Electro-Pneumatics PDF

ELECTRO- PNEUMATICS BEE 417L ELECTRO-PNEUMATICS ELECTRO—PNEUMATIC TERM IS DEFINED FROM THE WORDS ELECTRO WHICH MEANS ELECTRICAL AND PNEUMATIC WHICH MEANS PRESSURIZED AIR. USED IN PRODUCTION, ASSEMBLY, PHARMACEUTICAL, CHEMICAL AND PACKAGING SYSTEM. COMMONLY USED IN MANY AREAS OF I...

ELECTRO- PNEUMATICS BEE 417L ELECTRO-PNEUMATICS ELECTRO—PNEUMATIC TERM IS DEFINED FROM THE WORDS ELECTRO WHICH MEANS ELECTRICAL AND PNEUMATIC WHICH MEANS PRESSURIZED AIR. USED IN PRODUCTION, ASSEMBLY, PHARMACEUTICAL, CHEMICAL AND PACKAGING SYSTEM. COMMONLY USED IN MANY AREAS OF INDUSTRIAL LOW-COST AUTOMATION. THE CONTROL OF PNEUMATIC COMPONENTS BY ELECTRICAL IMPULSES (ELECTRICAL SIGNAL) IS KNOWN AS ELECTRO-PNEUMATIC. THE ELECTRO-PNEUMATIC EQUIPMENT AND SYSTEM IS AN INTEGRATION OF ELECTRICAL AND MECHANICAL COMPONENTS WITH A COMPRESSED AIR SOURCE. ADVANTAGES GREATER RELIABILITY REDUCED INSTALLATION COMPLEXITY THE CONTROL SYSTEM CAN BE EASILY MODIFIED AND ADAPTED EASY HANDLING SECURE MOUNTING ENVIRONMENTALLY-FRIENDLY COUPLING SYSTEM IN ELECTRO PNEUMATIC CONTROLS, MAINLY THREE IMPORTANT STEPS ARE INVOLVED SIGNAL INPUT DEVICES SIGNAL GENERATION SUCH AS SWITCHES AND CONTACTOR, VARIOUS TYPES OF CONTACT AND PROXIMITY SENSORS. SIGNAL PROCESSING USE OF A COMBINATION OF CONTACTORS OF RELAY OR USING PROGRAMMABLE LOGIC CONTROLLERS. SIGNAL OUTPUTS OUT PUTS OBTAINED AFTER PROCESSING ARE USED FOR ACTIVATION OF SOLENOIDS, INDICATORS OR AUDIBLE ALARMS. SIGNAL FLOW IN ELECTROPNEUMATIC SYSTEM SIGNAL FLOW IN ELECTROPNEUMATIC SYSTEM COMPONENTS OF ELECTRO- PNEUMATIC SYSTEM THE ELECTRO PNEUMATIC SYSTEM IS NORMALLY CONSISTS OF THE FOLLOWING ITEMS: 1. DC POWER SUPPLY 2. SWITCHES 3. RELAYS 4. SOLENOID VALVES 5. SENSOR POWER SUPPLY SWITCHES SWITCHES ARE INSTALLED IN AN ELECTRIC CIRCUIT TO CONNECT OR INTERRUPT THE ELECTRIC CURRENT. CONTROL SWITCHES PUSH BUTTON SWITCHES PUSH BUTTON SWITCHES THESE SWITCHES ARE ACTIVATED MANUALLY AND USED CONNECT OR DISCONNECT THE ELECTRIC CURRENT IN HE CONTROL CIRCUIT. THERE ARE THREE TYPED OF THE PUSH BUTTON SWITCHES: NORMALLY OPEN CONTACT(MAKE) NORMALLY CLOSE CONTACT (BREAK) CHANGEOVER CONTACT (TWO WAY) NORMALLY OPEN CONTACT(MAKE) NORMALLY CLOSE CONTACT (BREAK) CHANGEOVER CONTACT (TWO WAY) PUSH BUTTONS ARE OF TWO TYPES I) MOMENTARY PUSH BUTTON II) MAINTAINED CONTACT OR DETENT PUSH BUTTON MOMENTARY