HUMANOID robotic ARM using pic microcontroller




The purpose of the HUMANOID robotic ARM project is to implement the position control and vision control on the robotic arm. The proficiency and precision of the robots in each field of work e.g. VLSI chip design and fabrication in the industry, working at high temperature in modern steel industries doing a hectic job all the time is well known.

HUMANOID robotic ARM using pic microcontroller

The “Vision Control” is implemented using the webcam as an image capturing device and the software “Matlab(acting as the brain of the project) “to apply image processing algorithms to calculate the coordinates of the obstacle. After the image is captured, gray scaled and threshold, an elliptical grid is applied over the entire image. Of all of the intersections in the grid, the algorithm chooses rectangular coordinates of one point most likely to be the center of the obstacle. The obstacle is assumed to be dark enough to produce sufficient contrast (as it is placed on white background).you may also like to read followings articles related to humanoid robot:

HUMANOID robotic ARM using pic microcontroller

Since the arm needs the coordinates be in the form of (R ), where  is the angular displacement of base disk in x-y plane. A slotted disk and sensor arrangement with each motor  required these coordinates to be in no: of integral slots between  the extreme values(say, min and max  for base disk) hence need is felt of developing calibration equation that calculates no: of slots( by mapping against the coordinates). Each of the remaining arm parts except gripper offers the variation both in R and.The above-stated methodology has been applied for all motors   

The “Position Control” or the feedback control is implemented using microcontroller “PIC16F877A” (acting as the heart of the project).It receives the no: of slots for each motor from PC (matlab 7), via serial cable and is responsible of taking the robotic arm (gripper) precisely to the obstacle.

HUMANOID robotic ARM using pic microcontroller

PIC microcontroller makes sure that each motor in the structure is held energized (and the related component of the arm continues to move) until the gripper reaches exactly where the obstacle is placed. At each instant the position of the arm is reported to the PIC via feedback through sensors.The gripper motor is then energized to allow picking of the obstacle.

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Part of HUMANOID robotic ARM

MOTORS:

Motors are the main muscles of our humanoid arm using pic microcontroller.  These motors are being used at locations in the structure where motion is required whether it is rotational or angular. Depending upon the locations, the load attached to the motors at these locations and the height from the ground level, motors of various torques, speeds, power and sizes have been chosen for the appropriate function.

Although these motors have different properties according to their usage but all are basically Direct Current Motors usually called DC Motors. The basic parts included in the construction of any DC Motor which are the same for all DC motors are:

  • Stator: It is the stationary part of the dc machine.
  • Field Magnets: These are used to produce the main magnetic flux in which the current carrying conductor is placed. These can be either permanent type or produced electrically.
  • Yoke: This is the outer shell of the motor which is used for protection and it holds the magnets.
  • Rotor: It is the rotating part of the motor. It contains the following parts:
  • Armature Coil: This is the coil in which current flows and upon the action of the magnetic field, a force acts on this coil resulting in the rotations of the rotor.
  • Shaft: This is the part of the motor on which the armature coil is placed.   
  • Commutator:It consists of commutator segments. This is the part of a dc machine which cannot be ignored. It keeps the current flow in only single direction hence a constant rotation of the rotor in single direction. The Commutator is also located on the shft near the top. This is mostly the split ring type.
  • Brushes: This is the part which slides over the commutator segments as the rotor rotates. These connect the power supply terminals with the armature coil through the commutator. These brushes are usually made of carbon and are commonly known as carbon brushes.
  • Power terminals: These are connected with the carbon brushes. These terminals are coming out of the stator where we connect the DC supply.The structure of a DC motor is shown in the following figure:
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The DC motor works on the principal of Faraday’s Law of Electromagnetic Induction , which states as:“Whenever a current carrying conductor is placed in the magnetic field, it experiences a force whose magnitude and direction depends upon the cross product of magnetic field flux vector B and current I in the armature winding.”

DC MOTORS USED:Depending upon these requirements following are the types of motors which are being used in our project the humanoid arm using microcontroller:

  • Wiper Motor ( quantity=2)
  • Johnson Motor ( quantity=3)

WIPER MOTOR:This type of motor is called a “gear head” or “gear motor” and has the advantage of having lots of torque.The standard voltage requirement for the wiper motor is 12 volts DC. The electrical system in our robot usually puts out voltage between 13 and 13.5 volts, so it’s safe to say the motor can handle up to 13.5 volts with no problem.

The minimum required current for the motor is 1.6 amps at 70 rpm, 0.9 amps at 41 rpm (and 4 amps if you elect to run it at 106 rpm. These current ratings are for the motor spinning with no load. As we add mechanical load, these numbers can increase dramatically, doubling or even tripling under a heavy load. (When testing for torque, I found the motor to draw close to 14 amps in a stalled condition.) This factor must be taken into account when selecting a power supply. Since the motor will only use what it needs when it comes to current, it’s best to provide a source with a higher current rating than you think you might need. I would recommend a 5 amp or greater supply to handle most circumstances.Most power sources are labeled as to their output current. Be aware that the milliamp (or ma) is 1/1000 of an amp, so something labeled 500 ma is only 1/2 amp, and probably will not drive the motor.

JOHNSON MOTOR:

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It is a very power DC motor. Johnson is the name of the company which is manufacturing DC motors. We have chosen this type of motor because of its cheap price. This is a gear reduced dc motor. We did not put load directly on the shaft of the motor but converted its rotary motion into linear motion by using mechanical assembly.

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