PATTESH(A bomb disposing spider-bot)

BY: T.AAKARSH DEEP (e-mail:aakarsh5292@gmail.com;cell.no:9488459253) P.ALAGU LAXMANA (e-mail:alagulaxmana1991@gmail.com;cell.no:9500203436) M.KAILASHNATH (e-mail:kailash1591@gmail.com;cell.no:9994741465) A.LEO DIXON (e-mail:leodixon91@gmail.com;cell.no:9789476381) II-YEAR MECHANICAL ENGINEERING DEPARTMENT SRI RAMAKRISHNA ENGINEERING COLLEGE COIMBATORE-641022

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ABSTRACT: The absence of automation in the defense department of our country has led to

bloodshed of our soldiers in the past. The unavailability of intelligent war equipments crippled

our soldiers in the battle ground. Without knowing the status of the enemy they were fighting

blind, as a result those who went for rescuing hostages became hostages. Our robot PATTESH

was designed to help the military in situations like this.Pattesh is remote controlled

multipurpose octopod (eight legged robot).The motion of a Tarantula is the inspiration behind

pattesh .It has mobile base which uses Klann linkage for copying the motion of spider. It can

step over curbs, climb stairs, or travel into areas that are currently not accessible with wheels

but do not require microprocessor control or multitudes of inefficient actuator mechanisms. It

fits into the technological void between these walking devices and axle-driven wheels.

In addition Pattesh has a manipulator (three degrees of freedom) with a gripper and a

wireless camera is also mounted on it. Thus it could be used for reconnaissance; patrolling,

handling hazardous materials like bombs, clearing minefields, or secure an area without putting

anyone at risk. Besides it also has extra provisions like Leading edge spurs(as found on the legs

of a tarantula) on its leg which allows the robot to step onto obstacles taller than it's step height,

and Spines(as found on the legs of a cockroach)on its foot which allows Pattesh to walk on wire

meshes. Thus it is capable of handling rough terrains, especially those found in urban cities.

Implementing technologies like these, as soon as possible, could possibly spell the difference

between winning and losing a battle.

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TABLE OF CONTENTS:

1. INTRODUCTION……………………………………………………….4

2. BOMB DISPOSAL……………………………………………………....4

2.1 TECHNIQUES……………………………………………………………...4

3. MOBILE BASE…………………………………………………………..4

3.1 KLANN LINKAGE…………………………………………………………5

3.1.1 CONCEPT……………………………………………………….....5

3.1.2 MOTION…………………………………………………………...6

3.2 ACTUATORS………………………………………………………………6

3.2.1 DIFFERENTIAL DRIVE…………………………………………..7

4. MANIPULATOR………………………………………………………...7

4.1 ACTUATORS AND LINKS……………………………………………….7

4.2 GRIPPER…………………………………………………………………...7

5. RF TRANSMITTER AND RECEIVER……………………………….8

6. WIRELESS CAMERA………………………………………………….8

7. ADDITIONAL APPLICATIONS……………………………………....8

8. CONCLUSION…………………………………………………………..8

9. PHOTOGRAPH OF THE ROBOT………………………………….…9

10. REFERENCE………………………………………………………….…9

11. APPENDIX-I……………………………………………………………10

12. APPENDIX-II…………………………………………………………..14

13. APPENDIX-III………………………………………………………….18

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1. INTRODUCTION

The absence of automation in

the defense department of our country has

led to bloodshed of our soldiers in the past.

The unavailability of intelligent war

equipments crippled our soldiers in the

battle ground. Without knowing the status of

the enemy they were fighting blind. Our aim

is to provide the military with an intelligent

multi- purpose war recruitment that will

enhance their standard over the enemies.

PATTESH is a remote controlled

multipurpose octopod (eight legged robot).

It is capable of stepping over curbs, climb

stairs, or travel into areas that are currently

not accessible with wheels.

2. BOMB DISPOSAL

Bomb disposal is the process by

which hazardous explosive devices are

rendered safe. Bomb disposal is an all

encompassing term to describe the separate,

but interrelated functions in the following

fields:

MILITARY:

o Explosive Ordnance

Disposal (EOD)

o Improvised Explosive Device

Disposal (IEDD)

PUBLIC SAFETY:

o Public Safety Bomb

Disposal (PSBD)

o Bomb Squad

2.1. TECHNIQUES

Many techniques exist for the

making safe of a bomb or munitions.

