WO2026017973A1

WO2026017973A1 - Laser encoder device

Info

Publication number: WO2026017973A1
Application number: PCT/GB2025/051533
Authority: WO
Inventors: Michael Jackson Hill
Original assignee: Renishaw PLC
Current assignee: Renishaw PLC
Priority date: 2024-07-15
Filing date: 2025-07-11
Publication date: 2026-01-22
Anticipated expiration: 2027-01-15
Also published as: GB202410256D0

Abstract

A laser encoder device is disclosed which is adapted to receive an optical fibre assembly. The optical fibre assembly comprises first and second parts (15, 17) which are mechanically coupled to one another. The laser encoder device 5 comprises a decoupling arrangement (40) which is operable to decouple the second part (17) mechanically from the first part (15). In a specific embodiment, the laser encoder device is a detector head, the first part (15) is a strain relief component, and the second part (17) is a collimator.

Description

Laser Encoder Device

The present invention relates to a laser encoder device. The present invention relates in particular, but not exclusively, to improvements in the setup and operation of such a laser encoder device.

Figure 1 of the accompanying drawings illustrates a fibre optic laser encoder system 1 which is made and sold by Renishaw pic. The laser encoder system 1 provides position feedback signals suitable for use in precision position feedback applications such as machine calibration and motion control.

The main components of the laser encoder system 1 are a laser unit 2, a detector head (or detector unit) 4 and a machine interface 6. The detector head 4 is the core of the optical measuring system and will be described in further detail below with reference to Figure 2 of the accompanying drawings. The laser unit 2 comprises a laser source and signal processing electronics, with an electrical cable 3 for receiving signals from and providing power to the detector head 4 and a fibre optic conduit 5 that delivers laser light directly to the detector head 4 through a fibre optic cable (not visible in Figure 1) within the fibre optic conduit 5. The machine interface 6 forms part of a controller 31 and communicates with the laser unit 2 via an electrical cable 7.

To complete the configuration, a target optic 8 is provided in the path of a laser beam 9 emitted from the detector head 4, such that the laser beam 9 is reflected off the target optic 8 and returned to the detector head 4. In this example, the target optic 8 is in the form of a retroreflector but with a variant of the detector head 4 the target optic 8 could instead be a plane mirror. The beam 9 is a measurement beam, with the return measurement beam interfering with a reference beam which in this example is internal to the detector head 4, with the distance to the target optic 8 (or rather changes in this distance relative to a chosen datum position) being determinable from the interference signal in a known way.

Figure 2 is a schematic illustration of the main components of the detector head 4 of Figure 1. The fibre optic cable 11 passes through into the body or housing 24 of the detector head 4 and into a collimator 17. The fibre optic cable 11 is terminated within and held in place via a ferrule 21, with laser light being emitted from the end of the fibre optic cable 11 in a diverging cone. The role of the collimator 17 is to collimate this diverging beam, using a lens 23, before it passes further through the detector head 4. As shown by the arrows, the collimated beam passes first to a beam splitter 14, with some of the light being reflected up to a reference retroreflector 18 (as a reference beam) and the remainder of the beam passing out through the laser aperture 16, via a beam steerer 30, and onwards (as the measurement beam 9) to the retroreflector target optic 8. Also shown in Figure 2 is a circuit board 12, which supports various processing, detection, and control electronics (such as a light detector 19), as well as an optical shutter 26 which can be used to shut off the measurement beam 9.

The return measurement beam from retroreflector target optic 8 re-enters the detector head 4 via the laser aperture 16, and through the beam splitter 14 where it joins (and interferes with) the measurement beam from the reference retroreflector 18 and is incident on a light detector 19. An analogue quadrature interference signal (or detection signal) from the light detector 19 then passes out from the detector head 4 via the electrical cable 3 where it is received at the laser unit 2 shown in Figure 1. Although there may be some processing performed on the interference signal at the laser unit 2, the main processing is typically performed at the interface 6, having received the interference signal from the laser unit 2 via electrical cable 7.

By digitising, interpolating and processing the interference signal the interface 6 can determine with high accuracy how far the retroreflector target optic 8 has moved by counting fringes, or rather pulses in the digitised/interpolated version of the signal. The positional data from the interface 6 can then be used by the controller 31 for the intended purpose, such as machine calibration or motion control. It should be noted that the laser unit 2 can be set to output a digital rather than analogue quadrature output signal, in which case the digitising and interpolating would be performed at the laser unit 2 rather than at the interface 6.

The exterior of the detector head 4 of Figure 1 is shown in more detail in Figure 3 of the accompanying drawings. The fibre optic cable 11 can just be seen within the fibre optic conduit 5. The fibre optic conduit 5 is itself coupled to the body of the detector head 4 via a strain relief 15, which is intended to prevent or at least limit forces on the fibre optic conduit 5 and the enclosed fibre optic cable 11 being transferred to any internal optical components to which the fibre optic cable 11 is connected. A laser aperture 16 is also apparent in Figure 3, through which both the outgoing and returning measurement beams 9 will pass.

