Patent Description:
A Time-of-Flight (ToF) range meter is configured to provide a distance measurement based on measuring the time-of-flight of a light signal between an emitter and detection of reflected emitted light, using the known speed of light. Normally, a ToF range meter includes a chipset comprising both a light emitter and a light detector, and a circuit for measuring time between emission and detection of received light, reflected from a ranged target. ToF range meters are typically employed as distance meters in cameras, and for assisting autofocus mechanisms.

<FIG> schematically illustrates a typical state of the art ToF range meter <NUM>. It should be noted that the ToF range meter <NUM> is primarily arranged to measure time but may be additionally be configured to calculate and output a distance measurement based on the measured time. In alternative embodiments, a ToF range meter may simply output a time value, which may be further processed or used, e.g. for calculating a distance, in other devices. The ToF range meter <NUM> may include an electromagnetic emitter <NUM>, configured to emit an electromagnetic signal wave through an opening <NUM> within an angle, e.g. a cone angle, as indicated by the dashed lines. Upon reflection at a surface <NUM> of a reflector member <NUM>, at least a portion of the emitted signal is directed back towards the ToF range meter <NUM>, where it is received through an opening <NUM> and sensed in a detector <NUM>. The detector <NUM> is preferably configured with a field of view corresponding to or at least overlapping the emission angle of the emitter <NUM>. A control unit <NUM> preferably includes a measurement circuit configured to measure time and optionally recalculate it to distance to the point of reflection <NUM> dependent on the emitted signal and the reflected signal. In the ToF range meter <NUM>, the emitter <NUM> may typically be a light emitter configured to emit a periodic signal, e.g. a near infrared (NIR) signal. The detector <NUM> may comprise a light-sensitive detector such as a single-photon avalanche diode (SPAD), and typically a plurality of adjacent SPADs forming a detector or sensor array. The emitter <NUM> and the detector <NUM> are preferably provided on a common carrier <NUM>, such as a PCB, such that they are reliably interconnected and commonly aligned. A ToF range meter or sensor <NUM> may e.g. operate according to the principles disclosed in <CIT>, the content of which is incorporated herein by reference. That disclosure provides a method for measuring a distance by measuring phase of a series of bursts of pulses relative to a periodic generator signal.

<CIT> discloses optoelectronic modules, operable to distinguish between signals indicative of reflections from an object of interest and signals indicative of a spurious reflection. Various modules are operable to recognize spurious reflections by means of dedicated spurious-reflection detection pixels and, in some cases, also to compensate for errors caused by spurious reflections.

<CIT> discloses a laser distance measuring apparatus having an internal reference beam length determined by a retro-reflector which is movable into and out of the beam path. The retro-reflector is opaque relying on specular reflection. This, together with a light trap arrangement, reduces spurious reflections. The laser and detection optics are carried on a shock proof sub-chassis but the retro-reflector is fixed to the housing to retain alignment with an exterior datum.

<CIT> discloses a measuring unit for a weight-stack gym machine where a frame supports a load unit equipped with a plurality of substantially identical weights. The weights have a hole through them to form a vertical channel for a load selecting bar (<NUM>). A remote load measuring unit (<NUM>) is envisaged to calculate static and dynamic training parameters.

<CIT> discloses a measurement system for use in an exercise machine, which exercise machine comprises a lifting mechanism and an engaging member for selectively engaging a number of stacked weights to the lifting mechanism, the measurement system comprising a pair of cooperating members including a range meter and a reflector member, wherein one of the cooperating members is connected to the lifting mechanism and the other of the cooperating members is connected to the engaging member, wherein the range meter is directed to measure a distance to the reflector member to determine a distance which correlates to the weight of the selectively engaged weights.

