Abstract:
An ultrasonic scanner includes an assembly mounted within a housing and pivoting between two positions. The assembly includes an ultrasonic module that generates an ultrasonic beam directed at a target, such a tissue and detecting the corresponding return beam. A worm screw with a block contacting the assembly is used to selectively pivot the assembly to a desired position. The worm screw is driven by a DC motor and the position of the assembly is monitored using a proximity sensor, such as a Hall Effect Device. A hybrid controller in one mode receives analog signals from the Hall Effect Device and uses them as a feedback signal to an analog OP AMP driving the DC motor to move said assembly to a predetermined position. In another embodiment, the motor is activated for a predetermined time to move the assembly by a predetermined amount.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of application Ser. No. 12/046,681 filed Mar. 12, 2008 and incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    A. Field of Invention 
         [0003]    This invention pertains to an ultrasonic scanner incorporating a linear scanning device, and more particularly, a scanning device with a hybrid analog-digital controller incorporating a Hall effect device as a feedback or position sensor and a DC motor. 
         [0004]    B. Description of the Prior Art 
         [0005]    Many electronic instruments include an element or component that is moved or positioned very accurately in order to insure that a desired parameter is measured properly, that a mechanical or electromagnetic force is applied at a desired location or that a physical phenomenon is measured properly. For example, ultrasonic scanner devices typically include an ultrasonic transducer that directs an ultrasonic beam at biological tissues or other samples of interest and a detector that detects the ultrasonic beam reflected from various layers within the tissues or samples. The resulting signals are then analyzed and information is produced about various aspects of the tissues, or sample, such as, for example, their internal structure. Normally, information is sought for not just a single point within the tissues but with regard to a whole area or zone. In order to obtain this information, it is necessary to move the transducer and the detector by a predetermined distance. Often in such a situation, a scanning operation is performed wherein a signal is obtained when the transducer and the detector are at a predetermined location, the transducer and detector are moved by a small amount and a new signal is obtained. This process can be repeated numerous times until the whole area or zone of interest within the tissue or sample has been scanned. 
         [0006]    There are many prior art scanners that obtain information about tissue structures and other similar information by using the scanning operation described above. The scanning operation could be accomplished using either analog or digital techniques. Purely analog techniques may not be ideal for this type of operation because they may not be accurate enough, especially if the incremental movement required is very small. That is why existing devices (such as the transducers available from Capistrano Labs, Inc., San Clemente, Calif. 92672) use a digital scheme requiring stepping motors, digital resolvers and other expensive and complicated precision components. 
         [0007]    The present inventor has discovered that this problem is solved by using a hybrid analog/digital control scheme, as described below. 
       SUMMARY OF THE INVENTION 
       [0008]    Briefly, an ultrasonic scanner constructed in accordance with this invention includes an elongated assembly having one end pivotably mounted by a hinge in a housing and supporting an ultrasonic module at a second end. The ultrasonic module generates a beam of ultrasonic sound pulses in a direction parallel with the longitudinal axis of the assembly, and the echoing sounds are detected and used to generate information about a tissue or other sample or target of interest. More particularly, the echoing sounds detected by the module are used to generate a two-dimensional image of the target. In a preferred embodiment, in the subject apparatus, the ultrasonic transducer module is placed at several predetermined points that are equidistant from each other and are disposed generally along a trajectory normal to the axis of the module. At each point a two-dimensional image is obtained as described above. In this manner a plurality of two-dimensional images are collected, which can then be combined to generate a three-dimensional image. 
         [0009]    A mechanism with a hybrid controller is used to pivot the assembly. The mechanism includes a worm screw disposed in the housing. One end of the worm screw is engaged by a small DC motor so that the worm screw can be selectively turned in one direction or another around its longitudinal axis. The other end of the worm screw passes through a threaded hole in a block. The block is restrained within the housing so that it can be translated or reciprocated along the axis of the worm screw as the screw is turned in one direction or another. The axes of the assembly and the worm screw are disposed at an angle and a side surface of the block is in contact with a side surface of the assembly. As a result, as the worm screw turns and translates the block, the block causes the assembly to move in a camming action. 
