Patent Publication Number: US-2015071627-A1

Title: Automated Stabilizing Apparatus

Description:
BACKGROUND OF THE INVENTION 
     When shooting videos using an imaging device such as a camera phone or a light camcorder, hand and body movements tend to transmit to the camera thus producing shaky videos. There are imaging devices with features such as built-in image stabilization to improve the video quality, and these features utilize either a software image stabilization technique to smooth minor jitters in the video or an optical stabilization technique where a lens is physically shifted inside the camera to counter the movements of the camera body. In general, these techniques work well for small vibrations measured within a few degrees of movement, however, larger rotating movements of the camera associated with walking or running requires other external devices to stabilize the camera. 
     For many years, a device such as a steadycam uses a counterweight to balance the camera such that the camera and the counterweigh pivot about a swivel joint located somewhere in between. As the operator&#39;s hand rocks back and forth during operation, the camera remains leveled due to the counterweight and the resulting video image is generally steady. 
     There are a few disadvantages to this design. The camera has to be balanced with the counterweight to remain leveled and once it is in a balanced position, it cannot be pitched up or down and still remain stabilized. The device is bulky and general difficult to operate due to the inherent lack of controls in pitching or panning motion. 
     In the past few years, motorized camera stabilizer commonly called brushless gimbals have been introduced that solve many of the problems associated with the mechanical, counterweight stabilizers. Generally, brushless gimbals utilize motors to drive the camera about the pitch, roll, and yaw axis and allow the user to pitch the camera up and down smoothly by pressing a corresponding button. 
     While brushless gimbals are relatively easy to use when paired with a predefined camera, however the low torque, brushless motors require calibration when used with cameras of slightly difference in weight. Also, a unique mounting bracket is needed for cameras of different geometries such that the center of gravity of the camera has to be in line with the center axis of motor rotation at all times. This makes the brushless gimbal not conveniently adaptable to different camera types, and therefore most manufacturers simply make a unique brushless gimbal for one or two of the most popular camera models. Lastly, the configuration of the brushless motors relative to the camera prevents the operator to view the camera screen during operation. 
     SUMMARY OF THE INVENTION 
     It is the object of the present invention to provide an automatic stabilizer apparatus using a differential gear configuration that is compact, lightweight, attractive, simple to use, inexpensive to manufacture, and versatile in adapting to multiple types of imaging devices. 
     The apparatus includes: a first and second drive assembly that are positioned opposite and collinear to each other and attached to the electrical compartment, a differential gear assembly containing three miter gears housed in a configuration such that two opposing drive gears mesh with the third gear being the driven gear, and each drive gear is attached to the output shaft of the drive assembly, a camera bracket, having a thumb screw to secure an imaging device, attached to one end of the driven gear such that the driven gear and the camera bracket rotates in unison, an electronic housing having orientation sensors, main processor unit, power management and drive circuit, and a removable handle, attached to the underside of the electronic housing, having batteries to power the device. 
     When both drive gears rotate in the opposite direction, and at the same speed, the camera pitches about the axis along the centerline of the drive gears, and when the drive gears rotate in the same direction, and at the same speed, the camera rolls about the axis along the centerline of the driven gear. Varied speed and direction of the two drive motors enable the camera to rotate in any combinations of motions about the two axes. 
     In my present application I have developed and applied the benefit of the differential drive system to an automatic stabilizer apparatus to provide stabilization of the camera in the pitch and roll axis while maintaining a small footprint and allowing the operator to have full view of the camera display screen. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS: 
       These, as well as other features of the present invention, will become more apparent upon reference to the drawings wherein: 
         FIG. 1  is a perspective view of the automatic stabilization apparatus with a handle attached to the bottom surface of the body structure, illustrating the apparatus in the handheld operation; 
         FIG. 2  is an exploded view of the automatic stabilization apparatus breaking up into major assemblies; 
         FIG. 3  is a perspective and exploded view of the first and second drive assembly; 
         FIG. 4  is a perspective view of the rotary optical encoder; 
         FIG. 5  is a perspective and exploded view of the rotary magnetic encoder; 
         FIG. 6  is a perspective and exploded view of the rotary potentiometer; 
         FIG. 7  is an exploded view of the differential gear assembly; 
         FIG. 8  is an exploded view of the main support structure with electronic boards; 
         FIG. 9   c  is a perspective view of a portable battery pack; 
         FIG. 9   b  is a perspective view of a 12V vehicle power adapter; 
         FIG. 9   c  is a perspective view of a removable handle with battery cells; 
         FIG. 10   a  is a perspective view of the automated stabilizer apparatus with reference coordinate frames; 
         FIG. 10   b  is a side view of the automated stabilizer apparatus with reference coordinate frames; 
         FIG. 10   c  is a front view of the automated stabilizer apparatus with reference coordinate frames. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While the invention is described in conjunction with the accompanying drawings, the drawings are for purposes of illustrating exemplary embodiments of the invention and are not to be construed as limiting the invention to such embodiments. It is understood that the invention may take form in various components and arrangement of components beyond those provided in the drawings and associated description. Within the drawings, like reference numerals denote like elements. The term “device” is frequently used in describing an imaging object mounted to the apparatus which means a camera, video recorder, camera phone, laser, lens, and sensors. 