The detector head 4 as shown in Figures 1 to 3 is just one type of detector head made and sold by Renishaw pic. Figure 4 of the accompanying drawings shows another type of detector head 4, which differs from that shown in Figure 3 mainly in that the measurement beam 9 is emitted at a ninety-degree angle to main axis of the detector head 4 (rather than zero-degree angle). The detector head 4 of Figure 4 would typically be used as a pair, with one detector head 4 of the pair measuring along an X machine axis and the other measuring along a Y machine axis, and would typically use a target optic 8 in the form of a plane mirror (though a retroreflector target could also be used). It can be seen that the laser unit 2 of Figure 1 has a spare set of connections available for accommodating a second detector head 4 in this way.

Figure 5 of the accompanying drawings shows yet another type of detector head 4, which differs more substantially from that of Figures 3 and 4. The detector head 4 of Figure 5 is a differential interferometer detector head 4, with a pair of measurement beams 9M emitted from the laser aperture 16 as well as a pair of reference beams 9R. By using an external reference beam 9M, the differential interferometer detector head 4 is able to measure the relative displacement between two plane mirror targets, one of which (the reference target) would typically be in a fixed position, for example on a fixed column of the machine, and the other of which (the measurement target) would be moving, for example on a moving stage of the machine on which a semiconductor wafer or other workpiece is supported. This helps to ensure accurate positioning between process critical components and to eliminate common mode errors.

For a detector head 4 of a type as shown in Figures 3 and 4 the electrical cable 3 is fixedly connected to the detector head 4, but for a detector head 4 of a type as shown in Figure 5 an electrical connector 13 is provided for releasably connecting the electrical cable 3 to the detector head 4. For all of these detector heads 4 the electrical cable 3 is releasably connectable at the other end to the laser unit 2. On the other hand, for all of these detector heads 4 the fibre optic conduit 5 (with enclosed fibre optic cable 11) is detachable from the detector head 4 (as will be explained in more detail below) but is fixedly coupled into the laser unit 2. In this respect, the fibre optic cable 11 is continuous from the fibre launch within the laser unit 2 all the way to the collimator 17 and therefore cannot easily be disconnected from the laser unit 2. The detector head 4 typically incorporates a feature that prevents the laser beam 9 being emitted if either the fibre optic cable 11 or electrical cable 3 is disconnected.

The collimator 17, the strain relief 15, fibre optic conduit 5 (with enclosed fibre optic cable 11) and fibre optic connector 34 (see Figure 1) can be considered to form a single optical fibre assembly 32, with the collimator 17 being considered as an integral part of the optical fibre assembly 32 because it terminates the fibre optic cable 11 in a manner required by the detector head 4 (and the laser encoder system 1 as a whole). The components of the optical fibre assembly 32 (and the internal components of the collimator 17) are assembled and aligned precisely in the manufacturing facility, and supplied to the customer as a unit, and as such are considered to be inseparable in normal use. The way in which the detector head 4 is adapted to receive the optical fibre assembly 32 will be more apparent from Figures 6 and 7 of the accompanying drawings.

When the laser encoder system 1 is being configured for operational use, the supplied optical fibre assembly 32 is connected to the detector head 4 simply by pushing the collimator 17 through a correspondingly sized opening formed in the housing 24 and into the body of the detector head 4, with the strain relief 15 remaining outside the body and in contact with the housing 24. This connection operation is illustrated in Figure 6 for a differential interferometer detector head 4 of a type shown in Figure 5, but the connection would be entirely equivalent for a detector head 4 of a type shown in Figures 3 and 4. The combination of the strain relief 15 and collimator 17 can be referred to as a fibre barrel 10, with the optical fibre assembly 32 being terminated by the fibre barrel 10.

Figure 7 shows a view of the differential interferometer detector head 4 of Figure 4 with the upper part (or lid) of the housing 24 removed. This illustrates how the collimator 17, having been pushed into the body of the detector head 4, is held in place tightly by a clamp 20, which is in turn tightened via a locking screw 22. It will also be apparent from Figures 6 and 7 that the collimator 17 is rigidly coupled to the strain relief 15, consistent with the above explanation that the collimator 17 and the strain relief 15 form part of a unitary optical fibre assembly 32. The strain relief 15 and collimator 17 are prevented from being pulled away from the detector head 4 by action of the clamp 20 on the collimator 17, but there could be an additional coupling of the strain relief 15 to the housing 24 (e.g. via a screw thread connection).

For a proper connection, the fibre barrel 10 (and in particular the collimator 17) must be inserted into the detector head 4 in the correct orientation. To achieve this, and as shown in Figure 6, a line L marked on the fibre barrel 10 is aligned visually with an alignment dot D marked on the detector head 4. The fibre barrel 10 is inserted fully and then rotated slightly until a ball bearing inside the clamp 20 can be felt to engage in a recess 38 in an outer surface of the collimator 17 (specifically in a lid of the collimator 17), with the ball bearing being biased by a spring 39 (see Figure 7) into the indent 38 to form a detent feature. There would also be an end stop in the lid of the detector head 4 which sets the position along the insertion axis, so that the indent 38 is in the correct axial position to receive the ball bearing that is biased into it by the spring 39.

Whilst the strain relief 15 does help to redirect some of any radial and axial forces acting externally on the fibre optic conduit 5 into the rigid support structure (e.g. housing 24) of the detector head 4, rather than to the internal optical components, the present applicant has appreciated that this arrangement does not fully address some of the problems caused by these external forces, and the effect that these can have on the performance and stability of the detector head 4. The present applicant has also appreciated that the way in which the collimator 17 is received into the body of the detector head 4 and the held in place by the clamp 20 can cause some issues in relation to the configuration of the detector head 4 for operational use.