Selection of a technique depends on several

variables. The greatest variable is the

proximity of the munitions or device to

people or critical facilities. Explosives in

remote localities are handled very

differently from those in densely-populated

areas. Contrary to the image portrayed in

modern day movies, the role of the Bomb

Disposal Operator is to accomplish their task

as remotely as possible. Actually laying

hands on a bomb is only done in an

extremely life-threatening situation, where

the hazards to people and critical structures

cannot be reduced.

Our robot Pattesh is designed to

help the army in situations like this.

3. MOBILE BASE

The mobile base of Pattesh doesn’t

have any wheels but it has legs. Pattesh has

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eight legs in total and it moves like a

tarantula spider. We have gone for legs

instead of wheels for the mobile base

because it has many advantages over

wheels, when it comes to climbing stairs.

We have used KLANN linkage to copy the

motion of a spider.

3.1. KLANN LINKAGE

The Klann linkage is a six bar

linkage named after its inventor. The links

are connected by pivot joints and convert the

rotating motion of the crank into the

movement of a foot similar to that of an

animal walking.

While providing a smooth even ride.

Initially it was called the Spider Bike but the

applications for this linkage have expanded

well beyond the initial design purpose of a

human-powered walking machine. This

linkage could be utilized almost anywhere a

wheel is employed from small wind-up toys

to large vehicles capable of transporting

people Two of these legs coupled together at

the crank can act as a wheel replacement and

provide vehicles with a greater ability to

handle obstacles and travel across uneven

terrain. 

The Klann linkage provides many

of the benefits of more advanced walking

vehicles without some of their limitations. It

can step over curbs, climb stairs, or travel

into an area that are currently not accessible

with wheels but does not require

microprocessor control or multitudes of

inefficient actuator mechanisms. It fits into

the technological void between these

walking devices and axel-driven wheels

3.1.1. CONCEPT

One hundred and eighty degrees

of the input crank results in the straight-line

portion of the path traced by the foot. The

result of two of these linkages coupled

together at the crank and one-half cycle out

of phase with each other is a device that can

replace a wheel and allow the frame of the

vehicle to travel relatively parallel to the

ground. The remaining rotation of the input

crank allows the foot to be raised to a

predetermined height before returning to the

starting position and repeating the cycle. 

These figures show a single linkage in the

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fully extended, mid-stride, retracted, and

lifted positions of the walking cycle. These

four figures show the crank (rightmost link

in the first figure on the left with the

extended pin) in the 0, 90, 180, and 270

degree positions.

The process of geometrically determining

the positions necessary to construct a single

leg is given in the appendix-I.

3.1.2. MOTION

A reasonable understanding of the

functioning of the linkage can be gained by

focusing on a specific point and following it

through several cycles. Each of the pivot

points is displayed in green. The three

positions grounded to the frame for each leg

are stationary. The upper and lower rockers

move back and forth along a fixed arc and

the crank traces out a circle.

The foot travels along a straight line for one-

half rotation of the crank and is raised for

the second half. This walking motion

provides a smooth ride on a flat surface,

steps over curbs or obstacles, climbs stairs,

and can also be used to paddle through water

with appropriately designed legs. 

3.2. ACTUATORS

Two 12V DC motors each of

torque 2 kg-m and speed 100 rpm, are used

to actuate the legs of Pattesh. The legs are

mounted on two side panels; each side panel

carries four legs(two on the inner side and

two on the outer).The two side panels are

connected together through five studs of dia

¼” and length 10” each. One of the motors

drives a pinion gear (10 teeth) which in turn

drives two larger gears (50 teeth), these two

gears are connected to two cranks on the

inner side of the side panel. Thus the power

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is transmitted likewise:

motor→pinnion→gear→crank. The two

gears act as cranks for the outside legs. We

have sacrificed the motor speed for extra

torque, as high torque motor available in the

market are larger, heavier and consume

more power. The gear reduction ratio is 5:1,

therefore the actual output torque per motor

is 10 kg-m and output speed is 20 rpm.

3.2.1. DIFFERENTIAL DRIVE

The differential drive mechanism

implemented in pattesh allows it to turn like

a tank. The term 'differential' means that

robot turning speed is determined by the

speed difference between both sets of legs,

each on either side of Pattesh. For example:

keep the motor attached to the left side panel

still and run the motor attached to the right

panel forward and the robot will turn left,

and the opposite is true.

