Abstract:
A leadless motor rotation detector apparatus for determining the direction of shaft rotation of a motor providing a fluctuating magnetic field when rotating includes: at least two sensors separated a predetermined distance from one another. Each sensor senses the magnetic field and generates a corresponding sensor signal having an amplitude and phase associated with said sensed magnetic field. A processor is responsive to the sensor signals, and compares temporal aspects associated with the relative phase of each of the sensor signals to determine a leading or lagging signal. The leading or lagging signal is associated with a corresponding one of the at least two sensors and is indicative of the direction of motor rotation.

Description:
FIELD OF THE INVENTION 
     The present invention relates to magnetic rotation sensors and in particular, to a non-intrusive motor rotation detector for determining the direction of shaft rotation of an electrical alternating current induction motor without requiring physical contact with the motor. 
     BACKGROUND OF THE INVENTION 
     Knowledge of the proper direction of motor shaft rotation is essential when integrating today&#39;s industrial motors within systems and machines designed to perform particular applications and tasks. Previously, one could view the direction of motor shaft rotation because few motors possessed hidden shafts or shafts covered by a safety guard. However, as time progressed, regulatory requirements, specific applications, and economic considerations required many motor shafts to become hidden in housings, covered with safety guards, or made an integral part of a mechanical assembly. This inhibited visible determination of the direction of motor shaft rotation. Although rotation direction could still be determined by viewing the motor prior to assembly within the machine or by viewing the process results, these methods often proved inadequate for a number of reasons. First, costly equipment may be damaged by reverse operation for any period above a short time interval; viewing the results of a process that takes even a relatively small amount of time to complete may result in irreparable damage to the machine. Moreover, reverse operation of shaft rotation may not be obvious from viewing the results and may inadvertently be accepted as normal. In addition, original equipment vendors may have a need to check rotation of hidden shaft units so that the final manufacturer can install the motor without the cost of re-connecting motors to obtain the proper shaft rotation. 
     A number of detectors exist in the prior art for determining shaft rotation direction. However, these instruments require electrical connections to the motor. This imposes added cost, time and labor in order to stop the motor, connect the rotation detector, start the motor, determine the rotation, and disconnect the detector, before moving on to the next unit under test. 
     Consequently, a compact means for providing an indication of the direction of rotation of a motor shaft without incurring the labor and time investment associated with connecting and disconnecting electrical leads and stopping and starting the motor is greatly desired. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an improved rotation detection sensor for determining the direction of shaft rotations of an electric motor. 
     Another object of the invention is to provide an improved motor rotation detector that does not require electrical leads connected to the motor or any physical contact with the motor. 
     Another object of the invention is to provide a leadless motor rotation detector apparatus for determining the direction of shaft rotation of a motor, the motor of the type providing a fluctuating magnetic field when rotating, the apparatus having at least two sensors separated a predetermined distance D 1  from one another, each sensor operable for sensing the magnetic field and generating a corresponding signal having an amplitude and phase associated with the sensed magnetic field; and a processor responsive to the signals for comparing temporal aspects associated with the relative phase of each of the signals to determine a leading signal, the leading signal associated with a corresponding one of the at least two sensors and is indicative of the direction of motor rotation. 
     A further object of the invention is to provide a small, compact, handheld moisture resistant rotation detection apparatus which senses the phase difference between two signals induced by a fluctuating magnetic field from the rotation of an electric motor shaft and operates on the relative signal phase difference to indicate the direction of the rotation of the motor shaft. 
     There is provided a compact portable motor rotation detector apparatus for determining the direction of shaft rotation of a motor, the motor of the type providing a fluctuating magnetic field when rotating, the apparatus comprising first and second sensors displaced a predetermined distance D 1  from one another for detecting the fluctuating magnetic field and producing corresponding first and second sensor signal waveforms, each having an amplitude and phase corresponding to the sensed fluctuating magnetic field from each of the corresponding first and second sensors; amplifier circuitry for amplifying the respective first and second sensor signal waveforms; a processor having first and second input channels for receiving the corresponding amplified first and second sensor signal waveforms, wherein the processor includes an algorithm for determining the phase angle between the two signal waveforms to determine the time shift between the first and second signal waveforms for determining a leading signal associated with a corresponding one of the first and second sensors; and output means for providing a control signal indicative of the direction of motor rotation based on the determination of which sensor is associated with the leading signal. 
