DE202013003263U1 - Rotary position detection device - Google Patents

Abstract

A rotational position detecting device comprising: a housing having an interior space; a shaft extending into the housing interior, the shaft being rotatable about an axis thereof; a light source positioned to emit light beams into the housing interior; a light sensing device positioned in spaced relation to the light source within the housing interior, the light sensing device including a first number of segmented light sensors arranged in pairs about the axis, each pair having an "A" sensing element and a "B" Sensing element, the pairs being arranged such that each "A" sensing element is positioned circumferentially between two "B" sensing elements and each "B" sensing element is positioned between two "A" sensing elements; a light blocker positioned between the light sensing device and the light source, the light blocker having a second number of opaque elements of substantially equal surface area rotatable with the shaft, the second number being equal to half the first number, wherein a radial extension of the light blocker elements is smaller than a radial extension of the light sensors; and a signal connection to the light detecting means for measuring an amount of light incident on the segmented light sensors so as to measure a rotational position of the shaft.

Description

Field of the invention

This invention relates

Rotational position detecting means for indicating the angular position of a shaft or other rotating member. More particularly, this invention relates to such position detectors used in motor and galvanometer based optical scanners.

Description of the Related Art

Rotary position detectors have many uses, such as sensing the position of the shaft on a motor for the purpose of electrical commutation. Another use is to detect the position of a tension roller in a magnetic tape player or web press for the purpose of maintaining a constant tension on the tape or paper. One of the recent uses of a rotational position detecting device is to sense the position of the acceleration (gas) pedal in an automobile using electric motors as a partial or complete means for driving the wheels.

Galvanometer-based optical scanners are used to direct immobile input light beams to a target area. This type of scanner uses a rotation-limited motor to impart rotational motion to an optical element, such as a mirror. Normally, the mirror is mounted directly on the output shaft of the motor. A position detecting means is included in the engine either close to the output shaft or on the "rear" portion of the engine. The position detector normally outputs a current or voltage signal which is proportional to the relative angle of the motor shaft and thus relative to the angle of the mirror with respect to the non-moving input light beam.

Galvanometer-based optical scanners direct a laser beam for marking, cutting, or displaying purposes, for which positioning accuracy and repeatability can be critical. Therefore, one of the limiting factors of accuracy and repeatability is the performance of the position detecting device used with the optical pickup.

Ideally, the rotational position detecting means should only be sensitive to the rotational angle of the shaft of the scanning device. Since a mirror is directly connected to the shaft of the scanner, it is the angle of rotation of the shaft, which dictates the direction of the exiting light beam. The axial motion and the radial motion will typically not affect the target position of the light beam reflected from the mirror, and since it is the target light beam position that is important to the scanning system, the output of the position detector should indicate the target position and be insensitive for things that do not affect that target position, such as axial and radial motion. The axial wave motion can occur as a dynamic behavior of the scanner. For example, if the magnetic structure of the scanner is not perfect, the wave may fluctuate outwardly or inwardly if strong current pulses are fed into the scanner during high acceleration and deceleration. The radial movement of the scanner may occur as a result of bearing "rumble" or manufacturing errors that allow a small amount of radial movement of the shaft. The radial wave motion can also occur as a dynamic effect if the rotor is not perfectly concentric with the stator components or if the inertial load (mirror and mount) attached to the output shaft is not perfectly balanced.

A servo control is connected between the position detecting device and the motor. If the position sensing device produces an output as a result of axial or radial shaft motion, the servo control will erroneously interpret this misdirected output as a change in rotational position, resulting in a positioning error of the overall system. For this reason, a perfect rotational position detecting device will only produce an output as the result of the rotational movement and will not produce any output as the result of an axial or radial movement.

An additional desirable feature of a rotational position sensing device, particularly for galvanometer sensing devices used with analog servo systems, includes the feature that the output voltage or current is linear with respect to the rotational angle. Namely, an incremental change in the shaft rotation should produce an incremental change as well in the output signal from the position detector, although a small degree of nonlinearity is often tolerable. Furthermore, the signal-to-noise ratio should be as high as possible.

There are several ways to scan the position of the shaft in an optical scanner. Two popular types of position detectors include capacitive position detectors and optical position detectors.

Capacitive position detectors have been used in some of the very earliest galvanometer-based optical scanners. In a known scanning device, a rotating dielectric flap is connected to the shaft of the scanner, and the detection plates are fixed.

Optical position detectors have recently come to be the position-sensing device of choice in the field of galvanometer-based optical scanning. Typically, optical position detectors can be made small and have low inertia and can be manufactured at low cost. These features make optical position detectors for optical scanners used in commercial and hypermarkets desirable.

