the sensor, thus reducing the noise floor of the system and mitigating the effects of positional noise.

[0037] A scale may include a set of features that a sensor can detect to determine the relative motion / position of the scale and the readhead. Such features may be arranged periodically or aperiodically. As can be understood, there are many suitable ways in which features may be defined on a scale. For example, features may be defined by markings having specific electromagnetic radiation (EMR) properties, e.g., specific optical properties, e.g., by a specific light transmittance or reflectance of a part of the scale. Thus, a feature may be defined, for example, by a part of the scale having the smallest reflectance or transmittance value. Optionally, a feature may be defined, for example, by a part of the scale having the largest reflectance or transmittance value. Optionally, a feature may be defined, for example, by the way (e.g., direction) in which it reflects light (e.g., towards and away from the readhead). Features may take the form of lines, points, or other configurations that can be detected by a sensor. A preferred configuration for a one-dimensional scale may include lines in a dimension perpendicular to the measurement dimension, extending across the entire width of the track.

[0038] As described above, the readhead may include at least one optical device. At least one light-emitting element, at least one sensor, and at least one optical device together may form an optical system in which the optical device forms an image of the illuminated area of ​​the reflective scale on the sensor. Preferably, the optical path of the system from the light-emitting element to the sensor passes through the optical device in its path toward the scale and after reflection from the scale. Preferably, the optical path between the light-emitting element and the optical device is direct / non-reflective. Preferably, the optical path between the optical device and the sensor is direct / non-reflective. In other words, the device (e.g., readhead) may include a non-reflective optical path between the light-emitting element and the optical device, and a non-reflective optical path between the optical device and the sensor.

[0039] Preferably, the optical path of light between the light-emitting element and the scale is direct / non-reflective, and the optical path of light between the scale and the sensor proximity is also direct / non-reflective.

[0040] In embodiments where the readhead includes a shell / housing and a window through which light (from the light-emitting element) exits and enters the readhead (in other words, light enters and exits the shell / housing), it is preferable that the entire optical path within the readhead (or within the shell / housing) is direct / non-reflective.

[0041] Such arrangements can enable particularly compact readheads for optical absolute position measuring devices. For example, configuring the readhead so that light emitted from a light-emitting element passes through the same optical device on both the outward and return paths can reduce the number of optical components required. Furthermore, ensuring direct / reflectionless optical paths between the light-emitting element and the optical device, and between the optical device and the sensor, means that reflective optical components (such as mirrors and / or beam splitters) are not required (for example, the readhead may be free of reflective optical components in its optical path). Thus, the number of optical components in the readhead can be further reduced, the compactness of the readhead can be improved, and the complexity can be reduced.

[0042] The device (e.g., a read head, in particular, an e.g., a light-emitting element support structure) may be configured such that the light-emitting element is placed / positioned between the sensor and the optical device (e.g., a lens) in a dimension perpendicular to the plane of the sensor. For example, the light-emitting element may be positioned in the space (or "volume") between the sensor and the optical device (e.g., defined by the outer edges / sides of the sensor and the optical device).

[0043] The light-emitting element can be substantially positioned at the focal plane of the optical device, and as a result, the emitted light is collimated by the optical device. For example, preferably, the light-emitting element is positioned 500 μm (microns) or less from the focal plane of the optical device, more preferably 250 μm (microns) or less from the focal plane of the optical device, and particularly preferably 100 μm (microns) or less from the focal plane of the optical device.

[0044] Optionally, the light reflected by the scale and imaged by the optical device onto the sensor converges toward a point at a specific distance between the optical device and the sensor. Furthermore, the light-emitting element may be positioned at approximately the aforementioned specific distance between the optical device and the sensor.

[0045] Optionally, the ratio of i) the distance between the center (or emission point) of the light-emitting surface of the light-emitting element and the sensing plane of the sensor in a direction perpendicular to the plane of the sensor, and ii) the distance between the center (or emission point) of the light-emitting element and the optical device in a direction perpendicular to the plane of the sensor, is 35:65 or greater, for example 40:60 or greater, optionally 50:50 or greater, preferably 60:40 or greater, for example 65:35 or greater.

