Abstract:
An apparatus and method for noncontact, optical measuring of any of torque, torque angle, shaft speed, and shaft direction by at least one of a rotatable and compressible flexure with input and output ends plus input and output couplers, a light source for generating a light signal, a field mask formed of a pattern of opaque and transparent lines adapted to receive the light signal and generate a phase shifted light signal, and detector means for receiving a light signal from overlaid lines on the flexure and the field mask. Alternatively, the detector means may receive the light signal from overlaid lines on the input and output couplers of the flexure and the field mask and generate an output signal indicative of the combined pattern of the lines.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of the Jun. 12, 2003 filing date of U.S. Provisional Application No. 60/478,120, the entire contents of which are hereby incorporated by reference. 
     
    
     
       BACKGROUND  
         [0002]    The present invention relates to torque sensors, specifically to torque sensors using non-contact optics for the measurement of torque, torque angle, flexure speed, flexure direction and flexure rotational travel.  
           [0003]    A conventional method and device for measuring torque generally requires physical contact with the torque sensor&#39;s center shaft. Applying torque to a shaft generates two principal lines of stress along helical lines which are orthogonal to each other on the surface of the shaft. Strain gauges are bonded in a cross arrangement along the helical lines. The strain gauges are coupled to measuring electronics by slip rings. However, these arrangements are difficult to implement.  
           [0004]    Non-contact, optical based torque sensors are also known. Such sensors make use of a flexure or shaft, typically formed of metal. One end of the shaft is connected to a driving member, such as a motor, and the other end is connected to a tool or bit which drives a fastener, such as a bolt, to a tightened state, for example. Increased torque on the output end of the shaft as the bolt tightens causes rotation of the output end to lag behind rotation of the driven input end of the shaft. This lag can be used as an indicator of the amount of rotation of the output end which is proportional to the applied torque.  
           [0005]    An example of an optically based torsion sensor is described by Bechtel, U.S. Pat. No. 5,001,937. Bechtel discloses a device for measuring torsion in a rotating shaft. The Bechtel device requires usage of a band consisting of alternating high and low reflectivity regions. The band is stationed on the shaft at the desired location of measurement. One sensor head is located to correspond to each band. Light is projected onto the respective band by the corresponding sensor. Furthermore, each sensor collects the light reflected by the high reflectivity region(s) of the corresponding band. The phase displacement between the intensities of the reflected light at the sensor heads is used to determine torsion on the rotating shaft.  
           [0006]    However, it would be desirable to provide a torque sensor with non-contact optics to make implementation a lot simpler than conventional torque measurement methods and devices. It would also be desirable to provide a dynamic torque sensor that is not just limited to the measurement of torque, but is also capable of measuring torque angle, flexure speed, and flexure direction of travel.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention is an apparatus for the measurement of any of the torque, torque angle, flexure speed, flexure direction, and flexure rotational travel. The apparatus includes a non-contact rotary optical displacement sensor, and a rotatable and compressible flexure with input and output ends. The non-contact rotary optical displacement sensor also includes a light source for generating a light signal, a field mask adapted to receive the light signal and generate a phase shifted light signal. The flexure may contain a pattern of reflective and non-reflective lines associated with input and output ends. Alternatively, patterns of reflective and non-reflective lines may be on the input and output shaft of the flexure or projected onto the input and output shafts.  
           [0008]    The sensor also includes detector means for receiving a light signal. The detector means receives the phase shifted light signal of the overlaid lines associated with the flexure and the field mask or the overlaid lines on the input and output end of the flexure and the field mask and generates an output signal indicative of the combined pattern of the lines.  
           [0009]    The flexure of the apparatus can include the reflective and non-reflective lines being equi-circumferentially spaced about the input and output ends of the flexure.  
           [0010]    The field mask of the apparatus is mounted about a circumference of the flexure. Furthermore, the field mask is fixed and stationarily supported relative to the flexure by mounting means. The mounting means includes, in one aspect, an arm securely fixed to an angle bracket that is fixed to a housing surrounding the flexure. Alternatively, the field mask may be mounted about a circumference of the input and output shaft of the flexure.  
           [0011]    The field mask opaque and transparent lines of the apparatus share the same size and direction.  
           [0012]    The field mask opaque and transparent lines and the flexure input and output lines form a Moire pattern for reflective and non-reflective lines. Alternatively, the field mask opaque and transparent lines and the input and output end coupler lines form a Moire pattern for reflective and non-reflective lines.  
           [0013]    The light signal received by the detector in the apparatus is digitized and transmitted to a signal processor for analysis.  