         [0010]    The position of the assembly is monitored using a position sensor that may be a proximity sensor, preferably incorporating a Hall effect device and a magnet. This device generates a signal that is indicative but not normally linearly proportional to a distance between two elements of the assembly. 
         [0011]    A hybrid controller is used to operate the motor. The controller includes an analog operational amplifier and a translator that receives the signal from the position detector and translates into a corresponding signal indicative of actual distance. The controller receives a command to pivot the assembly to a certain position. This command and the output of the translator are fed to the operational amplifier which then activates the motor and pivots the assembly until the desired position is reached using the signal from the sensor for feedback. 
         [0012]    In an alternate embodiment, the feedback signal is used for large movements of the assembly, such as to some end points or center point. For incremental movement between frame scans, a pulse is used to activate a low friction, high torque electric motor/reduction-gear/worm screw combination which then pivots the assembly very accurately, 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  shows a somewhat diagrammatic view of an ultrasonic scanner constructed in accordance with this invention; 
           [0014]      FIG. 2  shows a proximity sensor used for the scanner in  FIG. 1 ; 
           [0015]      FIG. 3  shows the response of the sensor of  FIG. 2 ; 
           [0016]      FIG. 4  shows a block diagram of the hybrid control scheme used in the scanner of  FIG. 1 ; 
           [0017]      FIG. 5  shows a first isometric view of the ultrasonic scanner of  FIG. 1  with portions cut out to show the inner elements thereof; 
           [0018]      FIG. 6  shows a second isometric view of the ultrasonic scanner of  FIG. 1 ; and 
           [0019]      FIG. 7  shows an alternate embodiment of the invention, 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    In  FIG. 1 , for the sake of clarity, a very diagrammatic side view of an ultrasonic scanner constructed in accordance with this invention is presented. The scanner  10  includes a housing  12  with a rod-shaped ultrasonic assembly  14 . The assembly  14  is pivotably attached at one end  16  to the housing  12  by a hinge  18 . At the opposite end, the assembly  14  has a head  20 . The hinge  18  allows the head to move or pivot along an arc A extending between points A 1  and A 2  as it is disposed near a target such as tissue  22  or other sample of interest. The head  20  includes an ultrasonic module including an ultrasonic source (not shown) that generates short ultrasonic pulses  24  toward the tissue  22 . The module further includes a detector (not shown) that detects the echoing pulses  26  returned from the tissue  22 . The signals from the detector are then analyzed using known methods, which do not pertain to the present invention, and, accordingly, shall not be described. 
         [0021]    A biasing spring  30  is disposed between a sidewall of the housing  12  and the assembly  14 . This spring biases the assembly  14  so that its longitudinal axis X-X passes through point A 1 . The purpose of the present invention is to selectively deflect the assembly from this first position toward any intermediate point desired. The furthest that the assembly  14  can travel is the angle at which its axis X-X passes through point A 2 . For this purpose, the scanner  10  is provided with a worm screw or lead screw  32  having a longitudinal axis Y-Y. (For the purpose of clarity, in  FIG. 1 , only the axis of the worm screw is shown). The ends of the worm screw  32  are supported so that the axis Y-Y within the housing  12  remains fixed. A motor  34  engages one end of the worm screw  32 . The motor  34  is provided to rotate the worm screw  32  selectively clockwise or counterclockwise about axis Y-Y. 
         [0022]    A block  36  with a threaded hole (not shown) is mounted on the worm screw  32  and is captured by guides (not shown) that limit the block  36  to a translational or reciprocating movement, as indicated by arrow B. That is, when the worm screw  32  is turned in one way, the block  36  moves to the right along arrow B, when the worm screw is turned the other way, the block  36  moves linearly in the opposite direction. In this manner, the rotational movement of the worm screw  32  is transformed into a translational or reciprocating movement of block  36 . 