Fig 3.2.1

4. MANIPULATOR

Pattesh has a remote controlled

manipulator with 3 DOF and can lift weights

up to 100g. This manipulator allows pattesh

to carry the defused bombs and detonate it in

safer place.

4.1. ACTUATORS AND LINKS

The robotic manipulator consists

of three servo motors (two for the links and

one for the gripper) of torques 5 kgf-cm(for

link 1), 3 kgf-cm(for link 2) and 3kgf-cm(for

the gripper).The motor torque calculations

are given in appendix II

The length of link 1 is 150 mm

and that of link 2 is 120 mm, the gripper

length is 120mm.Therefore the total range of ~ 7 ~

the arm is 330 mm(distance from the point

on link 1 (where the servo motor is attached)

to the centre of gravity of the gripper).The

free body diagram of the manipulator is

given in fig 4.1.1

4.2 GRIPPER

The gripper has two jaws, one is

fixed and the other is movable. The servo

motor is mounted on the fixed jaw and the

shaft of the servo motor is connected to the

movable jaw. The gripper provides half

encompassing grip and the frictional torque

from it is 3.2kgf-cm.The robotic gripper

torque requirement calculations are given in

the appendix III.

5. RF TRANSMITTER AND

RECEIVER

We have used two separate remote

controls for the mobile base and

manipulator. The transmitter of the mobile

base transmits radio waves of 49 MHz and

that of the manipulator transmits signals at

29 MHz. The wireless range of pattesh is

around 15m.The schematic diagram of the

transmitter and receiver is given in fig5.1.

6. WIRELESS CAMERA:

We have used a wireless camera for the

purpose of reconnaissance. A camera mobile

phone (nokia) plays the role of the wireless

camera .A software named smartcam allows

the mobile phone to transmit the continues

captured picture through Bluetooth to the

designated laptop .It has a range of 10m

approximately. This software is under

development to increase the usability of

mobile phone’s audio and video options,

wireless range of operation and transmission

clarity.

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7. ADDITIONAL APPLICATIONS

Besides bomb disposal Pattesh has

many other additional applications like

Rapid reconnaissance.

Negotiation with terrorists.

Helps to locate earth quake and other

disaster victims.

8. CONCLUSION

Thus by implementing the technology

in the field of prime importance which

carries the pride and power of the nation

through security and safety. PATTESH

values the life of our jawans who are

absolutely priceless.

9. PHOTOGRAPH OF THE ROBOT

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10. REFERENCE

i )www.mechanicalspider.com

ii )www.societyofrobots.com

iii )www.letsmakerobots.com

iv )Robotics Engineering – An Integrated Approach by Appukuttan.

APPENDIX-I

The process for geometrically determining the positions necessary to construct a single leg

includes 6 input variables. The inputs used for figures 1 and 2 are listed in table 1.

This process is described as follows: 

The length of the stride is selected as one unit and is represented by a horizontal line segment

50s (shown in Figure 1). The left endpoint 33x of this line segment represents the foot 33 when

the device is fully extended in the grounded stride position as shown in figure 2. The remaining

endpoint 33y represents the foot 33 at the end of the grounded gait position. A line 51n is drawn

perpendicular to and centered on line 50s. Point 52p is located on this line a given distance

above 50s (input 1). A circle 53c is drawn centered at 52p. The radius of the circle is greater

than one-half the stride length. This radius is input 2. Point 62p is located at the intersection of

line 51n and circle 53c. A vertical line 54s is drawn from point 33x. Another vertical line 55s is

drawn from point 33y. The intersections of these two lines and the upper half of circle 53c form

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the points 56p and 57p,

 

Point 9 is located on circle 53c to the right of 55s or to the left of 54s. Its location on the circle

is input 3. Three lines are drawn from point 9 to points 56p, 62p, and 57p which are labeled 58s,

59s, and 60s respectively. Line 61s is drawn from point 33x to point 62p. The angle 63a

between line 51n and line 61s is measured. A line 64s is drawn from point 62p so that angle 63a

is recreated between 64s and 59s. Point 37x is located at the intersection of 64s and 58s. Point

37y is located on line 60s the same distance from point 9 as the distance between point 37x and

point 9. 