<CIT> discloses a TOF depth camera and methods for projecting illumination light into an image environment are disclosed. One example embodiment of a TOF depth camera includes a light source configured to generate coherent light; a first optical stage including an array of periodically-arranged lens elements positioned to receive at least a portion of the coherent light and to form divergent light; a second optical stage positioned to receive at least a portion of the divergent light and to reduce an intensity of one or more diffraction artifacts in the divergent light to form illumination light for projection into an illumination environment; and an image sensor configured to detect at least a portion of return illumination light reflected from the illumination environment.

<CIT> relates to hybrid three-dimensional imagers and to a laser source for active illumination for hybrid three-dimensional imagers (i.e. 3D imagers that make combined use of different 3D imaging technologies). The invention is applicable to three-dimensional imaging systems which use a combination of different imaging techniques (hybrid technologies) to achieve a higher precision or a higher level of reliability.

A problem identified in the art of ToF range meters is related to stability and repeatability of measurement results. For state of the art compact ToF range meters, which are configured to be used in e.g. mobile phones and portable camera devices, the distance measuring accuracy may be in the area of <NUM>% at indoor conditions, when measuring against a white surface up to <NUM> away from the sensor. This may oftentimes be sufficient for various fields of use. However, such ToF range meters are generally optimized to be used with a diffuse flat large target. When measuring against other types of targets, such as a relatively small surface with high reflectance, it has been noted that the measurement results may drift over time. With a maintained level of accuracy between successive repetitions, and the added deviation due to sensor drift, the overall accuracy may for certain use cases be unsatisfactory.

An overall objective is thus to provide a ToF ranging device configured to provide consistent distance measurement results over time. An aspect of this objective is to improve the measurement consistency of a ToF ranging device when used together with a small high reflective target. A further objective is to provide a solution for measuring distance to a highly reflective target within a large field of view. An aspect of this objective is to provide a solution for discriminating highly reflective targets better against the surrounding. These objectives are targeted by the combined features of the independent claim <NUM>. Further embodiments are set out in the dependent claims, and in the following description.

According to a first aspect, a Time-of-Flight (ToF) range meter according to claim <NUM> is provided together with various embodiments corresponding to dependent claims <NUM>-<NUM>.

According to a second aspect, a measurement system for an exercise machine according to claim <NUM> is provided, which exercise machine comprises a lifting mechanism and an engaging member for selectively engaging a number of stacked weights to the lifting mechanism, the measurement system comprising a pair of cooperating members including ToF ranging device of the preceding embodiment, and a reflector member, wherein one of the cooperating members is connected to the lifting mechanism and the other of the cooperating members is connected to the engaging member, wherein the ToF ranging device is directed to measure a distance to the reflector member to determine a distance which correlates to the weight of the selectively engaged weights.

Details, function, effects and benefits of various embodiments are outlined in the detail description and the appended drawings.

Various embodiments are described below with reference to the accompanying drawings.

Embodiments will now be described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. To facilitate the discussion of any particular element, the most significant digit or digits of any reference number refer to the Figure in which that element is first introduced. Also, features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments. It may further be noted that reference signs for all elements are not included in every figure, but the same references numbers are consistently used to indicate the same or corresponding features.

Certain details are set forth in the following description and in the drawings to provide a thorough understanding of various embodiments of the present disclosure. Other details describing well-known structures and systems often associated with weight training machines, signal processing systems, and electronic display devices, however, are not set forth in the following disclosure to avoid unnecessarily obscuring the description of various embodiments. Many of the details, dimensions, and other features shown in the figures are merely illustrative of particular embodiments of the disclosure. Accordingly, other embodiments can have other details, dimensions, and features without departing from the scope of the present disclosure. In addition, further embodiments of the present disclosure can be practiced without several of the details described below.

