Encoder

Abstract

In some cases, such as in the machine tool industry, where the working environment is not clean and fluid and solid debris dominates, the encoder scale and read head must be protected against such harmful environments. A sealed encoder module for mounting on a machine to measure relative displacement of first and second portions of the machine may include a readhead having a scale, a scale signal receiver, and an integral protective housing encapsulating at least the scale and the scale signal receiver. The sealed encoder module may be configured to measure and output diagnostic information related to the scale signal detected by the readhead.

Description

[Technical field]

[0001] The present invention relates to encoder devices, for example, what are commonly known as sealed encoders, also commonly known as encapsulated encoders. [Background technology]

[0002] Encoders are used in many industries to provide position (or derivatives thereof, e.g. velocity and / or acceleration) feedback to the control systems of machines, e.g. feedback control for the position / motion of one part of the machine relative to another part of the machine. As will be appreciated, typically one part of the machine is provided with a scale and another part of the machine is provided with a readhead for reading the scale, and the relative position of the scale and the readhead, and therefore the relative position of the part of the machine, is detected by the readhead along the measurement dimension of the encoder.

[0003] The technology utilised by such encoders may require that the environment in which they are used be clean and free of contaminants, such as dirt, dust and moisture (which may be oil and / or water based, for example). Contamination of the scale and / or read head may adversely affect the performance of the encoder. In many industries, such machines using encoders operate in suitably clean environments, in which case what are commonly referred to as "exposed encoders" (or "unsealed encoders") may be used. The read head of an exposed / unsealed encoder may be provided with a visual set-up indicator (see, for example, the "TONiC" and "RESOLUTE" encoders available from the applicant (Renishaw plc.), see also US Pat. No. 5,241,173 and US Pat. No. 8,505,210). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 5,241,173 [Patent Document 2] U.S. Patent No. 8,505,210 [Patent Document 3] U.S. Patent Publication No. 2012 / 072169 Summary of the Invention [Problem to be solved by the invention]

[0005] However, there are cases, for example in the machine tool industry, where the working environment is not clean and fluids and solid debris dominate. In such cases, it is necessary to protect the scale and readhead of the encoder against such harmful environments. As is known, this is achieved by placing a cover over the installed exposed / unsealed encoder, such as over the "TONiC" or "RESOLUTE" encoders available from the applicant (Renishaw plc.), to provide a sealed barrier that protects the scale and readhead from such contamination. Typically, however, in these situations, a different type of encoder is used, commonly referred to as a sealed (also known as an encapsulated) encoder. Such a sealed / encapsulated encoder comprises a scale, a readhead and an integral protective housing, which encloses at least the scale signal receiving parts of the scale and readhead, and which are together provided and installed as a single module.

[0006] The present invention provides an improved encoder apparatus. In particular, the present invention relates to improvements in sealed encoders. For example, the present invention provides a sealed encoder module including a scale, a readhead, and a protective housing (e.g., an integral protective housing). [Means for solving the problem]

[0007] According to a first aspect of the invention, there is provided a sealed encoder module for mounting to a machine to measure relative displacement of a first and a second part of the machine in a measurement dimension / degree of freedom (which may for example be linear or rotational). The sealed encoder module may comprise a readhead comprising a scale, a scale signal receiver, and a protective housing encapsulating at least the scale and the scale signal receiver. The sealed encoder module may be configured to measure and output diagnostic information. The diagnostic information may be indicative, inter alia, of the relative arrangement of the scale and the scale signal receiver in at least one dimension / degree of freedom other than the measurement dimension / degree of freedom of the encoder module. The diagnostic information may therefore depend, inter alia, on the relative arrangement of the scale and the scale signal receiver in at least one dimension / degree of freedom other than the measurement dimension / degree of freedom of the encoder module. The sealed encoder module may be configured to measure and output diagnostic information relating to the scale signal detected by the readhead.

[0008] Thus, as described in more detail below, the scale signal detected by the readhead may depend on the relative positioning of the scale and the scale signal receiver in at least one dimension / degree of freedom other than the measurement dimension / degree of freedom of the encoder module. As will be appreciated, the encoder module (e.g., readhead) may also be configured to measure and output information regarding the relative position of the scale and readhead (i.e., position information in the measurement dimension / degree of freedom). Thus, the encoder module may be configured to measure and output both position and diagnostic information.

[0009] Outputting measurement and diagnostic information has been found to be particularly useful for monitoring the performance of the sealed encoder module and / or to aid in installation / setup of the sealed encoder module, for example, for sealed encoder modules having a scale signal receiver located independently of the scale, as described in more detail below.

[0010] Thus, the sealed encoder module may comprise at least one processor configured to measure the diagnostic information. As will be appreciated, the processor may comprise a custom processor configured for a particular application (e.g., a Field Programmable Gate Array "FPGA"), as well as a more general processor that may be programmed (e.g., via software) depending on the needs of the application to be used. At least one processor may be configured to analyze the scale signal detected by the readhead to measure the diagnostic information. This or at least one other processor may be configured to control the output of the diagnostic information. For example, this or at least one other processor may be configured to control the operation of an output device (e.g., a visual output device) based on the results of the analysis of the scale signal. Position and diagnostic information may be measured by the same or different processors.

[0011] As will be appreciated, the encoder module may be configured such that the measured and output diagnostic information may comprise information regarding the quality of the scale signal detected by the readhead. The diagnostic information may provide position information (e.g. in a measurement dimension / degree of freedom) and in particular, for example, a measure of the suitability of a representation to provide reliable and / or accurate position information. Outputting said diagnostic information may comprise providing an output based at least in part on at least one parameter measured as a result of a process configured to analyze the quality of the scale signal. For example, control of an output device, such as a visual output device, may be based on said at least one parameter.

[0012] The diagnostic information output may be limited to one of a number of predefined categories. Such categories may represent different levels of quality of the detected scale signal. For example, the diagnostic information may be limited to indicate whether the detected scale signal is bad or good. As will be appreciated, additional / alternative categories, such as acceptable and / or optimal, may also be available. Thus, the encoder module may be configured to determine and output the category in which the scale signal falls. For example, in an embodiment in which at least one parameter is measured via a process of analyzing the quality of the detected scale signal, the method may comprise determining (e.g., via the use of a predefined threshold) which category the parameter falls into. Optionally, one or more visual output devices, such as light emitters, may be controlled to reflect the determined category (e.g., the color of the emitted light depends on the determined category).

[0013] As will be appreciated, the diagnostic information need not necessarily be limited to one of a number of predefined categories: rather, for example, in embodiments in which at least one parameter is measured via a process that analyzes the quality of the detected scale signal, the measured raw parameter may be output as the diagnostic information.

[0014] As noted above, the diagnostic information is particularly dependent on (and therefore indicative of) the relative arrangement of the scale and scale signal receiver in at least one dimension / degree of freedom other than that of the measurement dimension of the encoder module. For example, the diagnostic information is dependent on (and therefore indicative of) any one, any combination, or all of the lateral position, ride height, pitch, roll, or yaw of the scale and scale signal receiver relative to one another. Thus, for example, the diagnostic information is dependent on (and therefore indicative of) when the scale and scale signal receiver are or are not in a desired relative arrangement in at least one degree of freedom other than that of the measurement dimension. Such arrangement information is particularly useful for embodiments having a scale signal receiver that is positioned independently of the scale, as described in more detail below.

[0015] Optionally, a part of the encoder module that is moveable relative to the scale may be configured to measure and output said diagnostic information. For example, the readhead may optionally be configured to measure and output said diagnostic information. Thus, optionally the readhead may comprise said at least one processor.

[0016] Optionally, the encoder module is configured to output diagnostic information in the form of one or more human detectable signals. The sealed encoder module may comprise at least one output device for outputting said diagnostic information as a human detectable signal. The output device may output a signal indicative of said diagnostic information. The output device may comprise a visual output device. The output device may be configured to emit an optical signal. Optionally, at least one output device is provided on the readhead. Optionally, the at least one output device is provided on the protective housing. As will be explained in more detail below, the readhead may comprise a mounting block outside the protective housing for mounting the readhead to one of the first and second moving parts of the machine, and the output device may be provided on the mounting block.

[0017] Optionally, the encoder module is configured to output the diagnostic information in the form of one or more electronic signals. For example, the encoder module may be configured to output the diagnostic information to an external device. Thus, the encoder module may comprise an interface for transmitting said electronic signals wirelessly or along a wire.

[0018] The scale signal may be a signal detected by one or more sensors (e.g. in the readhead) configured (and in use used) to detect the scale to measure said measure of relative displacement of the first and second parts of the machine (in the measurement dimension / degree of freedom). The scale signal may be a detected signal from a scale used to measure said measure of relative displacement of the first and second parts of the machine. The scale signal may be an incremental scale signal. Thus, the diagnostic information may be measured from an output of an incremental signal sensor of the readhead. The incremental scale signal may be an interference fringe. The scale signal may be a reference mark signal. Thus, the diagnostic information may be measured from an output of a reference mark signal sensor of the readhead. The scale signal may be an absolute scale signal. The scale signal may be an image of the scale (e.g. a one or two dimensional image of the scale). Thus, the diagnostic information may be measured from an output of an image sensor of the readhead. In other words, the diagnostic information may be measured from an image of the scale (e.g. a one or two dimensional image).

[0019] Optionally, the scale signal used to measure diagnostic information is not a signal used to measure said measure of relative displacement. Optionally, the scale signal from which diagnostic information is measured is detected by at least one sensor other than a sensor whose output is configured to be used to measure said measure of relative displacement of the first and second parts of the machine. Such a sensor may be referred to as a "diagnostic sensor". Thus, in other words, the encoder module may be configured such that the output of the diagnostic sensor is not used to measure said measure of relative displacement of the first and second parts of the machine.