According to a first aspect of the present invention there is provided a device which is adapted to receive an optical assembly. The optical assembly comprises first and second parts which are mechanically coupled to one another. The device comprises a decoupling arrangement which is operable to decouple the second part mechanically from the first part.

As will be explained in more detail below, this helps to overcome the above- mentioned issue by preventing any forces which are acting on the first part of the optical assembly from transferring to the second part of the optical assembly, such that the alignment of the second part of relative to the device is not affected by such forces. This avoids having to repeat a complicated alignment procedure to re-align the second part correctly each time the first part is inadvertently knocked during use.

The device may be a laser encoder device.

The optical assembly may be an optical fibre assembly.

The first part may be one that is subject to forces applied to the assembly externally of the device, for example after installation of the assembly into the device.

The second part may be one that is located internally to the device, after installation of the assembly into the device.

The assembly may comprise a fibre optic conduit (with an enclosed fibre optic cable) coupled mechanically to the first part.

The assembly may comprise a fibre optic cable (enclosed by a fibre optic conduit) for providing light to the device in use.

The assembly may comprise a fibre optic connector coupled mechanically to the fibre optic conduit.

The laser encoder device may be a detector head (or detector unit).

The second part may terminate the assembly.

The first part may be a strain relief component.

The second part may be an optical or metrology component.

The second part may be a collimator. The first and second parts may form a fibre barrel component. The fibre barrel component may terminate the assembly.

The first part may be moveable into contact with the second part, for example while inserting (or pushing or sliding or installing or connecting or coupling) the assembly into the device.

The device may comprise a retaining pin on one of the first and second parts which is received into an opening on the other of the first and second parts to hold the first and second parts together when not installed into the device.

The assembly may comprise a spacer component which maintains a gap (or spacing) between the first and second parts, and wherein the decoupling arrangement is operable to remove the spacer component.

The decoupling arrangement may comprise at least a first member which is operable to engage with the assembly to establish and/or maintain a gap (or spacing) between the first and second parts (for example by pushing the second part away from the first part).

The decoupling arrangement may comprise a second member which is operable to engage with the assembly to prevent substantial axial movement of the first part.

The decoupling arrangement may be moveable between first, second and third states, with the first member being engaged in the second state (thereby opening a gap) but not in the first and third states (thereby being clear of any gap).

The second member may be engaged in at least the third state and optionally in the second state (thereby preventing the assembly being removed axially from the device) but not in the first state (thereby allowing the assembly to be removed axially from the device).

The decoupling arrangement may be a cam arrangement. In this case, the first member may be a first cam of the cam arrangement, the second member may be a second cam of the cam arrangement, and the states may be rotational positions of the cam arrangement.

The cam arrangement may comprise at least one detent feature which provides tactile feedback in the first and/or third rotational positions.

The cam arrangement may comprise at least one stop feature which prevents movement beyond the first and/or third rotational positions in a direction away from the second rotational position.

The assembly may comprise a damping member which is arranged to dampen movements of the first part when the assembly has been installed into the device (for example to prevent rattling).

According to a second aspect of the present invention, there is provided a method of installing an optical fibre assembly into a laser encoder device as claimed in any preceding claim, comprising inserting the assembly into an opening in the device and operating the decoupling arrangement to decouple the second part mechanically from the first part. The assembly may be installed into the device through the opening without having to open the device (e.g. to remove or lift a lid or a part of the housing or enclosure).

Reference will now be made, by way of example, to the accompanying drawings, in which:

Figure 1, discussed hereinbefore, illustrates a known fibre optic laser encoder system comprising a laser unit, detector head and machine interface; Figure 2, also discussed hereinbefore, is a schematic view of some of the internal components of the detector head of Figure 1;

Figure 3, also discussed hereinbefore, shows in more detail a detector head of the type shown in Figures 1 and 2;

Figure 4, also discussed hereinbefore, shows a different type of detector head in which the laser beam is emitted from the body at a different angle;

Figure 5, also discussed hereinbefore, shows a differential interferometer type of detector head which emits both measurement and reference beams;

Figure 6, also discussed hereinbefore, shows how the fibre barrel of an optical fibre assembly is connected to a differential interferometer type of detector head;

Figure 7, also discussed hereinbefore, shows a view of the detector head of Figure 6 with the upper part of the housing removed;

Figure 8 is a schematic illustration of a fibre barrel having a two-part construction, which is the basis for an embodiment of the present invention;

Figure 9 shows a corresponding view after insertion into the detector head, with contact between the two parts of the fibre barrel;

Figure 10 is the first in a series of schematic illustrations showing the use of a cam arrangement in an embodiment of the present invention, with the cam arrangement in a first rotational position;

Figure 11 is the second in the series of schematic illustrations, with the cam arrangement in a second rotational position; Figure 12 is the third in the series of schematic illustrations, with the cam arrangement in a third rotational position;

Figure 13 is a perspective view of showing the outside of the detector head with the strain relief protruding and a locking head used to operate the cam arrangement internally;

Figure 14 is a perspective view from a similar vantage point as Figure 13 but with parts of the detector head removed to show more clearly the fibre barrel and cam arrangement in the first rotational position;