An area of implementation of ToF range meters, investigated by the instant applicant, is training equipment in the form of exercise machines. A common type of weight machines makes use of gravity as the primary source of resistance. A combination of devices such as pulleys, levers, wheels, inclines, etc. are engaged to change the mechanical advantage of the overall machine relative to the weight and convey the resistance to the person using the machine. Conventional stacked weight machines typically include a stack of weight plates through which a lifting mechanism, e.g. comprising a vertical lifting bar, passes. The lifting bar may include a plurality of holes configured to accept an engaging member, such as a load pin. Each of the plates has a corresponding channel that aligns with one of the holes in the lifting bar when the lifting bar is in the lowered or at-rest position. To lift a selected number of the plates, the user operates the engaging member, e.g. by inserting a load pin through the channel and the corresponding hole in the lift bar at a selected weight level. As the user goes through the exercise motion, the lift bar is raised while the engaging member supports all of the plates stacked above it. The various settings on the weight machine allow the user to select from several different levels of resistance over the same range of motion by simply inserting the load pin into the lift bar at a desired weight level.

One important aspect of any type of exercise program is the ability to track personal performance and progress. For this purpose, an automated measurement system may be employed, configured to track weight and repetitions. An exercise machine may comprise a lifting mechanism and an engaging member for selectively engaging a number of stacked weights to the lifting mechanism, and may further be fitted with a measurement system comprising a pair of cooperating members including a range meter and a reflector member. One of the cooperating members may be connected to the lifting mechanism and the other of the cooperating members may be connected to the engaging member, wherein the range meter is directed to measure a distance to the reflector member to determine a distance which correlates to the weight of the selectively engaged weights. The range meter may include a ToF sensor.

In one setup of such a system, the range meter is attached to the lifting mechanism at the top of the weight stack, and rages towards the load pin. In the weight stack, each weight is generally a plate with a certain a thickness, which may be in the order of <NUM>-<NUM>. This can be seen as a minimum level of accuracy for proper distance determination, in order to correctly detect applied weight. However, various tests have shown that the overall accuracy is not sufficient. Instead of a drift of only a few millimetres, e.g. +/- <NUM>, in a stable setup with a big white diffuse target, the drift over time with a small high reflectance target might be tens of mm, e.g. +/-<NUM>. The result may be incorrect reading of distance, and thus weight.

The inventors have concluded that a reason for this drawback may be associated with the small size target of the load pin. However, an installation of a measurement system as described is typically made on an existing exercise machine design. In many of such designs, the handle of the load pin is rounded, e.g. cylindrical. Typically, the load pin is provided with a reflective tape or paint, so as to be properly detectable by the ToF range meter. One theory is that such a high reflectance target with a comparably small size, since only a small part of the load pin will create a detectable reflex back to the range meter, may give rise to interference effects in the optical path from the coherent laser source emitter <NUM> to a SPAD array-detector <NUM>.

Based on the detected drift problems, the inventors have found that improved consistency and repeatability may be obtained by means of appropriate configuration of a housing construction for the ToF range meter. Various embodiments associated with such a housing will now de described with reference to the drawings.

<FIG> schematically illustrate cross-sectional views of various embodiments, where a housing <NUM> is provided onto a ToF sensor or range meter <NUM>, so as to collectively form a ToF ranging device <NUM>. The ToF range meter <NUM> may e.g. be configured as described with reference to the range meter <NUM> of <FIG>. As an example, the range meter may be a VL53L0 device, as provided by STMicroelectronics. The ToF range meter <NUM> may thus include an emitter <NUM> configured to emit electromagnetic radiation at one or more frequencies, and a detector <NUM> configured to detect electromagnetic radiation of at least one of the frequencies of the emitter <NUM>. The emitter <NUM> and the detector <NUM> may be configured to operate at optical light frequencies, e.g. in the near infrared (NIR). The emitter may include a laser, or optionally a LED with a lens system. The emitter <NUM> and the detector <NUM> may be attached to a carrier member <NUM>, such as a PCB, preferably such that the emitter <NUM> and the detector <NUM> have at least overlapping fields of view. Normally, the emitter <NUM> and the detector <NUM> are arranged with parallel optical axes. The ToF range meter <NUM> may include a casing <NUM>, covering and housing the emitter <NUM> and the detector <NUM>. An emitter opening <NUM> is associated with the emitter <NUM>, such as an orifice in the casing <NUM> which allows the emitter <NUM> to emit light. In various embodiments, the orifice may define an aperture for the emitter of the ToF range meter <NUM>, while in other embodiments the emitter aperture is defined by the light source of the emitter <NUM>. A detector opening <NUM> is associated with the detector <NUM>, such as an orifice in the casing <NUM> which allows the detector <NUM> to receive light. In various embodiments, the orifice may have a smaller cross-section than the surface of the detector <NUM>.