[0020] As will be appreciated, the protective housing may be an integral part of the sealed encoder module. At least one of the scale and the readhead may be attached to the protective housing. The sealed encoder module may be configured such that at least one of the scale and the scale signal receiver is attached to a portion of a machine (whose position is measured by the sealed encoder module) via the protective housing. The housing may be configured to be attached to the portion of a machine. The protective housing may include one or more mounting features configured to mount the scale and / or the scale signal receiver to the portion of a machine. Thus, as an option, the protective housing may be located between the scale and the portion of the machine to which the encoder module is configured to be attached. Optionally, the protective housing may be located between the scale signal receiver and the portion of the machine to which the encoder module is configured to be attached.

[0021] A seal (e.g. at least one sealing lip) may be provided between the relatively movable parts of the sealed encoder module, for example between the protective housing and the relatively movable readhead (described in more detail below). Optionally, the protective housing comprises a plurality of relatively movable (e.g. first and second) parts. Optionally, the plurality of relatively movable (e.g. first and second) parts of the housing are configured to be mounted to respective different parts of a machine whose relative position is measured by the sealed encoder module. A seal (e.g. at least one sealing lip) may be provided between the relatively movable parts of the protective housing. Optionally, the scale may be mounted to a first part of the protective housing and the readhead may be mounted to a second part of the protective housing.

[0022] Optionally, the scale or scale signal receiver is mounted on a first part (e.g., shaft part) of the protective housing configured to be mounted on a shaft of the machine and configured to be rotatable relative to a second part of the protective housing to which the other of the scale and signal receiver is mounted. Optionally, at least one compliant sealing ring is provided between the first and second parts of the protective housing. Optionally, first and second compliant sealing rings are provided between the first and second parts of the protective housing. The first and second sealing rings may be provided on opposite sides of the scale / scale signal receiver.

[0023] The scale signal receiver may be configured to be biased / supported against the scale and / or the portion of the protective housing to which the scale is attached. Thus, the sealed encoder module may include an "integral bearing" (hence what is known as an "integral bearing" or "guided" encoder module). However, this is not necessarily the case. For example, the arrangement of the scale signal receiver into the protective housing may be independent of the scale and the protective housing. Thus, the encoder module may be described as having "no integral bearing", i.e., being a "bearingless" encoder module. Thus, as will be appreciated, the scale signal receiver may also be described as being "externally constrained" or "unguided". Another way of looking at this is that the scale signal receiver is suspended (in other words, suspended) within the protective housing.

[0024] Optionally, the scale signal receiver and the protective housing are movable relative to each other along the measurement dimension of the scale. Optionally, the scale signal receiver may be located inside (and protected by) the protective housing, but is not attached to the protective housing. Optionally, the seal allows relative movement between the scale signal receiver and the protective housing along the measurement dimension of the scale. Thus, as described in more detail below, the seal may extend along the measurement dimension. The seal may also accommodate some relative movement between the scale signal receiver and the protective housing in other dimensions as well.

[0025] Optionally, the arrangement of the scale and scale signal receiver (in at least one degree of freedom other than along the measurement dimension of the encoder) is selectively adjustable. For example, optionally, at least one or any combination of the lateral position, ride height, pitch, roll or yaw of the scale and scale signal receiver with respect to one another may be selectively adjusted. Thus, optionally, the encoder module may include an adjustment mechanism to facilitate such adjustment. Additionally or alternatively, such adjustment may be facilitated by the features with which the scale and / or readhead are mounted to the respective parts of the machine. For example, the features with which the scale and / or readhead are mounted to the respective parts of the machine may allow some flexibility in the positional relationship of the scale and scale signal receiver in said at least one degree of freedom. Such adjustability is particularly useful in embodiments where the arrangement of the scale signal receiver within the protective housing is independent of the scale and protective housing (e.g., "integral bearingless" / "unguided" / "bearingless" / "externally constrained" etc.).

[0026] Alternatively, the scale signal receiver is located inside (and protected by) the protective housing but is not attached to the protective housing. In this case, the protective housing may comprise a seal through which the scale signal receiver may be connected to an outer part of the protective housing. As will be appreciated, the outer part of the protective housing to which the scale signal receiver may be configured to be connected may be a part of the machine, the position / movement of which relative to another part of the machine (to which the scale is fixed) is measured. The scale signal receiver may be connected to the part of the machine located outside the protective housing via a mounting member. In an embodiment where the arrangement of the scale signal receiver within the protective housing is independent of the scale and the protective housing, the scale signal receiver may be rigidly connected to the part of the machine located outside the protective housing. The mounting member may thus be a rigid mounting member. Said rigid connection / rigid mounting member may thus be such that the position and orientation of the scale signal receiver within the protective housing may be dictated (and learned) in all six degrees of freedom by the outer part of the protective housing to which the scale signal receiver is configured to be attached. For example, in embodiments in which the readhead includes mounting features (described below), the position and orientation of the scale signal receiver within the protective housing may be dictated (and mastered) by the mounting features (e.g., dictated / mastered by a mounting block on which said mounting features are provided) in all six degrees of freedom. For example, the scale signal receiver may be rigidly fixed to a rigid readhead mount member that passes through the seal. Thus, the position and orientation of the first side of the seal (within the protective housing) of the scale signal receiver may be dictated (and mastered) by the readhead mount.

[0027] Optionally, the protective housing comprises at least one compliant (eg, elongated, optionally linear) sealing member that can be attached to a portion of the machine via the scale signal receiver.

[0028] Said mount may be provided by the part of the machine to which the scale signal receiver is attached. For example, the machine itself may comprise a (rigid) mounting bracket inserted into the protective housing and connected to the scale signal receiver. Optionally, the readhead may comprise a readhead mount comprising one or more mounting features arranged on the outside of the protective housing for fixing the readhead to the part of the machine. As will be appreciated, the readhead may be configured to be releasably fixed to the part of the machine. The one or more mounting features may be provided on a mounting block. The mounting features may comprise, for example, holes into and / or through which (and optionally engage) releasable fasteners (e.g. bolts). As will be appreciated, the scale signal receiver of the readhead may be rigidly connected to the readhead mount (which may be adapted to ensure a rigid connection between the scale signal receiver and the part outside the protective housing, as described above). As will be appreciated, the scale signal receiver, the readhead mount and the blade may be formed as a single monolithic structure or may comprise multiple separately formed units rigidly connected to each other.

[0029] The mount may comprise a (e.g. rigid) blade-like member configured to extend through the seal. In an embodiment in which the readhead comprises a readhead mount as described above, the blade-like member may extend through the seal between the scale signal receiver located inside the protective housing and the mounting feature located outside the protective housing. The blade-like member may comprise first and second edges (in other words leading and trailing edges). The blade-like member may be tapered towards the first and second ends. The blade-like member may comprise an internal passage / channel for wires and / or air passing between the inside and outside of the protective housing, for example between the scale signal receiver and a mounting block on which the one or more mounting features are provided.

[0030] The protective housing may include one or more mounting features for mounting the protective housing to a portion of a machine (e.g., a different portion of a machine to which the scale signal receiver is configured to be mounted, said portions of the machine being relatively movable with respect to one another). The one or more mounting features may be configured to facilitate removable mounting of the protective housing. The mounting features may be holes into and / or through which a releasable fastener (e.g., a bolt) may extend (and optionally engage).

[0031] As will be appreciated, the scale signal receiver may be a portion of the readhead disposed inside the protective housing that receives a signal from the scale. The scale signal receiver may comprise one or more components to interact with the scale signal, e.g., detect the scale signal, and / or manipulate the scale signal before it is detected. For example, in the case of an optical encoder, the scale signal receiver may comprise one or more optical elements, such as diffractive and / or refractive optical elements. For example, the scale signal receiver may comprise one or more lenses and / or one or more diffraction gratings. The scale signal receiver may comprise one or more signal guides for directing the scale signal to another component. For example, in the case of an optical encoder, the scale signal receiver may comprise a waveguide, e.g., a light guide (e.g., optical fiber). The signal guide may be configured to convey the scale signal to a next component that interacts with the scale signal, e.g., manipulates the scale signal. The signal guide may be configured to convey the scale signal to one or more detectors / sensors, e.g., transducers, configured to detect the scale signal.

[0032] Optionally, the readhead comprises one or more sensors for sensing the scale signal (which may or may not have been manipulated by one or more components of the readhead, as described above). The sensor may comprise a plurality of sensor elements, for example an array of sensor elements. The scale signal receiver may comprise the sensor. Optionally, the sensor may be located elsewhere in the readhead. For example, the sensor may be located in a part of the readhead that is located outside the protective housing. For example, in embodiments in which the readhead comprises a mounting block (described in more detail below), the sensor (and indeed any other components mentioned above) may be located in the mounting block.

[0033] In embodiments in which the scale signal receiver comprises an outer casing (described in more detail below), the scale signal receiver may comprise one or more features that allow a signal from the scale to be input to the scale signal receiver, for example in the case of an optical encoder, the scale signal receiver may comprise a window.

[0034] The readhead may comprise one or more emitters for emitting energy towards the scale. For example, the readhead may comprise at least one light source arranged to illuminate the scale (e.g. with light in the infrared to ultraviolet range). The scale signal receiver may comprise said one or more emitters. As an option, said one or more emitters may be provided by another part of the readhead (e.g. outside a protective housing such as by a mounting block).

[0035] Optionally, the readhead, e.g. the scale signal receiver (e.g. its sensor(s)) is configured to detect a signal generated by light coming from the scale. Optionally, the light is transmitted through the scale. Optionally, the light is reflected from the scale. Thus, optionally, the readhead, e.g. the scale signal receiver, comprises an emitter (e.g. a light source) and a sensor. The emitter and the sensor may be located on the same side of the scale. Thus, the encoder may be a reflective encoder device.