         [0023]    The block  36  has a lateral contact surface  38  facing and contacting a side surface  40  of the assembly  14 . The spring  30  pushes the assembly  14  and it&#39;s contact surface  40  against the contact surface  38 . Because the two axes X-X and Y-Y are disposed at an angle, the block  36  and the spring  30  cooperate to cause the assembly  14  to pivot in one direction or another, depending on whether the block  36  moves to the left or the right. Thus the block  36 , worm screw  32  and motor  34  together form a pivoting mechanism for pivoting the assembly  14  around hinge  18  by generating a camming force between the contact surfaces  38  and  40 . 
         [0024]    The position of the assembly  14  can be determined in many different ways. For example, the angular position of the worm screw  32  is directly related to this position and therefore it may be determined by counting the number of revolutions of the screw. However, the assembly position can be determined more accurately using an active sensor. For example, the device  10  can include a position sensor  44  which determines the position of the assembly  14  with respect to a predetermined reference point and generates an appropriate position signal, as described in more detail below. 
         [0025]    The device  10  generally operates as follows. A controller  46  receives a position command P from an external source (such as a command signal generator  90  shown in  FIG. 7  and discussed in more detail below). The controller  46  also receives a position signal AP from the position sensor  44  and it compares this signal to the position command P. The controller then sends an appropriate control signal MC to motor  34 . The motor  34  turns the worm screw  32  either clockwise or counterclockwise depending on whether the assembly  14  has to pivot towards point A 1  or A 2 . The rotation of the worm screw causes the block  36  to move in the appropriate direction thereby causing the assembly  14  to pivot. The position of the assembly  14  is detected and indicated by the position sensor  44 . When the desired position, i.e., the position requested by the position command is reached, the controller cuts off the control signal to the motor  34  and the motor  34 , block  36  and assembly  14  stop moving. 
         [0026]    The position sensor  44  can be implemented in a number of different ways. The present inventor has found that a Hall Effect Device (HED) is particularly useful for this purpose. A sensor using such a device is illustrated in  FIG. 2 . In this figure, a surface  48  of assembly  14  is provided with a magnet  50 . The magnet can be attached to the surface  48  or it can be imbedded in it. An HED  52  is disposed adjacent to the magnet  50  and is affixed to the housing  12  by a pair of brackets  54  or other similar means. The HED  52  sends an analog position signal AP to the controller  46 . As is well known in the field, the signal AP generated by the HED  52  is generally a function of the distance D between the HED  52  and magnet  50 . In fact, a typical HED  52  generates a voltage output (that is, signal AP) that is a hyperbolic function of the distance D as shown in  FIG. 3 . Other proximity sensors may also be used, instead of one using an HED. Moreover, the sensor can be used to measure the distance D directly, as shown in  FIG. 2 , or indirectly, for example by measuring the position or movement of the block  36 . 
         [0027]      FIG. 4  shows a block diagram of the controller  46 . The controller  46  includes an A/D converter  60  that receives the signal AP and converts it to a corresponding digital signal. The digital signal is then provided to a translator  62 . The purpose of the translator  62  is to provide an adjusted position signal ADP. This adjusted position signal is generated using a translation function corresponding to the curve of  FIG. 3 . In other words, the signal ADP is a digital signal that indicates the actual position of the assembly  14  based on the signal AP from the HED  52 . This signal ADP is converted to an analog position signal APS by D/A converter  63  and fed to the inverting input of an operational amplifier (OPAMP)  64 . OPAMP  64  is a standard analog amplifier that is provided with various standard biasing and filtering circuits designed to insure that the OPAMP  64  has a limited gain at low frequencies. A method of determining the function used by the translator  62  is described below. 