Point 65p is located on the lower portion of circle 53c and its location is considered input 4.

Three lines are drawn from 65p to points 56p, 62p, and 57p which are labeled 66s, 67s, and 68s

respectively. A line 69s is drawn from point 62p so that angle 63a is recreated between 69s and

67s. Point 35x is located at the intersection of lines 66s and 69s. Point 35y is located on line 68s

the same distance from point 65p as the distance between points 35x and 65p. 

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A line 70s is drawn from point 35x to point 35y. The intersection of line 70s and 67s form point

71p. Point 72p is located on line 67s the same distance from point 65p as the distance between

points 35x and 65p. A line 73s is drawn perpendicular to line 67s midway between points 71p

and 72p. Point 74p is located at the intersection of lines 67s and 73s. Point 75p is located on

line 73s. The distance between points 75p and 74p is considered input 5. 

A line segment 76s with the length of one-quarter of the length of line 70s is drawn

perpendicular to line 73s and on the downward side of 73s at point 75p. The end of line 76s

opposite point 75p is labeled point 15 which is the location of the crank shaft. A line segment

77s the same length, as line 76s is drawn perpendicular to line 73s at point 75p on the upward

side of line 73s. The endpoint of line 77s opposite point 75p is labeled 78p. 

A line 79s is drawn parallel to line 73s that passes through point 15. Point 29y is located on line

79s on the opposite side of line 76s as line 67s which is at a distance from point 15 equal to

one-half the length of line segment 70s. Point 29x is located on line 79s on the opposite side of

point 15 as point 29y at a distance from point 15 equal to one-half the length of line segment

70s. 

Point 27x is located on line 79s. The distance between 27x and 29x is considered input 6. Point

27y is located on line 79s the same distance from point 29y as the distance between points 27x

and 29x. Point 80p is located at a point that is the same distance from point 72p as the distance

between points 35x and 27x, and the same distance from point 78p as the distance between

points 27x and 29x. A line 81s is drawn from point 27x to point 80p. A line 82s is drawn from

point 80p to point 27y. A line 83s is drawn perpendicular to line 81s midway between points

27x and 80p. A line 84s is drawn perpendicular to 82s midway between points 80p and 27y.

The intersection of lines 83s and 84s is the location of the second rocker arm axle 11.

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This is the generic description for determining points. The positions of the pivot points for the

linkage are determined by the points 33x, 35x, 37x, 27x, 29x, 9, 11, and 15. The suffix "x"

denotes the locations in the fully extended position as shown in figure 2. Points 9, 11, and 15

are pivot points located directly on the frame 3. Slight variations from the exact positions can

provide a functional linkage. Figures 1 and 2 use different input variables, which are shown in

table 1. Several points and lines coincide in the configuration shown in figure 2 that would

complicate figure 1. 

Links 5, 7, 13, 21, and 31 are the links created by connecting the appropriate points from figure

1. The links as described in the patent application are the first rocker arm 5, the second rocker

arm 7, the powering crank 13, the connecting rod 21, and the reciprocating leg 31 as labeled in

figure 2. 

 

Due to the dynamics within the relationships, there are combinations of input variables that

produce a nonfunctioning linkage where the configuration results in a locking position. 

TABLE 1

.

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Inputs and Results FIGURE 1 FIGURE 2

Distance from point 52p above line segment 50s 0.966 units 0.866 units

Radius of circle 53c 1.000 units 1.000 units

Location of point 9 on circle above horizontal 15° 30°

Location of point 65p on circle above horizontal -85° -90°

Distance from point 74p to point 75p 1.564 units 1.099 units

Distance from point 27x to point 29x 0.782 units 0.590 units

Resulting stride length 1.000 units 1.000 units

Maximum stride height 0.690 units 0.520 unitsDeviation from linear for 0° to 180° of crank (±) 0.025 units 0.028 units

APPENDIX-II

Torque (T) is defined as a turning or twisting “force” and is calculated using the following

relation:

The force (F) acts at a length (L) from a pivot point. In a vertical plane, the force acting on an

object (causing it to fall) is the acceleration due to gravity (g = 9.81m/s2) multiplied by its mass:

The force above is also considered the object's weight (W).

