Robotic Arm having two Robotic Arm having two degrees of freedomdegrees of freedom

Its development, applications Its development, applications and advantages over a and advantages over a conventional X-Y table conventional X-Y table

The X-Y TableThe X-Y Table

A two guided A two guided system controlled system controlled by two stepper by two stepper motors forms this motors forms this assembly.assembly.

A pointer attached A pointer attached to the top of the to the top of the table can access table can access any given vertex in any given vertex in a 2-D plane.a 2-D plane.

Major Drawbacks in the X-Y Major Drawbacks in the X-Y approachapproach

If another degree of freedom is to be If another degree of freedom is to be incorporated, both X-Y tables will have to be incorporated, both X-Y tables will have to be moved/rotated together in another plane.moved/rotated together in another plane.

The cost of manufacturing such a robot for a The cost of manufacturing such a robot for a simple application of accessing 2-D coordinates simple application of accessing 2-D coordinates is quite large.is quite large.

Both stepper motors need to be of same power Both stepper motors need to be of same power as they are required to translate similar tables, as they are required to translate similar tables, thus power consumption is also large.thus power consumption is also large.

The Polar Coordinate SystemThe Polar Coordinate System To eliminate the shortcomings To eliminate the shortcomings

faced by the conventional X-Y faced by the conventional X-Y table operated robotic arm, polar table operated robotic arm, polar coordinate system is adopted, in coordinate system is adopted, in which the X and Y coordinates are which the X and Y coordinates are calculated in terms of radius r and calculated in terms of radius r and angle θ by using the formulae angle θ by using the formulae given below:given below:

X coordinate = R sin θX coordinate = R sin θY coordinate = R cos θY coordinate = R cos θ

Where,Where, RR22 = (x = (x22 + y + y22)) θ = tanθ = tan-1-1 (x/y) (x/y)

To access any cell, the arm will To access any cell, the arm will rotate by an angle θ and then rotate by an angle θ and then shall translate the pointer by “R-shall translate the pointer by “R-d” distance. d” distance.

Designing the ArmDesigning the Arm A stepper motor of large A stepper motor of large

power rating for getting power rating for getting angle θ.angle θ.

A stepper motor of much A stepper motor of much less power rating for less power rating for getting linear displacement getting linear displacement R.R.

A guide (grooved shaft) to A guide (grooved shaft) to convert rotary motion into convert rotary motion into linear. Also a table attached linear. Also a table attached to this shaft.to this shaft.

Bearings to transfer the Bearings to transfer the weight and to prevent weight and to prevent horizontal displacement of horizontal displacement of the shafts.the shafts.

A stand on which entire A stand on which entire assembly can be mounted.assembly can be mounted.

Rotary motion into linear Rotary motion into linear displacementdisplacement

A grooved shaft A grooved shaft attached to the attached to the motor from one motor from one end and to the end and to the table from the table from the other.other.

Roller guides to Roller guides to smoothen the smoothen the movement.movement.

Bearing holder in Bearing holder in which bearings which bearings are embedded are embedded and also to hold and also to hold the motor.the motor.

How bearings help…How bearings help… Two bearings are Two bearings are

embedded into embedded into the bearing the bearing holder from one holder from one end. The other end. The other end is coupled to end is coupled to the shaft/s. the shaft/s. Therefore, only Therefore, only rotary motion is rotary motion is permitted and permitted and vertical/horizontavertical/horizontal movement due l movement due to improper to improper handling can be handling can be prevented. Also prevented. Also all the weight is all the weight is transferred to the transferred to the ground and load ground and load on the motor is on the motor is far less.far less.

The Rods/ShaftsThe Rods/Shafts

Electronics UsedElectronics Used(Initial attempt)(Initial attempt)

Problems FacedProblems Faced

Four BJTs and four power Four BJTs and four power amplifiers were used to run a amplifiers were used to run a single motor.single motor.

Many resistors were required Many resistors were required for biasing these transistors for biasing these transistors which made the circuit which made the circuit cumbersome.cumbersome.

Soldering was complicated Soldering was complicated owing to a large number of owing to a large number of components and not feasible components and not feasible for controlling 2-3 motors.for controlling 2-3 motors.

The Circuitry EmployedThe Circuitry Employed

PWM for Current Control PWM for Current Control (How L297 and L298N help…)(How L297 and L298N help…)

The L297 has two PWM The L297 has two PWM choppers. In each chopper choppers. In each chopper the flip flop is set by each the flip flop is set by each pulse from the oscillator, pulse from the oscillator, enabling the output and enabling the output and allowing the load current allowing the load current to increase. As it increases to increase. As it increases the voltage across the the voltage across the sensing resistor increases, sensing resistor increases, and when this voltage and when this voltage reaches Vref the flip flop is reaches Vref the flip flop is reset, disabling the output reset, disabling the output until the next oscillator until the next oscillator pulse arrives. The output pulse arrives. The output of this circuit is therefore a of this circuit is therefore a constant rate PWM signal. constant rate PWM signal. Note that Vref determines Note that Vref determines the peak load current. the peak load current.

What the circuit looks likeWhat the circuit looks like

Circuitry set-upCircuitry set-up

The Robotic ArmThe Robotic Arm

Advantages of this Robotic ArmAdvantages of this Robotic Arm The design is simple enough to incorporate subsequent The design is simple enough to incorporate subsequent

degrees of freedom, since there is just one grooved shaft to degrees of freedom, since there is just one grooved shaft to be moved in other planes.be moved in other planes.

The cost of manufacturing is greatly reduced owing to the The cost of manufacturing is greatly reduced owing to the use of just one shaft-controlled table.use of just one shaft-controlled table.

The motors required are of different power ratings. The motors required are of different power ratings.

The arm is lighter in weight and occupies lesser floor area The arm is lighter in weight and occupies lesser floor area to accomplish a given task. to accomplish a given task.

A larger area can be swept, i.e. more cells can be visited by A larger area can be swept, i.e. more cells can be visited by the arm even if the length of the grooved shaft is same as the arm even if the length of the grooved shaft is same as that of the X-Y table. that of the X-Y table.

Areas of ApplicationsAreas of Applications It can be used to fill liquids of varying amounts in It can be used to fill liquids of varying amounts in

test-tubes that are arranged in a matrix. test-tubes that are arranged in a matrix.

It can also be used to make incisions at specified It can also be used to make incisions at specified locations, the concept vastly applicable in PCB locations, the concept vastly applicable in PCB design, making engraved patterns on metal, design, making engraved patterns on metal, soldering components on the PCB.soldering components on the PCB.

Jobs like welding, picking/putting objects to a Jobs like welding, picking/putting objects to a particular place, screwing nuts at inaccessible particular place, screwing nuts at inaccessible locations, etc can be easily accomplished using locations, etc can be easily accomplished using this robot.this robot.

ReferencesReferences Books on mechanical design of robots. Books on mechanical design of robots.

(Machining Fundamentals: From basic to (Machining Fundamentals: From basic to advanced techniques by John R. Walker)advanced techniques by John R. Walker)

Basic machines and how they work by Basic machines and how they work by Henry T. Brown.Henry T. Brown.

Datasheets of L297 and L298N from Datasheets of L297 and L298N from S.T.Microelectronics.S.T.Microelectronics.

Stepper motor concepts from study material Stepper motor concepts from study material taught in the college ( V.Deltoro) and internet.taught in the college ( V.Deltoro) and internet.