[0046] The light-emitting element may be positioned so as to be offset from the optical axis of the optical device. For example, the light-emitting element may be offset from the optical axis of the optical device by 1 mm or less, e.g., 750 μm or less, e.g., 500 μm or less (e.g., measured from the center of the light source's emission zone). Optionally, the ratio of the offset to the focal length of the lens is 1:2.5 or less, e.g., 0.5:2.5 or less.

[0047] Optionally, the direction of the optical path when it strikes the scale and / or reflects from the scale is not perpendicular to the scale. For example, the angle between a line extending perpendicular to the scale (in the illuminated area) and the direction of the optical path when it strikes the scale (and / or reflects from the scale) is 1° or greater, e.g., 2° or greater, e.g., 5° or greater, and optionally, 20° or less, e.g., 15° or less. In other words, optionally, there is an angle (i.e., greater than 0°) between the incident direction and the reflected direction of light that strikes the scale and reflects from the scale, e.g., an angle of at least 2°, e.g., at least 4°, optionally, at least 10°, and e.g., 40° or less, e.g., 30° or less.

[0048] Therefore, optionally, the shape of the optical path when it strikes the scale and / or reflects from the scale is V-shaped. Optionally, the optical path of the system from the light-emitting element to the sensor is substantially diamond-shaped.

[0049] The optical path through the optical device, both toward the scale and after reflection from the scale, may be laterally offset. Therefore, for any given ray passing through the optical system, for example, the point where it exits the optical device toward the scale and the point where it re-enters the optical device after reflection from the scale are different / laterally offset. As can be understood, the optical paths (e.g., light beams) toward the scale and after reflection from the scale may overlap (e.g., partially and, optionally, substantially, but not completely).

[0050] Optionally, both the light-emitting element and the sensor face the optical device and the scale. Both the light-emitting element and the sensor may face the same direction. In other words, the light-emitting element and the sensor may be mounted on the readhead such that the sensor surface is substantially parallel to the light-emitting surface of the light-emitting element.

[0051] Optionally, the image of the scale formed by the sensor and optical device lies behind (e.g., directly behind) the light-emitting element. Optionally, the light-emitting element is positioned such that light rays from the element, reflected by the scale, converge to a single point on their return path, bypassing the element, and then diverge, forming an image of the scale on the sensor (behind the light source).

[0052] As can be understood, an image of a scale is formed when rays from any given point on the scale converge substantially to a specific point of shared location on the image plane (where the sensor is positioned). (A point is "specific" in that, for any given point on the scale, the rays from that point converge substantially to a different point of shared location.) The image may be a spatially filtered image.

[0053] This document describes an encoder device including a read head for reading a reflective scale positioned adjacent to the read head, the read head including a circuit board to which a sensor comprising one or more photodiodes for detecting light reflected from a scale positioned adjacent to the read head is mounted, and at least one light-emitting element, the light-emitting element being held away from the sensing surface of the sensor, and as a result, the distance between the light-emitting element and the sensor, measured in a direction perpendicular to the sensing surface of the sensor, is at least 1 mm. More specifically, the distance between the center of the light-emitting surface (or light-emitting point) of the light-emitting element and the sensing surface of the sensor, in a direction perpendicular to the sensing surface of the sensor, may be at least 1 mm. The distance may be at least 1.5 mm, optionally at least 2 mm, for example, at least 2.5 mm. The distance may be between 2 mm and 3 mm, for example, about 2.5 mm.