PUSH BUTTONS RETURN TO THEIR UNACTUATED POSITION WHEN THEY ARE RELEASED. MAINTAINED (OR MECHANICALLY LATCHED) PUSH BUTTONS HAS A LATCHING MECHANISM TO HOLD IT IN THE SELECTED POSITION. THE CONTACT OF THE PUSH BUTTONS, DISTINGUISHED ACCORDING TO THEIR FUNCTIONS, I) NORMALLY OPEN (NO) TYPE II) NORMALLY CLOSED (NC) TYPE III) CHANGE OVER (CO) TYPE. LIMIT SWITCHES THE LIMIT SWITCH IS ACTUATED WHEN A MACHINE PART OR A WORK-PIECE IS IN A CERTAIN POSITION. NORMALLY, ACTUATION IS AFFECTED BY A CAM OR CYLINDER PISTON. DETENT SWITCHES THESE SWITCHES KEEP THE SELECTED POSITION; THE SWITCH POSITION REMAINS UNCHANGED UNTIL A NEW SWITCH POSITION IS SELECTED. IT IS CALLED DETENT SWITCH OR A LATCHING SWITCH.  LIMIT SWITCHES ANY SWITCH THAT IS ACTUATED DUE TO THE POSITION OF A FLUID POWER COMPONENT (USUALLY A PISTON ROD OR HYDRAULIC MOTOR SHAFT OR THE POSITION OF LOAD IS TERMED AS LIMIT SWITCH. THE ACTUATION OF A LIMIT SWITCH PROVIDES AN ELECTRICAL SIGNAL THAT CAUSES AN APPROPRIATE SYSTEM RESPONSE. LIMIT SWITCHES PERFORM THE SAME FUNCTION AS PUSH BUTTON SWITCHES. PUSH BUTTONS ARE MANUALLY ACTUATED WHEREAS LIMIT SWITCHES ARE MECHANICALLY ACTUATED. LIMIT SWITCHES LIMIT SWITCHES ARE NORMALLY CHANGEOVER CONTACTS AND CAN BE CONNECTED ACCORDING TO THE REQUIRED CONTROL CIRCUIT. THE LIMIT SWITCH CAN BE USED IN CIRCUIT ACCORDING TO ONE OF THE FOLLOWING: ❖ NORMALLY OPEN SWITCH ❖ NORMALLY CLOSED SWITCH ❖ CHANGEOVER SWITCH  LIMIT SWITCHES THERE ARE TWO TYPES CLASSIFICATION OF LIMIT SWITCHES DEPENDING UPON METHOD OF ACTUATIONS OF CONTACTS A) LEVER ACTUATED CONTACTS B) SPRING LOADED CONTACTS LEVER TYPE LIMIT SWITCHES PRESSURE SWITCHES A PRESSURE SWITCH IS A PNEUMATIC-ELECTRIC SIGNAL CONVERTER. PRESSURE SWITCHES ARE USED TO SENSE A CHANGE IN PRESSURE, AND OPENS OR CLOSES AN ELECTRICAL SWITCH WHEN A PREDETERMINED PRESSURE IS REACHED.  TEMPERATURE SWITCH TEMPERATURE SWITCHES AUTOMATICALLY SENSES A CHANGE IN TEMPERATURE AND OPENS OR CLOSES AN ELECTRICAL SWITCH WHEN A PREDETERMINED TEMPERATURE IS REACHED. THIS SWITCH CAN BE WIRED EITHER NORMALLY OPEN OR NORMALLY CLOSED. TEMPERATURE SWITCHES CAN BE USED TO PROTECT A FLUID POWER SYSTEM FROM SERIOUS DAMAGE WHEN A A COMPONENT SUCH AS A PUMP OR A STRAINER OR COOLER BEGINS TO MALFUNCTION. REED PROXIMITY SWITCHES REED SWITCHES ARE MAGNETICALLY ACTUATED PROXIMITY SWITCHES. REED SWITCHES ARE SIMILAR