[0036] As will be appreciated, the scale will have some form of features / markings that can be read by a readhead to measure displacement, position (or derivatives thereof, e.g. velocity and / or acceleration). Such features may define a pattern. For example, an incremental scale may comprise scale features / marks that define a periodic pattern and can be used to generate a periodic signal in the readhead (e.g. when relative movement occurs between the scale and the readhead). The scale may be elongated. The scale may comprise a substrate in which and / or on which the features / markings are formed.

[0037] Optionally, the encoder device is a diffraction-based encoder device. Optionally, the scale comprises features configured to diffract light (in the ultraviolet to infrared range), which is then used to form a resultant signal at a sensor in the readhead. Optionally, the readhead comprises one or more optical elements configured to interact with light before and / or after the scale to form a signal at a sensor in the readhead assembly. Optionally, the readhead comprises one or more lenses and / or one or more diffraction gratings. Optionally, the readhead comprises a diffraction grating configured to interact with light from the scale to form interference fringes at a sensor in the readhead. Optionally, the sensor comprises an electrograting comprising two or more interdigitated sets of sensors, each set configured to detect a different phase of the interference fringes.

[0038] Optionally, the scale comprises absolute scale features that define a series (eg consecutive) of uniquely identifiable positions along the length of the scale.

[0039] Optionally, the readhead is configured to detect an image of the scale. Optionally, the readhead (e.g. the scale signal receiver) comprises at least one imaging optical element configured to form an image of the scale on a sensor. Optionally, the readhead comprises at least one sensor suitable for capturing an image, at least one CCD (Charge-Coupled Device) or CMOS (Complementary Metal-Oxide-Semiconductor) sensor.

[0040] As will be understood, references to optics and light in this application are intended to refer to electromagnetic radiation (EMR) in the ultraviolet to infrared range (inclusive).

[0041] As will be appreciated, the readhead may be configured to measure and output information regarding the relative position of the scale signal receiver and the scale (referred to herein as "position information"). Optionally, the readhead comprises one or more processor units configured to process output from one or more detectors / sensors, for example to form said position information. The position signals may be incremental position information. For example, the position signals may comprise quadrature signals. Optionally, the position signals comprise absolute position information. The one or more processor units may be located in the scale signal receiver and / or in another part of the readhead assembly (e.g. in the readhead mount).

[0042] The encoder device may comprise a magnetic, inductive, capacitive and / or optical encoder device. Thus, the scale may comprise a magnetic, inductive, capacitive and / or optical scale. Optionally, the encoder device may comprise an optical encoder device.

[0043] The scale may be a rotary scale. The rotary scale may be what is commonly referred to as a disk scale (where the scale features are located on a surface of a disk). The rotary scale may be what is commonly referred to as a ring scale (where the scale features are located on the periphery of a disk). Optionally, the scale is arcuate. Optionally, the scale may comprise a linear scale.

[0044] Optionally, the encoder module has a nominal ride-height of 0.1 mm or more, such as 0.2 mm or more, such as 0.5 mm or more. Optionally, the encoder arrangement has a nominal ride-height of 5 mm or less, such as 2 mm or less, such as 1 mm or less. Optionally, the allowed ride-height variation ("tolerance") of the encoder module is + / - 50 μm (microns) or more, optionally + / - 75 μm (microns) or more, such as at least + / - 100 μm (microns).

[0045] The protective housing may be elongated. The protective housing may be substantially straight. The protective housing may have a substantially tubular form. The cross-sectional shape of the tubular protective housing is not necessarily circular, but may for example have other regular or irregular shapes. For example, the cross-sectional shape of the tubular protective housing may be substantially rectangular. Optionally, the protective housing is circular, e.g. annular, e.g. ring-shaped.

[0046] The seal may extend along a measurement dimension of the encoder device. Optionally, the seal is provided by gas flow, for example across a gap in the protective housing and / or via positive (e.g. air) pressure within the protective housing. Optionally, the seal comprises a physical barrier. The seal may comprise multiple, for example a pair of, sealing members. For example, the seal may comprise multiple (e.g. a pair of) sealing lips (which may be elongated or annular / ring-shaped, for example). In an embodiment in which the scale signal receiver may be configured to be connected to a portion of the machine located outside the protective housing via a mounting member, the mounting member may also pass through the seal, for example between the sealing lips. For example, the blade-like member described above may pass through the seal, for example between the sealing lips.

[0047] Optionally, the seals (e.g., sealing lips) are compliant. Optionally, the seals (e.g., sealing lips) are resilient. For example, the seals (e.g., sealing lips) are sufficiently compliant to allow relative movement of relatively movable parts of the encoder module. For example, the seals may allow relative movement of the scale / protective housing and the scale signal receiver, for example, by allowing a member, e.g., a blade-like member, and the protective housing / seal, to move relative to one another. Optionally, the seals (e.g., sealing lips) are biased by their resilience towards the sealed configuration. The seals (e.g., sealing lips) may be comprised of, for example, a polyurethane, such as a thermoplastic polyurethane, and / or a fluorinated elastomer.

[0048] The readhead may comprise at least one vibration control device. Such a device may be particularly beneficial for embodiments described in more detail below in which the scale signal receiver is arranged independently of the scale (e.g. "externally constrained"). As will be appreciated, such a vibration control device may be configured to reduce the susceptibility of the readhead (e.g. of the scale signal receiver) to vibration. The vibration control device may be a device configured to reduce the response of at least a portion of the system (e.g. the scale signal receiver of the readhead) due to external excitation. The vibration control device may comprise at least one member configured to vibrate independently of the readhead, e.g. independent of the scale signal receiver. The vibration control device may comprise at least one member arranged inside the protective housing with a resonant frequency independent of the portion of the readhead assembly (e.g. the scale signal receiver m). Optionally, the vibration control device comprises at least one member arranged with a resonant frequency different from the portion of the readhead arranged inside the protective housing (e.g. different from that of the scale signal receiver).

[0049] The vibration control device may comprise a tuned mass damper. The tuned mass damper may be adjusted to reduce a magnitude of vibration of at least a portion of the readhead assembly on which it is mounted (e.g. at least a portion of the scale signal receiver) at and around a resonant frequency of that part. The tuned mass damper may comprise at least one spring element. The tuned mass damper may comprise at least one damper element. The tuned mass damper may comprise at least one mass element. A stiffness "k" of the at least one spring, a damping coefficient "c" of the at least one damper and a mass "m" of the at least one mass may be selected (in other words adjusted) to reduce a magnitude of vibration of at least a portion of the readhead assembly on which it is mounted (e.g. at least a portion of the scale signal receiver) at and around a resonant frequency of that part.

[0050] The scale signal receiver may comprise an external case. The external case may be configured to protect the components of the scale signal receiver disposed inside the protective housing from contaminants (e.g. solids or fluids such as chips or coolant, or e.g. moisture) that happen to enter the protective housing. In particular, the external case may be configured to provide protection against fluids, e.g. liquids. The external case may encapsulate the components. The components may comprise electrical components including any wires and / or any printed circuit board. The components may comprise the above-mentioned components configured to interact with the scale signal. The external case may be a hermetically sealed body, e.g. a hermetically sealed case.

[0051] Thus, the sensor components of the scale signal receiver may be housed within the sealed body / external case. In other words, for example, electrical and / or other components of the scale signal receiver used to detect the scale signal may be housed within the sealed body / external case. For example, in the case of an optical encoder device, optical elements such as lenses, diffraction gratings, beam steering devices, or beam dividers may be housed within the sealed body / external case. The emitter (e.g., light emitter) of the readhead may be housed within the sealed body / external case. A window (e.g., a sealed window) of the sealed body / external case may be provided to allow the scale signal to enter the sealed body / external case.

[0052] Further optional features of the outer case are described below in relation to the second aspect of the invention and are not repeated here for the sake of brevity, but are equally applicable to the first and other aspects of the invention and vice versa.

[0053] According to a second aspect of the invention there is provided a sealed encoder module for mounting to a machine to measure relative displacement of first and second parts of the machine, the sealed encoder module comprising a scale, a readhead comprising a scale signal receiver and a protective housing encapsulating at least the scale and said scale signal receiver, the scale signal receiver comprising an outer casing within which one or more components of the readhead are housed.

[0054] Providing an external case for the scale signal receiver helps ensure that one or more components of the scale signal detector (i.e. components effective in detecting the scale signal, e.g. electronic components and / or other components used for generating and / or interacting with, such as sensing and / or manipulating, a signal from the scale) are protected even though contaminants may get inside the protective housing. In particular, the external case may be configured to provide protection against fluids, e.g. liquids. This may improve the reliability and lifespan of the encoder device. Such components may include electronic components including any wires and / or any printed circuit boards. Such components may include sensors. Such components may include components that interact with the scale signal (e.g. used to manipulate a signal from the scale before it is sensed by a sensor in the readhead). Such components may include emitters, e.g. light emitters for illuminating the scale. If the encoder device comprises an optical encoder device, the optical components of the scale signal receiver may also be located within said external case.

[0055] The external case may be a rigid case. Such a rigid case may be configured to protect one or more components (including any wires and / or any printed circuit board) against solid objects entering the protective housing. The external case may be substantially box-like. For example, it may have a generally rectangular cross-sectional profile. The external case may provide a space / internal volume in which one or more components of the scale signal receiver are disposed. The external case may provide a structure (e.g., a load-bearing structure) to which one or more components of the scale signal receiver are attached. The external case may be attached (configured) to one of the first and second parts of the machine. This may be done via the protective housing. This may be via a readhead mount, for example, as described above in relation to other aspects of the invention. For example, the external case may be attached to one of the first and second parts of the machine via a mounting block. In embodiments in which the protective housing comprises a seal through which the scale signal receiver may be connected to a portion outside the protective housing, the external case may comprise a portion extending through the seal. For example, in embodiments where a blade-like member (as described above) is present, the blade-like member may be part of the outer case, in particular the blade-like member may contain wires or other electrical / optical components and protect them from contaminants entering the protective housing.