         [0028]    The controller  46  also includes a command interface  66  receiving a position command P. This command P is preferably received from a PC, a user interface, or any other source and is usually a digital signal and is converted into an analog command AC, and this command AC is then fed to the non-inverting input of OPAMP  64 . The OPAMP  64  compares the two signals AC and APS and generates a motor control signal MC that is either a positive pulse if this difference indicates that the motor  34  has to turn in one direction or a negative pulse if the motor has to turn in the other direction. The rotation of the motor causes the assembly  14  to pivot to the position requested by the position command P. The HED  52  tracks the position of the assembly  14 . When the requested position is reached, the difference between signals AC and APS is zero and the output of OPAMP  64  drops to zero as well. Thus, the duration TD of the pulse is equal to the time that it takes for the assembly  14  to pivot from an initial position to the requested position. 
         [0029]    The translator  62  is preferably an ASIC chip or other similarly custom made element. It can be set to perform in several different ways. The easiest, but perhaps not the most reliable way is to use the published specs that are provided by the manufacturer of the HED  42 . A more reliable way is to have the motor  34 , block  36  and assembly  14  cooperate to pivot one or more times between points A 1 , A 2  with stops at several intermediate points therebetween. At each intermediate point, the distance D and the corresponding voltage AP output by the HED are measured and recorded. A curve fitting program is then used to determine the function correlating the voltage AP to the distance D. As indicated above, this function is normally a hyperbolic curve. The function is then programmed into the translator  62 , and each time the translator  62  receives a signal AP, it is translated into corresponding signal ADP. 
         [0030]    Yet another approach is to repeat the process described above, but instead of generating a function, a look-up table  72  can be created. In this implementation, for each value AP, the translator  62  looks up the corresponding signal ADP in a look-up table  72 . 
         [0031]    Of course, strictly speaking, the distance D detected by device  52  is not the important parameter. The important parameter is the distance that head  20  moves as a result of the rotation of the worm screw  32 . However, this latter distance is proportional to distance D and therefore, the translator  62  automatically scales distance D accordingly. For example, if the device  52  is disposed at the middle of the assembly  16 , the distance D is automatically doubled. 
         [0032]    As mentioned above, the device  10  is an ultrasonic scanner, and as such can be used in several different ways. One way is to point it at a particular direction using the position command and then obtain a two-dimensional picture of the target with head  20 . However, a more common practice is to scan the tissue or other target and generate a plurality of two-dimensional images that can be converted into a corresponding 3-D image. For this purpose, commands can be generated, for example, from a PC to, move the assembly  14  so that it is pointing at A 1 . Then assembly  14  can be sequentially pivoted to many intermediate positions between A 1  and A 2  and ultrasonic signals can be collected at each. For this operation, the controller  46  can be connected to a standard PC, which then generates the positioning commands sequentially. A standard connection can be used for this purpose, such as a USB connector. For a typical 3-D ultrasonic image the head  12  is moved 5 mm in increments of 10μ. The device  10  performs this operation very fast and accurately. 
         [0033]    In  FIGS. 1 and 2 , the device  10  is illustrated somewhat diagrammatically, with many elements being omitted, and other elements being shown with disproportionate dimensions. In  FIGS. 5 and 6  the device  10  is represented more realistically. As illustrated in these figures, the block  36  is accommodated in a guide  36 A, which limits its movement to a linear motion. In other words, guide  36 A insures that the block  36  does not rotate with worm screw  32 . 
         [0034]    In addition, as is clear from these drawings, preferably, the block  36  is provided with two rollers  38 A and  36 B. Roller  38 A provides the contact with surface  40  of the assembly  16 . In this manner, frictional forces between the block  36  and assembly  16  are reduced considerably to insure that the motion of block  36  is transmitted smoothly to the assembly  16  and to reduce wear and tear on these elements. Similarly roller  36 B eliminates or reduces friction between the block  36  and its guide  36 A. 
         [0035]    Basically, in a typical scanning procedure, the apparatus operates in one of two modes. In a first mode, the head  20  is situated either in a center position, or at one of the end points A 1 , A 2  and must be pivoted to another specific position. In a second mode, the head  20  starts from a specific position, typically point A 1  and is pivoted in minute increments through many intermediate positions towards a second specific position, typically A 2 . At each intermediate position, a scan is performed and data is collected as described above. 