TO RELAYS, EXCEPT A PERMANENT MAGNET IS USED INSTEAD OF A WIRE COIL RELAYS A RELAY IS DEFINED AS AN ELECTROMAGNETICALLY ACTUATED SWITCH. RELAYS WHEN THE VOLTAGE IS APPLIED TO A SOLENOID COIL TERMINALS (A1, A2) IN IT WILL BECOME AN ELECTROMAGNET WHICH IN TURN ATTRACTS THE CONTACTS OF THE RELAY EITHER CLOSING OR OPENING THEM. THE SPRING RETURNS THE CONTACTS TO THE INITIAL POSITION IMMEDIATELY AFTER DISCONNECTING THE VOLTAGE AT THE COIL TERMINALS.  SOLENOIDS ELECTRICALLY ACTUATED DIRECTIONAL CONTROL VALVES FORM THE INTERFACE BETWEEN THE TWO PARTS OF AN ELECTRO-PNEUMATIC CONTROL. THE MOST IMPORTANT TASKS OF ELECTRICALLY ACTUATED DCVS INCLUDE. I) SWITCHING SUPPLY AIR ON OR OFF II) EXTENSION AND RETRACTION OF CYLINDER DRIVES ELECTRICALLY ACTUATED DIRECTIONAL CONTROL VALVES ARE SWITCHED WITH THE AID OF SOLENOIDS. THEY CAN BE DIVIDED INTO TWO GROUPS: I) SPRING RETURN VALVES ONLY REMAIN IN THE ACTUATED POSITION AS LONG AS CURRENT FLOWS THROUGH THE SOLENOID II) DOUBLE SOLENOID VALVES RETAIN THE LAST SWITCHED POSITION EVEN WHEN NO CURRENT FLOWS THROUGH THE SOLENOID. 3/2 WAY SINGLE SOLENOID VALVE, SPRING RETURN 2/2 SOLENOID OPERATED VALVE 5/2 WAY SINGLE SOLENOID VALVE, SPRING RETURN 5/2 WAY SINGLE DOUBLE SOLENOID VALVE THE SYMBOLS FOR THE VARIOUS SOLENOID/PILOT ACTUATED VALVES  RELAYS A RELAY IS AN ELECTRO MAGNETICALLY ACTUATED SWITCH. IT IS A SIMPLE ELECTRICAL DEVICE USED FOR SIGNAL PROCESSING. RELAYS ARE DESIGNED TO WITHSTAND HEAVY POWER SURGES AND HARSH ENVIRONMENT CONDITIONS. WHEN A VOLTAGE IS APPLIED TO THE SOLENOID COIL, AN ELECTROMAGNET FIELD RESULTS. THIS CAUSES THE ARMATURE TO BE ATTRACTED TO THE COIL CORE. THE ARMATURE ACTUATES THE RELAY CONTACTS, EITHER CLOSING OR OPENING THEM, DEPENDING ON THE DESIGN. A RETURN SPRING RETURNS THE ARMATURE TO ITS INITIAL POSITION WHEN THE CURRENT TO THE COIL IS INTERRUPTED. CROSS SECTIONAL VIEW OF A RELAY  TIMER OR TIME DELAY RELAYS TIMERS ARE REQUIRED IN CONTROL SYSTEMS TO EFFECT TIME DELAY BETWEEN WORK OPERATIONS. THIS IS POSSIBLE BY DELAYING THE OPERATION OF THE ASSOCIATED CONTROL ELEMENT THROUGH A TIMER. MOST OF THE TIMERS WE USE IS ELECTRONIC TIMERS. THERE ARE TWO TYPES OF TIME RELAY I) PULL IN DELAY ( ON –DELAY TIMER) II) DROP –OUT DELAY (OFF DELAY TIMER)  TIMER OR TIME DELAY RELAYS IN THE ON-DELAY TIMER, SHOWN IN FIGURE CC, WHEN PUSH BUTTON PB IS PRESSED (ON), CAPACITOR C IS CHARGED THROUGH POTENTIOMETER R1 AS DIODE D IS REVERSE –BIASED. THE TIME TAKEN TO CHARGE THE CAPACITOR, DEPENDS ON THE RESISTANCE OF THE POTENTIOMETER (R1) AND THE CAPACITANCE(C) OF THE CAPACITOR. BY ADJUSTING THE RESISTANCE OF THE POTENTIOMETER, THE REQUIRED TIME DELAY CAN BE SET. WHEN THE CAPACITOR IS CHARGED SUFFICIENTLY, COIL K IS ENERGIZED, AND ITS CONTACTS ARE OPERATED AFTER THE SET TIME DELAY. WHEN THE PUSH BUTTON IS RELEASED (OFF), THE CAPACITOR DISCHARGES QUICKLY THROUGH A SMALL RESISTANCE (R2) AS THE DIODE BY PASSES RESISTOR R1, AND THE CONTACTS OF RELAY (K) RETURN TO THEIR NORMAL POSITION WITHOUT ANY DELAY.  TIMER OR TIME DELAY RELAYS IN THE OFF-DELAY TIMER, THE CONTACTS ARE OPERATED WITHOUT ANY DELAY WHEN THE PUSH BUTTON IS PRESSED (ON). THE CONTACTS RETURN TO THE NORMAL POSITION AFTER THE SET DELAY WHEN THE PUSH BUTTON IS RELEASED (OFF ELECTRONIC SENSORS INDUCTIVE, OPTICAL AND CAPACITIVE PROXIMITY SWITCHES ARE ELECTRONIC SENSORS. THEY NORMALLY HAVE THREE ELECTRICAL CONTACTS. ONE CONTACT FOR SUPPLY VOLTAGE , OTHER FOR GROUND AND THIRD FOR OUTPUT SIGNAL. IN THESE SENSORS, NO MOVABLE CONTACT IS SWITCHED. INSTEAD, THE OUTPUT IS EITHER ELECTRICALLY CONNECTED TO SUPPLY VOLTAGE OR TO GROUND. THERE ARE TWO TYPES OF ELECTRONIC SENSORS WITH REGARD TO THE POLARITY OF OUTPUT VOLTAGE. POSITIVE SWITCHING SENSORS: IN THIS OUTPUT VOLTAGE IS ZERO IF NO PART IS DETECTED IN THE PROXIMITY. THE APPROACH OF A WORK PIECE OR MACHINE PART LEADS TO SWITCH OVER OF THE OUTPUT, APPLYING THE SUPPLY VOLTAGE. NEGATIVE SWITCHING SENSORS: IN THIS THE SUPPLY VOLTAGE ARE APPLIED TO THE OUTPUT IF NO PART IS DETECTED IN THE PROXIMITY. THE APPROACH OF A WORK PIECE OR MACHINE PART LEADS TO SWITCH OVER OF THE OUTPUT, SWITCHING THE OUTPUT VOLTAGE TO 0 VOLTS. A) INDUCTIVE SENSORS INDUCTIVE SENSOR USE CURRENTS INDUCED BY MAGNETIC FIELD TO DETECT THE NEARBY METAL OBJECTS A) INDUCTIVE SENSORS INDUCTIVE SENSOR USE CURRENTS INDUCED BY MAGNETIC FIELD TO DETECT THE NEARBY METAL OBJECTS FACTORS INFLUENCES THE SENSING DISTANCE THE SWITCHING DISTANCE OF INDUCTIVE SENSORS DEPENDS ON THE CONDUCTIVITY AND PERMEABILITY OF THE METAL PART WHOSE PRESENCE OR ABSENCE TO BE DETECTED ANOTHER FACTOR WHICH AFFECTS THE SENSING RANGE OF INDUCTIVE SENSORS IS THE DIAMETER OF SENSING COIL. A SMALL SENSOR WITH A COIL DIAMETER 0F 18MM HAS A TYPICAL