[0054] Herein, embodiments of the present invention will be described simply as examples with reference to the following drawings. [Brief explanation of the drawing]

[0055] [Figure 1] This is a schematic isometric view of the position measuring device according to the present invention. [Figure 2] Figure 1 is a schematic diagram of the various optical and electronic components of the lead head of the position measuring device. [Figure 3a] Figures 1 and 2 show schematic diagrams of the optical arrangement of the position measuring devices. [Figure 3b] Figures 1 and 2 show schematic diagrams of the optical arrangement of the position measuring devices. [Figure 4] Figure 1 is a cross-sectional view of the read head. [Figure 5] Figure 1 shows an isometric view of the readhead circuit board, light source, light source support structure, and sensor. [Figure 6a] This is an isometric front view of the light source support structure. [Figure 6b] This is an isometric rear view of the light source support structure. [Figure 6c] This is a top view of the light source support structure. [Figure 7a] This is an isometric front view of the support structure for the bond wire of the light source. [Figure 7b] This is an isometric rear view of the support structure for the bond wire of the light source. [Figure 8] This figure shows an alternative embodiment of the read head according to the present invention. [Figure 9a] This is a schematic plan view of a read head according to the present invention, in which the light source is positioned directly above the sensor. [Figure 9b] This is a schematic plan view of a read head according to the present invention, in which the light source is positioned directly above the sensor. [Modes for carrying out the invention]

[0056] Referring to Figure 1, an encoder device 2 is shown, including a read head 4, a scale 6, and a controller 7. The read head 4 and the scale 6 are mounted on first and second objects (not shown), respectively, which are movable relative to each other. Although the velocity of relative motion may vary, in the embodiment described, the read head 4 and the scale 6 have a known maximum relative acceleration.

[0057] In the embodiments described, scale 6 is a linear scale. However, it will be understood that scale 6 can be a nonlinear scale, for example, a rotational scale (e.g., a disk or ring scale). Furthermore, scale 6 only allows for one-dimensional measurement. However, it does not have to be so; for example, the scale could allow for two-dimensional measurement.

[0058] In the embodiments described, scale 6 is an absolute scale and includes a series of reflective lines 8 and non-reflective lines 10 arranged to encode unique positional data along its length. The data may be, for example, a pseudo-random sequence or a discrete codeword. In other embodiments, the scale may be an incremental scale (with or without reference marks).

[0059] The line width depends on the required position resolution and is typically in the range of 1 μm to 100 μm, more commonly in the range of 5 μm to 50 μm, for example, 10 μm to 30 μm. In the embodiment described, the line width is on the order of 15 μm. The reflected lines 8 and the unreflected lines 10 are typically arranged alternately at a predetermined period. However, to encode absolute position data on scale 6, selected unreflected lines 10 are omitted from scale 6. For example, the presence of an unreflected line may be used to represent a "1" bit, and the absence of an unreflected line may represent a "0" bit.

[0060] As shown in Figure 2, the readhead 4 comprises a light-emitting element / light source 12, an optical device 18, a sensor 20, and a window 22. In this embodiment, the light-emitting element / light source 12 includes a light-emitting diode (LED). Also in this embodiment, the optical device includes a lens 18, but other optical devices may be used. For example, diffractive optical elements such as Fresnel zone plates and / or holographic optical elements, such as a hologram of the lens, may be used. In this embodiment, the sensor 20 includes a complementary metal-oxide-semiconductor ("CMOS") sensor. As is understood, other image sensors may be used instead of the CMOS sensor. For example, a CCD or photodiode array may be used instead.

[0061] The readhead 4 also comprises a CPU 24, a memory device 25 (e.g., an electrically erasable and rewritable read-only memory (EEPROM), or flash memory), and an interface 26. The readhead 4 may also include an analog-to-digital converter for digitizing image data from the sensor 20. Optionally, the analog-to-digital conversion may be performed within the sensor 20 or the CPU 24.