[0056] As will be appreciated, the outer case comprises several components, eg, a body and a lid, which together define an interior volume within which one or more components of the readhead are housed.

[0057] The external case may encapsulate at least all of the electronic components, including any wires and any printed circuit board of the scale signal receiver disposed within a protective housing. In the case of an optical encoder, the external case may encapsulate all of the optical elements used to detect the scale signal (e.g., any combination of one or more lenses, diffraction gratings, beam splitters, light sources, and beam steerers) except outside one or more windows through which the scale signal enters the casing and / or through which light from the light emitter exits the external case toward the scale. Thus, as will be appreciated, any such windows may form part of the external case. As an option, any electronic component that includes a protective shell or body (e.g., shielding the bare electronics of the electronic component) may itself form part of the external case.

[0058] The encoder device may comprise a reflective optical encoder device. In such an embodiment, the light source for illuminating the scale and the detector for detecting the scale may be located on the same side of the scale. In such an embodiment, the same (e.g., single) external case may comprise the light source and the detector.

[0059] Preferably, the outer case provides at least level 4 solid particle protection and at least level 4 liquid ingress protection according to the International Protection Marking (also known as ingress protection marking), standard 60529 of the International Electrotechnical Commission (IEC). In other words, preferably, the outer case has an IP rating of at least IP44. The outer case may provide solid particle protection up to at least level 5, optionally at least level 6. The outer case may provide liquid ingress protection up to at least level 5, optionally at least level 6, for example at least level 7. In other words, the outer case may have an IP rating of IPxy, where x (related to solid particle protection) is at least 4 (e.g. 4 to 6) and y (related to liquid ingress protection) is at least 4 (e.g. 4 to 7). As will be appreciated, features described above and below in relation to other aspects of the invention are equally applicable to this aspect of the invention, and vice versa.

[0060] According to a third aspect of the invention there is provided an encoder apparatus comprising a scale and a readhead assembly movable relative to one another, the readhead assembly comprising a scale signal receiver, the scale and the scale signal receiver being disposed within a protective housing configured to protect them from contaminants disposed outside the protective housing, and the protective housing comprising a seal through which the scale signal receiver can be connected to an outer portion of the protective housing, the arrangement of the scale signal receiver within the protective housing being independent of the scale and the protective housing. It will be appreciated that features described above and below in relation to the other aspects of the invention are equally applicable to this aspect of the invention and vice versa.

[0061] According to a fourth aspect of the invention, there is provided a readhead assembly for an encoder device (e.g. comprising at least one sensor for detecting scale features) comprising at least one vibration control device configured to reduce susceptibility of at least one portion of the readhead assembly (e.g. a scale signal receiver portion) to vibration. The present application thus describes a readhead for an encoder device comprising at least one sensor for detecting scale features and at least one vibration control device configured to vibrate independently of the remainder of the readhead. By providing the readhead with at least one vibration control device, vibrations transmitted from the machine to which it is attached can be controlled. This is particularly useful where the readhead is attached to the machine via a structure susceptible to vibrations (e.g. via an elongated member). As will be appreciated, features described above and below in relation to other aspects of the invention are equally applicable to this aspect of the invention and vice versa. Thus, for example, the readhead may comprise a scale signal receiver. The scale signal receiver may comprise at least one vibration control device. In embodiments in which the scale signal receiver is mounted via the elongated blade, the scale signal receiver and / or the elongated blade may include at least one vibration control device.

[0062] According to a fifth aspect of the present invention there is provided a machine comprising an encoder arrangement and / or a readhead as described above.

[0063] According to another aspect of the invention, there is provided a method of setting up a sealed encoder module for measuring the relative position of two relatively movable parts of a machine in a first degree of freedom, the sealed encoder module comprising a readhead with a scale, a scale signal receiver, and an integral protective housing encapsulating at least the scale and said scale signal receiver, the sealed encoder module being configured to measure and output diagnostic information, the method comprising using said diagnostic information to determine whether the scale and the scale signal receiver are in a desired relative positional relationship in at least one degree of freedom other than the first degree of freedom. The method may comprise an operator adjusting the relative position of the scale and the scale signal receiver in response to an indication that the scale and the scale signal receiver are not in a desired relative positional relationship in at least one degree of freedom other than the first degree of freedom. In accordance with the above and below description, the diagnostic information is presented to the operator via an emitter. Thus, the method may comprise an operator adjusting the relative position of the scale and the scale signal receiver in response to an output of the emitter, for example in response to a color of light emitted by the emitter. [Brief description of the drawings]

[0064] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Figure 1a] FIG. 1a shows a schematic representation of a hermetically sealed encoder according to one embodiment of the present invention. [Figure 1b] FIG. 1b shows a schematic of the sealed encoder of FIG. 1a with a portion of the protective housing cut away to reveal the scale and scale sensor assembly disposed within the protective housing. [Figure 1c] FIG. 1c is a cross-sectional view through the sealed encoder device of FIG. 1a. [Figure 1d] FIG. 1d shows a schematic of the sealed encoder of FIG. 1a with a portion of the protective housing cut away to reveal the scale and scale sensor assembly disposed within the protective housing. [Figure 2a] FIG. 2a is a schematic diagram of another embodiment of a sealed encoder apparatus according to an aspect of the present invention, with a portion of the protective housing cut away to reveal a scale and scale sensor assembly disposed within the protective housing. [Figure 2b] FIG. 2b is a schematic diagram of another embodiment of a sealed encoder apparatus according to an aspect of the present invention, with a portion of the protective housing cut away to reveal the scale and scale sensor assembly disposed within the protective housing. [Figure 2c] FIG. 2c is a cross-sectional view of the sealed encoder arrangement of FIGS. 2a and 2b. [Figure 2d] FIG. 2d is a cross-sectional view of another embodiment of a sealed encoder device. [Diagram 3] FIG. 3 is a diagram of another alternative embodiment of a readhead assembly suitable for use with a sealed encoder, with a portion of the signal-receiving module cut away to expose its internal components. [Figure 4] FIG. 4 is a diagram of a signal receiving module of the sealed encoder device of FIG. [Diagram 5] FIG. 5 is a diagram of a tuned mass damper used in the signal receiving modules of FIGS. [Figure 6a] FIG. 6a shows an alternative method of implementing vibration control on a readhead assembly. [Figure 6b] FIG. 6b shows an alternative method of implementing vibration control on the readhead assembly. [Figure 7a] FIG. 7a shows yet another method of implementing vibration control on a readhead assembly. [Figure 7b] FIG. 7b shows yet another method of implementing vibration control on a readhead assembly. [Figure 8a] FIG. 8a shows a schematic diagram of a further way of implementing a vibration controller. [Figure 8b] FIG. 8b shows a schematic diagram of a further way of implementing a vibration controller. [Figure 8c] FIG. 8c illustrates generally a further way of implementing a vibration controller. [Figure 9a] FIG. 9a shows a schematic diagram of a rotary embodiment of the present invention. [Figure 9b] FIG. 9b shows a schematic diagram of a rotary embodiment of the present invention. [Figure 10a] FIG. 10a shows another embodiment of a rotary encoder implementation according to the present invention. [Figure 10b] FIG. 10b shows another embodiment of a rotary encoder implementation according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0065] 2a-2d, there is shown a sealed encoder module 102 according to the present invention. The sealed encoder module 102 comprises a scale 104 having a number of features (not shown) and a readhead assembly 103 comprising a scale signal receiver 106 for receiving signals from the scale. In the described embodiment, the sealed encoder module 102 is an optical encoder in that the readhead assembly 103 utilises electromagnetic radiation (EMR) in the infrared to ultraviolet range to read the scale 104. In particular, in this described embodiment, the position measuring encoder device is an optical absolute encoder. Thus, the scale comprises a series of uniquely identifiable features, e.g. a code, which the readhead assembly 103 can read and process to measure a unique position along the length of the scale 104. However, it will be appreciated that the position measuring encoder device does not necessarily have to be an absolute encoder. For example, it may be an incremental optical encoder. Furthermore, the encoder device does not have to be an optical encoder, for example the encoder device may be a magnetic encoder or, for example, an inductive encoder.

[0066] The readhead assembly 103 communicates with an external processor device (not shown), e.g., a controller, in the described embodiment, via a communication channel that consists of a physical connection (e.g., cable 105) rather than a wireless connection. The communication channel may be bidirectional such that the readhead assembly 103 can receive data (e.g., instructions) from the external processor device as well as transmit data (e.g., position information / signals) to the external processor device. Power to the readhead assembly 103 may be provided via a physical connection, e.g., cable 105. However, this is not necessarily the case. For example, the readhead assembly 103 may include an internal power source, such as a battery.

[0067] The scale 104 and the scale signal receiver 106 are disposed inside a protective housing 108 that protects them from contaminants outside the protective housing 108. The scale 104 is fixed to the protective housing 108 while the scale signal receiver 106 may move within the protective housing 108 along the length of the scale 104. In use, the protective housing 108 is fixed to a first part of a machine (not shown) and the scale signal receiver 106 is fixed to a second part of the machine (not shown). As will be appreciated, the first and second parts of the machine are movable relative to one another. The readhead assembly further comprises a mounting block 114 that is fixed directly to the second part of the machine (e.g., via one or more releasable fasteners such as threaded bolts through holes 115) and a blade 116 that is connected between and extends between the mounting block 114 and the scale signal receiver 106. A light source 113 is provided at one end of the mounting block 114 and is used to relay diagnostic information regarding the encoder to the operator / installer (as will be described in more detail below in connection with other embodiments of the invention).