     The automatic stabilization apparatus is comprised of several subassemblies, which combined to provide device control while giving special consideration to the physical size, visual obtrusiveness, adaptability to different devices, and cost of manufacturability. In other words, an automatic stabilization apparatus is small, light, attractive, and inexpensive. 
       FIGS. 1 and 2  depicts the preferred embodiment of the apparatus  10  incorporating aspects of the invention in the perspective view. The apparatus  10  includes a first  20  and a second  30  drive system each having an output shaft  20   a  attaching to two sides of the differential gear assembly  40 . A device mounting bracket  4  attaches to the differential gear assembly  40  on one end while securing a device such as a camera  2  on top utilizing a thumb screw  5 . The controls electronics are housed inside the main support  50  having a top  50   a  and a bottom  50   b  shell that are rigidly held together; the main support  50  has attachment screw holes on the sides to support first  20  and second  30  drive system and a threaded screw hole on the bottom surface for mounting the apparatus to external structure or to a handle  3  in handheld applications. 
     Drive System  
       FIG. 3  illustrates the inner components of the drive systems  20  &amp;  30  having a motor  6  transmitting torque through a gear train  8  to an output shaft  7   a  of the final gear  7  of the assembly. The output shaft  7   a,  supported by at least one ball bearing  11 , extends beyond the drive housing  9  to couple to the differential gear. The gear train  8  contains a series of spur gears  12  with varied pitch diameters to produce mechanical leverage through gear reduction. A high gear reduction is achieved when the motor shaft  6   a  rotates many rotations for every rotation of the output shaft  7   a.  Gear reduction allows a motor to rotate a load that requires much larger torque than the motor can produce on its own. 
     It is worth to mention that although  FIG. 3  illustrates three spur gears arranged in series to transfer torque to the output shaft  7   a,  the present invention is not limited by the quantity or configuration of gears. A gear train of any configuration and components that achieve a gear reduction as previously described can be used in the system of the present invention. Similarly, the motor  6  in the preferred embodiment is a high speed DC motor having an output shaft  6   a  attached to a spur gear in the train  8 . In some other embodiment the motor can be a stepper motor, brushless motor, or geared motors. 
     Referring to  FIGS. 1 to 3 , both output shafts  7   a  transmit torque from the motor  6  to the differential gear assembly  40  as well as support the weight of the differential gear assembly  40  and the device; Ball bearings  11  located on both sides of the final gear  7  provide rigidity to the output shaft  7   a  while minimizes rotation friction. Coupled to one end of the final gear  7  is a rotary encoder  13  that record and transmit angular position used as feedback signal to the main processor. By coupling the rotary encoder  13  to the output shaft  7   b,  the feedback position reading is more accurate without being affected by gear backlash as compared to coupling the encoder directly to the motor shaft. 
     The enclosure  14 , is injection molded or machined, having means to mates to the drive housing  9  to add rigidity to the drive system and to prevent dirt from contaminating the spur gears. The drive housing  9  is a central structural component of the drive system because it provides rigidity for the drive train and contains location holes for gear shafts and ball bearings  11 . It is this component that allows the spur gears to rotate smoothly without rub or play during operation. In the preferred embodiment, the housing  9  is made from high strength engineer plastic through injection molding using manufacturing technics required to hold very tight tolerances. In some other embodiment, the housing  9  is fabricated from metal such as aluminum where tight tolerances can be easily achieved. 