[0062] Light emitted from LED 12 is collimated by optical device 18, then passes through window 22, and strikes scale 6. Scale 6 reflects the light back through window 22, and the light passes through lens 18, then forms a two-dimensional image of the scale on sensor 20 using the light reflected by the scale. Thus, sensor 20 detects a two-dimensional image of a portion of scale 6 illuminated by LED 12. The sensor may include a one-dimensional or two-dimensional array of pixels. For example, the sensor may include a one-dimensional array of 256 elongated pixels whose length is parallel to the lengths of the reflective line 8 and non-reflective line 10 on the scale. Instead of the two-dimensional image arrangement described, a one-dimensional image arrangement may be used, in which a one-dimensional image of the scale is formed on the sensor by the lens.

[0063] LED12 is connected to CPU24, and as a result, LED12 can be operated on demand by CPU24. Sensor20 is connected to CPU24, and as a result, CPU24 can receive an image of the intensity of light striking across image sensor20. Sensor20 is also directly connected to CPU24, and as a result, sensor20 can be operated by CPU24 to take a snapshot of the intensity of light striking across sensor20 on demand. CPU24 is connected to memory25, and as a result, CPU24 can store and retrieve data for use in its processing. Interface26 is connected to CPU24, and as a result, CPU24 can receive requests from external devices such as controller7 (shown in Figure 1) via line40 and output results to external devices. Line40 also includes a power line from which readhead4 is powered.

[0064] As can be understood, absolute position data may be encoded in scale 6 by the absence of not only the non-reflective line 10 but also the reflective line 8, or by the absence of the reflective line 8 instead of the non-reflective line 10. Furthermore, absolute position data may be embedded in scale 6 without adding or removing the reflective line 8 or non-reflective line 10. For example, the line width, the distance between lines, or the line color may be changed in order to embed absolute position data in scale 6. Furthermore, the scale may have features that define absolute position by a specific combination of features acquired along the width of the scale, rather than defining absolute position by a specific combination of features acquired along the measured length of the scale. For example, the scale may contain multiple "barcodes" whose length extends across the scale, for example, approximately perpendicular to the measured length of the scale. Optionally, the scale may contain multiple tracks, and at least one of these tracks, optionally at least two, or possibly all, may contain multiple regularly spaced features (i.e., the tracks may essentially contain incremental scale features of different fundamental frequencies), the scale periods of the tracks are different from one another, and as a result, the combination of features across the width of the scale is unique at any point along the measured length of the scale.

[0065] A set of markings may be used to encode a set of unique binary codewords that define specific, i.e., absolute positional information along the length of the scale, while still retaining enough information to allow for the extraction of phase information from the set of markings, enabling the determination of fine-grained positional information (e.g., positional information with a resolution finer than the period of the scale markings). Thus, in such a system, the positional information may consist of coarse absolute position (determined from codewords extracted from the image) and fine-grained position (determined by examining the substantially periodic phase offset of the markings). Further details of such so-called hybrid incremental and absolute scales are described in Patent Document 3, the contents of which are incorporated herein by reference.

[0066] In an alternative embodiment, the scale may include an absolute track containing features that define absolute position information, and separate incremental tracks containing equally spaced features.

[0067] The optical system of the readhead 4 in Figures 1 and 2 will be described in more detail with reference to Figures 3a and 3b. Figures 3a and 3b schematically show the path from the light source 12 to the sensor 20, through the optical system that forms a scale 6 image on the sensor 20.

[0068] As shown, the optical device 18 comprises a lens 18 having an optical axis OA, a focal length f, and a focal plane fp. As shown, the point light source 12 is positioned substantially at the focal plane fp of the lens 18, but slightly offset from the optical axis OA of the lens 18. For example, the light source 12 is offset by only about 450 μm from the optical axis OA of the lens 18 (measured from the center of the light-emitting zone of the light source). In particular, the ratio of the offset to the focal length of the lens is about 0.45:2.5. Positioning the light source 12 substantially at the focal plane 18 of the lens helps to ensure that the light emitted from it is substantially collimated by the lens 18 as it approaches the scale 6. Thus, the light reflected by the scale 6 is then focused to a point at the focal plane fp of the lens 18 before diverging behind the light source 12 to form a two-dimensional image of the scale 6 at the sensor 20. As understood, the image of the light source 12 will be formed at the focal plane fp. The light source 12 is positioned at the focal plane fp of the lens 18, but offset from the optical axis OA of the lens 18. This means that the light source 12 can be positioned in the space (or "volume") between the sensor 20 and the lens 18 (indicated by the hatched area shown in Figure 3b), which makes the readhead compact but helps not interfere with light reflected by the scale on the return path of light to the sensor 20.