One type of optical position detector is a "shadow cast" position detector which attempts to uniformly illuminate a large area of light sensor material and cast a shadow on the light sensor by a light blocker. Optical position detectors may use photocells as the light sensors. These photocells are most commonly large area PIN photodiodes, and are used in the "photovoltaic" mode of operation where an electric current is generated by the photocell and amplified by an operational amplifier. The magnitude of the electric current increases linearly as the intensity of the light increases linearly over the entire area of the photocell. The magnitude of the electric current also increases linearly when the illuminated portion of the photocell is linearly increased as long as the illumination is constant over the entire area. That is, when light illuminates half of the light sensor surface and light is blocked on the other half of the light sensor surface, the electric current that is output becomes half the size of that for complete illumination of the light sensor, resulting in a linear relationship of the output the position detection device results in the area illumination of the photocell.

Regardless of the type of position sensing device used, capacitive or optical, it is believed that all known position sensing devices suffer from a common problem: they all output a signal indicative of relative shaft rotation, but they do not output a signal indicative of absolute shaft rotation. That is, it is impossible for the servo controller to read the position signal voltage or the current and to know the precise mechanical angle of the shaft in absolute values. This is because the output from the photocells or capacitive plates is proportional to either the light generated by the LED or the signal generated by the oscillator. If the light from the LED increases in the case of the optical position detectors due to environmental changes or component shift, the output generated by the photocells will increase proportionally. This proportional increase will deceive the servo, so he believes the shaft has been turned to a larger mechanical angle. The servo will then try to compensate for this and generate an error.

All known position detectors attempt to correct this using automatic gain control (AGC) circuitry, such as known in the art. In the case of the optical position detectors, the light received by all photocells is added together to form a "total light" signal voltage. This "total light" voltage is compared to a reference voltage and an error signal is generated which drives the LED. If it is sensed that the "total light" has increased, then the light output by the LED is made to decrease a corresponding magnitude, thereby attempting to maintain the sensitivity of the rotational position detecting means over time. However, the use of AGC is only good enough to correct first order problems. All known position detectors suffer from positional offset displacement (a change in what the absolute zero position sensor detects) due to second order effects such as the displacement of the reference voltage itself or the change in the feedback resistors used in the operational amplifier circuits Shaft holding) and the position scale shift (a change in what the position detector indicates in terms of volts per degree). These changes occur with time and temperature.

Attempts have been made in the past to provide additional signals to rotational position detectors which indicate certain absolute positions. On an optional or automatic basis, the servo can apply the galvanometer scanner in search of these additional signals, and thus on the absolute position scale and position offset of the position detector be aware. When implemented in a capacitive position detector, this method has several parasitic problems. First, capacitive position sensors are very sensitive to the shape of the plate elements. Plates with protrusions or notches will have impaired linearity due to edge effects that occur as a result of the protrusions or notches. Edge effects will also affect linearity if additional capacitive plates are used. The specially shaped moving wing flap is more expensive to manufacture, whether this technique is used in an optical position detecting device or in a capacitive position detecting device. The predominant servo used to control galvanometer-based optical scanners was the PID servo-based system, which is made entirely of analog components (analog servos). Analog servo systems have been used because they are relatively inexpensive and relatively simple and also because digital servo systems so far can not achieve the high resolution and high sampling rate necessary to be usable with the fastest galvanometer scanners. In order to support the fastest galvanometer scanners currently on the market and achieving steps in the sub-100 microsecond range, a sample rate of 200 kHz must be used along with a 16 bit sample resolution. And due to the many internal computation steps required, floating point calculations are highly desirable. Until recently, it has been unaffordable to implement servo control in a digital form with this high sampling rate and resolution. However, with the continual advances inevitably taking place in technological fields, digital signal processors (DSPs) and analog-to-digital (A / D) converters are now becoming available at a reasonable speed and at a reasonable cost, which will contribute to a shift in analogue Servos to DSP based servos for use with galvanometer scanners.

In analog servos, a relatively large number of potentiometers are typically used to "tune" the servo for optimal performance. These potentiometers adjust a number of servo parameters including servo gain, attenuation, notch filter frequency, notch depth, input gain, input offset, etc. There are also typically two additional potentiometers to adjust the position scale and the positional offset of the position detector. Although these last two are not servo parameters in the strictest sense, they certainly affect servo performance and accuracy. All of these potentiometers must be manually adjusted or "tuned" by humans. Typically, this tuning is done in the factory, but sometimes further tuning is required in the field. Since engineers do not have to be the end users of systems with galvanometer scanners, any off-factory tuning can result in suboptimal operation.

The shift toward DSP-based servo systems will eliminate the need for all of these tuning potentiometers because servo parameters such as servo gain, attenuation, notch filter frequency, etc. are determined by algorithm constants. These algorithm constants may be "tuned" by humans in a similar manner that resulted in the potentiometer settings by merely using a user interface to make the adjustments, or alternatively, these algorithm constants may be automatically tuned by an intelligent tuning algorithm. This is possible because almost all information about the scanning system can only be found by applying the scanner and observing what happens to the position signal. For example, the torque constant of the scanner may be derived by observing the back electromotive force (back EMF) of the scanner. In terms of mechanical engineering KT = KE. That is, the torque-per-ampule dynes are directly proportional to the motor back EMF volts per degree per second. Thus, if the servo generates the movement of the scanner and can measure the "per second" and the motor back EMF, then the servo can derive the precise torque constant (KT) of the scanner.