[0068] The protective housing 108 further comprises a seal 111 in the form of a pair of sealing lips 112 that seal the interior of the protective housing 108, where the scale 104 and scale signal receiver 106 reside, from external contaminants. The blade 116 passes between the pair of sealing lips 112. The sealing lips 112 are compliant so that they can separate to allow the blade 116, and thus the scale signal receiver 106, to move along the length of the protective housing 108 and thus the scale 104, but are also sufficiently elastic to close together around the blade 116, thereby forming a physical barrier against solid and fluid (particularly liquid and moisture) contaminants. In other words, the blade 116 causes the sealing lips 112 to separate as it moves along the length of the seal between the sealing lips 112, and the sealing lips are sufficiently elastic to close together in the absence of the blade 116.

[0069] The placement of the scale signal receiver 106 within the protective housing is independent of the scale 104 or the protective housing 108. It is rigidly connected to the mounting block 114. In particular, the scale signal receiver 106 is rigidly connected to the blade 116 which is in turn rigidly connected to the mounting block 114. The position of the scale signal receiver 106 in all degrees of freedom is therefore determined by the position of the mounting block 114 and therefore by the position of a second part of the machine to which the mounting block 114 is fixed during use, and not by the scale 104 or other parts inside the protective housing 108.

[0070] In the described embodiment, the position and movement of the scale signal receiver 106 is not constrained or guided in any way by the scale 104 or the protective housing 108. Because of the rigid attachment between the scale signal receiver 106 and the mounting block 114, the position and movement of the scale signal receiver 106 in all six degrees of freedom is constrained and guided by the position and movement of the mounting block 114 and, therefore, the part of the machine to which the mounting block 114 is fixed. Thus, the position and movement of the scale signal receiver 106 may be described as "externally constrained." Also, the scale signal receiver 106 does not rest against the scale 104. Thus, such a sealed encoder may be described as "without integral bearings," i.e., "bearingless." We believe that this "bearingless" is a novel arrangement for a sealed encoder (which is the subject of a co-pending PCT patent application entitled "Encoder Apparatus" having the same priority date and claim as this application) and is in contrast to known configurations of sealed "integral bearing" linear encoders that bias / bear the scale signal receiver against the scale, resulting in a compliant coupling between the scale signal receiver and its mounting block. An example of such an "integral bearing" configuration is described below in connection with the embodiment shown in Figures 1a-1d. Such a configuration may also be described as "internally constrained."

[0071] As will be appreciated, if desired, an adjustment mechanism may be provided for adjusting the relative set-up position of the scale signal receiver 106 with respect to the mounting block 114 (e.g. the scale signal receiver may be connected to the blade 116 and / or the blade 116 may be attached to the mounting block 114 via a joint that facilitates selective adjustment of their relative position in at least one linear and / or one rotational degree of freedom, for example by manipulation of a micro / grub screw). Such selective adjustment mechanisms may be useful to aid in set-up / alignment of the encoder apparatus. However, as will be appreciated, such selective adjustment mechanisms result in a rigid connection between the scale signal receiver 106 and the readhead mount 114, and therefore a rigid connection between the scale signal receiver 106 and the part of the machine to which it is mounted (i.e. during use / operation the position / orientation in all degrees of freedom of the scale signal receiver 106 is still conquered / directed by the second part of the machine to which the mounting block 114 is mounted).

[0072] In the described embodiment, the scale signal receiver 106 does not contact the scale 104 or the protective housing 108 at all. Thus, there is a gap around the scale signal receiver 106 between it and the interior of the scale 104 and protective housing 108. In fact, in the described embodiment, as shown, the only contact between the readhead assembly 103 (including the scale signal receiver 106 and the readhead mount 110) and the protective housing 108 is between the blade 116 and the pair of sealing lips 112. As will be appreciated, the pair of sealing lips 112 are flexible and resilient in behavior and contraction to accommodate the blade 116, thereby not constraining or controlling the position of the scale signal receiver 106.

[0073] Furthermore, in the described embodiment, the scale signal receiver 106 comprises an outer case 107 within which the electrical components of the scale signal receiver are disposed. The sensor of the scale signal receiver 106 for detecting the scale signal coming from the scale 104 and any associated components (e.g., optical elements such as lenses, gratings and / or mirrors) for forming the scale signal on the sensor may also be provided within the scale signal receiver's outer case 107. The outer case 107 is configured (e.g., sealed) such that if dirt inadvertently passes through the lip seal 112, the components of the scale signal receiver 106 inside the outer case 107 (e.g., electrical and optical components in particular) are protected.

[0074] As will be appreciated, in embodiments where an external case 107 is provided, a window (e.g., window 232 in Figures 3 and 4) may be provided to allow the scale signal to reach a sensor located inside the external case 107. Optionally, the window does not have any material that affects the scale signal (e.g., its only purpose is to simply allow the signal from the scale to enter the external case 107 without contributing to the form of the signal received at the sensor of the readhead). Optionally, the window may be configured to redirect the signal coming from the scale (e.g., it may comprise a mirror). Optionally, the window may be configured to interact with the signal from the scale to generate a desired signal detected at the sensor. For example, it may comprise a diffraction grating and / or a lens. In any case, as will be appreciated, the outside of the window 232 is not sealed from contamination entering the protective housing 108, since the window forms part of the external case 107, but the inside of the window and other components (e.g., optical elements) configured to manipulate the signal coming from the scale 104 are protected from contamination.

[0075] The advantage of providing the scale signal receiver 106 with an external case 107 is not only beneficial for embodiments in which the scale signal receiver 106 is independently positioned relative to the scale (e.g., "bearingless" or "externally constrained"), but may also be beneficial in embodiments in which the scale signal receiver is biased relative to the scale (with an "integral bearing"), e.g., attached to the readhead mount via an articulating linkage and its position is "internally constrained" (e.g., in an encapsulated encoder of the type described below in relation to Figures 1a-1d). Thus, as will be appreciated, in relation to this aspect, an articulating linkage as described in relation to Figures 1a-1d may be provided. However, although the provision of an external case 107 may improve the resilience of an encapsulated encoder with an "integral bearing" (e.g. this may adversely affect the performance of the encoder arrangement if contaminants get past the sealing lip 12 and land on the scale. For example if enough contaminants land on the scale features this may adversely affect the signal coming from the scale. Also, if solid contaminants such as shavings get into the protective housing and fall onto the track that the readhead bearings 20 run on this can adversely affect the relative position / orientation of the scale signal receiver and the scale as the scale signal receiver rides over the dirt. Of course, encapsulated encoders with a scale signal receiver located independently of the scale (e.g. "externally constrained") have the added advantage of not suffering from such problems.

[0076] As described in more detail below in relation to other embodiments of the invention, the scale signal receiver 106 receives signals from the scale that are processed to provide, for example, position signals, via the cable 105 to an external device (such as a machine controller). For example, processing to measure position may be performed by one or more processor units in the scale signal receiver 106 and / or by one or more processor units in another part of the readhead assembly, such as the mounting block 114. Alternatively, the blade 116 may include one or more channels to allow wires to pass between the scale signal receiver 106 and the mounting block 114. Alternatively, wireless communication may be used, or an external wired connection to the blade 116 may be used. If the blade 116 includes one or more channels, air (e.g., supplied via the air supply line 109) may be passed through the blade 116 (e.g., through holes in the blade 116) to the scale signal receiver inside the protective housing 108.

[0077] It will be appreciated that Figures 2a-d are schematic and typically the separation between the scale 104 and the scale signal receiver 106 (often referred to as the ride-height) will be much less than is shown. The desired ride-height will depend on the encoder, but for example, a typical ride-height for an optical encoder can be in the range of 0.24mm to 2mm. In the particular example described, the nominal ride-height is 0.8mm with a tolerance of + / - 0.15mm.

[0078] The sealed encoder module 102 shown in Figures 2a-2d may be used in any orientation. In Figures 2a-2d, the mounting block 114 is shown to be located directly above the scale signal receiver 106 and protective housing 108. However, this does not necessarily have to be the case. For example, the sealed encoder module 102 could be mounted on its side or even upside down (so that the mounting block 114 is located directly below the scale signal receiver 106 and protective housing 108). In fact, such an arrangement is advantageous because external contaminants will tend to fall off the lip seal 112 of the protective housing 108 due to gravity.

[0079] Likewise, the pair of sealing lips 112 need not be provided directly on the side of the protective housing 108 opposite the side of the protective housing 108 on which the scale is located. For example, referring to the orientation shown in Figure 2c, the sealing lips 112 are provided on one of the vertical sides of the protective housing such that the blades 116 extend horizontally in vertical opposition. Alternatively, they can be provided between two sides along one of the corners / edges of the protective housing as shown in Figure 2d (where the seal 111 includes two pairs of sealing lips 112 as shown in this embodiment).

[0080] 3-5, an alternative readhead assembly 203 is shown. The readhead assembly 203 of FIGS. 3-5 shares many similarities with the readhead assembly 103 of FIG. 2, including a scale signal receiver 206, a mounting block 214, a light emitter 213, and a blade 216 that provides a rigid connection between the scale signal receiver 206 and the mounting block 214 (thus the scale signal receiver 206 is "externally constrained"). Although FIG. 3 shows the readhead assembly 203 in isolation, it will be understood that the readhead assembly 203 is intended to be used to read a scale that is disposed inside a protective housing such as that shown in FIGS. 2a-2d. Thus, the scale signal receiver 206 is also disposed inside the protective housing, and the blade 216 is also intended to pass through an elongated seal in the protective housing, such as a pair of sealing lips. As with the embodiment of FIGS. 2a-2d, the scale signal receiver 206 is an optical readhead, but this is not necessarily the case.