The housing <NUM> may comprise a wall structure <NUM>, which is provided around and over the ToF range meter <NUM>, or a part of the ToF range meter <NUM>. The wall structure <NUM> may define a first optical beam path <NUM> to the emitter <NUM> of the ToF range meter, serving as a channel for leading light from the emitter <NUM>. In addition, a second optical beam path <NUM> to the detector <NUM> of the ToF range meter <NUM> may be configured by the wall structure <NUM>, forming a channel for accepting light to the detector <NUM>. Furthermore, a transmissive optical diffusor <NUM>, <NUM> is comprised in the housing <NUM>, configured to cover the beam path to at least one of said emitter <NUM> and said detector <NUM>. In various embodiments (not shown), the wall structure may be configured to define a specific beam path to only one of the emitter <NUM> and the detector, whereas the beam path to the other of the emitter <NUM> and the detector <NUM> is defined by passing outside the housing <NUM>. As an example, the housing <NUM> may include a channel provided about either the emitter <NUM> or about the detector <NUM>.

Careful and repeated tests have shown that by arranging a diffusor <NUM>, <NUM> in at least one of the optical paths <NUM>, <NUM> of the emitter <NUM> and the detector <NUM>, a distinct improvement has been detected in terms of consistency and stability to drift.

In various embodiments, the wall structure <NUM> of the housing <NUM> comprises a wall member <NUM> between the emitter opening and the detector opening, which wall member <NUM> separates first optical beam path from second optical beam path.

In various embodiments, such as shown in the drawings, the diffusor <NUM>, <NUM> is suspended in the housing construction <NUM> such that it is arranged spaced apart from the at least one of said emitter <NUM> and detector <NUM>. This way, the risk for reflections occurring at the interface or the surface of the diffusor <NUM>, <NUM>, which may cause optical leakage at an interface between the ToF range meter <NUM> and the housing <NUM>, such as at the interface between the wall member <NUM> and a casing <NUM> of the ToF range meter, causing cross-talk between the emitter beam path <NUM> and the detector beam path <NUM>, may be minimized.

The wall structure <NUM> may define an engagement interface to the emitter <NUM>, including e.g. an end portion of the wall portion <NUM>, which orients the wall structure <NUM> with respect to the range meter <NUM> by means of at least abutment. The emitter diffusor <NUM> is preferably arranged and suspended spaced apart from said engagement interface by a distance, such that a spacing D1 between the diffusor <NUM> to the emitter is obtained.

By suspending the diffusor <NUM>, <NUM> at a distance from the openings <NUM>, <NUM> to the emitter <NUM>, and possibly the detector <NUM>, respectively, tests have shown that it is possible to fit the housing <NUM> onto the ToF range meter <NUM> without the need for using any adhesive or sealing at the interface between the wall member <NUM> and the casing <NUM> of the range meter <NUM>. Rather, a snug planar fitting at that interface is sufficient, which may be accomplished by snapping or sliding on the housing <NUM> onto the ToF range meter <NUM>. A mechanism for attachment may e.g. be provided at the carrier <NUM> of the ToF range meter, such as guide rails or snap-on locks (not shown).