[0069] As shown, both the light source 12 and the sensor 20 face the lens 18 (and the window 22 and scale 6). (In other words, the light-emitting surface of the light source 12 and the sensing surface of the sensor 20 face the lens 18.) Furthermore, there is a non-reflected (in other words, "direct") optical path between the light source 12 and the lens 18, and there is also a non-reflected (in other words, "direct") optical path between the lens 18 and the sensor 20. Therefore, reflective optical components are not needed or used to fold or guide the light. Avoiding the use of reflective optical components such as mirrors and beam splitters can help to significantly reduce the size of the readhead.

[0070] Furthermore, in the specific embodiments described, the same optical device / lens 18 is used for both collimating light from the light source 12 and forming an image of scale 6 on the sensor. Thus, the optical arrangement of the readhead 4 described uses only one optical device / lens 18 and is therefore particularly compact and inexpensive. In the embodiments described, the lens 18 is a singlet lens, but it could be a different type of lens (e.g., a doublet lens, a composite lens, or a distributed refractive index (GRIN) lens). As can be understood, the optical device does not necessarily have to be a lens and could be another type of optical device, such as a Fresnel zone plate or a holographic optical element (HOE), such as a hologram of a lens.

[0071] As shown in Figure 3a, the light source is much closer to the lens 18 than to the sensor 20. Such a configuration differs from conventional encoder designs in which the light source would typically be mounted on the same board as the sensor, and in approximately the same plane as the sensor. As shown in Figure 3a, in this embodiment, the readhead is configured such that the ratio of i) the distance (D1) between the center of the light-emitting surface (or light-emitting point) of the light-emitting element and the sensing surface of the sensor in a direction perpendicular to the plane of the sensor, and ii) the distance (D2) between the center of the light-emitting surface (or light-emitting point) of the light-emitting element and the optical device in a direction perpendicular to the plane of the sensor, is approximately 70:30. In absolute terms, the distance between the center of the light-emitting surface (or light-emitting point) of the light-emitting element and the sensing surface of the sensor is approximately 2.5 mm, e.g., 2.6 mm, in a direction perpendicular to the sensing surface of the sensor.

[0072] As schematically shown by the thick black line in Figure 3b, the configuration of the light source 12, lens 18, and sensor 20 results in a substantially diamond / rhombus optical path from the light source to the sensor, and a substantially V-shaped optical path between the lens 18 and the scale 6. In the embodiment described, the angle θ between the line extending perpendicular to the scale (dotted line in Figure 3b) and the direction of the optical path when it enters the scale is approximately 10°.

[0073] As shown, the sensor 20 may be tilted such that its sensing surface / plane is not perpendicular to the optical axis of the lens. Such a tilt may help compensate for trapezoidal distortion in the image formed on the sensor, which may be formed by the image formed by the out-of-axis portion of the lens 18. In the embodiment shown, the sensor 20 is tilted such that the angle α between a plane extending parallel to its sensing surface (e.g., its sensing plane) and a plane extending perpendicular to the optical axis is about 3°. However, this is not necessarily required, and the sensor may be configured such that its sensing surface extends perpendicular to the optical axis of the lens (i.e., the angle α is less than 1°). As will be described in more detail below, such a tilt of the sensor 20 may be achieved by mounting the PCB 32 (on which the sensor is mounted) at an angle of inclination. Thus, any other components mounted on the sensor 20 or PCB 12, including, for example, the light source 12, may also be tilted for mechanical convenience, but this is not necessarily required. As can be understood, other methods are available to compensate for trapezoidal distortion, such as appropriately shaping the sensor element, or, for example, "trapezoidally deforming" the sensor element itself.