     Further objects of this invention, as well as the novel features thereof, will become apparent by reference to the following description, taken in conjunction with the accompanying figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A complete understanding of the present invention may be gained by considering the following detailed description in conjunction with the accompanying drawings in which: 
     FIG. 1 illustrates a block diagram of the motor rotation detector apparatus according to the present invention. 
     FIGS. 2A and 2B represent end views of a motor illustrative of the alignment and displacement positions of the magnetic rotation detector apparatus relative to the motor for determining proper rotation detection according to the present invention. 
     FIG. 3 shows a block diagram of an embodiment of the magnetic rotation detector apparatus enclosed within a housing and having a depressible switch for supplying power to the detector according to an aspect of the present invention. 
     FIG. 4 represents a circuit schematic diagram of the magnetic rotation detector apparatus according to the present invention. 
     FIGS. 5A and 5B are end views of a motor and shaft illustrating the alignment position of the magnetic rotation detector apparatus fixedly coupled to the side of the motor according to another aspect of the present invention. 
     FIGS. 6A-D represent an exemplary illustration of a flow chart depicting the steps involved in processing the signals within the microprocessor for determining shaft rotation according to the present invention. 
     FIG. 7 is an exemplary illustration of left and right side magnetic field signals detected by the sensors and used to determine phase and zero crossing information according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIG. 1, there is shown an embodiment of the present invention motor rotation detector apparatus  10  for detecting the direction of rotation of the shaft of an electrical alternating current induction motor  20  without being in physical contact with the motor (or with electrical lead wires for connecting to the motor). Note that when referring to the drawings, like reference numerals are used to indicate like parts. FIG. 1 illustrates a schematic block diagram of the detector  10  comprising a pair of small sensing coils RY 1  and RY 2  used to sense the magnetic field flux output from motor  20 . Each of the coil sensors RY 1  and RY 2  are separated from one another by a predetermined distance D which, in the preferred embodiment, is approximately 1-2 inches. In the preferred embodiment, coil sensor RY 1  is defined to be the right coil sensor, while coil sensor RY 2  represents the left coil sensor. The right coil sensor indicates a right directional rotation, while the left coil sensor will indicate a left directional rotation of the motor shaft. The basic concept is to detect a phase shift in the magnetic field sensed between each of the sensors separated by the predetermined physical distance in order to determine the particular rotation direction (i.e. left or right) of the running motor. The motor rotation detector is held against or near the side of an energized AC induction motor to determine the direction of rotation by rotating magnetic fields created by the interaction of the winding and the induced magnetic field in the rotor. The coil sensors operate to transduce the sensed magnetic field strengths into electrical signals at the outputs of RY 1  and RY 2  which are proportional to the sensed magnetic fields. Each of the coil sensors is coupled to a respective high gain amplifier U 3 A and U 3 B via respective low pass filters, so that the corresponding output signals  12  and  13  from the respective coil sensors RY 1  and RY 2  are input to the corresponding amplifier. Preferably, a 5 volt power supply (not shown) is resistively divided to 2.5 volts to bias both the amplifiers (U 3 A, U 3 B) and the coil sensors (RY 2 , RY 1 ). Note that by having the amplifiers and the coils at the same potential, the high gain amplifiers can quickly come to equilibrium when power is turned on. 