Once the KT is known, the servo could next apply a pulse of known current for a short time and measure the angular acceleration that results, and thus the servo can sense the system inertia (J) of the rotor, mirror, and position detector Find out because the force equals mass times acceleration. Therefore, the inertia is equal to KT divided by the acceleration.

Next, the servo could loop a light loop around the scanner and execute a bottom plot, thereby making all system resonances clear. With this information, the servo could set all the constants for the poles and zeros of the notch and bi-quad filters.

If the torque constant, system inertia, and system resonances are all known, then all servo parameters could easily be set in seconds with digital precision, the absolute maximum power is achieved by the scanner and the servo system. However, for all this to happen, the servo needs substantial information. The servo must know the "position scale". That is, the servo must first know the volts per degree from the position detector.

As discussed earlier with known position sensing devices, it is impossible for servos to know the position scale with absolute certainty; so it is impossible to make a digital servo that tunes itself completely. So far, scanner manufacturers have circumvented this problem by plugging small memory chips into the scanner. A digital servo could read this memory chip and this memory chip is pre-programmed in the factory with information including torque constants, position scale and position offset, and other information about the scanner. The problem with this approach is that these parameters may change over time. The torque constant of the scanner depends on the magnetism of the rotor (or other components of the defrosting direction), and this magnetism certainly changes with temperature and, as the scanner is abused or overheated, may also change over time. Components of the position detecting device also change with time due to the component displacement and also due to temperature and other environmental effects.

Therefore, it would be beneficial to provide a rotational position detecting device with an improved signal-to-noise ratio, and also to provide absolute positional accuracy.

Summary of the invention

The current invention is directed to an optical position detector and provides embodiments that include low inertia operation and that can be used with small optical scanners. Moreover, embodiments of the invention provide an improved signal-to-noise ratio and can optionally provide absolute positional accuracy.

Here, a rotational position detecting device is provided which may include a housing having an inner space defined by an inner wall. A light source is positioned to emit light rays from its bottom into the interior of the housing. A socket is positioned in the interior of the housing.

A light detection assembly is positioned in the interior of the housing and includes a first plurality of light sensors positioned on the pedestal and disposed in pairs about an axis of a motor shaft. Each pair has an "A" detection element and a "B" detection element. The pairs are arranged such that each "A" detector is positioned circumferentially between two "B" detectors and each "B" detector is positioned between two "A" detectors. The term "light sensor" is intended to mean an area of photosensitive material here.

A light blocker is mounted for rotation with the motor shaft above the light source in the interior of the housing substantially between the light source and the light detection assembly. The light blocker may have a second number of opaque, opaque, and / or opaque elements having substantially equal sized surfaces disposed about the motor shaft axis. The second number is equal to one half of the first number. Consequently, the light rays emanating from the light source which are not blocked by the light blocker will reach the light detection device, and light rays blocked by the light blocker will not be received by the light detection device.

A signal connection between the light detecting elements and a circuit for measuring a signal from the "A" detecting means and the "B" detecting means relating to an amount of light incident thereon is provided. A difference between the "A" detection signal and the "B" detection signal is related to an angular position of the motor shaft.

In aspects, the present invention may relate to a rotational position detection device having a housing with an interior having a reflective element. A light source emits light rays upwards. A pedestal holds a light detection assembly having a first number of annular sectored light detectors arranged in pairs about a motor shaft axis, with an "A" detection element and a "B" detection element alternately provided. A light blocker is positioned between the light source and the light detection devices and rotates with the shaft. The light blocker comprises a second number of opaque, opaque and / or opaque elements having the same surface area disposed about the axis, the second number being equal to one-half of the first number. A circuit measures a signal from the "A" and "B" detection elements related to a quantity of light which falls on them, with a difference correlated with the angular position of the shaft.

Brief description of the drawings

Features which characterize embodiments of the invention, both as to the organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description taken in conjunction with the accompanying drawings. It is to be expressly understood that the drawings are for purposes of illustration and description and are not intended as a definition of the limits of the invention. These and other objects and advantages offered by the present invention will become more fully apparent when the following description is read in conjunction with the accompanying drawings, in which:

1 is a side perspective view of an embodiment of an optical position detecting device, wherein the housing is shown in a sectional view;

2 is a side perspective view of another embodiment of the optical position detecting device of the current invention, wherein the light blocker is formed by a lower end of the motor shaft and the light sensors are rectangular, wherein the housing is shown in a sectional view;

3 Figure 11 is a top plan view of one embodiment of the present invention position sensor with the circuit boards, annular light sensors and light blocker, showing a light blocker much smaller than the outer diameter of the light sensors;

4 Figure 11 is a top plan view of a relationship between light blocking elements and light sensors, with broken lines showing where individual light sensor elements are located with respect to the light blocker;