[0081] Similar to the scale signal receiver 106 of Figure 2, the scale signal receiver 206 of Figures 3 and 4 includes a protective outer case 207. In this case, the components within the scale signal receiver 206 are protected (e.g., sealed) by the protective outer case 207 and a mounting surface 217 provided at the end of the blade 216 proximate the scale signal receiver 206, where the scale signal receiver 206 is attached to the blade 216. A sealing member may be provided at the interface between the outer case 207 and the mounting surface 217 (e.g., a gasket may be sandwiched between the outer case 207 and the mounting surface 217 of the blade 216).

[0082] As shown, rather than the blade 216 extending vertically between the scale signal receiver 206 and the mounting block 214 (as in the configuration of FIG. 2), in this embodiment the blade extends between the scale signal receiver 206 and the mounting block 214 at a non-vertical angle, e.g., about 45 degrees. This is so that the blade can be oriented such that any liquid that falls on it falls away from the sealing lip, regardless of whether the sealed encoder module is mounted vertically or horizontally.

[0083] As shown in Figures 3 and 4, an optical unit 230 is shown that includes components of a scale signal receiver for detecting a scale signal. Specifically, the optical unit includes a light source 252 for illuminating the scale, a lens 254 configured to image the scale, a sensor 256 (e.g., a one- or two-dimensional CCD or CMOS sensor) on which the image falls and configured to detect the image, and a beam steerer 258 configured to direct light from the light source to the scale. As shown, the sensor 256 may be mounted on a printed circuit board (PCB) 240. A cable (not shown) connects the PCB 240 to a processor device in the mounting block 214. Once an image is acquired by the sensor, the image is passed to a processor device located in the mounting block 214, which processes the image (in a known manner, for example, as described in US2012 / 072169) to measure the position. The contents of US2012 / 072169 are incorporated herein by reference. The measured position is communicated to an external device (such as, for example, a machine controller) via, for example, one or more signals transmitted along cable 205. As will be appreciated, other configurations are possible. For example, all processing may be performed by one or more processor devices located in the scale signal receiver 206. In another alternative embodiment, a sensor device (e.g., CCD or CMOS) may be located in the mounting block and receive the scale signal via a light guide (e.g., optical fiber) extending through the blade 216. Thus, in this case, the scale signal receiver 206 simply collects the signal / light from the scale and passes it to a sensor located elsewhere in the readhead assembly.

[0084] As mentioned above, a light emitter 213 (113 in the embodiment of Figures 2a-2d) for relaying diagnostic information may be provided by the encoder module, e.g., the readhead assembly. Such a light emitter may be used to relay diagnostic information to an operator / installer. For example, the color and / or brightness of the light emitted by the light source is controlled to reproduce the diagnostic information. Optionally, the light emitter may be configured to blink in a particular manner to relay the diagnostic information. Thus, for example, during setup of the encoder, which may occur at installation or at a subsequent time (e.g., if the encoder needs to be set up again at a subsequent time), the diagnostic information (e.g., the output of the light emitter) may be used by the operator / installer to ensure that the encoder is set up properly. Particularly in the case of embodiments in which the scale signal receiver is located independently of the scale, the operator may use the diagnostic information to check whether the scale signal receiver is located in the desired position relative to the scale (in degrees of freedom other than the measurement dimension) and, if not, adjust the positional relationship accordingly.

[0085] For example, the light emitters may be controlled to emit visual signals that depend on the relative setup of the readhead (e.g., scale signal receiver) and the scale. This is particularly useful during installation of the encoder module to ensure that the readhead is receiving a good signal from the scale. For example, the encoder module may be configured such that the color of the light emitters 213 depends on the relative setup (e.g., green light may be emitted when the readhead is receiving a good / strong scale signal, and red light may be emitted when the readhead is receiving a poor / weak scale signal). Such visual indications for the relative setup of the readhead and scale are useful for both "independently positioned" and "internal constrained" encoder devices. Such visual indications for the relative setup of the readhead and scale are particularly useful when an adjustment mechanism is provided for adjusting the relative setup position of the scale signal receiver with respect to the mounting block (as described above).

[0086] In the described embodiment, the processor in the mounting block 214 used to measure the position is also configured to process the image detected by the sensor 256 to measure the diagnostic information (however, as will be appreciated, this is not necessarily the case and another processor may be used). In the described embodiment, the processor is configured to measure the diagnostic information based on the quality of the signal detected by the sensor. In this particular embodiment, it is configured to Fourier transform the image acquired by the sensor at the fundamental spatial frequency ω of the scale features (which may be provided during the setup of the encoder module or by analysis of the image). The magnitude A of the Fourier transform is then established. As will be appreciated, the Fourier transform provides a real part R and an imaginary part τ, and the magnitude A may be calculated from the following equation (1): A = √[R(F(ω)] 2 + [τ(F(ω)] 2or A 2 = [R(F(ω)] 2 + [τ(F(ω)] 2 (1) where F(ω) denotes the Fourier transform of the representation at spatial frequency ω.

[0087] Because calculating the square root is computationally intensive, we use A instead of A to measure the setup instruction output. 2 It will be appreciated that it is preferable to use A (or A 2 ) to a threshold. For example, A (or A 2 ) has a value below the threshold, the light emitter is controlled to output red light, and A (or A 2 ) has a value above the threshold, the light emitter is controlled to output green light.

[0088] As will be understood, A (or A 2 ) depends on the size of the feature as obtained in the representation. This in turn is affected by the setup of the read head relative to the scale (that is to be measured). A (or A 2 ) also depends on the number of features in the representation. Thus, if there is a significant variation in the density of features along the scale, the method may comprise a step to compensate for this. For example, this compensation may be 2 ) by the number of features in the representation.

[0089] In the described embodiment, the method includes Fourier transforming the representation at substantially the fundamental spatial frequency of the feature. The Fourier transform may use an assumed fundamental spatial frequency of the feature based on the scale with which it is being used. Even if the assumed fundamental frequency is not exactly correct, the method can still provide a useful indication of the quality of the representation. As an alternative, the fundamental spatial frequency of the feature may be determined by analyzing the image prior to performing the Fourier transform. This may be useful in embodiments where the actual fundamental spatial frequency of the feature when imaged changes significantly due to rideheight / magnification effects.

[0090] Further, it will be appreciated that it is not necessary that the Fourier transform be performed substantially at the fundamental spatial frequency of the feature. For example, the method may include performing a Fourier transform at some other frequency, e.g., a harmonic of the spatial frequency. As an option, the method may include performing a Fourier transform at one or more frequencies and comparing the magnitude of the Fourier transform at different spatial frequencies.

[0091] Further details on how images of absolute scales may be processed to measure diagnostic information are described in U.S. Pat. No. 8,505,210, the contents of which are incorporated herein by reference. As will be appreciated, there are other ways in which diagnostic information may be measured. For example, as described in U.S. Pat. No. 8,505,210, the relative size of features of different types of scales as imaged may be measured, which may indicate the quality of the detected scale signal.

[0092] As shown, in this embodiment, the scale signal receiver 206 also includes a vibration control device, which in this particular embodiment consists of a tuned mass damper 260 (in practice, this embodiment consists of multiple vibration control devices). The inventors have found that the use of at least one vibration control device can improve the life and / or metrological performance of the encoder device. This is particularly the case when the scale signal receiver is rigidly attached to the structure via a vibration sensitive member (e.g., a member that transmits and / or amplifies vibrations), such as an elongated arm or thin blade to which the scale signal receiver is rigidly attached. For example, in the case of the "externally constrained" scale signal receiver of the embodiment described above, vibrations are passed to the scale signal receiver via a rigid mounting arrangement. The vibration control device provides a way to control such undesirable vibrations to which the scale signal receiver is exposed.

[0093] As will be appreciated, a vibration control device may be any device configured to reduce the response of a system (e.g., a scale signal receiver) to an external excitation. As mentioned above, in this particular example, the vibration control device comprises a tuned mass damper 260 that is tuned to reduce the magnitude of vibration of the system to which it is attached at and near the resonant frequency of the system. As will be appreciated, the tuned mass damper comprises a spring, a damper, and a mass. The stiffness "k" of the spring, the damping coefficient "c" of the damper, and the mass "m" of the mass are selected (in other words "tuned") to reduce the magnitude of vibration of the system to which it is attached around the resonant frequency of the system. In this embodiment, the tuned mass damper comprises a pair of elastomeric rings 262 (e.g., rubber rings) that provide the spring and damper elements, and a body 264 that provides the mass element. Each elastomeric ring 262 thus acts as a spring and a damper by absorbing energy and converting the energy into heat. The body 264 is made of a sufficiently dense material (eg, brass) so that the body 264 may have a sufficiently small size while providing a suitably high mass.

[0094] Typically, the mass of the tuned mass damper needs to be a significant fraction of the mass of the system it is trying to damp (in this case the portion of the readhead assembly that is located inside the protective housing, in particular the scale signal receiver 206). For example, in this case the mass of the tuned mass damper 260 is at least 1% of the mass of the scale signal receiver 206, alternatively at least 2% of the mass of the scale signal receiver 206, for example about 5% of the mass of the scale signal receiver 206. For example, in this case the mass of the tuned mass damper 260 may be configured to be less than 30% of the mass of the scale signal receiver 206, alternatively less than 25% of the mass of the scale signal receiver 206.

[0095] As shown in FIG. 4, the tuned mass damper 260 is disposed inside a cylindrical bore provided by the scale signal receiver 206. Although not shown in the particular embodiment described above, the side of the cylindrical bore is provided with a plurality of elongated axially extending ridges (or "splines") such that the outer periphery of the elastomeric ring 262 engages with the ridges, thereby reducing the contact area between the elastomeric ring 262 and the inside of the bore. This helps to keep the stiffness of the elastomeric ring 262 low, which in turn helps to reduce the natural frequency of the tuned mass damper 260. Such a configuration avoids the need to use a larger mass 264 or a softer elastomeric ring 262 to achieve the desired damping effect.