     As shown in FIG. 1, the output signals  22   s  and  23   s  from each of the corresponding high gain amplifies are fed to analog input channels on the microprocessor unit U 2 . The signals input to the microprocessor are multiplexed by multiplexer  30  and converted into digital signals via analog to digital converter (A/D) 40 . The microprocessor U 2  includes software algorithms  100 * which execute various software programs resident within microprocessor program memory in order to ultimately determine the direction of shaft rotation. The software programs  100  are stored in memory in conventional fashion within the microprocessor, as is well known in the art. (Note however that it is contemplated that the programs may also be stored external to the microprocessor, such as in a database or the like.) The software functions within module  100  include software routine  110 , which determines if the processed signals from each of the coil sensors RY 1  and RY 2  are of sufficient amplitude to perform the rotation detection processing. Software module  110  also includes functionality which determines the phase of the motor based on the signal amplitudes so as to expedite processing determination of motor rotation. Software functionality module  130  operates to determine the relative phase angle between the signals by determining the zero crossing of one phase signal in relation to the other. Based on the relative signal amplitudes detected and based on the relative phase difference between the two signals, rotation logic software  140  within software module  100  determines the direction of motor rotation. (Note that if the signal amplitude as determined by the software is too low, an output signal  303  indicative of a low signal condition is output from the microprocessor to indicate that the motor rotation could not be determined because of the low signal level received by the coil sensors. 
     Upon determining the relative phase difference between the two sensed signals and determining which coil contains the leading signal, an output control signal is output from the microprocessor indicative of the determination of detection rotation. In the preferred embodiment, three LEDs labeled  301 ,  302 , and  303 , are electrically coupled to the microprocessor U 2  and are used to indicate LEFT motor rotation, RIGHT motor rotation, and Low Signal conditions respectively. Preferably, control signals  201 ,  202 , and  203  from processor U 2  are coupled to each of the respective LEDs  301 ,  302 , and  303 , so as to illuminate the corresponding LED when the associated condition (left rotation, right rotation, or low signal condition) is detected. 
     As shown in FIGS. 2A and 2B, the rotation detector  10  may be packaged by enclosing it within a housing  99  of plastic or other lightweight non-conducting (non-interfering) material, so as to form a compact, lightweight and portable device. The overall dimensions of the device is approximately 4 inches long by 2 inches wide, enabling it to be held within the palm of a user&#39;s hand. 
     Still referring to FIGS. 2A and 2B, in a preferred embodiment the apparatus  10  enclosed within housing  99  is positioned a distance X from the motor with sensing face  11  arranged perpendicular to the longitudinal axis of the motor shaft and at an angle of substantially 90 degrees in relation to the motor shaft. That is, the device is operated by holding the device perpendicular to the longitudinal axis of the motor. The axis of the sensing face is rotated 90 degrees from the motor&#39;s longitudinal axis. While the motor is running, a “push-to-test button”  77  (see FIG. 3) is pressed thereby providing power to the device. Rotational LEDs  301  and  302  are then illuminated to indicate that data is being sampled. Low signal LED  303  will illuminate if a strong enough signal is not detected. The detector should then be moved to another location on the motor if the low signal LED  303  illuminates. Once the data buffer is full, the directional LED that is not true will be extinguished, and the remaining LED that is illuminated will indicate the direction of rotation. A battery may be used to supply power to the device. Note that in the preferred embodiment, the distance X from which the apparatus is displaced from the motor, is approximately 1-2 inches. However, this distance may vary according to the strength of the magnetic field emitted from the motor. That is, for single phase motors it is probable that the distance X may be somewhat greater than for 3-phase motors, for example. 
     As shown in FIG. 3, a switch or depressable button  77  disposed in housing  99  is in electrical communication with the detector  10 , such that depression of the switch causes electrical communication with dry cell battery  88  for supplying power to and thus engaging the device. 