5A and 5B respectively show top / side and bottom perspective views of an alternative embodiment of the light blocker which is cup-shaped;

6 and 6A represent top / side views of other light blocker embodiments;

7 and 7A each are partial top plan and perspective views of a printed circuit board and rectangular light sensors of another embodiment of the current invention;

8th Figure 5 is a graphical representation of the output signal from the "A" and "B" pairs of the light sensors along with the composite "A minus B" output, illustrating that the composite output is linear until the "A" pair or "B" pair of light sensors is completely uncovered; after that, the position detecting means still provides an output but with a reduced rate of change;

9 FIG. 5 illustrates one embodiment of the light sensor element connectivity to provide output signals with diametrically opposed light sensor elements connected and providing only two outputs; FIG. and

10 Fig. 10 illustrates another embodiment of the light sensor element connectivity to provide output signals, wherein the output of each light sensor element is used directly without connecting to other light sensor elements.

Detailed description of the embodiments

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. Any publications, patent applications, patents or other sources mentioned herein are incorporated by reference in their entirety. In the case of contradiction the present specification including all definitions applies. In addition, the specified materials, methods and examples are merely illustrative and are not intended to be limiting. Thus, this invention may be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein. Rather, these illustrated embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Other features and advantages of the invention will become apparent from the following detailed description.

The here for an optical position detecting device according to the teachings of The present invention uses a shadow casting method. The individual elements of this position detecting device are improved in comparison with other known optical position detecting devices, providing improved results from the standpoint of positional accuracy and also from the standpoint of signal-to-noise ratio. Moreover, some embodiments of this position sensing device allow for absolute position determination based on the ability of the position sensing device to indicate when it has reached certain angular conditions.

Embodiments of the invention will be described initially with reference to FIG 1 and 2 for a rotational position detecting device 10 and an alternative embodiment of the detection device 10A each described a housing 12 with an interior 14 having. A wave 16 around an axis 18 is rotatable extends into the housing interior 14 , A light source 20 is positioned to light rays 22 in the housing interior 14 to emit. A light source 20 is positioned to light rays 22 in the housing interior 14 to emit. A light detection device 24 is in the housing interior 14 in a spaced relationship to the light source 22 positioned. The light detection device 24 has a first number of segmented light sensors 26 . 27 on that in pairs 28 . 30 around the axis 18 are arranged. Every couple 28 . 30 has an "A" detection element 26A . 27A and a "B" detection element 26B . 27B on, with the pairs 28 . 30 are arranged such that each "A" detection element is positioned circumferentially between two "B" detection elements and each "B" detection element is positioned between two "A" detection elements. A light blocker 32 is between the light detection device 24 and the light source 20 positioned. The light blocker 32 has a second number of opaque, opaque and / or opaque light blocking elements 34 with substantially equal sized surfaces, with the shaft 16 are rotatable. The second number of light blocking elements 34 is equal to one half of the first number of segmented light sensors 26 wherein a radial extent 36 the light blocking elements 34 smaller than a radial extent 38 the light sensors 26 . 27 is. As will be described in more detail in this section, a signal connection will be made 40 with the light detection device 24 for measuring an amount of light incident on the segmented light sensors 26 . 27 impinges, and thus for measuring a rotational position of the shaft 16 provided.

The embodiment described herein will be further described with reference to FIG 1 and 2 by way of example in the context of its use in a motor or galvanometer scanner, although not intended as a limitation. The housing 12 is suitable for picking up the sensor components and absorbing unwanted light rays from the environment and also around the shaft 16 in a particular embodiment, directly or indirectly with an engine 42 connect to. The housing 12 For example, although not intended as a limitation, it may include injection-molded plastic or machined metal.

The light source 20 preferably produces a substantially circumferentially uniform light field, the light rays 22 in the direction of the multiple light sensors 26 . 27 may be directed, for example, having annular sector-shaped elements, as with respect to the detection device 10 from 1 shown in one plane 44 are arranged, which are generally perpendicular to the rotating shaft 16 is. The light sensors 26 . 27 can, as with respect to 1 shown on chips 46A . 46B be manufactured by light sensing devices, or can, as with reference to 2 shown, be separated and on a circuit board 48 to be assembled. The light detection device 24 is on the same side of the engine 42 like the light source 20 positioned, but is spaced from the light source, wherein the light blocker 32 between the light source and the light sensor elements 26A . 26B . 27A . 27B is arranged.

As here exemplary for the detection device 10 with reference to 1 described, points the light blocker 32 the Elements 34 which, as generally cake-shaped projections 34A . 34B are formed, and separates the light beams 22 periodically, allowing them certain areas of the light sensor elements 26A . 26B . 27A . 27B can not reach by casting a shadow over the sensors.