Figure 15 shows a corresponding view after the cam arrangement has been moved towards the second rotational position;

Figure 16 shows a corresponding view after the cam arrangement has been moved beyond the second rotational position and towards the third rotational position;

Figure 17 shows a corresponding view after the cam arrangement has been moved into the third rotational position;

Figure 18 shows a perspective view of the cam arrangement in isolation;

Figure 19 shows an end view of the cam arrangement;

Figure 20 shows an end view of the cam arrangement, strain relief and collimator, to illustrate how key features of these parts are positioned relative to one another in the first rotational position;

Figure 21 shows a view corresponding that of Figure 20 but with the cam arrangement in the second rotational position; Figure 22 shows a view corresponding that of Figures 20 and 21 but with the cam arrangement in the third rotational position;

Figure 23 shows a section through the fibre barrel to illustrate a gap between the collimator and the strain relief;

Figure 24 shows a side view of the collimator and strain relief with the cam arrangement in the locked position;

Figure 25 illustrates a feature of the strain relief which provides constraint in a rotational degree of freedom (around the axis of the fibre barrel);

Figure 26 illustrates the addition of a constraint in a translational degree of freedom (along the axis of the fibre barrel) by operation of the cam arrangement;

Figure 27 is a perspective view for use in explaining a load path in operation when the optical fibre assembly is pulled axially away from the detector head;

Figure 28 is a sectional view for use in explaining the load path;

Figure 29 is a view showing a detent feature of the cam arrangement, at least partly for providing tactile feedback to the user;

Figure 30 is a view similar to that of Figure 13, showing an end cap surrounding the locking head;

Figure 31 shows how the load path is arranged to prevent the end cap popping off when the optical fibre assembly is pulled axially away from the detector head;

Figure 32 shows the operation of a first rotational end stop which prevents rotation of the cam arrangement beyond the first rotational position; and

Figure 33 shows the operation of a second rotational end stop which prevents rotation of the cam arrangement beyond the third rotational position.

As discussed above, the strain relief 15 used in the detector head 4 described with reference to Figures 1 to 7 helps to prevent some of the forces acting externally on the fibre optic conduit 5 from transferring to the internal optical components of the detector head 4. However, because of the rigid coupling between the strain relief 15 and the collimator 17 (see in particular Figures 6 and 7), with these parts forming the fibre barrel 10, the present applicant has appreciated there can still be some residual transfer of force directly from the strain relief 15 to the collimator 17. For example, if there is a slight movement or flexing of the fibre optic conduit 5 after the laser encoder system 1 has been set up, or if the strain relief 15 itself is inadvertently knocked, this can cause the collimator 17 to become slightly misaligned. In the most demanding of applications, this has a noticeable effect on the overall performance of the laser encoder system 1.

Figure 8 is a schematic illustration of a fibre barrel 10 for a laser encoder device (or detector head) embodying the present invention. The fibre barrel 10 comprises a strain relief 15 and a collimator 17, with these parts being generally similar in overall function to those described above so that a detailed further description of them is not required. However, it will be apparent that, compared to what is described above with reference to Figures 6 and 7, the fibre barrel 10 of Figure 8 has a two-piece type of construction, with the strain relief 15 being physically decoupled from the collimator 17 by virtue of a gap G between them. The decoupling feature used to achieve (and maintain) the decoupling of the strain relief 15 from the collimator 17 is not shown in Figure 8 itself but will be described in detail below.

Figure 9 illustrates what happens when the fibre barrel 10 is initially inserted into the detector head 4 with a push on the strain relief 15 in the direction of the arrow P. The strain relief 15 is pushed as far as a housing 24 of the detector head 4, and in this position the collimator 17 is inside the detector head 4. A seating arrangement 25 is adapted to hold the collimator 17 in place within the detector head 4 after insertion, and by providing a biasing force to the collimator 17 as part of this function it also offers some frictional resistance to the movement of the collimator 17 during insertion. This resistance causes the strain relief 15 to push up against the collimator 17 and thereby causes the gap G shown in Figure 8 to close. The seating arrangement 25 is not described in further detail herein but the features of such a seating arrangement are explored further in our co-pending application filed on the same date as the present application.

Whilst the coupling between the strain relief 15 and the collimator 17 is not completely rigid, as it was with the fibre barrel 10 described above with reference to Figures 6 and 7, there is nevertheless some degree of contact in Figure 9 between the strain relief 15 and the collimator 17 after the insertion operation. As a result, any further movement of the strain relief 15 (e.g. if the strain relief 15, or the fibre optic conduit 5 to which the strain relief 15 is mechanically coupled, is knocked inadvertently) will likely result in some movement of the collimator 17. This would be undesirable, particularly after a time-consuming setup procedure has been completed, because it would potentially nudge the collimator 17 out of alignment.

Accordingly, the present applicant has appreciated that it would be beneficial to prevent such contact between the strain relief 15 and the collimator 17, at least when required, by maintaining (or by re-opening and then maintaining) the gap G shown in Figure 8. This would provide a degree of mechanical decoupling between the strain relief 15 and the collimator 17, and would prevent inadvertent movements of the strain relief 15 being transferred directly to the collimator 17.