     Referring to  FIG. 4 , where in one embodiment, the rotary encoder coupled to the output shaft  7   a  is an optical incremental encoder utilizing a light sensor  22  and a slotted wheel  21  to detect changes in movement in the output shaft  7   a.  This type of encoder is well known and frequently used in industrial applications where the encoder is commonly mounted to the shaft of the drive motor. The slotted wheel  21  is rigidly attached to the output shaft  7   a;  thus, when the output shaft  7   a  rotates, the slits near the edge of the wheel  21  move over the LED  22   a  and light sensor  22   b  creating interruptions to the light path between the LED  22   a  and the light sensor  22   b.  This interruption is transmitted as a signal to the main processor to indicate changes in rotary position. 
     In some other embodiment feedback signal, illustrated in  FIG. 5 , is provided by a magnetic encoder  25  consist of two main components. The first component is the disc  26  which is magnetized with north and south poles divided diametrically along the centerline of the circular surface. The second component is the chip based hall effect sensor  28  soldered to a circuit board  29  having mounting holes for attachment to drive housing. The magnetic disc  26  is securely housed in a tube  27  attached to the output shaft  7   a,  therefore all three components turn in unison. There is an air gap between the sensor  28  and the magnetic disc  26 ; as the disc  26  turns and hovers over the sensor  28 , change in output signal is generated due to the change in magnetic field. A controller built inside the chip  28  converts this signal into meaningful rotary positions to feed to the main processor. One example of this particular type of sensor is the AS5048 by Austria Micro Systems. 
     In yet another embodiment, illustrated in  FIG. 6 , feedback signal is provided by a rotary potentiometer  31  used to sense absolute position of the output shaft  7   a . Potentiometers are generally not as accurate as the two encoders mentioned above, but they are very inexpensive due to availability and simplicity in construction. The major components of the rotary potentiometer  31  include a wiper, resistive arc, and housing with terminals soldered to a circuit board  32  having mounting holes for attachment to drive housing. The wiper attached to the shaft adaptor  7   b  such that as the output shaft  7   a  rotates, the wiper sweeps over the resistive arc producing change in electrical resistivity at the output terminals between the wiper and resistive arc. When a constant voltage is applied across the resistive arc, change in electrical resistivity results in a corresponding change in voltage at the output terminals between the wiper and any terminal of the arc. This signal is sensed by the main processor to compute as absolute rotary position of the output shaft  7   a.    
     Differential Gear Assembly 
       FIG. 7  depicts the differential gear assembly  40  of the apparatus where the three miter gears  36  &amp;  37  are situated inside a bearing housing. The bearing housing consists of a body  34  and one leaf  35  attached to each side of the body  34 . Each leave  35  is rigidly attached to the body  34  using two fastening screws  38  and houses at least one ball bearing  33  that slides over the shaft of the drive gear  36 . The ball bearings  33  enable the differential gear assembly  40  to tilt about the center axis of the drive gears  36  with minimal friction. The body  34  contains two ball bearings  39  that slide over the shaft of the driven gear  37 . These ball bearings  39  enable the gear adaptor  41  to roll about the center axis of the driven gear  37  with minimal friction. The bearing housing aligns the gears  36  &amp;  37  at a predetermined distance that enables the drive gears  36  and a driven gear  37  to mesh with minimal rub and backlash. This is an important factor since backlash has a direct effect on ability to precisely position the device during operation; a minute backlash in the differential gear is amplified by the distance of the device to the gear. In some other embodiments, crown gears, spiral gears, or spur gears are used in place of miter gears. 
     In  FIGS. 1 &amp; 7 , the angle bracket  4  is attached to a gear adaptor  41  that is rigidly coupled to the output shaft of the differential gear drive  40 . A cam feature on the mating surfaces of the adaptor  41  and the bracket  4  enable the two members to rotate in unison with no backlash during operation. The device is mounted on top of the angle bracket using a thumb screw  5  having a mating threaded end, usually thread size ¼-20. Different angle brackets are used depending on the shape of various devices mounted on the apparatus 
     This invention does not restrict the device to be positioned on top of the apparatus. In some other embodiments, the device is positioned in front of the apparatus or below the apparatus by using different device mounting brackets. 
     Main Structure and Electronic Enclosure 
       FIG. 8  illustrates the preferred embodiment of the main structure  50  of the apparatus having a top  51  and bottom  52  shell enclosing electronic components contained within. Four threaded holes allow the drive systems to rigidly mount to both sides of the structure  50 ; a threaded screw hole, size ¼-20, located on the bottom surface of the structure  50  enables the apparatus to be attached to a moving vehicle or to a handle for handheld applications. The main structure  50  directly supports the entire weight of the apparatus and the device, therefore mechanical strength is the primary consideration in its design without sacrificing the overall footprint and weight. 