The light blocker described here by way of example 12 is operational with the shaft 16 connected. The engine 42 driven rotation of the shaft 16 causes the light blocker 32 turns. When the lighting surfaces of some light sensor elements 26A . 26B . 27A . 27B increase (when less of the light sensor surface is under a shadow), an output signal from the light sensors also increases. At the same time and the same size as the illuminated areas of other light sensor elements 26A . 26B . 27A . 27B decrease (if more of the sensor surface is under a shadow), the output of these light sensors decreases.

With continued reference to 1 and 2 indicates the light source 20 preferably a single LED on top of the circuit board 48 or another suitable surface attached to the housing 12 is attached, is mounted. For the here described embodiments, the LED is exemplary on a bottom 48B the circuit board 48 mounted, and that of the light source 20 emitted light rays 22 be through a hole 50 passed in the circuit board. Such a structure is desirable because any light that radiates in a lateral manner is bounded by walls defining the hole in the circuit board 48 form, and will not be able to, indirectly on the light sensor elements 26A . 26B . 27A . 27B to shine. However, other embodiments are also possible as long as the light source 20 is suitable and, as further with reference to 1 and 2 represented, generally along the axis 18 and below the wave 16 is arranged. The rays of light 22 be from the light source 20 in the direction of the light sensor elements 26A . 26B . 27A . 27B projected.

Although the light source 20 has been described as an LED, the light source may also be embodied as a phosphorescent spot or any other source having a suitable cone of light including the light beams 22 generated in the required direction.

Note that the light source 20 through a fiber 52 can be provided, wherein the light source can be removed, for example, can be arranged on a servo driver board and the detection means can be supplied to the optical fiber. This may be preferred in military applications where the detector must operate at higher temperatures that would be prohibitive for LED operation. Also, a laser, when supplied through the fiber, may be used as the light generating means for the light source.

With continued reference to 1 and now up 3 There are four light sensor elements 26A . 26B . 27A . 278 which, as described here by way of example, are ring-sector-shaped and which, as described here, in the pairs 28 . 30 around the axis 18 are arranged. The structure of the sensor elements 26A . 26B . 27A . 27B essentially gives a structure of the light blocker 32 and its elements 34A . 34B in front. As described here by way of example, the light blocker 32 two opaque, opaque and / or opaque elements 34A . 34B with substantially equal sized surfaces, also around the axis 10 are arranged. Note that the second number (for example, two) is equal to one half of the first number (for example, four).

As with respect to 4 shown, sets the light blocker 32 the "B" pair of annular light sensor elements 26B . 27B completely free, but covers the "A" pair of elements 26A . 27A not perfect, as by the cone of light 22 shown. An angular dimension or basic angle 54 each of the open areas of the light blocker 32 (here 60 degrees) can be a different second angle or angle basic measure 58 (here 5 degrees) greater than a first angle measure or basic angle measure 56 (here 55 degrees) of the light sensor elements 26A . 26B . 27A . 27B be. Because of this, the further incremental clockwise rotation does not provide an incremental increase in the signal output from the "B" pair of light sensors, but provides an incremental decrease in the signal output from the "A" pair. If the angle measure 54 the openings for the light blocker 32 larger than that of the light sensor elements 26A . 26B . 27A . 27B is, sets the light detection device 24 a linear output for an angle change up to the angular extent of the light sensor elements 26A . 26B . 27A . 27B and then provides a non-linear output for angle change beyond this point.

With continued reference to 4 and as above with reference to 1 and 2 described is the radial extent 36 each of the light blocking elements 34A . 34B smaller than the radial extent 38 an outer edge of the light sensor elements 26A . 26B . 27A . 27B and in fact can not be greater than the radial extent 38A an inner edge of the light sensor elements. In some cases, the radial extent 36 the light blocking elements 34A . 34B depending on factors including the cone angle of the light source 20 and the distance of the light sensor elements 26A . 26B . 27A . 27B be significantly lower from the light source. This is greater than the radial extent of the outer diameter of the light sensor elements in comparison with sensors of the prior art whose radial extent of the light blocker 26A . 26B . 27A . 27B had to be, beneficial. A smaller radial expansion significantly reduces inertia and thus increases system performance.

The light blocker 32 may be constructed such that when the shaft 16 as if by an arrow 85 in 3 displayed in a "positive" direction is rotated (from the in 1 shown construction in the in 3 as shown), most of the surface of the "A" light sensor element from the light source 20 is illuminated and most of the area of the "B" light sensor element will be under a shadow. When the light blocker 32 thus being turned, he can, once he gets the "A" light sensors 26A . 27A completely uncovered, actually continue to be rotated before blocking the light completely, making it the "B" light sensors 26B . 27B not reached. This allows the servo to precisely detect when the "A" or "B" sensors are completely covered, thus accurately detecting the outer angles of the position sensor in absolute terms. However, some applications may not require this absolute positioning and can use a light blocker whose openings have the same angular extent as the sensor elements.

Although the figures show four light sensor elements and a light blocker with two protruding elements, it should be understood that as few as four light sensor elements and two light block elements or as many as eight light sensor elements and four light block elements or more are possible and still fall within the scope of this invention.