The torque required to hold a mass at a given distance from a pivot is therefore:

This can be found similarly by doing a torque balance about a point. Note that the length L is

the PERPENDICULAR length from the pivot to the force.

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Therefore, replacing F with m*g, we find the same equation above. This method is the more

accurate way to find torque (using a torque balance).

In order to estimate the torque required at each joint, we must choose the worst case scenario.

In the above image, a link of length L is rotated clockwise. Only the perpendicular component

of length between the pivot and the force is taken into account. We observe that this distance

decreases from L3 to L1 (L1 being zero). Since the equation for torque is length (or distance)

multiplied by the force, the greatest value will be obtained using L3, since F does not change.

You can similarly rotate the link counterclockwise and observe the same effect.

It can be safe to assume that the actuators in the arm will be subjected to the highest torque

when the arm is stretched horizontally. Although your robot may never be designed to

encounter this scenario, it should not fail under its own weight if stretched horizontally without

a load.

The weight of the object (the "load") being held (A1 in the diagram), multiplied by the distance

between its center of mass and the pivot gives the torque required at the pivot. The tool takes

into consideration that the links may have a significant weight (W1,W2..) and assumes its

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center of mass is located at roughly the center of its length. The torques caused by these

different masses must be added:

Note: do not confuse 'A' (the weight of the actuator or load) with 'a' (acceleration).

You may note that the actuator weight A2 as shown in the diagram below is not included when

calculating the torque at that point. This is because the length between its center of mass and the

pivot point is zero. Similarly, when calculating the torque required by the actuator A3, its own

mass is not considered. The torque required at the second joint must be re-calculated with new

lengths, as shown below (applied torque shown in pink):

Knowing that the link weight (W1, W2) are located in the center (middle) of the lengths, and

the distance between actuators (L1and L3 as in the diagram above) we re-write the equation as:

                   

                The tool only requires that the user enter the lengths of each link, which would be L1

and L3 above so the equation is shown accordingly. The torques at each subsequent joint can be

found similarly, by re-calculating the lengths between each weight and each new pivot point.

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Note: if any of the joints have two or more motors, they share the torque required evenly.

Because the base of the arm is subjected to the highest torque, often two actuators are used

instead of one.

More Advanced:

The above equations only deal with the case where the robot arm is being held horizontally (not

in motion). This is not necessarily the "worst case" scenario. For the arm to move from a rest

position, an acceleration is required. To solve for this added torque, it is known that the sum of

torques acting at a pivot point is equal to the moment of inertia (I) multiplied by the angular

acceleration (alpha):

To calculate the extra torque required to move (i.e. create an angular acceleration) you would

calculate the moment of inertia of the part from the end to the pivot using the equation (or an

equation similar to):

Note this equation calculates the moment of inertia about the center of mass. In the case of a

robotic arm, the moment of inertia must take into consideration that the part is being

rotated about a pivot point located a distance away from the center of mass and a second

term ( +MR2 ) needs to be added. For each joint, the moment of inertia is calculated by adding

the products of each individual mass (mi) by the square of its respective length from the pivot

(ri). Note that the equation for calculating the moment of inertia to consider for actuator N omits

the mass of the actuator at the pivot point (N-1):

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Note: The equation used to calculate the moment of inertia above (in this case multiplied by a

constant value of 1/2) is not universal but rather varies from part to part (hollow vs. solid bar,

cylindrical vs. rectangular cross-section etc.). The moment of inertia also differs depending on

which axis is considered (Ixx, Iyy, Izz can all be different). More information about moment of

inertia can be found by doing a search on the internet.

In all cases considered here, ‘r’ represents the distance from the center of mass to the pivot.

Since the moment of inertia varies tremendously from part to part, angular acceleration is not

taken into consideration with the Robot Arm Torque Calculator. Instead, to correct for possible

angular acceleration, a “safety factor” is used and set to 2 by default. As with all dynamic tools,

inefficiencies in the actuators and joints themselves must also be taken into consideration. This

way, the motor at each joint will be able to provide more than the required torque to keep the

arm stationary. The required torque to accelerate the weight being support by an actuator from a

static position can be calculated using the following relation:

APPENDIX-III

Robotic Gripper Force Requirements

Jaw Factor

The style of jaw that is used plays a major role in determining the force required in a gripper

application. There are two types or styles of jaws: Friction or Encompassing. Friction grip jaws

rely totally on the force of the gripper to hold the part, the “squeeze” of the gripper does all of

the work. Encompassing jaws add stability and power by cradling the part. Encompassing jaws

provide a major advantage, 4 to 1, in force required because the jaws must be driven open for a

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part to be dropped from an encompassing grip. Therefore, the inefficiency of the slides works to

help keep the part in place. In the case of the friction grip the jaws need not be moved

significantly for the part to fall and a rule of thumb coefficient of friction is .2 to .25.

