ROBOTIC ARM

INTRODUCTION:

The industrial robot arm consists of four rollers (as seen in the figure above), one of which revolves around the X - Y, and the remaining three wheels that make the arm revolve around the axis Z - X. This arm is operated by a stepper motor.

Stepper Motor (Bipolar): Features and performance.

Like any motor, the stepper motor is an electromechanical converter, which converts electrical energy into mechanical, but in a different way than it does an engine of C. C. (Current).




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While a conventional motor turns freely by applying a voltage within certain limits, the stepper motor is designed in such a way that turns an angle proportional to the "codification" of voltages applied to its inputs (4, 6, etc .). The ability to control at all times, this encoding allows sufficiently accurate angular displacements, depending on the pitch angle (or angular resolution) of the type of engine (can be as small as 1.80 º to 15 º).

These engines have the ability to lock into a position either entirely free. If one or more of its coils are energized, the motor is located at the corresponding position and instead be completely free if no current flows through its coils.

Operating principle of stepper motor (Bipolar).

Basically, these engines are made usually by a rotor on which are applied by different permanent magnets and a number of exciting coils wound in the stator. The coils are part of the stator and rotor is a permanent magnet. All switching (or excitation coil) should be externally managed by a controller.



Image of the rotor



Image of a stator coil 4

Then the stepper motor depending on the electromagnetic impulses it receives, this will move the robot arm at an angle of rotation.

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Understanding the parts of the conveyor belt.



The conveyor belt used in this system is of the endless and the material used to manufacture the rubber would. The conveyor belt speed be regulated to give him time industrial robot arm to grab a piece and make their respective tour with her.

At the end of the conveyor belt is an inductive sensor (or other sensor) which is responsible for detecting the metal and send the electrical signal by an electronic circuit to the industrial robot arm and that make your mission.





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STUDY OF ALTERNATIVES.


Now I will explain three alternatives on the device for determining the position of the piece.


1 st choice:

Would a photocell with the barrier system. The infrared beam cross the conveyor belt, placing the transmitter on one side of the ribbon and the receiver to another, right on the spot where you want to pick up the piece. Thus, when the piece passed between sender and receiver and interrupted the infrared beam (the beam does not reach the receiver), the cell would send a signal to the circuit so that the arm is activated and collect the piece.

I believe this proposal is right, as if the piece was displaced to one side of the tape, the photocell's also thanks to detect barrier system. Besides its maximum detection distance can be up to 200 m. Therefore, this system ensures the detection of the part where you are.


2 nd choice:

Another possibility would be to an inductive or capacitive transducer (depending on the material of the part to pick up) on one side of the conveyor belt. When the piece pass in front of the transducer, electric or magnetic field (depending on transducer) this would be disturbed and send a signal to the circuit so that the arm picked up the piece in place.

This alternative is cheaper and simpler than the previous one, but has the disadvantage that these transducers detected at a maximum distance of 4 cm., So that if the piece is slightly displaced to one side of the tape, you run the risk not be detected.


3 rd choice:


And the last alternative would put a limit on the end of the conveyor belt, and this would limit a thin sheet in which to play the piece on it, the switch by an electronic circuit would send a signal to the arm the robot and this would take the piece and took it to the other side.


I believe this alternative is worse because it will eventually wear out and the blade should be long enough to cover the entire conveyor belt.



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ISSUES.


1 ª. Question:

For positioning control industrial robot arm, use a tachometer encoder.

This device consists of a brush in contact with the motor shaft and connected to a voltmeter via cable, and a pair of permanent magnets on both sides of the shaft. By rotating the axis within the magnetic field created by magnets induces a current in the motor shaft, which is taken to the voltmeter through the brush. Another device connected to the voltmeter we could visually show the rpm at which the motor turns depending on the strain.

If you also want to know the position of the robot, just put a counter of pulses (each pulse is a revolution of the motor shaft), as its name suggests, would counting the number of twists and turns the shaft of the motor, whether the motor rotates in one direction or another (the machine tells you which way is spinning at a time). Additionally, this device can predetermine after few pulses want to stop the engine, setting position limits for the arm. Then we descodificaría an encoder pulse number and its variation, and also the maximum that we have pre-pulse in digits. And finally, through an LCD display the user would see the number of momentum and thus deduce the position of the arm.



2 ª. Question:

The difference would be performing open-loop control the output would have no effect on the control action. And by closed loop control would be a feedback of the signal, or put another way, the signal would have an effect on the input signal.