The individual light sensor elements 26A . 26B . 27A . 27B may comprise a light sensor material or a device operating on this principle, wherein a linear increase in light per unit area produces a linear increase in the output signal. As a non-limiting example, silicon photodiodes, PIN photodiodes, avalanche photodiodes, and cadmium sulfide cells may be used as the light sensing elements in this invention. These are generically referred to as "photocells".

While it is known, individual pairs of light sensor elements 26A . 26B . 27A . 27B , as in 1 shown on a single rectangular "photocell" chip or chip 46A . 46B To arrange the individual light sensor elements can be arranged in any way, as long as the above-mentioned linearity and molding conditions are met. Furthermore, the light sensor elements 26A . 26B . 27A . 27B For example, each may have a chip of any shape with a masking element disposed over it to produce the sector shape that is desired to be used.

As described above, the light blocker prevents 32 that from the light source 20 radiating light rays 22 Portions of the light sensor elements 26A . 26B . 27A . 27B to reach. The light blocker 32 that the cake-shaped elements 34A . 34B is directly with the shaft 16 connected, and the shaft is integral with the engine 42 but alternative embodiments with shaft extensions or gear arrangements may be used without departing from the teachings of the present invention. As the light blocker 32 Furthermore, it must only prevent light from the light sensor elements 26A . 26B . 27A . 27B achieved, it can be made from a variety of materials. For example, it may be made of ceramic, fiberglass / epoxy, sheet metal, glass, plastic, or any other suitable material that can block light. The light blocker 32 can be fabricated using conventional manufacturing techniques, such as injection molding, laser cutting, stamping, photoetching, or standard mechanical processing, to conform to the form described herein by way of example, or made from a transparent disc or tube, performing the blocking function by: an opaque material is applied to the transparent pane or tube. In addition, as here by way of example with reference to 5A and 5B shown for an alternative embodiment 32A of the light blocker 32 Other embodiments possible, the cup-shaped and here as the blocking elements 34A . 34B containing described earlier with reference to 1 for the light blocker 32 were described as two essentially cake-shaped elements and here as around a central disk 32C are arranged around. From the blocker elements 34A . 34B depending down are side walls 32D . 32E that has a partially enclosed cylinder with an upper edge 33F form, with an outer edge of the upper blocker elements 34A . 34B extends together.

As with respect to 6 has a further embodiment of a light blocker 33 a substantially cylindrical wall 33A an interior 33B defined by the wall positioned to receive the light rays from the light source. The cylindrically shaped light blocker 33 includes a pair of opposing openings 33C with substantially the same area through a top 33D of it and the diametrically around a central disc 33E are opposite. The openings 33C let the light rays pass through to reach the light sensor elements.

With reference to 6A shows an additional embodiment of a light blocker 35 a substantially conical wall 35A on, wherein an interior defined by the wall 35B is positioned to receive the light rays from the light source. The conically shaped light blocker 35 includes a pair of opposite openings 35C with substantially the same area through its wall 35A around a central hub 35 are diametrically opposite. The openings 35C let the light rays pass through to reach the light sensor elements.

Again referring to 2 and now up 7 and 7A becomes the detection device 10A although described in the context of its use with a motor or galvanometer scanner, although not intended as a limitation. In the position detection device 10A includes the light detection device 24 as described above, rectangular Light sensor elements 26A . 26B . 27A . 27B that are generally parallel to the axis 18 and thus the rotating shaft 16 are arranged. The light sensor elements 26A . 26B . 27A . 27B are on the circuit board 48 and on the same side of the engine 42 like the light source 20 assembled. The light blocker 32 is integral with a lower section 16A the wave 16 educated. The lower section 16A has a generally cylindrical section 62 with an interior 64 which is positioned to receive the light rays from the light source 20 to recieve. The cylindrical section 62 that as an extension of the wave 16 is formed, has two opposite openings 66 of the same size or "window", for example, extending from its lower edge through it in this embodiment, although not as a limitation. The openings 66 define sections 68 of the cylindrical section 62 which serve as the light blocking elements. Again, the word "pair" is not intended as a limitation, and the number may be up to 8 or even more in some applications. For the embodiment of the detection device 10A , which is exemplified here, has every opening 66 a height dimension 70 again referring to 2 sufficient to allow the light rays through to the light sensor elements 26A . 26B . 27A . 27B to reach.

Note that although here with reference to 2 described light blocker comprises the lower portion of the shaft, other light blocker, such as those with reference to above 5A . 6 and 6A described, can be used. The light blockers may also be formed from a transparent tube or light guide having transparent and opaque and / or opaque areas which function as the openings 66 than the "windows" run.

Because the light sensor elements 26A . 26B . 27A . 27B with continued reference to 2 and 7 rectangular rather than circular, is the distance 72 the light rays 22 must travel to the center of a light sensor element, different from the distance 74 the light rays must travel to the edge of a light sensor element. This causes an error in the output signal, the error being proportional to the tangent of the shaft rotation. However, this error for the angular range used in the galvanometer-based optical scanners is readily tolerated and generally corrected externally in the servo system or with computer software that drives the servo system.