     Referring now to FIG. 4, there is shown a schematic circuit diagram illustrating the electrical components associated with the motor rotation detector apparatus  10 . The designations left and right represent the view of the top of the board from the motor end of the unit. Note that the circuit illustrated in FIG. 4 has been found to provide satisfactory operation using the numeric values indicated for each of the labeled components which are given only by way of example. When the apparatus  10  is properly positioned in relation to shaft  21  (see FIGS. 2A,  2 B or  4 A,  4 B) of motor  20  and power is applied (via depression of switch  77  causing closure of switches  77 A and  77 B), left sensor RY 2  senses a shifting magnetic field from rotary shaft  21  and converts it into a first signal  13 . Right sensor RY 1  aligned parallel to RY 2  but separated a distance D from sensor RY 2 , operates to sense the shifting magnetic field from rotary shaft  21  and converts it into a second signal  12 . Each sensor is spaced a distance D apart from one another, as measured from the centers of each sensor. Both sensors are separated from the motor by the same distance X. Thus, both sensors are in alignment along a first (“x”) axis, but are displaced a distance D from one another along a second (“Y”) axis. In the preferred embodiment, the sensors are separated by about 1 to 2 inches. Preferably, the sensors RY 1  and RY 2  are 24 volt reed relay coils (coils used only) having a large number of wire turns on each coil. The voltage induced into each coil from the magnetic field emanating from the motor shaft rotation will vary between microvolts to a few volts depending on the style of the motor. The output signal  13  from the left coil RY 2  is filtered using a low pass filter formed from the combination of resistor R 7  and capacitor C 4  to remove the high frequency noise from the signal. In similar fashion, output signal  12  from the right coil RY 1  is filtered via the resistor capacitor combination R 6  and C 8  to remove the high frequency noise. 
     More particularly, in the preferred embodiment illustrated in FIG. 4, the signal  13  output from sensor RY 2  is input to operational amplifier U 3 A via a low pass filter structure. Capacitor C 4  disposed between nodes  21  and  26  has its positive terminal coupled to Vpp/2 and its negative terminal coupled to resistor R 7 , so that the combination of C 4  and R 7  forms a low pass filter to remove high frequency noise within signal  13 . Capacitor C 5  is disposed between nodes  26  and  22 , its negative terminal coupled to resistor R 11  which in turn is coupled to input terminal  6  of amplifier U 3 A. Resistor R 10  is arranged in a feedback configuration having terminal ends disposed between nodes  22  and  25 . The combination of R 10 , C 5 , R 11 , and amplifier U 3 A forms a high frequency gain amplifier operative on signal  13 . The combinational arrangement of resistor R 10  and capacitor C 5  permits signal  23   s  output from amplifier U 3 A to track the input signal having transition times matching the zero crossing of sensor signal  13 . 
     In similar fashion, signal  12  output from sensor RY 1  is input to operational amplifier U 3 B via a low pass filter. Capacitor C 8  is disposed between nodes  61  and  66  with positive terminal coupled to Vpp/2 and negative terminal coupled to resistor R 6 , so that the combination of C 8  and R 6  forms a low pass filter to remove high frequency noise within signal  12 . Capacitor C 7  is disposed between nodes  66  and  62 , with negative terminal coupled to resistor R 8  which in turn is coupled to inverting terminal  2  of amplifier U 3 B. Resistor R 9  is arranged in feedback configuration with terminal ends disposed between nodes  62  and  65 . The combination of C 7 , R 8 , R 9  and amplifier U 3 B forms a high frequency gain amplifier circuit operative on signal  12 . The combinational arrangement permits signal  22   s  output from amplifier U 3 B to track the input signal with transition times matching the zero crossing of sensor signal  12 . Signals  22   s  and  23   s  output from the preprocessor circuitry therefore represent signals corresponding to sensor signals  12  and  13  of varying amplitudes which are shifted in phase relative to one another. 
     As shown in FIG. 4, the output signals  22   s  and  23   s  output from respective amplifiers U 3 A and U 3 B are fed to analog input channels A 1  and A 0  of microprocessor U 2 . The signals feed to an 8-bit successive approximation analog to digital converter  40  via a multiplexer  30  (see FIG. 1) within the microprocessor. The microprocessor U 2  is operated by a 4 MHZ ceramic resonator Y 1 . A 5 volt regulator U 1  is used to provide a well regulated voltage to the processor, as well as to the amplifiers. As one can ascertain, the 5 volts is divided into 2.5 volts to offer a center biasing point. Single push button switch  77  (SW 1 ) on the top cover of the housing  99  (see FIG. 3) is used to connect power to the regulator, and is to be depressed when a measurement is to be made. The power source is, in the preferred embodiment, a standard  9  volt alkaline battery (e.g. NEDA 1604A or equivalent) connected to battery connector J 1 . Battery reverse polarity is provided using blocking diode CR 1 . Port pin connections B 0 , B 1 , and B 2  on microprocessor U 2  are configured as digital output ports. These digital outputs are connected to and used to energize indicating light emitting diodes (LEDs) CR 4 , CR 2 , and CR 3  which are coupled to respective resistors R 14 , R 12 , and R 13 . As shown in the circuit, the current to each of the LEDs is limited by the corresponding series dropping resistors. In the embodiment shown in FIG. 4, the light emitting diodes are defined as follows: “left rotation is associated with diode CR 4 , right rotation is associated with diode CR 2  and a low signal condition is associated with diode CR 3 . 
