Indian Institute of TechnologyHyderabad

THE BENCH SAW BRAKE SYSTEM

ATUL S VIVEK ME12B1004

JOPHIN GEORGE JOSEPH CH12B1010

INTRODUCTION

By this project ,we intend to make a system which automatically switches of a working bench saw if a person ‘ s limbs comes into contact the blades of the saw .

This is accomplished by using an electronic touch sensor which is activated when a person touches the saw blades & this touch sensor in turn activates an electric circuit which switches off the saw and triggers a stopping mechanism which is used to bring the saw blades rotating at speed of 1000 RPM [on an average] ,to rest instantaneously.

The touch sensor works by detecting the small potential associated with the human body and thereby creating a potential difference which activates a relay controlled stopping mechanism

NEED FOR AN AUTOMATIC SAW STOP SYSTEM

Bench saws are devices which are crucial for furniture and construction industries , for they make wood working a much less tedious task

But along with this ease comes an inherent danger of accidental amputation of limbs of personnel involved in this business.

Globally a saw accident happens every 9 minutes The automatic saw stop system provide a simple but effective

solution to this problem WWSSD

CHALLENGES IN THE PROJECT

There are number of challenges which arises with this project , some of them are listed below : SA

The project’s prime concern is to reduce the risk of injuring one’s hand while cutting wood using a bench saw .So the touch sensor must be designed in such a way that it is not triggered when wood comes into contact with the saw

The second major thing to be taken into consideration is the response time of the system & The stopping mechanism . Ideally the stopping mechanism should have a reaction time of not more than .05 seconds or else it won’t effective and the risk of injury is not eliminated

WORKING OF TOUCH SENSOR

The touch sensor is a circuit which amplifies the small potential associated our body .

It employs two IC 741 amplifier circuits to amplify this voltage .

IC 741

IC 741

+5V

GND

-5V

2I/P From blade

3

7

4

6 2

3

7

4

6

88 O/P to relay circuits

SCHEMATIC DIAGRAM

SAW BLADE

CONDUCTING WIRE

ELECTRONIC CIRCUIT WHICH

MONITORS SIGNAL FROM

THE BLADE

MOTOR

POWER

ON DETECTING TOUCH , A

POTENTIAL IS DEVOLOPED

RELAY CIRUITS CONTROLLING SUPPLY TO THE

MOTOR

SWITCHES OFF THE MOTOR

STOPPING MECHANISM TO

BRING THE BLADE TO REST

TOUCH

STOPPING MECHANISM

Stopping mechanism is used to bring the saw blade rotating at a very high speed suddenly to a halt ,thereby reducing damage to limbs

Here , we are designing a stopping mechanism which works with the help of an electromagnet

When the touch sensor is activated , it triggers the stopping mechanism using a relay circuit

The stopping mechanism has a metal strip attached to a permanent magnet kept close to an electromagnet ,the whole system is kept close to the saw blade.

When the electromagnet is powered using an AC supply , the metal strips oscillates with a very frequency of the AC .During this oscillation ,It continuously hits the blade and stops the blade within a short period ,without causing much damage to the blade as well as the person touching it

PROs OF THE SYSTEM

T he system is activated only the touch of human limbs or such bodies with a small associated potential .

Even though it may cause slight Damage the saw blade , It does not do much damage to the saw as a whole.

It can be reused without replacing many parts , In the extreme case the saw blade or the metal strip used for stopping may have to be replaced

Most importantly it keeps the limbs of the saw operator intact.

CONs OF THE SYSTEM

The saw brake cannot be use with wet or newly cut wood or metals

Even though it reduces the chance of damage to the body , one cannot escape without a slight cut .