To achieve this aim, an embodiment of the present invention provides a cam arrangement 40 as shown in Figure 10 which is adapted to decouple the strain relief 15 from the collimator 17. Figure 10 shows the state of the fibre barrel 10 after insertion into the detector head 4, with the gap G still closed up. The cam arrangement 40 comprises two cams A and B (shown side-on in Figure 10) that are connected via and rotate with a camshaft 41. The camshaft 41 is terminated by a head 42 exposed on an outer surface of the housing 24, with the exposed head 42 enabling the user to turn the camshaft 41 (along with cams A and B) using a suitable tool.

Figure 10 shows the cam arrangement in a first rotational position (denoted as Pl) in which the cams A and B are disengaged from corresponding respective recesses C and D provided in an outer surface of the strain relief 15, such that the fibre barrel 10 is free to move axially (for example for insertion into or removal from the detector head 4), and also such that the collimator 17 is free to move relative to (and into contact with) the strain relief 15.

When rotated into a second rotational position (denoted as P2) by turning the head 42 and camshaft 41 as shown by R2 in Figure 11, the displacement profile of cams A and B is such that both cams A and B move into engagement with corresponding respective recesses C and D. Not only does this lock (or hold) the strain relief 15 to prevent axial removal of the fibre barrel 10 from the detector head 4 (by interaction between cam B and recess D), but it also pushes the collimator 17 away from the strain relief 15 in the direction of arrow H (by interaction between cam A and recess C). In so doing, the gap G has been opened up again, returning it to the state as shown in Figure 8, albeit that the gap G is filled to some extent by the presence of cam A within recess C.

When rotated into a third rotational position (denoted as P3) by turning the head 42 and camshaft 41 as shown by R3 in Figure 12, the displacement profile of cams A and B is such that cam B remains engaged with corresponding recess D, while cam A becomes disengaged from corresponding recess C. Therefore, the strain relief 15 is still locked in place by the interaction between cam B and recess D (to prevent axial removal of the fibre barrel 10 from the detector head 4). However, the collimator 17 is no longer constrained relative to the strain relief 15 (because cam A is no longer engaged with recess C), and the gap G shown in Figure 8 has therefore been fully restored.

In the position as shown in Figure 12, because there is clearance between the strain relief 15 and the collimator 17, movements of the strain relief 15 will no longer impact the collimator 17. Indeed, cam B can be a relatively loose fit within recess D, so that a small amount of rotational and translational movement of the strain relief 15 can be expected. However, sufficient clearance between the strain relief 15 and the collimator 17 can be arranged such that, even with these small movements of the strain relief 15, no part of the strain relief 15 will contact any part of the collimator 17. This therefore provides mechanical isolation of the collimator 17 from the strain relief 15 (and parts of the optical fibre assembly 32 further back that will impart movements to the strain relief 15, such as the fibre optic conduit 5). There will be contact between the strain relief 15 and the housing 24, both directly and via the cam arrangement 40, but not directly between the strain relief 15 and the collimator 17.

By using a decoupling arrangement embodying the present invention, performance of the detector head 4 will be less sensitive to movement of the fibre optic conduit 5 (which is a routine occurrence in all but the most controlled environments), compared to previously-considered designs, leading to better and/or more consistent results, and a lower risk of having to repeat a timeconsuming setup procedure if part of the optical fibre assembly 32 has to be moved.

In addition, the cam arrangement 40 described particularly with reference to Figures 8 to 12 provides a convenient way to couple the optical fibre assembly 32 correctly to the detector head 4, whereby the user just needs to push the fibre barrel 10 into an opening of the detector head 4 as far as it will go, and then turn the locking head 42 with a light turning force until an end stop is reached (this end stop will be discussed further below).

With the previously considered detector head 4 as shown in Figures 6 and 7, turning of the locking screw 22 causes the clamp 20 to tighten onto the outer surface of the collimator 17 to hold it in place, and a judgement needs to be made about how much torque to apply. If too little torque is applied then there is a risk that the collimator 17 will slip out of position during use, and if too much torque is applied then there is a risk that the collimator 17 will be pushed away from the correct position or may even be damaged.

On the other hand, with the cam arrangement 40 shown in Figures 8 to 12, turning of the locking head 42 does not itself apply any holding force to the collimator 17, but is merely used to rotate the camshaft 41 and cams A and B. Therefore, a light turning force can be applied to the head 42 until a stop position is reached, and there is no danger of overtightening. It is the interaction between cam B and recess D which keeps the fibre barrel 10 from coming away from the detector head 4, and because the collimator 17 is mechanically isolated from the strain relief 15 only a relatively light biasing force (which can be provided by the seating arrangement 25) is required to hold the collimator 17 in position.

Some further views showing more detail of the cam arrangement 40, and how it interacts with features of the fibre barrel 10, are shown in Figures 13 to 17, in less schematic form compared to Figures 8 to 12. Like reference numerals are used for like parts. As will be explained in more detail below, the shape of cams A and B is such that the first rotational position (corresponding to Figure 10) is at 0 degrees of rotation, the second rotational position (corresponding to Figure 11) is at 75 degrees of rotation, and the third rotational position (corresponding to Figure 12) is at 150 degrees of rotation. Figure 13 is an external perspective view showing the locking head 42 exposed on an external surface of the housing 24, alongside the strain relief 15 after insertion of the collimator 17 into the detector head 4. This view also shows a convenient graphical instruction next to the locking head 42 which informs the user to turn the locking head 42 clockwise to lock the fibre barrel 10 (and activate the mechanical decoupling between the strain relief 15 and the collimator 17) and anticlockwise to unlock (so that the fibre barrel 10 can be removed).