     Software functionality  100  resident within the microprocessor U 2  is utilized to analyze the signals input from each of the channels A 0  and A 1 . The signals are analyzed for the following conditions: 
     a) to determine the number of phases powering the motor by analyzing the signal amplitude form each coil, 
     b) to define the zero crossing point of the incoming signal from each coil, 
     c) using the zero crossing point to confirm that the signal from each coil has the shape of a sine wave, 
     d) determine the time shift between the sine waves of the left and right coils, 
     e) based on the determined time shift, determine the sensor coil with the leading signal, 
     f) determine valid data points based on the determined motor phase; and 
     g) use software functionality to determine the consistency of the data prior to indicating the motor rotation. 
     FIGS. 6A-D represent a flow chart depicting the processing steps involved in the software algorithm  100  for determining the motor rotation utilizing the sensed input signals. Referring now to FIG. 6A, when power is applied to the device initialization process  101  operates to perform initial setup and configuration, including register file and bit configuration, port definitions, and threshold data values including min/max signal values, maximum number of samples, flag settings and comparison threshold data among others. Amplitude determination software routine  110  within the microprocessor then operates on the sampled data output from the A/D converter by measuring the amplitude values associated with the left side coil sensor (RY 2 ) and the right side coil sensor (RY 1 ) to determine the peak-to-peak amplitude values. The amplitude data obtained from steps  112  and  114  are then used in step  116  to determine the type of motor (i.e. single phase or three phase motor). The amplitude data is compared to a predetermined threshold value T 1  (module  1161 ) which is stored in memory. If the amplitude data does not meet the minimum threshold level, then the data is discarded (module  1165 ) and control is returned to the measurement of amplitude data in steps  112  and  114 . If the amplitude data exceeds the threshold value T 1 , the data is then compared with a second threshold value T 2  (module  1162 ). If the data exceeds the second threshold value T 2 , then the amplitude data represents a strong magnetic field (strong B field) indicative of a single phase motor type (module  1163 ). If the amplitude data exceeds the first threshold, but is less than the second threshold value, then the amplitude data indicates that the motor type is a three phase motor (module  1164 ). Upon determination of the motor type, processing proceeds by calculating the left side zero value of the signal waveform amplitude data (step  118 ) and the right side zero value (step  119 ). 
     FIG. 7 provides an exemplary illustration of determination of the left side zero crossing values  91 ,  93  right side zero crossing values  92 ,  94  and the determination of left phase ΔT 1  and right phase ΔT 2  values associated with amplitude data from each of the input signals from the corresponding left and right coil sensors respectively. Processing proceeds in step  120  and  121  where further determination of the appropriateness of the left and right signals is made by comparing it with threshold data associated with the determined motor type. This is illustrated in FIG.  6 B. If the data is not within the predetermined values associated with good or acceptable data, then the data is discarded and processing returns to step  112  for measuring additional input data. Steps  122  and  123  operate to confirm the shape of the signal supplied from each of the left and right sensor coils meet the requirements of a sine wave prior to proceeding with determination of the direction of rotation. This is determined using the left side and right side zero values calculated in steps  118  and  119 . If the sample values associated with the signal waveform correspond to a sine wave signal, then processing proceeds to step  124  (FIG. 6C) where the time difference ΔT 1  from the left side zero crossing  91  to the right side zero crossing  92  is determined. Similarly, step  125  calculates the time ΔT 2  from the right side zero crossing  92  to the left side zero crossing  93 . This information is illustrated in FIG.  7 . The time interval ΔT 1  is defined to be associated with the left phase, while the time interval ΔT 2  defines the right phase. 