As illustrated in <FIG>, the housing <NUM> is arranged with a first aperture <NUM> to the first optical beam path <NUM>, and a second aperture <NUM> to the second optical beam path <NUM>, so as to allow light to pass from and to the ToF range meter <NUM>. Furthermore, in various embodiments, the first aperture, i.e. the emitter aperture <NUM>, may be arranged farther away from a plane of the detector <NUM> than the detector aperture <NUM>. Tests have shown that by applying a protruding emitter aperture <NUM>, compared to the detector aperture <NUM>, unwanted reflections occurring in or near the emitter aperture <NUM>, as e.g. caused by dust or other near objects, are less likely to be detected by the detector <NUM> of the ToF range meter <NUM> and cause cross-talk.

In various embodiment, such as shown in <FIG>, <FIG> and <FIG>, the diffusor includes an emitter diffusor <NUM>, arranged in the first optical beam path <NUM>. Furthermore, in various embodiments, the emitter diffusor <NUM> is suspended in the housing <NUM> between the emitter <NUM> and the first aperture <NUM>, preferably completely covering the first optical beam path <NUM>. In various embodiments, as shown in the drawings, the emitter diffusor <NUM> is attached to a rim or lip facing the emitter <NUM>, such as to an outer surface of the wall structure <NUM>. As indicated with reference to <FIG>, the housing may be provided only with an emitter diffusor <NUM> and no detector diffusor.

In various embodiments, the output aperture <NUM> for the emitter light may be covered by a cover element, such as a glass or plastic film or piece which is transmissive to at least the wavelength of the intended ToF range meter <NUM>. Preferably, the transmissive element is non-refractive.

In various embodiments, such as shown in <FIG> and <FIG>, the diffusor includes a detector diffusor <NUM>, arranged in the second optical beam path <NUM>. The detector diffusor <NUM> is preferably arranged at the second aperture <NUM>, which is spaced apart from the detector <NUM>. This way, received light, which is substantially collimated when measurement is made towards a small target surface <NUM>, may be collected from each point of the surface of the detector diffusor <NUM>. The detector diffusor <NUM> is preferably substantially wider, i.e. has a larger cross-section area, than the detector opening <NUM>. In various embodiments, as shown in the drawings, the detector diffusor <NUM> may be attached to a rim or lip facing away from the detector <NUM>, such as to an outer surface of the wall structure <NUM>. As indicated with reference to <FIG>, the housing <NUM> may be provided only with a detector diffusor <NUM> and no emitter diffusor.

While improvements have been detected with respect to drift of ToF measurement results with embodiments realized as indicated in <FIG>, further improved stability in range measurements has been detected with the combined use of an emitter diffusor <NUM> and a detector diffusor <NUM>, as shown in <FIG>. In various embodiments, as described with reference the drawings of <FIG>, the housing <NUM> may be devised as a mechanical add-on component, e.g. an opaque plastic device, with one or more diffusors. In other embodiments, a ToF ranging device <NUM> may be designed as a combined unit, where the housing is configured to act as a casing for the emitter <NUM> and the detector <NUM>, possibly without any inner casing corresponding to casing <NUM>. In this context, opaque refers to an operating wavelength of the emitter <NUM> and the detector <NUM>, such as NIR.

In various embodiments, one function of the diffusor or diffusors <NUM>, <NUM> is to disturb or destroy the coherence of the emitter <NUM> and reduce the interference problem in the optical system. This is particularly relevant when the emitter <NUM> includes a laser source. A technical effect obtained by means of the disclosed embodiments is that the detector <NUM>, such as a SPAD detector array, is fully illuminated by the incoming beam, and that interference is minimized or completely supressed. The function of the TOF-component itself is not changed, it is only the light characteristics, such as coherence, beam width and beam angle, between the laser and the detector-array which will be influenced by the add on optics.

Referring again to the exemplary embodiment of <FIG>, and also to <FIG>, the light path through the optical system will now be explained, for a ToF ranging device <NUM>, comprising a ToF range meter <NUM> provided with a housing <NUM>.