[0074] Next, with reference to Figures 4 and 5, exemplary embodiments of how a readhead can be constructed to achieve the above optical layout will be described.

[0075] As shown in Figure 4, the readhead 4 includes a body 30 to which a lens 18, a window 22, and a printed circuit board (PCB) 32 are attached (e.g., by adhesive, mechanical, and / or frictional means). Sensors 20, LEDs 12, and other electronic components (such as the CPU 24, memory 25, and interface 26 mentioned above, not shown in Figure 4 or 5) are attached to the PCB 32 mechanically and electrically.

[0076] As illustrated, the LED 12 is mounted on the PCB 32, but it is mounted "away from the substrate" in the sense that it is mounted on the PCB 32, but via a raised support structure 34 that holds the LED 12 away from the PCB 32. In particular, the support structure 34 extends beyond the sensor 20 so as to hold the LED 12 even further away from the PCB 32 than the sensor 20. Thus, as shown, the sensor 20 is mounted relatively close to the PCB 32, while the LED 12 is mounted relatively far from the PCB 32. As shown in Figure 4, the LED 12 is much closer to the lens 18 than to the PCB 32, while the sensor 20 is much closer to the PCB 32 than to the lens 18. Thus, as shown, the light-emitting element and the sensor are separated in a dimension that extends perpendicular to the plane of the sensor / circuit board. In particular, in a dimension that extends perpendicular to the plane of the sensor / circuit board, there is (free) space between the light-emitting element and the sensor. In this example, the ratio of i) the distance between the light-emitting surface (or light-emitting point) of the LED 12 and the sensing surface of the sensor 20 in a direction parallel to the optical axis OA of the imaging member, and ii) the distance from the light-emitting surface (or light-emitting point) of the LED 12 to the lens 18 in a direction parallel to the optical axis OA of the imaging member, is approximately 70:30.

[0077] In the embodiments described, the support structure 34 also forms / provides an electrical connection between the LED 12 and the PCB 32. Thus, in the embodiments described, the support structure 34 for holding the LED 12 away from the PCB 32 is the cathode 34 between the LED 12 and the PCB 32. Thus, the cathode 34 comprises a rigid conductive support structure for the LED 12 rising from the PCB 32. As shown in Figures 4 and 5, the support structure / cathode 34 comprises an opening / window 35 through which light reflected by the scale 6 can pass to reach the sensor 20.

[0078] In this embodiment, the anode 36 also includes a rigid conductive structure rising from the PCB 32, which is wire-bonded to the LED 12 via bond wires 38, as shown in Figures 4 and 5. In other words, the leadhead includes a raised bond wire support structure extending from the PCB 32, with the bond wires 38 extending between it and the light-emitting element 12. While not necessary in this embodiment due to the shape and size of the anode, in other embodiments, the anode 36 may also have an aperture / window through which light emitted from the LED 12 can pass toward the lens 18 / scale 6, and light reflected by the scale 6 can pass through to reach the sensor 20.

[0079] As can be understood, the rigid structure of the anode 36 may be omitted, and the LED 12 may be wire-bonded via a bond wire extending between the LED 12 and the PCB 32. However, bond wires can be brittle, and the longer the bond wire, the higher the likelihood of it breaking, so it may be effective to keep the length of the bond wire as short as possible.

[0080] In this particular embodiment, the LED support structure / cathode 34 and the bond wire support structure / anode 36 each include a sheet material portion, each of which is bent to provide a three-dimensional frame and soldered to the PCB 32. In the particular embodiment described, the cathode 34 is brass and the anode is brass and nickel-gold plated. As shown in Figures 6 and 7, fold lines 37 are chemically etched into the sheet material to facilitate bending. When bent, each of the support structures 34, 36 comprises a top surface 31 and a plurality of side supports (or "legs") 33 which are soldered to the PCB 32. As can be understood, the support structure / cathode 34 may be formed in other ways, for example, it may be machined / cut into shape and / or stamped / pressed into shape. The bare die LED 12 is directly attached to the support structure / cathode 34 via conductive epoxy, and a wire bond extends between the LED 12 and the upper surface 31 of the anode 36.