           [0014]    The present invention also defines a method of optically measuring one of torque, torque angle, shaft speed, and shaft direction comprising the steps of providing a flexure element, coupling an input end of the flexure to a torque transmitting mechanism that will displace the flexure in proportion to the torque transmitted by an output end of the flexure to a rotatable element engaged by the flexure and measuring the displacement of one end of the flexure relative to the other end to yield a measurement of torque.  
           [0015]    The present invention has been designed to simplify the complex audit method required for critical joints with high installation torque and frictional scatter. The sensor has been designed to provide a torque sensor with non-contact optics to make implementation simpler than conventional torque measurement methods and devices. Furthermore, the present invention provides a dynamic torque sensor that is not limited to the measurement of torque as conventional torque measurement devices because the invention is also capable of measuring torque angle, flexure speed, and flexure direction of travel. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0016]    The description herein makes reference to the accompanying drawing wherein like reference numerals refer to like parts throughout the several views, and wherein:  
         [0017]    [0017]FIG. 1 is a front elevational view of an optical displacement torque sensor according to the present invention;  
         [0018]    [0018]FIG. 2 is a pictorial representation of the sensor of FIG. 1 coupled to control circuitry;  
         [0019]    [0019]FIG. 3 is waveform of the output of the sensor shown in FIG. 1;  
         [0020]    [0020]FIG. 4 is a perspective of the flexure of the present invention;  
         [0021]    [0021]FIGS. 5A and 5B are end and plan elevational views showing the reflected light paths between the light emitters and light detectors of the sensor shown in FIG. 2;  
         [0022]    [0022]FIG. 6A is a pictorial side-by-side representation of gradient lines on the flexure and field mask;  
         [0023]    [0023]FIG. 6B is a pictorial representation of the gradient lines prior to loading;  
         [0024]    [0024]FIG. 6C is a pictorial representation, similar to FIG. 6B, but showing the gradient lines resulting from torsional lag in the lines on the output end of the flexure;  
         [0025]    [0025]FIG. 7 is a waveform diagram depicting the lag between the input end and output end sensors of the present invention; and  
         [0026]    [0026]FIG. 8 is an end view showing the mounting of the field mask over the flexure shown in FIG. 2.  
         [0027]    [0027]FIG. 9 is a side view of an input coupler of the present invention possessing reflective and non-reflective lines.  
         [0028]    [0028]FIG. 9A is a perspective view of the input coupler of FIG. 9 possessing an internal mating spline fitting for a splined flexure.  
         [0029]    [0029]FIG. 10 is a perspective view of the splined flexure.  
         [0030]    [0030]FIG. 10A is a perspective view of the splined flexure inserted into the internal mating spline fitting of the input coupler of FIG. 9. 
     
    
     DETAILED DESCRIPTION  
       [0031]    With reference now to the drawings, the preferred aspects of the invention are illustrated only by example and not for purposes of limiting same. FIGS. 1 and 2 show a rotary optical displacement sensor apparatus  9  which is particularly useful in measuring torque being transmitted to a rotatable element, such as a fastener. The apparatus  9  includes an element, called a flexure  18  with an input end  30 A and an output end  34 A, in line with the torque transmitting mechanism, that will displace to a degree that is proportional to the torque transmitted to the fastener. The displacement is then measured to yield a measurement of torque. The non-contact optical method of measurement described herein measures the amount of flexure displacement, flexure speed, and/or flexure direction and flexure rotational travel.  
         [0032]    Displacement can occur by twist or compression of the flexure  18  relative to the rotation of an input and output coupler  30  and  34 , respectively, attached to the input and output end  30 A and  34 A, respectively, of the flexure  18 .  
         [0033]    Although the flexure  18  could be formed of a metal, such as steel, according to one aspect of the present invention, the flexure  18  is formed of a displaceable polymer, such as urethane, elastomer, synthetic rubber, etc. A urethane formed flexure  18  will have sufficient rigidity so that an output end  34 A will repeatedly displace the same amount under the same applied torque or force over a wide load and temperature range. Further, forming the flexure  18  of a polymer, such as urethane for example only, provides the flexure  18  with a greater amount of flex or displace at lower torque, which facilitates accurate measurement of low torque devices, such as power screwdrivers.  
         [0034]    A pattern of fine parallel lines  28  and  32 , alternatively reflective and non-reflective, are applied to the ends of the flexure  18  as shown in FIGS. 2 and 4. Alternatively, reflective and non-reflective lines  28  and  32  may be applied onto or projected onto an input and output couplers  30  and  34 , respectively, as shown in FIG. 9, to which the flexure  18  is firmly attached. When the lines  28  and  32  are applied to the ends of the flexure  18 , the lines  28  and  32  may be parallel to the longitudinal axis of the flexure  18  when the flexure  18  is not subjected to external forces.  