[0096] As will be appreciated, the cylindrical hole in which the elastomeric ring 262 and tuned mass damper 260 are disposed may be shaped and sized such that the elastomeric ring 262 is crushed / compressed within the hole. As will be appreciated, even in such a case, the mass element 264 moves / vibrates independently of the scale signal receiver 206. Alternatively, the cylindrical hole in which the elastomeric ring 262 and tuned mass damper 260 are disposed may be shaped and sized such that the elastomeric ring 262 is not crushed / compressed within the hole. Thus, the cylindrical hole in which the elastomeric ring 262 and tuned mass damper 260 are disposed may be shaped and sized such that the elastomeric ring 262 rocks / bounces within the hole.

[0097] 6a, 6b, 7a and 7b show further alternative embodiments of a suitable vibration control device. With reference to Figs. 6a and 6b, the vibration control device comprises a mass element 364 connected to the outer case 207 of the scale signal receiver 206 via a spring and damper element 362. In this case, the spring and damper element 362 is a block of elastomeric material, such as rubber. The mass element 364 is therefore able to vibrate independently of the scale signal receiver 206 due to the flexibility of the spring and damper element 362 (acting as a spring and damper by absorbing energy and converting the energy into heat).

[0098] 7a and 7b show another alternative embodiment comprising a tuned mass damper 460. In this case, the tuned mass damper 460 comprises a mass 464 formed as an integral part (e.g., via a single molding) of the outer case 207 of the scale signal receiver 206. The tuned mass damper also comprises a spring element 466 formed as an integral part of the outer case 207 of the scale signal receiver 206. As shown in the cross-sectional view of FIG. 7b, the material of the spring element 466 provided by the outer case 207 is thin enough to be flexible enough to allow the mass 464 to move and vibrate relative to the rest of the scale signal receiver 206. In this embodiment, as a result of the presence of the integrally formed spring element 466, a separate damping element 462 (shown in FIG. 7b) is provided, consisting of an elastomeric ring 462 extending around a trough in the outer case 207.

[0099] As will be appreciated, Figures 6b and 7b also show how the blade 216 can be hollow for the passage of wires (not shown) and / or air (as discussed above). These figures also show how the mounting block 214 can provide space for components such as at least one processor unit 242 (as described in more detail above).

[0100] As shown diagrammatically in Figure 8a, the spring and damper portions of a tuned mass-damper need not be provided by a common component. For example, one example of a tuned mass-damper 560 may comprise a mass 562, one or more (in this case four) springs 566 (which have little or no substantial damping action) and one or more (in this case four) damping elements 564.

[0101] In the above described embodiment, the vibration control device comprises a tuned mass damper. However, as will be appreciated, this does not necessarily have to be the case. For example, the vibration control device may comprise a vibration absorbing device 660, an example of which is shown in FIG. 8b. As shown diagrammatically, the vibration absorbing device 660 may comprise a mass element 662 and one or more springs 666 (four springs 666 in this example) that allow the mass 662 to move / vibrate independently of the outer case 207 and the other scale signal receiving units 206.

[0102] 8a and 8b, the vibration controller 560, 660 is disposed in a recess in the outer case 207 of the scale signal receiver 206, although it will be appreciated that other arrangements are possible. For example, as shown in FIG. 8c, a vibration controller 770 (comprising a mass element 762, a spring 766, and optionally a damper element 764) may be connected to a side of the outer case 207 of the scale signal receiving unit 206.

[0103] In the above described embodiment, the encoder and scale are linear. However, it will be appreciated that the present invention is equally applicable to non-linear encoders / scales, for example rotary encoders, such as disk and / or ring encoders. Figures 9a, 9b, 10a and 10b show schematic example implementations of such embodiments. In the embodiment of Figure 9a, a scale 804 is provided on the face of the disk (shown in dashed lines) and is housed in a cylindrical protective housing 808. A circular seal 811 is provided on the end face of the cylindrical protective housing 808, through which the blade 216 of the read head assembly can pass (although it will be appreciated that it may be provided on the cylindrical side of the cylindrical protective housing 808, if desired). In the embodiment of Figure 9b, the scale 904 is provided on the circumferential side of the ring (shown in dashed lines) and is housed in a cylindrical protective housing 908, through which the blade 216 of the read head assembly can pass. A circular seal 911 is provided on the cylindrical side of the cylindrical protective housing 908 (although it will be appreciated that it may be provided on an end face of the cylindrical protective housing 908 if desired). In these embodiments, the readhead assembly (comprising the scale signal receiver 207, mounting block 214, and blade 216) may be the same as described above (although in the embodiment of FIG. 9a it would be beneficial for the blade to be curved to follow the curvature of the seal 811). In both of these embodiments, a light emitter 213 is provided on the mounting block 214, and the encoder is configured to control the light emitter to relay diagnostic information.

[0104] Figures 10a and 10b show an alternative embodiment of a sealed rotary encoder module 302 in accordance with the present invention. In this embodiment, the sealed rotary encoder module 302 includes a scale 304 having a number of features (not shown) (as best seen in cross section in Figure 10b) and a readhead including a scale signal receiver 306 for receiving signals from the scale 304.

[0105] The scale 304 and the scale signal receiver 306 are disposed inside a protective housing 308, which protects them from contaminants outside the protective housing. In this embodiment, the protective housing comprises a first portion 308a and a second portion 308b. The scale signal receiver 306 is attached to the first portion 308a of the protective housing, and the scale 304 is attached to the second portion 308b of the protective housing. The first and second sealing lips 312 provide a seal between the first and second portions 308a and 308b while allowing relative movement of the first and second portions 308a and 308b of the protective housing about the axis of rotation A. Thus, for example, the second portion 308b of the protective housing can be attached (e.g., clamped) to a rotatable shaft of a machine (not shown), and the first portion 308a of the protective housing can be attached (e.g., clamped) to a stationary portion of the machine (not shown).

[0106] As in the above-described embodiment, the scale signal receiver 306 includes an outer case 307 in which the optical and electrical components of the scale signal receiver are housed and protected. Also as in the above-described embodiment, the encoder module 302 communicates with an external processor device (not shown), e.g., a controller, via a communication channel, which in the above-described embodiment includes a physical connection (e.g., cable 305). In particular, position signals may be transmitted to the external processor device via the cable. In this embodiment, the scale signal receiver 306 includes a sensor and a processor for detecting and processing the scale signal to form position information. However, it will be appreciated that other portions of the encoder module 302 may include the sensor and / or processor (e.g., separate components located elsewhere along the first portion 308a of the protective housing).

[0107] As with the embodiments described above, the sealed rotary module 302 includes lights 313 that relay diagnostic information to an operator / installer. Such lights 313 may be controlled by a processor (e.g., the same processor for processing the detected scale signal) in accordance with the methods described above in connection with other embodiments of the invention.

[0108] As with the previous embodiment, the encoder module 302 comprises an absolute optical encoder, although this is not required.

[0109] In the embodiments described above in relation to Figures 1-9, the readhead assembly comprises a scale signal receiver 106, 206, a mounting block 114, 214 and a blade 116, 216. However, it will be appreciated that the readhead assembly may comprise only the scale signal receiver. For example, the blade may be provided by the machine on which the scale signal receiver is mounted. For example, in relation to the embodiments described above, the sealed encoder module may be supplied without the mounting block and / or blade, but rather only the scale signal receiver disposed (or located) inside a protective housing. During set-up, the scale signal receiver may be connected to a blade or equivalent provided by the machine on which the encoder device is installed.

[0110] In the embodiments described above, the encoder is a reflective optical encoder (e.g. the readhead detects the scale by light reflected from the scale, and the readhead's light source and detector / sensor are located on the same side of the scale). It will be appreciated that the encoder may also be a transmissive optical encoder (where the readhead's light source and detector / sensor are on opposite sides of the scale). It will be appreciated that the invention is also applicable to non-optical encoders (e.g. magnetic, inductive and / or capacitive encoders).

[0111] As mentioned above, the scale comprises features that are used to provide a signal detectable by a sensor in the readhead assembly. In the above embodiment, the encoder / scale comprises an absolute encoder / scale. The readhead decodes the resulting image to measure the absolute position. However, this does not necessarily have to be the case. For example, the encoder / scale may be an incremental (relative value) encoder / scale (with or without reference marks). As is well known, the readhead may be configured to output a quadrature signal that may be used to measure the relative movement and / or position of the scale and the readhead. In this case, alternative techniques may be used to measure diagnostic information that may be used to determine how to control the light emitters 13, 113, 213. For example, the encoder module (e.g., the readhead) may be configured to determine whether the quadrature signal level is above or below a given threshold level to determine how to control the light emitters 13, 113, 213. Further details of such a process are described in US Pat. No. 5,241,173, the contents of which are incorporated herein by reference.

[0112] The encoder may be diffraction-based, for example, the signal detected by a sensor of the scale sensor assembly is formed by the scale (and one or more diffraction gratings in the scale sensor assembly) diffracting light (e.g., forming interference fringes at the sensor of the scale sensor assembly).

[0113] As will be appreciated, references to light in this application include electromagnetic radiation (EMR) in the ultraviolet to infrared range.

[0114] In the embodiments of Figures 2 to 9 described above, a vibration control device is used to reduce the susceptibility of the scale signal receiver to vibration. However, it will be appreciated that the vibration control device is optional. For example, the embodiment of Figure 10 does not include a vibration control device. There are many reasons why a vibration control device may not be required. For example, a vibration control device may be unnecessary depending on the frequency of vibration to which the encoder is to be exposed and the resonant frequency of the scale signal receiver. As an option, the vibration induced in the scale signal receiver may be made sufficiently small so as not to affect the structural stability of the scale signal receiver and / or to not produce measurement errors that are within the desired tolerances. Furthermore, in embodiments of the invention where the encoder device is not independently disposed relative to the scale (e.g., includes an "integral bearing"), a vibration control device is unlikely to be required due to the scale signal receiver being biased relative to the scale. Such an exemplary embodiment of the invention is described below in relation to Figures 1a to 1d.