     In some other embodiment, the bottom shell  52  of the main structure  50  and the motor housings  9  ( FIG. 3 ) are fabricated as one piece. This design further strengthens the overall structure of the apparatus as well as reduces the number of components in assembly. 
     There are two circuit boards  53  &amp;  56  housed inside the main structure; sensors and control components are located on the first board  53 , and power distribution components are located on the second board  56 . An opening on each side of the structure  50  enables power and signal wires to be routed from the circuit boards  53  &amp;  56  to the motors and rotary encoders in the drive systems. 
     A microcontroller, resides on the first circuit board  53 , performs continuous system control loops including updating sensor signals to determine the current physical orientation of the apparatus, processing controls algorithm to determine a trajectory path for the motors, and finally send commands to drive the motors. Also located on the first circuit board  53  are chip based sensors capable of measuring orientation of the apparatus at a very high rate of speed such that fresh orientation data are communicated to the microcontroller upon request. Finally, sharing the same circuit board  53  are the motor driver chips that convert signals from the microcontroller into speed and direction commands to the drive motors. 
     An ON-OFF switch  57 , control button  55 , and power socket  54  located around the sides of the apparatus provide means for the operator to interface with the apparatus. A socket, terminal strip or connector may be positioned such that the socket  54  is exposed for quick and error-proof connection of the power adaptor. The socket  54  is preferably attached firmly to the second circuit board  56  by soldering to eliminate the needs for power wires from the socket  54  to the circuit board  56 . Control buttons  55 , may be multi-position slide switch, momentary contact switch, or permanent contact switch, are used to select different modes of operation preprogrammed into the microcontroller. 
     It is worth to mention that although  FIG. 8  illustrates a control button and slide switch located around the sides of the main structure, the present invention is not limited by the quantity, type, or location of the input components or the number of circuit board or the location of electrical components. A mechanical button and slide switch may be replaced by a pressure switch, capacitive switch, or thermo switch. Two circuit boards may be replaced by one where all electronic components populate on top and bottom side of the board. 
     As shown in  FIG. 9   a , in the preferred embodiment, power is provided to the apparatus through a portable rechargeable battery pack  60 , having a cable  61  connected to a power adaptor  62 . The portable battery pack  60  contains a plurality of Lithium-ion cells such that sufficient power is provided to operate the apparatus for at least  15  minutes during normal operation. Built into the housing of the battery pack is a clip  63  or strap for attachment to an article of clothing. 
     Turning to  FIG. 9   b , power can also be provided to the apparatus through a voltage adaptor  64  connected to the industry standard cigarette lighter inside a vehicle. Power generated by the vehicle allows for lengthy operation of the apparatus as long as the vehicle engine is running and the vehicle battery is sufficiently charged. 
     Referring to  FIGS. 1 &amp; 9   c , in another embodiment, battery cells  65  providing power to the apparatus are housed inside the handle  3  which attaches to the bottom face of the main structure  50 . The mating surface of the handle  3  contains two rails  3   a,  a screw hole  3   c , and spring-loaded terminals  3   b.  The rails  3   a  and the screw hole  3   c  are designed to firmly latch the handle  3  to the main structure  50  such that the terminals  3   b,  which transmit power from the battery cell  65 , make sufficient contact with electrical pads on the bottom face of the main structure  50 . 
     Main Electronic Components and their Functions 
     The microcontroller is a main processor that coordinates and controls all major activities in the system. The sequence of operation, written in program codes and resides in the memory within the microcontroller, is performed in a perpetual programming loop at a high rate of speed. 
     When magnetic encoders are used for feedback, the magnetic encoder chips communicate the current angle positions of the drive shafts to the microcontroller. These values are then converted to orientation angles of the device relative to a fixed frame by the microcontroller.  FIG. 10   a  illustrates the three frames denoted by X, Y, and Z coordinates where:
         Xd, Yd, Zd represent rotation coordinates of the device   Xs, Ys, Zs represent rotation coordinates of the sensor   Xf, Yf, Zf represent fixed coordinates used as reference       

     In applications where the device coordinates (Xd, Yd, Zd) need to be stabilized with respect to the fixed coordinates (Xf, Yf, Zf), the sensor measures its absolute orientation (Xs, Ys, Zs) relative to the fixed coordinates and feeds this data to the microcontroller. The device coordinates are usually not equal to fixed coordinates while the apparatus is in motion; this is because the sensor measures current rotation of the apparatus and the device is at the position based on previous loop command. Adjustments are always made by the microcontroller to minimize the error between the device coordinate and the fixed coordinate. 