The emitter <NUM> of the ToF range meter may typically include one or more semiconductor lasers, configured to emit coherent light in a diverging beam out through the emitter opening <NUM> in the casing <NUM> of the ToF range meter. The emitter <NUM> may comprise a Vertical-Cavity Surface-Emitting Laser (VCSEL). The output divergence of the emitter <NUM> may by the geometry of such laser or lasers, such as the geometry of an aperture of each laser, of the emitter <NUM> and is not restricted by the output opening <NUM>.

The light hits the emitter diffusor <NUM> disposed just outside the package ToF range meter, but preferably spaced apart a distance from an outer surface of the casing <NUM>. The emitter diffuser <NUM> spreads the light in a controlled way. The illuminated portion of the emitter diffusor <NUM> spot can be regarded as a new light source with larger diameter and with less coherence, since the light is scrambled in the diffusor <NUM>. The size of this light source can be controlled by design or at assembly, by selecting the distance D1 between the diffusor <NUM> and the emitter <NUM> laser source, see <FIG>. The divergence and the scrambling of the light is controlled by the strength of the diffusor.

Light from the emitter diffusor <NUM> reaches and passes through the comparatively small aperture <NUM> at the top of the housing <NUM>. Referring to <FIG>, which only displays the emitter portion of the housing <NUM> and the ToF range meter <NUM>, the diameter of the hole of the aperture <NUM> and the distance D2 between the emitter diffusor <NUM> and the aperture <NUM> controls the divergence of the output beam from the plastic housing. This way, the emitter aperture <NUM> is configured to screen a portion of light diverging from an illuminated portion of the emitter diffusor <NUM>. In various embodiments, the housing is configured such that the distance D2, the size of the aperture and the strength of the diffusor results in a major portion of the emitted light being screened. The housing is thus configured such that only <NUM>% of the light from the emitter of an attached range meter passes through the aperture <NUM>, or less than <NUM>%, or even less than <NUM>%.

Emitted light hits a target, such as a small reflective target. In various embodiments, the reflective target may be selected to act as a target, such as a load pin of an exercise machine, and the reflective target may be built up by many small retroreflectors, provided e.g. by means of a reflective tape. Some of the light will be reflected back towards the ToF ranging device <NUM> from the target.

A small amount of the light is reflected back to hit the detector diffusor <NUM>. The light is almost parallel since the distance from the reflective target to the TOF sensor is normally very large compared to the reflective surface size. The detector diffusor <NUM> will spread the light to fully illuminate the sensor-array through the pinhole opening <NUM> in the casing <NUM> of the ToF range meter <NUM>.

Light passes through the entrance pinhole opening <NUM> and onto the ToF detector <NUM>, to light up the entire array of sensors (SPADS) of the detector <NUM>.

ToF range meter electronics, corresponding to <NUM> in <FIG>, proceeds to calculate the distance to the target by measuring the time of flight for the optical path.

The size of the aperture restrictions and the distance between the diffusors <NUM> and/or <NUM> and the ToF range meter <NUM>, in combination with the diffusor strength of the two diffusors will set the performance of the system.

<FIG> schematically illustrates a diffusor <NUM>, usable as an emitter diffusor <NUM> or a detector diffusor <NUM> in various embodiments. The diffusor <NUM> has at least one surface <NUM> configured to provide a desired light shaping effect to an incoming light beam. One example of a usable diffusor type, which has been tested with beneficial results in a ToF ranging device <NUM> according to the embodiments disclosed herein, is LSD® Light Shaping Diffuser sheet, as marketed by Luminit, which provide a transmission efficiency exceeding <NUM>% at NIR by holographic beam shaping. The exemplary diffusor <NUM> of <FIG> may be configured to provide a <NUM> degree cone angle from collimated light, and will generate divergence also for already divergent light, such as from a VCSEL of an emitter <NUM>. The emitter diffusor <NUM> is preferably selected to be configured to shape light into a predetermined cone angle suitable for the geometry of the housing <NUM>. Referring to <FIG>, the illuminated portion of the emitter diffusor <NUM> may act as a new light source or emitter. Due to the beam shaping inflicted by the diffusor <NUM> on the beam from the emitter <NUM>, a substantially greater divergence than what is allowed through the aperture <NUM> is obtained. The aperture <NUM> will thus admit emission of only a portion of the light from the diffusor <NUM>. As indicated by the crossing rays in <FIG>, the emitter diffusor is configured to shape light to obtain divergence, and by arranging the emitter diffusor at a distance D2 from the first aperture, only a portion of the diverging light from an illuminated portion of the emitter diffusor is emitted from first aperture.