         [0035]    When the reflective and non-reflective lines  28  and  32 , as shown in FIGS. 9 and 9A, are applied onto or projected onto the input coupler  30  and output coupler  34 , a splined flexure  18 A is used, as shown in FIGS. 10 and 10A. FIG. 10A depicts the splined flexure  18 A inserted into the input coupling  30  spline fitting  30 B. The input coupler  30  and output coupler  34  possess internal mating spline fittings  30 B, as shown in FIG. 10A, corresponding to the splined flexure  18 A to hold and drive the flexure  18 A. As shown in FIG. 9A, the bearing  66  mounted coupler  30  includes a silver ring  64 . The ring  64  is centered by use of an o-ring  68  pressed around the spline fitting  30 B that is welded to the backside of the coupling  30 .  
         [0036]    When the reflective and non-reflective lines  28  and  32 , shown in FIGS. 6A, 6B and  6 C, are applied to the flexure  18 , the lines  28  and  32  may be applied to the ends of the flexure  18  by any suitable means, including printing, photoetching, etc. The lines  28 ,  32  are preferably equi-circumferentially spaced about the ends of the flexure  18 . The lines  28 ,  32  may be formed partially or completely around the circumference of the flexure  18  or couplers  30  and  34 .  
         [0037]    As the flexure  18  displaces due to the torque applied to one end, such as the input end  30 A, the lines  32  on the output end  34 A become displaced relative to the lines  28  on the input end  30 A. Optical systems  9  at each end of the flexure  18 , consisting of a light source  12 , a field mask  14  and a silicon diode detector  16 , measure this displacement as shown in FIGS. 2, 5A and  5 B.  
         [0038]    Although two pairs of light sources  12  and detectors  16  are employed at each end of the flexure  18 , it will be understood that this is by way of example only, as an optical sensor  9  according to the present invention may have a single light source/detector at each input  30 A and output end  34 A.  
         [0039]    The light source  12  may be any suitable light source. Although a laser can be employed as the light source  12 , according to one aspect of the present invention, the light source  12  may be formed of an inexpensive LED.  
         [0040]    The field mask  14  is formed of a thin, transparent material, such as a plastic film, which is mounted a slight distance about the circumference of the flexure  18 , preferably over each series of lines  28  and  32 . The mask  14  is fixedly and stationarily supported relative to the rotating flexure  18  by means of a mount  50 , as shown in FIG. 8. The mount  50  includes a support  52  in the form of a ring mounted intermediate to the ends of an elongated, cylindrically shaped sleeve used to form and carry the field masks  14  for each end of the flexure  18 . Grating or gradient lines  15  as shown in FIG. 2 are formed, as described hereafter, on each end of the sleeve. Alternatively, the field mask  14  may be mounted a slight distance about the circumference of the input  30  and output couplers  34  when the reflective and non-reflective lines  28  and  32  are applied onto or projected onto the input  30  and output couplers  34 .  
         [0041]    As shown in FIG. 8, the field mask  14  is fixed a short distance away from the outer surface of the flexure  18  by the mount  50  which, by example only, includes an arm  54  connected to the ring  52 . The arm  54  is secured to an angle bracket  56  by suitable attachment means, such as a fastener  58 . The angle bracket  56  is in turn fixed by a fastener  60  to a housing  62  surrounding the flexure  18 .  
         [0042]    As shown in FIG. 2, the field mask  14  includes a pattern of transparent and opaque lines  15  that are identical in size and direction and may be substantially identical in spacing to the patterns of the lines  28  and  32  on the ends of the flexure  18 . Alternately, the lines  15  on the field mask  14  may also have a different spacing than the spacing of corresponding lines  28  and  32  on the flexure  18 . The lines  15  may be printed, etched or otherwise formed on the film at the appropriate positions by suitable means.  
         [0043]    Light from the light source  12  passes through the mask  14  and is reflected by the pattern of lines  28 ,  32  on the rotating flexure  18 . The result of the interaction between the pattern of lines  28  and  32  on the flexure  18  and the pattern of lines  15  on the field mask  14 , as the flexure  18  rotates, is a periodic variation in light flux passing through the field mask  14  as the reflective lines  28 ,  32  on the flexure  18  align and misalign with lines  15  on the field mask  14  as seen in FIGS. 6B and 6C. The signal produced in FIG. 3 by the detector  16  will be an analog triangular wave  20  whose frequency is equal to the frequency of the lines  28  or  32  on the rotating flexure  18  as they pass under the field mask  14 .  
         [0044]    The lines  15  on the mask  14  and the lines  28 ,  32  on the flexure  18  are arranged so as to form Moire patterns which are reflective and non-reflective regions that result when two identical, repetitive patterns of lines, circles, or arrays of dots are overlapped with imperfect alignment.  