Above-described embodiments of the light blocker improve the shadow cast on the respective photosensor elements, particularly when the light source is not a point source. Furthermore, strictly speaking, it is not necessary for the alternative light blocker embodiments to have rectangular features. As in 6A As shown, the cup may be fabricated with cone-like features that may provide for easier manufacture or lower inertia of the light blocker or better light blocking. Moreover, the light blocker itself may be formed into sheets or even wedges which are machined directly on a motor shaft itself to perform the light blocking function.

In contrast to previously known rotational position sensors, the openings of the light blocker can have a different angular dimension than the individual light sensor elements. When this is done, there are several advantages. One advantage is that, since the angular size of the light block openings is greater than the angular size of the light sensors, as described above with reference to FIGS 1 and 3 is rotated in the "positive" direction, the "A" light sensors for the embodiment of 2 be completely unblocked before the "B" sensors are completely blocked. Furthermore, the "positive" rotation still produces detectable output from the "B" sensors, but does not produce output from the "A" sensors. Consequently, this state of further changing one output can be used without further changing the other to precisely determine the shaft angle in absolute values. Another advantage is that if the A and B outputs are subtracted, as is the typical method for this type of sensor, there will be a "linear" portion of the shaft rotation angle output signal ratio, and there will be a "Non-linear" section of the shaft angle output signal ratio. As with reference to the graphical representation of 8th exemplified, the rate of change of the sensor output is shown as changing above 25 degrees.

Preferably, light blocker openings generally have an angular dimension that is at least as great as the angular size of the light sensor. However, one skilled in the art will understand that the angular extent could be substantially the same or even smaller than that of the light sensors without departing from the spirit of the invention. In some embodiments, the angular extent of the light block apertures may be made larger or smaller than that of the light sensor elements by any desirable amount that meets the design requirements of the system. However, for optical scanning applications, the dimensional difference may typically be in a range of 2-10 degrees.

The number of light blocker openings may be as small as 2 and as much as 8 or more as long as there are two light sensors ("A" and "B") per light blocker opening, with a larger number of light blocker openings decreasing the operation angle of the position detecting device. The maximum angle (in degrees) over which this position detector can output a single rise signal from the "main" outputs is equivalent to 360 divided by the number of leaves minus (blade angle minus the light sensor angle measure).

Now referring to 9 For example, individual light sensor elements can be connected in parallel so that a minimum of wires goes to the servo control. An advantage of this connection scheme is that it reduces the number of wires that it needs to be connected to the servo system by the position sensing device. However, a common drawback of prior art position detectors is that if the individual light sensor elements connected in parallel do not produce the same magnitude of output signal as other individual light sensor elements for a given amount of light, the insensitivity to radial and axial motion is not optimal is.

As an alternative connection scheme, as with reference to FIG 10 shown, the output of individual light sensor elements are used individually. An advantage of this arrangement is that the servo can characterize the output of each light sensor and then algorithmically increase the linearity and radial insensitivity. In these embodiments, the connections to the outputs are via pads of the signal connection 40 on the circuit board 48 made.

The position detecting device of the present invention is particularly useful when connected to a digital servo system that can use the scanning device and can easily determine the point in the shaft rotation where the "A" and "B" light sensors are completely blocked, and thus determine the extent of the angular deviation in absolute values. Because of this, an AGC system may not be required and the light source can be operated at maximum output all the time, maximizing the signal-to-noise ratio.

In the drawings and the specification, typical preferred embodiments of the invention have been disclosed, and while specific terms may have been used, the terms are used in a descriptive sense only and not for purposes of limitation. The invention has been described in considerable detail with specific reference to these illustrated embodiments. It will, however, be evident that various modifications and changes may be made within the spirit and scope of the invention as described in the foregoing specification.

Claims (29)