[0081] As shown in Figure 6c, the upper surface 31 of the LED support structure 34 covers the sensor 20 entirely or partially (its contour is schematically shown in Figure 6c by a dashed line). In other words, a line passing through the plane of the sensor 20 (and PCB 32) and extending perpendicular to that plane also passes through the upper surface 31 of the LED support structure 34. Such a configuration allows the LED 12 to be placed very close to the sensor 20, and, if necessary, on the sensor 20.

[0082] The readhead 4 is assembled by dead reckoning the lens 18 into the body 30 of the readhead 4, and the body 30 is crimped to hold the lens 18 in place (however, other methods of securing the lens 18 to the body, such as epoxy and / or pressing the lens 18 into the bend that holds the lens, may be used). The PCB 32, including the already mounted LED 12, is then attached to the body 30 by mechanical means such as adhesive and / or crimping. If necessary, a alignment process may be used to align the PCB (and therefore the sensor and LED on it) with respect to the lens. Such an alignment process may include using the camera to check the PCB / components on it, make adjustments based on the camera output, and / or connect to the PCB / components on it, and the sensor output may be used to make adjustments. Once assembled, the cover 46 is secured to the body 30 by adhesive, crimping, and / or welding.

[0083] In the above embodiment, the bond wire support structure 34 also forms the cathode, but as can be understood, this is not necessarily required, and for example, the support structure 34 could instead form the anode.

[0084] In the embodiments described, the LED 12 is mechanically attached to the PCB 32 via electrodes 34, but as can be understood, this is not necessarily required. For example, the LED 12 may be mechanically attached directly to the PCB 32 via one or more nonconductive members and electrically connected to the PCB 32 via separate members, for example, one or more wires (for example, via wire bonds). Furthermore, the LED 12 does not necessarily have to be directly attached to the PCB 32. For example, the LED 12 may be mechanically attached directly to the body 30 and electrically connected to the PCB 32 via one or more wires (for example, via wire bonds). In another embodiment, the LED 12 may be electrically connected to a different PCB (i.e., not the same PCB 32 to which the sensor is attached).

[0085] Figure 8 shows a read head 4' according to another embodiment of the present invention. The read head 4' in Figure 8 shares many parts, being the same as parts of the embodiments in Figures 1 to 7, and similar parts share similar reference numerals. In the embodiment of Figure 8, the LED 12 is mounted to the circuit board via the sensor 20 using a transparent support structure 50 (e.g., a glass block 50). In particular, the glass block 50 is fixed to the sensor 20 via adhesive epoxy. The LED 12 then sits on a conductive pad 52 that faces the lens 18 and is attached to the side of the glass block 50 distal to the sensor 20. The LED 12 is electrically connected to the circuit board 32 via an anode 36' and a cathode 34', in this embodiment the anode 36' and cathode 34' each include a raised bond wire support structure extending from the PCB 32, and bond wires extending between them and the LED 12 / conductive pad 52. As can be understood, in variations of this embodiment, the LED 12 may also be connected to the circuit board in other ways, for example, via anodes and cathodes attached to the surface / side of the glass block 50 and running along the surface / side of the glass block 50, or via anodes and cathodes passing through the glass block 50.