Example:

Friction Grip: Pick up the bowling ball with your hands completely flat like paddles.

Encompassing Grip: Pick up the bowling ball with your fingers spread and “wrapped” around

the ball.

Now, imagine swinging the ball around. It will take a lot more force to keep the ball in place

when you are only using your palms. When you wrap your fingers in an encompassing grip less

“squeeze” is needed.

 While the encompassing style is preferred for strength and stability, the amount that the jaw

encompasses the part must be subtracted from the usable stroke. Therefore, as in most technical

discussions, there are trade-offs.

The rule of thumb is that a friction grip requires four times the force to handle the same part as

an encompassing grip. In the equations that are developed later in this article this translates to a

“Jaw Factor” as follows:

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Friction Grip Jaw Factor= 4

Encompassing Grip Jaw Factor=1

Part Weight

The next critical factor in determining the required gripper force is the weight of the part that

the gripper experiences both from gravity and from acceleration. Often, particularly in robot

applications, the acceleration that the robot imparts can be three or four times that which is

imparted due to gravity. Thus both “weights” must be considered when determining the gripper

force required.

(QUICK SIDE TRIP FOR NON-PHYSICISTS) Speed means nothing to a gripper. High velocity

(up to about light speed) is meaningless. ACCELERATION AND DECELERATION mean a

lot. Why? When you are traveling in your car at 80 MPH you are comfortable, you only feel

discomfort or added weight when you are getting up to speed or stopping. Thus, the faster you

start and stop the greater the force that will be experienced. Traveling at a constant velocity,

regardless of how fast, puts no force on the object moving. (SIDE TRIP OVER)

Acceleration (how fast the speed changes) means a lot to a gripper. The weight of the part must

be multiplied by the number of Gs (earth gravity 1G) to size the gripper.

1 G = 32 feet/sec² (9.75 Meters/ sec²)

Grip Force Required = Part Weight x (1+Part Gs) x Jaw Style factor

Robotic Gripper Torque Requirements

Jaw torque is the other critical factor when specifying a gripper. There are two sources of this

torque; torque generated by the gripper on itself, and torque generated by the acceleration and

weight of the part. These can be addressed separately.~ 20 ~

 Torque from the robotic gripper

Long Jaws are often required. Either the part is bulky, like an engine block, or the part must be

held at a distance to fit in a machine. In either case, the longer the jaw the greater the torque the

gripper imposes on itself. Therefore, the torque from the grippers is; GRIPPER

TORQUE=Gripper Force x Jaw Length (where jaw length is measured from the face of the

gripper to the center of gravity of the part).Gripper Example:

If we put 6” long jaws on a gripper with 100 pounds of closing force gripper (e.g. MAGNUM-

450) the jaws will see:

Jaw Torque= 100 Pounds x 6”= 600 in-pounds.

The rating on the gripper is 840 in-pounds. We used the majority of this rating without even

gripping a part because of the length of the jaws!

 Thus we can see that the length of the jaws plays a major factor in specifying a gripper. The

next task is to determine the torque the gripper will experience from the part.

 How Torque from the Part Effect the Gripper

Part torque is essentially acceleration (Gs) x part weight x jaw length. In the following case the

acceleration is not in the “up-down” direction so the G force from gravity need not be

considered for this example.

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We know that acceleration adds force. It also adds torque in addition to the force that the

gripper exerts.

However, if the acceleration of the robot is as shown below, one G must be added because

gravity will also be trying to torque the jaws.

The Torque Summed up

The total torque that the gripper will see is the addition of the Jaw Torque and the Part Torque.

In equation form it looks like:

Total Torque=

Jaw Length X Gripper Force + Jaw Length* X Part Weight X (Acceleration + 1G if Up and

Down)

* This is an approximation. The distance from the jaw face to the CG of the part should be used.

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