Even though the housing <NUM> has been illustrated in the drawings in connection with a ToF range meter <NUM>, it should be understood that the housing <NUM> may be provided as a separate device <NUM>, suited for post assembly with a ToF range meter <NUM>.

In an alternative embodiment, a ToF ranging device <NUM> may be provided, comprising a ToF range meter <NUM> including an emitter <NUM> configured to emit light, and a detector <NUM> configured to detect reflected light emitted by the emitter, and where a housing <NUM> as disclosed herein is arranged to the ToF range meter <NUM>, and possibly attached to the ToF range meter <NUM>.

In one embodiment, a measurement system for an exercise machine is provided, as will be described with reference to <FIG>. The measurement system includes a ToF ranging device <NUM> as described herein, i.e. a ToF range meter provided with a housing <NUM> according to any one of the described embodiments.

<FIG> show various views of a part of an exercise machine, comprising a lifting mechanism <NUM> and an engaging member <NUM> for selectively engaging a number of stacked weights <NUM> to the lifting mechanism. <FIG> illustrate perspective views, whereas Fig. B schematically illustrate a vertical cross-section through the weight stack <NUM>, the lifting mechanism <NUM> and the engaging member <NUM>. In the illustrated embodiment, the lifting mechanism <NUM> includes a support member having a rod-shaped portion, configured to pass vertically through corresponding holes in the weights <NUM>. The support member of the lifting mechanism <NUM> may furthermore include a top portion, such as a fixed top weight <NUM>.

The measurement system may comprise a pair of cooperating members including a ToF ranging device <NUM> and a reflector member <NUM>. One of the cooperating members is connected to the lifting mechanism <NUM> and the other of the cooperating members is connected to the engaging member <NUM>. The ToF ranging device <NUM> is directed to measure a distance to the reflector member <NUM> to determine a distance which correlates to the weight of the selectively engaged weights. In the illustrated embodiments, the ToF ranging device <NUM> is fixed to the lifting mechanism <NUM> and the reflector member <NUM> is connected to the engaging member <NUM>. The following description will be directed to this type of embodiment, but as will be readily understood by the skilled reader, the opposite arrangement may be employed in various embodiments, i.e. with the ToF ranging device <NUM> connected to the engaging member <NUM> and the reflector member being connected to the lifting mechanism <NUM>.

<FIG> schematically illustrates an engaging member <NUM> in the form of a load pin <NUM>, having a handle or knob to which the reflector member <NUM> is connected. In one embodiment, the reflector member <NUM> may be a reflective surface <NUM>, such as a reflective tape attached about a perimeter of the handle. In an alternative embodiment, the reflector member may comprise a paint or surface structure, configured to be diffusively or specularly reflective to electromagnetic radiation of at least the wavelength range within which a ToF ranging device <NUM> operates.

As can be seen in <FIG>, the ToF ranging device <NUM> is preferably connected to the lifting mechanism <NUM> vertically above the weight stack <NUM> and directed to carry out distance measurement downwards towards the engaging member <NUM>. Different embodiments may include different types of ToF ranging devices <NUM>. In various embodiments, the ToF ranging device <NUM> operates by emitting a signal towards the reflector member and detecting a reflection of the emitted signal. The ToF ranging device <NUM> is preferably configured to carry out signal processing to determine the distance to the point of reflection, based on at least the detected received signal.