Figure 14 is a cut-away perspective view showing the main parts (the strain relief 15, collimator 17, and cam arrangement 40) in a state corresponding to that shown in Figure 10, i.e. after insertion of the collimator 17 into the detector head 4, and without yet having turned the locking head 42. Therefore, the locking head 42 is in the first rotational position Pl, nominally at zero degrees, and both cams A and B are disengaged. The gap G has closed up as a result of the insertion operation.

Figure 15 shows a corresponding view after the locking head 42 has been turned clockwise by 50 degrees relative to the zero position, which is part-way towards the second rotational position P2 (which is at 75 degrees). As the camshaft 41 is turned through this position, an angled surface of cam A provides an axial force on the collimator 17 to push it away from the strain relief 15 in the direction marked by arrow H, so that a gap G is opening up. In this position, cam B is also moving into engagement with the strain relief 15, and also adjusting the axial position of the strain relief 15 so as to align with cam B.

Figure 16 shows a corresponding view after the locking head 42 has been turned clockwise by 100 degrees relative to the zero position, which is slightly beyond the second rotational position P2 (which is at 75 degrees). In this position, the gap G has fully re-established by operation of cam A, which is now starting to disengage, and the strain relief 15 is fully locked in place (albeit loosely) via cam B. However, cam A is still located partially within the gap G and therefore the decoupling of the strain relief 15 from the collimator 17 is not yet fully complete. Figure 17 shows a corresponding view after the locking head 42 has been turned fully into the third rotational position P3, at an angle of 150 degrees relative to the zero position, and corresponds to the view shown more schematically in Figure 12. In this position, the gap G is fully open with cam A out of the way, and the strain relief 15 is still locked in place (albeit loosely) via cam B.

Also apparent from Figures 14 to 17 is a flange 43 at the far end of the camshaft 41 relative to the locking head 42, recesses 9a and 9b in the surface of the camshaft 41, and a spring plunger 47. These features will be discussed further below.

Figure 18 shows a perspective view of the cam arrangement 40, thereby providing a clearer view of this part in isolation, while Figure 19 shows an end view of the cam arrangement 40 looking in the direction from cam A to cam B (and with the flange 43 in front), i.e. from the inside of the detector head 4 looking outward. These views more clearly illustrate the shape of cams A and B, and their relative rotational positioning, that enable them to perform their intended function as described above with reference to Figures 10 to 17.

From Figures 18 and 19 it will be apparent that sloped side surfaces la and lb are provided on leading edges of cams A and B respectively. Sloped side surface la acts axially on the collimator 17 as cam A turns into the second rotational position P2, thereby pushing the collimator 17 away and re-establishing or restoring the gap G, while sloped side surface lb acts axially on the strain relief 15 to nudge it into axial alignment with cam B (since it may not yet be perfectly aligned after pushing the fibre barrel 10 into the detector head 4).

Also apparent in Figures 18 and 19 are concave edge surfaces 2a and 2b of cams A and B respectively, and another concave edge surface 3 a of cam A on the other side of a projecting portion 4a. The reason for these will be apparent from a discussion of Figures 20 to 22.

Figure 20 shows the same view of the cam arrangement 40 as Figure 19, and also shows where the strain relief 15, collimator 17 and recesses C, D are in relation to the cam arrangement 40. The cam arrangement 40 of Figure 20 is in the first rotational position Pl mentioned above. In this position Pl, the concave edge surfaces 2a and 2b are both aligned with the outer convex surfaces of the strain relief 15 and collimator 17, with the surfaces being arranged such that there is no overlap between either of cam A and B and either of the strain relief 15 and the collimator 17 when looking in an axial direction into the page of Figure 20. Consequently, the fibre barrel 10 (comprising the strain relief 15 and collimator 17) is free to be pulled out of and inserted into the detector head 4 unimpeded, i.e. the cam arrangement 40 is fully unlocked in this position Pl.

When rotated by 75 degrees (anticlockwise in this view) into the second rotational position P2 as shown in Figure 21, cam B now protrudes into the corresponding recess D formed in the strain relief 15, thereby preventing axial movement of the strain relief 15. In addition, as cam A was rotating anticlockwise into this position P2 (and within recess C), the sloped side surface la (of the projecting portion 4a) was also acting to open the gap G between the strain relief 15 and the collimator 17. It is to be noted that an anticlockwise rotation in this view corresponds to a clockwise rotation of the head 42 from the point of view of the user.

When rotated anticlockwise by another 75 degrees into the third rotational position P3 as shown in Figure 22, the projecting portion 4a of cam A has now moved clear of recess C, and the concave edge surface 3a of cam A is now aligned with the outer convex surface of the strain relief 15 and collimator 17. Therefore, cam A no longer protrudes into the gap G (by virtue of being clear of recess C), but cam B remains protruding into its corresponding recess D. Accordingly, the cam arrangement 40 is now in a fully locked state, with the strain relief 15 held against axial movement, and with the collimator 17 mechanically decoupled from the strain relief 15 by virtue of gap G. The detector head 4 is now ready for use.