[0086] As described above, the light-emitting element support structure 34 and / or the light-emitting element 12 may be held directly on the sensor 20, and as a result, lines extending perpendicular to the plane of the circuit board / sensor pass through both the light-emitting element support structure 34 and the sensor 20, and / or both the light-emitting element 12 and the sensor 20. As can be understood, and as schematically shown in Figure 9, the sensor 20 may include at least one photosensitive element 21, and, for example, an array of photosensitive elements 21, as well as other sub-components and the packaging that constitutes the sensor 20. In other words, the sensor 20 may be a chip or component including at least one photosensitive element 21, for example, an array of photosensitive elements 21. For example, as shown in Figure 9a, the light-emitting element 12 may be positioned directly on the sensor chip 20 in such a way that the light-emitting element 12 is not positioned directly on the photosensitive elements 21. Alternatively, as shown in Figure 9b, the light-emitting element 12 may be positioned directly above the sensor chip 20 in such a manner that the light-emitting element 12 is positioned directly above the photosensitive element 21, for example, as a result, a line extending perpendicular to the plane of the circuit board / sensor (i.e., parallel to the Y-axis) passes through both the light-emitting element 12 and the photosensitive element 21.

[0087] In the embodiment shown, the LED 12 is mounted "away from the substrate" by the support structure 34. While this may be beneficial (for example, by positioning the LED 12 in the focal plane of the lens 18, thereby achieving collimation and allowing the sensor 20 to capture an image of the scale), it is not necessarily required. For example, the LED 12 could be mounted on the PCB 32 such that it is located in substantially the same plane as the sensor 20 (in other words, at substantially the same height as the sensor 20).

[0088] In the embodiments shown, light striking the scale is collimated, but this is not necessarily required. Furthermore, even if light striking the scale is collimated, light reflected by the scale does not necessarily need to be collimated. For example, if the scale is bent, for instance, if the scale is a ring scale, then the light reflected by the scale will not be collimated.

Claims

1. Encoder device comprising a read head for reading a reflective scale positioned adjacent to the read head, wherein the read head comprises a circuit board to which a sensor including one or more photodiodes for detecting light reflected from a scale positioned adjacent to the read head is attached, and at least one light-emitting element, the light-emitting element being mounted to the circuit board via a light-emitting element support structure that rises from the circuit board and holds the light-emitting element away from the sensing surfaces of the circuit board and the sensor, at least a portion of the light-emitting element support structure extending over the sensor, and the light-emitting element support structure being bent to provide a three-dimensional frame, comprising a folded sheet-material structure.

2. An encoder device according to claim 1, characterized in that the at least one light-emitting element and the sensing surface of the sensor are separated in a dimension that extends perpendicularly to the sensing surface of the sensor.

3. An encoder device according to claim 1 or 2, characterized in that the light-emitting element is held directly above the sensor such that a line extending perpendicularly to the sensing surface of the sensor passes through both the light-emitting element and the sensor.

4. An encoder device according to any one of claims 1 to 3, wherein the light-emitting element support structure includes a frame attached to the circuit board separately from the sensor.

5. An encoder device according to claim 4, wherein the frame is seated across the sensor.

6. An encoder device according to claim 4 or 5, wherein the frame comprises an upper surface and one or more support bodies, the light-emitting element is mounted on the upper surface of the frame, the upper surface is fixed to the circuit board via the one or more support bodies, and the one or more support bodies extend between the circuit board and the upper surface.

7. An encoder device according to claim 6, characterized in that the top surface and one or more supports include a single piece of material.

8. An encoder device according to any one of claims 4 to 7, wherein the frame comprises an opaque material and is configured such that light returning from the scale can pass through the frame and reach the sensor.

9. An encoder device according to any one of claims 1 to 8, wherein the light-emitting element includes a bare die semiconductor light-emitting element.

10. An encoder device according to any one of claims 1 to 9, wherein the light-emitting element support structure includes a conductive material and includes the anode and / or cathode of the light-emitting element.

11. An encoder device according to any one of claims 1 to 10, comprising a bond wire support structure extending from the circuit board, wherein the bond wire extends between the support structure and the light-emitting element.

12. An encoder device according to claim 1, characterized in that the folded sheet-material structure includes a folded sheet-metal structure.

13. An encoder device according to any one of claims 1 to 12, wherein the read head includes at least one optical device, and the light-emitting element is disposed between the sensor and the optical device.

14. An encoder device according to claim 13, wherein the optical device includes a lens.

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