     These values are stored in memory and phase determination software routine  130  accumulates the left and right phase values and determines if the sum is less than or equal to 360 degrees (module  131 ). If the accumulated left and right phase are less or equal to 360 degrees, then the phase difference is determined by subtracting the right phase value ΔT 2  from the left phase value ΔT 1  (module  132 ). Otherwise, processing returns to measuring new amplitude data from the left and right coils. As illustrated in module  133 , the software uses the number of phases detected in step  116  in order to increase detection accuracy and reduce detection time. This is illustrated by the processing steps  134  and  135  where different thresholds are utilized for comparing with the magnitude of the determined phase difference (from step  132 ) based on the determined motor phase. This is because large motors (i.e. three phase motors) are usually much more magnetically efficient and thereby produce small signals which do not saturate the amplifiers, and thus produce a smaller phase angle. In this case, a minimum of 10 degrees of phase difference must occur for detection of a valid signal (step  135 ). For small single phase motors, the magnetic field typically leaks out of the frame to produce a larger magnetic field. This signal saturates the amplifiers, thereby producing square waves. As shown in step  134 , the threshold value is used with a minimum of 4 degrees of phase shift to derive a valid signal. Approximately 50 valid readings are taken and are averaged together over a period of about 2 seconds. In the preferred embodiment, the logic works by simple majority voting. If the phase difference falls within the appropriate threshold as indicated in steps  134  and  135 , then processing proceeds to module  141  for determining the direction of motor rotation. This is determined by analyzing the phase shift difference associated with each of the corresponding left and right signal waveforms. If the phase shift difference is greater than or equal to zero, then the determination is made that the motor operates in a left direction (step  142 ). If the phase shift difference is less than zero, then the motor runs in a right direction (step  143 ). Depending on the determination, the control signal is then activated to turn on the appropriate left LED (module  144 ) or right LED (module  145 ) to indicate the direction of motor rotation. Note that as shown in step  116 , if the amplitude data is sufficiently small, then the data is discarded and a counter is incremented (module  204 ). The counter is then compared with a maximum threshold, as shown in unit  205 . If the counter is less than the maximum limit, then new data is obtained from the buffer and new left and right side coil amplitude measurements are obtained. If however, the maximum limit has been exceeded, then the software operates to generate a control signal to activate the low signal LED indicating that proper motor rotation detection could not be made. 
     As illustrated in FIGS. 5A and 5B, the inventive apparatus  10  may also be mounted to the side of a motor  20  for constant verification of rotation and direction of rotation of motor shaft  21 . This may be advantageous in critical processes such as nuclear power plants, where immediate knowledge of shaft rotation may be required. In accordance with a preferred embodiment, apparatus  10  would be mounted at an estimated mid-point of motor  20  away from heavy bases or pedestals, using bolts or other fixed connectors so as to resist vibration and properly secure the device. 
     In this manner, permanently mounting the unit onto a side of a motor enables a constant verification of the rotation and direction of the rotation. The depressable switch  77 , in this case may then be eliminated to provide a constant energizing signal, or may simply be in a constantly enabled position (rather than the disabled or non-connected position illustrated in FIG. 4) to provide constant power to the detector device. 
     As will be appreciated from the foregoing discussion, the present invention provides a practical mechanism for determining the direction of rotation of an AC induction motor without requiring physical contact with the motor or motor housing itself, and without providing electrical interconnection via wires or leads to the motor. As has also been described, the present invention provides a detector device which determines the number of electrical phases that are supplying power to the motor without disrupting the electrical connections at the input power to the motor, as well as confirming that the shape of the output signal supplied from each of the coils meets the requirements of the sine wave prior to proceeding with the determination of direction rotation. Finally, it has been shown that the apparatus determines the time shift between the sine waves supplied by the coils in order to determine which coil has the leading signal which in turn determines motor rotation. 
     It will be understood that a person skilled in the art may make many variations and modifications to the described embodiments utilizing functionally equivalent elements to those described. Any variations and modifications to those described herein above, are intended to be included within the scope of the invention as defined by the appended claims.