[0115] The embodiments of Figures 2 to 10 above include a scale signal receiver that is located independently of the scale. However, it will be appreciated that the invention is equally applicable to sealed encoder modules in which the scale signal receiver is not located independently of the scale (e.g. includes an "integral bearing"). Such an embodiment of the invention is described below in relation to Figures 1a to 1d.

[0116] In the above-described embodiments, the scale signal receiver comprises an outer casing that encapsulates the components of the scale signal receiver. However, this does not necessarily have to be the case. For example, electronic and / or other (e.g. optical) components may be exposed. For example, the PCB 240 may be exposed within the protective housing 108. Such an exemplary embodiment of the invention is described below in relation to Figures 1a to 1d.

[0117] The above embodiments illustrate how the invention of a sealed encoder apparatus configured to measure and output diagnostic information related to a scale signal may be implemented in conjunction with novel types of sealed encoders (particularly those in which the scale signal receiver is located inside a protective housing independent of the scale - in other words, "externally constrained"). However, it will be appreciated that the invention of a sealed encoder apparatus configured to measure and output diagnostic information related to the scale signal may also be used with more traditionally configured sealed encoder apparatus in which the readhead is constrained relative to the scale, which may be described as "internally constrained" (e.g. encoders such as those described in US4595991).

[0118] An example of an "internally constrained", "integral bearing" sealed encoder module 2 according to one aspect of the present invention is shown diagrammatically in Figures la-ld. As shown, the sealed encoder module 2 comprises a scale 4 and a readhead assembly comprising a scale signal receiver 6. The scale 4 and the scale signal receiver 6 are disposed inside a protective housing 8 which protects them from contaminants outside the protective housing. The scale 4 is fixed to the protective housing 8 whilst the scale signal receiver 6 of the readhead assembly is movable along the length of the scale 4 within the protective housing 8. In use, the protective housing 8 is fixed to a first part of a machine (not shown) and the readhead assembly is fixed to a second part which is movable along the x-axis relative to the first part of the machine. In practice, the first part of the machine (and therefore the protective housing / scale) may be arranged to move and / or the second part of the machine (and therefore the readhead) may be arranged to move during use.

[0119] The readhead assembly comprises a mounting block 14 which is secured directly to a second part of the machine (e.g. via bolts passing through bolt holes 15 in the mounting block 14), a blade 16 and an articulated linkage 18 connecting the scale signal receiver 6 to the blade 16 (described in more detail below). A light emitter 13 is provided on the mounting block which relays diagnostic information in a similar manner as described in connection with the previous embodiments.

[0120] The protective housing 8 further includes a seal in the form of a pair of sealing lips 12 which seal the interior of the protective housing 8, in which the scale 4 and scale signal receiver 6 reside, from external contaminants. The blade 16 passes through the seal (between the pair of sealing lips 12), which allow movement of the blade 16, and therefore the scale signal receiver 6, along the length of the protective housing 8 / scale 4.

[0121] The position of the scale signal receiver 6 relative to the scale 4 in all degrees of freedom other than along the length of the scale is tightly controlled by bearings 20 (e.g. roller bearings) in the scale signal receiver 6 which engage and support the scale 4 (but which could additionally / alternatively be supported against the inside of a protective housing, as will be appreciated). A spring (not shown) biases the scale signal receiver bearings 20 against the scale 4. Misalignment of the axes of the first and second parts of the machine is accommodated by an articulated linkage 18. In this embodiment, the articulated linkage 18 is provided by a joint including at least one pivot connection. The articulated linkage allows pitch, roll and yaw (i.e., rotational movement about three mutually orthogonal axes) of the scale signal receiver 6 relative to the mounting block 14, as well as lateral movement of the scale signal receiver 6 relative to the mounting block 14 in a direction orthogonal to the measurement dimension (the length of the scale). Thus, the position and movement of the scale signal receiver 6 other than along the measurement dimension (along the x-axis in the illustrated embodiment) is constrained by the scale 4. In other words, the scale signal receiver 6 is guided by the scale 4. The articulated linkage 18 therefore decouples the scale signal receiver 6 and the mounting block 14 in all degrees of freedom other than along the measurement dimension of the encoder arrangement (which must be consistent with the direction of motion of the first and second parts of the machine), which in the embodiment shown in Figure 1 is along the x-axis. As will be appreciated by those skilled in the art, the manner in which a readhead may be constrained relative to a scale, for example, is well known.

[0122] Also, as shown in FIG. 1b, a power / communication cable 5 may be provided for the readhead assembly to receive power and to facilitate communication between the readhead assembly and an external processor device (e.g., a machine controller). Additionally, an air supply line 9 may be provided to supply air into the protective housing 8 to create a positive pressure within the protective housing 8. Thus, if the sealing lip 12 does not form a perfect seal (especially if the lip seal is separated by the blade 16), the positive pressure will tend to force air out of the protective housing 8. The positive pressure thereby provides additional resistance to physical contaminants attempting to enter the protective housing 8. As will be appreciated, such contaminants may comprise solid and / or fluid contaminants, examples of which include shavings, liquids (e.g., coolants) and / or air-borne moisture. Also, as shown, a separate air supply line 7 may be provided to supply air to the interior of the protective housing through the readhead assembly (e.g., via a conduit through the mounting block 14 and the blade 16).

[0123] In the described embodiment, the encoder module is provided with an emitter 13, 113, 213, 313 for relaying diagnostic information. In other embodiments, where such emitters are additionally or alternatively provided, the encoder module may be configured to measure and output diagnostic information in the form of one or more electronic signals to an external device (e.g., a controller), for example via cable 105, 205, 305. For example, diagnostic information regarding the quality of the scale signal detected by the readhead may be measured and output by the encoder module. The external device receiving this information may, for example, display this information to an operator. Such diagnostic information may be useful to help an operator determine the status of the encoder module, for example, to determine whether the encoder module is operating properly and, if not, to take action (such as shutting down the machine in which the encoder module is installed and / or replacing the encoder module).

[0124] In most of the above-described embodiments, the light emitters 13, 113, 213 are provided in the readhead. However, as will be appreciated, this does not necessarily have to be the case. For example, as shown in Figs. 1a, 1b and 1d, the light emitters 13' may be provided in a protective housing 8. In this case, the protective housing 8 may comprise an internal power source (e.g. a battery) for powering the light emitters and / or may be connected to an external power source. Furthermore, the protective housing 8 may be configured to receive diagnostic information from the readhead in order to determine how to control the light emitters. As an option, the protective housing 8 is configured to receive the scale signals detected by the readhead and is configured to measure the diagnostic information itself in order to determine how to control the light emitters. In any case, the protective housing may comprise its own processor device configured to measure how to control the light emitters (e.g. in response to the received diagnostics and / or after measuring the diagnostic information itself).

[0125] As will be appreciated, providing the light emitter on the protective housing is not exclusive to encoder arrangements of the type shown in Figures 1a to 1d, but is equally applicable to the embodiments described above in relation to the other Figures. For example, as shown in Figures 2a, 2b, 9a and 9b, the light emitter 113', 213' may be provided on the protective housing 108, 808, 908 in addition to or instead of the readhead. Also, as mentioned above, the embodiment of Figure 10 includes a light emitter 313 on the protective housing 308.

[0126] It will also be appreciated that a bracket (e.g., a "transit bracket") or the like may be used to hold the readhead assembly and protective housing in a predetermined physical relationship, such as when they are not attached to the machine.

Claims

1. 1. A sealed encoder module for mounting to a machine to measure relative displacement of first and second portions of the machine, comprising: The sealed encoder module includes: scale, a readhead comprising a scale signal receiver; and a protective housing encapsulating at least the scale and the scale signal receiver; the scale signal receiver comprising a rigid outer case in which one or more components of the readhead are housed; the rigid outer case encapsulates at least all of the electronic components of the scale signal receiver, including any wires and any printed circuit board disposed within the protective housing, thereby protecting them from contamination entering the protective housing of the sealed encoder module that is within the protective housing; the protective housing includes a seal capable of connecting the scale signal receiver to an exterior portion of the protective housing; 11. A sealed encoder module comprising: a read head having a blade-like member extending through the seal of the protective housing, the blade-like member providing an internal passage for any wires to pass between the inside and outside of the protective housing.

2. 2. The sealed encoder module of claim 1, wherein the scale signal receiver includes an optical element for sensing the scale, the optical element being housed in the outer case so as to be protected from contaminants entering the protective housing of the sealed encoder module.

3. The sealed encoder module of claim 2 , wherein the optical element comprises at least one of a sensor, an emitter, a lens, a diffraction grating, a beam steering device, a beam splitter, and a mirror.

4. The sealed encoder module of claim 1 , wherein the outer case provides a space in which the one or more components are disposed.

5. The sealed encoder module of any of claims 1-4, wherein the outer case provides a structure to which the one or more components are mounted.

6. A sealed encoder module as described in any one of claims 1-5, comprising a reflective optical encoder device having a light source for illuminating the scale and a detector for detecting the scale located on the same side as the scale, the outer case comprising the light source and the detector.

7. The sealed encoder module of any preceding claim, wherein the outer case has an IP rating of at least IP44.

8. A sealed encoder module according to any preceding claim, wherein the outer case has an IP rating of at least IP65.

9. A sealed encoder module according to any preceding claim, wherein the outer case has an IP rating of at least IP67.

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