       FIG. 10   b  illustrates an instant when the device needs to tilt (rotate about the Xd axis) to maintain leveled with respect to the fixed axis. While the sensor reads the absolute tilt angle s of the apparatus, the encoders provides the tilt angle d 1  of the device relative to the sensor. The motors have to rotate the device an angle equivalent to d 2 , which is s minus d 1 . In the differential drive configuration, the microcontroller commands the motors to rotate in the opposite directions and at the same speed to achieve tilting motion. 
       FIG. 10   c  shows an example where the device needs to roll about the Zd axis to maintain leveled. The sensor reads the angle t, which is Xs relative to Xf, and the encoder provides roll angle a 2 , which is Xd relative to Xs. Thus, the motors must rotate the device an angle equivalent to a 1  (t minus a 2 ). The microcontroller commands the motors to rotate in the same direction and at the same speed to roll about the Zd axis. Varied speed and direction of the two drive motors enable the driven gear the device to rotate in any combinations of motions about the two axes. 
     In every process loop, the microcontroller communicates with the sensors through a high speed serial bus such as serial peripheral interface (SPI) to acquire current orientation data of the sensors relative to a fixed frame. In the preferred embodiment, the sensor is a microelectralmechanical (MEMS) inertial measurement unit (IMU) having a rate gyro, accelerometer, magnetometer (or compass), and a central processing engine built into one chip. Due to recent advanced in MEMS manufacturing techniques, this type of sensor has only been available for mass distribution in recent years. Sensors such as a MPU-6000 produced by Invensense and BMX055 by Bosch Sensortec enables a single chip to accommodate a footprint of approximately 4×4 mm on the circuit board whereas three components were needed in the past. 
     Another major advantage of having three sensors built into one chip is that the misalignments between sensors axes are dramatically reduced. For example, when individual chips such as rate gyro and an accelerometer are soldered separately on a circuit board, tolerances inherent in the handling process will cause the axes to not be parallel. Therefore, every board is unique and complicated calibration procedure is required to accommodate for axes misalignment. For the single chip sensor, misalignment is at a micron scale in the MEMS manufacturing processes and is negligible in most applications. 
     Furthermore, the benefit of having a processing engine on board the chip to perform complicated algorithms is to free up the microcontroller to complete other tasks. Typically, the accelerometer and rate gyro send out raw data, or unfiltered data, to the microcontroller for processing. Signals from the accelerometer are inherently unstable due to external vibration or electrical noise; likewise the measurements from the rate gyro are not entirely useful due to accumulating drift over time, which is typical of any MEMS rate gyro. Companies such as Invensense and Bosch Sensortec have developed their own algorithms to combine the features of both sensors while discriminate noise and unwanted vibration to produce smooth and accurate output signals. With the processor engine built in the sensor chip, the time consuming algorithm calculations are performed entirely inside the sensor chip and not the microcontroller. The result is an inexpensive and reliable sensor that measures absolute orientation of the base of the apparatus relative to a fixed frame. 
     Finally, the motor drivers are the last major control components on the circuit board. In this embodiment, the drive source consists of two bidirectional DC motors. In some other embodiments, stepper motors, brushless motors, or gear motors are used such that sufficient torque is generated by the motors to move the device expeditiously. For bidirectional DC motors, the driver typically consists of an H-bridge electronic circuit built into a chip that enables a voltage be applied across a motor in either direction. Pulsing this voltage effectively permits the motor to run at different speeds in either direction. The driver communicates with the microcontroller through a plurality of digital pins such that a low voltage pulse train from the microcontroller is received by the driver which then produces higher voltage required to drive the motors. Longer pulses or duty cycle correspond to higher output torque and faster motor speed. 
     In every processing loop, the microcontroller retrieves the latest signals from the two encoders to establish the most current position of the drive shafts. The drive motors are then commanded to rotate at speeds according to how far the device is from a desired position as calculated by the microcontroller. The farther the device is from a desired position, the faster the motors must move to compensate for the difference. A proportional-Integral-Differential (PID) control system is implemented by the microcontroller to control the motor most expediently as well as produce minimal system instability.