         [0045]    It will be understood that the Moire patterns are not produced in the mask  14  or the flexure  18 , but rather are a pattern of an image viewable by the human eye. In some places, opaque lines  15  on the mask  14  hide the reflective lines or spaces between the non-reflective lines  28 ,  32  on the flexure  18 , creating a non-reflective viewable region. When the opaque lines  15  on the mask  14  align with the non-reflective lines  28 ,  32  on the flexure  18 , the neighboring reflective areas between the non-reflective lines  15  and  28 ,  32  show through. The patterns formed by the regions of reflective and non-reflective lines compose the Moire patterns which are imaged by the internal optics of the sensor  16 .  
         [0046]    As torque builds up, the lines  32  at the output end  34 A of the flexure  18  lag more and more behind the lines  28  at the input end  30 A in proportion to the torque, due to the displacement in the flexure  18 . During such displacement, the relative position of the imaged Moire pattern will change as the output end  34 A of the sensor  9  connected to the rotating fastener head lags behind the input end  30 A of the flexure  18  connected to the rotating power tool or drive source. Correspondingly, the triangular wave signal  20  from the output end  34 A detector  16  lags behind the triangular wave signal  20  from the input end  30 A detector  16  signal. These signals  20  can be digitized via an analog to digital converter  22  which samples the waveforms shown in FIG. 7. The digital signal representation can then enter into a signal processor, such as a computer  26 , shown in FIG. 2, for analysis.  
         [0047]    Determination of the degree of rotational lag by comparing the signals from the output end  34 A of the flexure  18  to the input end  30 A of the flexure  18  is straightforward, but must take into account the varying speed of the rotating flexure  18 . The triangular waves  20  shown in FIG. 3 will change frequency, possibly rather abruptly, as the flexure  18  slows near the target torque value.  
         [0048]    At some degree of torque, the displacement of the flexure  18  will equal the width of a line pair (combined reflective and non-reflective lines). At this point, the input and output detector waveforms will again be in phase, as they were with no torque applied.  
         [0049]    To avoid ambiguity, the control program executed in the signal analysis device  26  shown in FIG. 2, must keep track of the number of complete cycles, line by line, of the 360° shift the waveforms  20  shown in FIG. 3, have gone through. The complete torque measurement will be a function of this number plus the fractional shift measured via the detector  16  shown in FIGS. 2 and 5A of the rotary optical displacement sensor  9  by the phase difference between the two signals.  
         [0050]    The rotational velocity of both the input end  30 A and the output end  34 A of the flexure  18  can be measured by measuring the frequency of the signals (peak to peak) generated by the detectors  16  at the input end  30 A and the output end  34 A of the flexure  18 , respectively.  
         [0051]    The direction of rotation of the flexure  18  can be determined by providing two detection systems  16  at each end of the flexure  18  and comparing the signals generated by the two detection systems  16 . These detectors  16  are positioned relative to one another, as shown in FIG. 5A, such that the signals generated by them are 90° out of phase with each other. Arbitrarily designating the two signals as A and B, rotation in one direction will produce signals where A leads B by 90°, see FIG. 7, whereas rotation in the opposite direction will produce signals where B leads A by 90°. Direction of rotation is thus determined by the relative phase between the two signals.  
         [0052]    Torque angle is the angle through which the fastener is turned past the point at which a threshold torque is reached and until the target torque is reached. The sequence of events culminating in this measurement are as follows: Before the fastener begins to tighten, little torque is generated and the input end  30 A and the output end  34 A of the flexure  18  rotate at a common velocity and with little displacement in the flexure  18 , as shown in FIG. 2. As the fastener begins to tighten, the torque begins to increase and reaches a threshold value. This results in an increase in the displacement of the flexure  18  that is detected and quantitatively measured by analysis of the input  30 A and output end  34 A detector  16  signals. Detection of the threshold torque initiates the measurement of angular rotation at the output end  34 A of the flexure  18 , as shown in FIG. 2. This measurement continues until the target torque is detected. At this point, the measurement of torque angle is complete and its value is stored in a memory for later display, printout or archiving.  
         [0053]    Final torque, which could be larger than target torque if the fastener driving mechanism is not properly controlled, can be measured by recording the measured torque at the point that the output end  34 A of the flexure  18  comes to a stop. As the output end  34 A of the flexure  18  slows to a near stop, the signals generated by the detectors  16  change very slowly. It is necessary to distinguish between a slow change and no change. For an accurate measure of final torque, it may preferred that the detector  16  signals be stored in a computer memory and subsequently analyzed to accurately determine the point in time that the output end  34 A of the flexure  18  came to a stop.