Figure 23 shows a section through the fibre barrel 10 with the cam arrangement 40 in a locked position, clearly showing a gap G all the way around the collimator 17. In this position, lateral movements of the fibre optic conduit 5 will cause the strain relief 15 to angle slightly from side to side but without ever touching the collimator 17. Axial movement of the strain relief 15 towards to the collimator 17 will be prevented by cam B (or contact between the strain relief 15 and the housing 24). Axial movement of the strain relief 15 away from the collimator 17 will be prevented by cam B (the load path will be discussed in more detail below).

Also shown in Figure 23 is a retaining pin 45 on the strain relief 15 which protrudes through an opening 46 in the collimator 17, thereby preventing the collimator 17 coming away from the strain relief 15 during the process of removing it from the detector head 4, and afterwards. As mentioned above, the collimator 17 and the strain relief 15 form part of an optical fibre assembly 32 that is typically assembled in a manufacturing facility and supplied to the customer as a unit, and therefore the collimator 17 must remain attached to the strain relief 15 even when not in use. The retaining pin 45 serves this purpose, but it is to be noted that that there is a clearance between the retaining pin 45 and the strain relief 15 when the cam arrangement 40 is in the locked position, thereby ensuring that mechanical decoupling between the collimator 17 and the strain relief 15 is maintained.

Figure 24 shows a side view with the collimator 17 and strain relief 15 inserted into the detector head 4 and with the cam arrangement 40 in the locked position. The strain relief 15 has a relatively loose fit within the housing 24, and is thereby able to move or rock slightly, but with the fit being tighter at gap T (between the strain relief 15 and the housing 24) than at gap G (between the strain relief 15 and the collimator 17), so that gap G does not close up with any slight rocking of the strain relief 15. Because the strain relief 15 has a relatively loose fit within the housing 24, it may be the case that a slight rattling is apparent when the strain relief 15 contacts the housing 24 as it moves around. Whilst this does not affect the overall function or effectiveness of the detector head 4, it may give the impression to the user that the optical fibre assembly 32 has not been securely docked into the detector head 4. To avoid giving this impression, a damping member may be provided to suppress or dampen the movements of the strain relief 15, and thereby preventing the rattling sound. Such a damping member is shown in Figures 14 to 17 in the form of a spring plunger 47 which passes radially through the camshaft 41 from one side to the other and which rotates with the camshaft 41. The head of the spring plunger 47 is formed of or covered by a resilient material, which is biased into the strain relief 15 when the cam arrangement 40 is rotated into the third rotational position P3 (but does not make contact when the cam arrangement 40 is in the first or second rotational positions Pl or P2). This dampens the movement of the strain relief 15 when in the locked position. Other forms of damping member may of course be used, such as a damping material arranged where the strain relief 15 contacts the housing 24.

Figure 25 shows that the strain relief 15 has a flattened portion 51 which (by interacting with a correspondingly shaped portion of the housing 24) prevents rotation of the strain relief 15 after insertion into the housing 24. Overall, the strain relief 15 is constrained in five degrees of freedom after insertion into the detector head 4, but before locking the cam arrangement 40, and then constrained in all six degrees of freedom after locking the cam arrangement 40 (as shown in Figure 26), albeit with a relatively loose fit to allow small rotational and translational movements.

Figures 27 and 28 are for use particularly in explaining the load paths when the optical fibre assembly 32 is pulled axially away from the detector head 4 when the cam arrangement 40 is in the locked position (or at least in a position in which cam B is engaged). The axial force on the optical fibre assembly 32 is transferred via cam B to the cam arrangement 40 which is in turn pulled in the direction of the force. After a slight movement, flange 43 at the far end of the camshaft 41 comes into contact with a stop plate 44 to prevent any further movement.

Also shown in Figures 27 and 28 are a spring 49 which pushes a ball bearing 48 into recess 9a (shown in Figures 14 to 17) when the cam arrangement 40 is in the unlocked position, and into recess 9b (shown in Figures 14 to 18) when the cam arrangement 40 is in the locked position. This provides some tactile feedback to the user that the locked or unlocked position has been reached, and also offers a small amount of resistance to being moved out of these key positions. Another view of this is shown in Figure 29.

Figure 30 shows an end cap or cover 55 which clips around the head 42 to provide a neat finish. Figure 31 shows how, when the flange 43 has contacted the stop plate 44 after an axial force has been applied, such that there is no gap at 57, there remains a gap at 56 between cam A and the end cap 55. This isolates the end cap 55 from the axial load path and prevents it from being pushed away from the housing 24.

Figures 32 and 33 show an end view of cam A and a partial end view of the collimator 17, looking in the opposite direction compared to the views shown in Figures 19 to 22. In other words, this is the view of cam A as it would be seen by a user who is turning the head 42 to lock or unlock the cam arrangement 40. Also shown in Figures 32 and 33 is a plate 53 which is arranged in the plane of cam A, and which is shaped to provide rotational end stops 52 and 54 for cam A. When turned fully anticlockwise (to unlock the cam arrangement 40), a lobe on cam A contacts first end stop 52 to prevent any further turning, and when turned fully clockwise (to lock the cam arrangement 40), another lobe on cam A contacts second end stop 54. In this way, there is no danger of overtightening, and furthermore it is very simple to operate because it just requires a simple turn one way to lock and another turn the other way to unlock, without any need for a specific torque.