The ToF ranging device <NUM> is preferably placed on top of the weight plates <NUM>, e.g. connected thereto by means of screws, an adhesive, clamps, magnet or other fastening means. The ToF ranging device <NUM> may be fastened to the rod portion, to the uppermost weight, or other part of the lifting mechanism <NUM>. The ToF ranging device, e.g. a time of flight sensor <NUM>, is configured to measure the distance to the pin <NUM>, more particularly to the reflector member <NUM> on the pin <NUM>. A benefit of using a time of flight sensor is the small packaging and high precision in available products, such as e.g. the VL53L0 from STMicroelectronics. In addition, by placing the ToF ranging device immediately on top of the weight stack <NUM>, and measuring the comparatively short distance to the engaging member <NUM>, the maximum distance will in most gym machines never exceed <NUM> meter, or even a maximum distance of <NUM>. This makes it possible to employ ToF ranging devices adapted for measurement of comparatively short distances, thereby minimising power consumption. Furthermore, since the ToF ranging device is placed vertically over the reflector member <NUM>, movement of the engaging member <NUM> to select a different weight setting will still entail displacement of the reflector member along the line of sight of the ToF ranging device. By fixedly attaching the ToF ranging device to the lifting mechanism, movement of the engaging member <NUM> will not lead to any change in position or direction of the emitter and receiver field of view. This means that a more reliable and less complex system can be obtained, than with a system employing an active sender or received in the movable load pin <NUM>, especially since most weight pins are freely rotatable.

In various embodiments, an operation detection mechanism is communicatively connected to trigger the ToF ranging device <NUM> to make a distance measurement responsive to detection of operation of the exercise machine. Operation detection mechanism may be e.g. provided by a motion sensor, which may be separate or be integrated with the ToF ranging device <NUM>. In one embodiment, the distance measurement is carried out dependent on detection of movement of the weight stack <NUM>. More particularly, the ToF ranging device <NUM> may be configured to carry out a new distance measurement at a point in time triggered by detection of movement of the weight stack <NUM>. As an alternative, the ToF ranging device <NUM> may be configured to carry out a new distance measurement at a point in time triggered by detection of operation of the engaging member <NUM>, e.g. as reported by a motion detector or proximity sensor. Preferably, the ToF ranging device <NUM> is held in sleep mode until the motion sensor or sensors detect absolution motion, i.e. by when movement of the engaging member <NUM> is sensed by sensed motion or proximity sensor, when movement of the weight stack is sensed, or when both criteria are fulfilled as outlined above. The measured distance to the reflector <NUM> on the engaging member <NUM> is converted into a weight measurement, e.g. in a server at the gym or in the cloud, or locally in the ToF ranging device control unit <NUM>, or in an app of a user device such as a mobile phone, a wristlet or similar, associated with a user of the exercise machine. Distance or weight data may be wirelessly transmitted to the user device, directly from a transmitter at the exercise machine, or through a communication network.

Claim 1:
A Time-of-Flight, ToF, ranging device (<NUM>), comprising:
a ToF range meter (<NUM>) including:
an emitter (<NUM>) configured to emit light, and
a detector (<NUM>) configured to detect reflected light emitted by the emitter; and
a housing (<NUM>), connected to the ToF range meter, said housing comprising:
a wall structure (<NUM>) defining an emitter beam path (<NUM>) for the emitter (<NUM>), said emitter beam path having an output aperture (<NUM>);
a detector beam path (<NUM>) to the detector (<NUM>), said detector beam path having an input aperture (<NUM>); and
an emitter diffusor (<NUM>) having a diffusor strength, arranged in the emitter beam path, spaced apart from said output aperture (<NUM>) by a distance (D2),
whereby said distance, the diffusor strength, and a diameter of the output aperture, determine an output divergence of light passing through the emitter beam path, and wherein at least <NUM>% of the light from the emitter is screened off by the housing.