A rotational position detecting device comprising: a housing having an interior space; a shaft extending into the housing interior, the shaft being rotatable about an axis thereof; a light source positioned to emit light rays into the housing interior; a light detection device positioned in the housing interior spaced apart from the light source, the light detection device comprising a first plurality of segmented light sensors arranged in pairs about the axis, each pair including an "A" detection element and a "B" Sensing element, the pairs being arranged such that each "A" sensing element is positioned circumferentially between two "B" sensing elements and each "B" sensing element is positioned between two "A" sensing elements; a light blocker positioned between the light detector and the light source, the light blocker having a second plurality of substantially equal surface area opaque elements rotatable with the shaft, the second number being equal to one half of the first number, wherein a radial extent of the light blocking elements is smaller than a radial extent of the light sensors; and a signal connection to the light detecting means for measuring an amount of light incident on the segmented light sensors so as to measure a rotational position of the shaft. A rotational position detecting device according to claim 1, further comprising a circuit operable with said signal connection for measuring signals from said "A" detection means and said "B" detection means related to an amount of light incident thereon, one Difference between the "A" detection signal and the "B" detection device signal is related to an angular position of the shaft. A rotational position detecting device according to claim 1 or 2, wherein the segmented light sensors are generally defined in a plane perpendicular to the axis. A rotational position detecting device according to claim 3, wherein each of the segmented light sensors has an arc-shaped sector shape. A rotational position detecting device according to claim 4, wherein said arcuate shape has a substantially annular shape. A rotational position detecting device according to claims 1 to 5, wherein the segmented light sensors are generally defined in a plane parallel to the axis. A rotational position detecting device according to claim 6, wherein the light sensors have a rectangular area receiving the light. A rotational position detecting device according to claims 1 to 7, wherein the radial extent of the light blocking elements is substantially smaller than the radial extent of the light sensors. The rotational position detecting device according to claim 8, wherein the radial extent of the light blocking elements is not greater than a radial extent of an inner edge of the light sensors. The rotary position detecting device according to claims 1 to 9, wherein the light blocker has a plurality of openings, each opening being between adjacent light blocking elements, and wherein the angular dimension of each of the light block openings is at least as large as the angular size of the light sensors. The rotary position detecting device according to claims 1 to 10, wherein the light source has a unitary light source that is generally aligned with the axis. A rotational position detection device according to claims 1 to 11, wherein the first number of segmented light sensors comprises four light sensors. The rotational position detector of claims 1-12, wherein the light sensors comprise a light sensor material responsive to light, and wherein a linear increase in the light per unit area impinging thereon causes a substantially linear increase in the output signal. A rotary position detecting device according to claims 1 to 13, wherein the light blocking elements comprise sheets. A rotational position detecting device according to claims 1 to 14, wherein the light blocker comprises a substantially transparent tube on which the opaque elements are applied. The rotary position detecting device according to claims 1 to 15, wherein each of the light blocking elements further has a side wall extending therefrom toward the light source to form a light blocker which is substantially cup-shaped. The rotary position detecting device according to claims 1 to 16, wherein the light blocker has a substantially cylindrical member having an inner space defined by a side wall and positioned to receive the light beams from the light source, the cylindrical member being a pair of spaced openings substantially equal has large surfaces through its top to let light rays through. The rotation position detecting device according to claim 17, wherein the openings have an angular dimension which is at least as large as the angular size of the light sensor. The rotary position detecting device according to claims 1 to 18, wherein the light blocker has a lower portion of the motor shaft, the lower portion having a generally cylindrical portion with an interior positioned to receive the light beams from the light source, the light blocking elements being segments of the cylindrical shaft Section which are separated by spaced openings extending from its lower edge. The rotary position detecting device according to claims 1 to 19, further comprising a motor, wherein the motor is operable with the shaft. The rotary position detector of claims 1 to 20, wherein the light blocker comprises a substantially conical member having an interior defined by a side wall and positioned to receive light rays from the light source, the conical member having a pair of spaced openings of substantially equal size Has area through the side wall to let light rays through them. A rotational position detecting device for detecting the rotational position of a shaft, the device enabling light to be transmitted to an interior of a housing having a shaft extending therethrough and being rotatable about an axis, the device comprising: a light detecting device for detecting at least a part of Light positioned in the housing interior, the light detecting means comprising a first plurality of segmented light sensors arranged in pairs about the axis of the shaft, each pair having an "A" detection element and a "B" detection element Pairs are arranged such that each "A" detection element is arranged circumferentially between two "B" detection elements and each "B" detection element is arranged between two "A" detection elements; a light blocker for blocking a portion of the light positioned in the housing interior and rotatable with the shaft, the light blocker having a second number of opaque elements of substantially equal surface area disposed about the shaft, the second number being equal to one half of the first number, the blocked portion of light thereby becoming incapable is to reach the light sensors, wherein an outer dimension of the light blocker is smaller than an outer dimension of the light sensors; and an apparatus for processing a signal received from the "A" detectors and the "B" detectors, which refers to an amount of the incident light thereon, wherein a difference between the "A" detector signal and the "B" Detector signal refers to a rotational position of the shaft. The device of claim 22, wherein a radial extent of the light blocking elements is substantially less than a radial extent of the light sensors. A device according to claim 22 or 23, wherein the radial extent of the light blocking elements is not greater than a radial extent of an inner edge of the light sensors. The device of claim 22, 23 or 24, wherein transmitting the light comprises emitting light from a unitary light source that is generally aligned with the axis of the wave. Device according to claims 22 to 25, wherein the first number of segmented light sensors comprises four light sensors. The device of claims 22 to 26, wherein the light sensors comprise a light sensor material responsive to light, and wherein a linear increase in the light per unit area impinging thereon causes a substantially linear increase in the output signal. The device of claims 22 to 27, wherein the light blocking elements comprise leaves. The device of claims 22 to 28, wherein the light blocker comprises a substantially transparent tube having opaque elements thereon.

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