The cam arrangement 40 described above is a particularly beneficial embodiment because of the way in which it performs a dual locking and decoupling function via a simple turning action. However, the locking function could be performed by a separate component, for example a clamp similar to that shown in Figure 7 (though with the clamping force being applied to the strain relief 15 rather than the collimator 17) or just a simple locking bolt. In this case, the cam arrangement 40 would still need cam A but would not need cam B. Without cam B, it could be that the cam arrangement 40 is turned through the same three rotational positions Pl, P2 and P3 as described previously, or it could be that the cam arrangement 40 is turned from the first rotational position Pl to the second rotational position P2 (to decouple the parts) and then back to the first rotational position Pl (in this case it can be considered there are still three rotational positions Pl, P2 and P3, with the third rotational position P3 just being the same as the first rotational position Pl).

It will also be appreciated that the decoupling function need not be performed using a cam arrangement 40 as described above, and some other form of decoupling arrangement can be used instead. For example, retractable plates A and B could be used instead of cams A and B, with the plates moving into corresponding respective recesses C and D in a linear rather than rotational manner. Therefore, first and second cams A and B can be referred to more generally as first and second members, and the first, second and third rotational positions Pl, P2 and P3 can be referred to more generally as first, second and third states of the decoupling arrangement.

Alternatively, a spacer element could be provided in the gap G between the two parts of the fibre barrel 10 when not installed into the detector head 4, with the spacer element ensuring that the gap G is maintained even as it is pushed into the detector head 4, and then a suitable decoupling arrangement can be operated to remove the spacer element from the gap. The spacer element would therefore perform a similar function to cam A in the embodiment described above but would be in place during the insertion operation and then removed.

Other forms of decoupling arrangement would be readily apparent to the person skilled in the art, with the function of the decoupling arrangement being to mechanically decouple the first and second parts.

Claims

1. A laser encoder device into which an optical fibre assembly is installable, the assembly comprising a first part mechanically coupled to a second part, and the device comprising a decoupling arrangement which is operable to decouple the second part mechanically from the first part.

2. A device as claimed in claim 1, wherein the first part is one that is subject to forces applied to the assembly externally of the device, after installation of the assembly into the device.

3. A device as claimed in claim 1 or 2, wherein the second part is one that is located internally to the device, after installation of the assembly into the device.

4. A device as claimed in claim 1, 2 or 3, wherein the assembly comprises a fibre optic conduit coupled mechanically to the first part.

5. A device as claimed in claim 4, wherein the assembly comprises a fibre optic connector coupled mechanically to the fibre optic conduit.

6. A device as claimed in any preceding claim, wherein the laser encoder device is a detector head.

7. A device as claimed in any preceding claim, wherein the second part terminates the assembly.

8. A device as claimed in any preceding claim, wherein the first part is a strain relief component.

9. A device as claimed in any preceding claim, wherein the second part is an optical or metrology component.

10. A device as claimed in any preceding claim, wherein the second part is a collimator.

11. A device as claimed in any preceding claim, wherein the first and second parts form a fibre barrel component.

12. A device as claimed in any preceding claim, wherein the first part is moveable into contact with the second part, for example while inserting the assembly into the device.

13. A device as claimed in any preceding claim, comprising a retaining pin on one of the first and second parts which is received into an opening on the other of the first and second parts to hold the first and second parts together when not installed into the device.

14. A device as claimed in any preceding claim, wherein the assembly comprises a spacer component which maintains a gap between the first and second parts, and wherein the decoupling arrangement is operable to remove the spacer component.

15. A device as claimed in any preceding claim, wherein the decoupling arrangement comprises at least a first member which is operable to engage with the assembly to establish and/or maintain a gap between the first and second parts.

16. A device as claimed in claim 15, wherein the decoupling arrangement comprises a second member which is operable to engage with the assembly to prevent substantial axial movement of the first part.

17. A device as claimed in claim 15 or 16, wherein the decoupling arrangement is moveable between first, second and third states, with the first member being engaged in the second state but not in the first and third states.

18. A device as claimed in claim 17, when dependent on claim 16, wherein the second member is engaged in at least the third state and optionally in the second state but not in the first state.

19. A device as claimed in any one of claims 15 to 18, wherein the decoupling arrangement is a cam arrangement.

20. A device as claimed in claim 19, wherein the first member is a first cam, and wherein when dependent on claim 16 the second member is a second cam, and wherein when dependent on claim 17 the states are rotational positions of the cam arrangement.

21. A device as claimed in claim 19 or 20, wherein the cam arrangement comprises at least one detent feature which provides tactile feedback in the first and/or third rotational positions.

22. A device as claimed in claim 19, 20 or 21, wherein the cam arrangement comprises at least one stop feature which prevents movement beyond the first and/or third rotational positions in a direction away from the second rotational position.

23. A device as claimed in any preceding claim, wherein the assembly comprises a damping member which is arranged to dampen movements of the first part when the assembly has been installed into the device.

24. A method of installing an optical fibre assembly into a laser encoder device as claimed in any preceding claim, comprising inserting the assembly into an opening in the device and operating the decoupling arrangement to decouple the second part mechanically from the first part.