         [0036]    In the first embodiment of the invention, the assembly  14  is moved or pivoted in either mode by using the controller  40  shown in  FIG. 4 . In another embodiment of the invention shown in  FIG. 7 , controller  40 A is modified so it operates in one of two modes. In this embodiment, a command signal generator  90  is used to generate commands for the controller. The command signal generator may be a PC or part of a device that controls the whole scanning operation. 
         [0037]    As seen in  FIG. 7 , the generator  90  generates one of two signals: P or SE. Signal P, as described above, designated the desired position of the assembly  14 . When this signal is received, the modified controller  40 A operates as described above, in conjunction with  FIG. 4 . Signal SE is preferably in the shape of a pulse having an amplitude that saturates the amplifier  64  and a duration T. This duration T is selected to activate the motor  34  for a period sufficient to move the assembly  14  by a predetermined incremental distance d. The head  20  on assembly  14  is activated to perform a scan. When the scan is completed, the command signal generator  90  generates a new signal SE. In other words, a signal SE is generated for every scanning frame. 
         [0038]    Amplifier  64  includes a standard biasing circuitry (not shown in detail) that controls its gain, its slew rate and other characteristics. For the present invention, the amplifier is overdamped and its other characteristics are selected so that its slew rate in response to the signal SE is very high. As a result, the output of the amplifier follows the signal SE very closely, allowing the signals to have a very short duration T in the order of microseconds. 
         [0039]    Because the motor  34  is enclosed in housing  12 , it is necessary to keep its size as small as possible. However, inherently, a small motor could not generate sufficient torque to turn worm screw  32  without a gear box. Therefore, in the present invention, the motor  34  includes a standard gear box, provided integrally within the motor housing and that couples the motor shaft (not shown) to the worm screw  32 . Preferably, the motor  34  with its gear box is capable of generating a high torque with low friction. For example, the motor  34  at nominal voltage can be operating at around 12,800 rpm and have a 6:1 reduction gear box. Worm screw  32  can have a pitch of  40  threads/in. In this combination, the motor  34  can rotate the worm screw  32  very effectively. 
         [0040]    The described motor/gear-box/worm screw combination has a further advantage. It is well known that once a body is set in motion, its inertia prevents it from coming to rest instantaneously and, instead it requires a finite time and distance to come to rest. Moreover, because of friction and other non-linear effects, the exact time and rest position are indeterminate. Therefore in many systems requiring highly accurate and reproducible results, special and expensive measures must be taken for inertial effects. However, the inventor has found that the structure described above has very little inertial effects. As a result, the assembly  14  can be pivoted very accurately in small increments (e.g., in the range of 5 μm) without any additional elements or even the need for a feedback loop. Therefore the apparatus described herein can be implemented easily using inexpensive parts. 
         [0041]    The controller  40 A in  FIG. 7  operates in the second mode as follows. The amplifier  64  receives signal SE having a duration or pulse width T, It immediately saturates and generates an essentially identical output motor control signal MC. This motor control signal MC turns on the motor  34  causing the worm screw  32  to rotate and move the assembly  14 . At the end of period T, the output of amplifier  64  drops to zero, and motor  34  and worm screw  32 . The period T is determined from the electrical characteristics of the motor  34 , its physical characteristics, and the dimensions of the worm screw  32  and the assembly  14 . As discussed above, T is selected to move the assembly  14  in predetermined increments of, e.g., 5 μm. In this mode of operation, the feed back signal APS never catches up to the signal SE and in essence, it is ignored. 
         [0042]    As discussed above, in the modified controller  40 , the operational amplifier  64  is used to generate the motor control signal MC in both modes of operation. Alternatively, a separate amplifier may be used for each mode. 
         [0043]    Numerous modifications may be made to this invention without departing from its scope as defined in the appended claims.