RANGE OF 1MM, WHILE A LARGE SENSOR WITH CORE DIAMETER OF 75MM HAS A SENSING RANGE UP TO 50MM OR EVEN MORE FACTORS INFLUENCES THE SENSING DISTANCE THE SWITCHING DISTANCE OF INDUCTIVE SENSORS DEPENDS ON THE CONDUCTIVITY AND PERMEABILITY OF THE METAL PART WHOSE PRESENCE OR ABSENCE TO BE DETECTED ANOTHER FACTOR WHICH AFFECTS THE SENSING RANGE OF INDUCTIVE SENSORS IS THE DIAMETER OF THE SENSING COIL. A SMALL SENSOR WITH A COIL DIAMETER 0F 18MM HAS A TYPICAL RANGE OF 1MM, WHILE A LARGE SENSOR WITH CORE DIAMETER OF 75MM HAS A SENSING RANGE UP TO 50MM OR EVEN MORE B) CAPACITIVE SENSORS CAPACITIVE SENSORS ARE ABLE TO DETECT MOST MATERIALS AT DISTANCES UP TO A FEW CENTIMETRES. C) OPTICAL PROXIMITY SENSORS LIGHT SENSORS HAVE BEEN USED FOR ALMOST A CENTURY - ORIGINALLY PHOTOCELLS WERE USED FOR APPLICATIONS SUCH AS READING AUDIO TRACKS ON MOTION PICTURES. BUT MODERN OPTICAL SENSORS ARE MUCH MORE SOPHISTICATED OPTICAL SENSORS REQUIRE BOTH A LIGHT SOURCE (EMITTER) AND DETECTOR. OPPOSED MODE OPTICAL SENSOR EMITTER AND DETECTOR IN ONE UNIT  POLARIZED LIGHT IN RETROREFLECTIVE SENSORS DIFFUSE SENSORS DIFFUSE SENSORS USE LIGHT FOCUSED OVER A GIVEN RANGE, AND A SENSITIVITY ADJUSTMENT IS USED TO SELECT A DISTANCE. THESE SENSORS ARE THE EASIEST TO SET UP, BUT THEY REQUIRE WELL CONTROLLED CONDITIONS. FOR EXAMPLE IF IT IS TO PICK UP LIGHT AND DARK COLORED OBJECTS PROBLEMS WOULD RESULT. DIFFUSE SENSOR ELECTRIC COUNTERS AN ELECTRIC COUNTER CONSIST OF A COIL, ASSOCIATED CIRCUITS AND CONTACTS, A RESET COIL, MANUAL RESET, RELEASE BUTTON AND A DISPLAY WINDOW. PRESSURE THE RELEASE BUTTON OF THE COUNTER AND ENTERING THE DESIRED COUNT VALVE SET THE PRE-DETERMINING COUNTER. THE PRE-DETERMINED COUNT VALVE IS DISPLAYED IN THE WINDOW. THERE ARE TWO TYPES OF COUNTERS 1. UP COUNTER 2. DOWN COUNTER UP COUNTER AN UP COUNTER COUNTS ELECTRICAL SIGNAL UPWARDS FROM ZERO. FOR EACH ELECTRICAL COUNTING PULSE INPUT TO AN UP-COUNTER COIL, THE COUNTER VALUE IS INCREMENTED BY 1. WHEN THE PREDETERMINED VALVE HAS BEEN REACHED, THE RELAY PICKS UP AND THE CONTACT SET IS ACTUATED UP COUNTER DOWN COUNTER AN DOWN COUNTER COUNTS ELECTRICAL SIGNAL DOWNWARDS FROM PRESET VALVE. IF THE COUNT VALVES OF ZERO IS REACHED THE RELAY PICKS UP AND THE CONTACT SET IS ACTUATED. THE COUNTER CAN BE RESET MANUALLY BY PRESSING THE RESET BUTTON OR ELECTRICALLY BY APPLYING A RESET PULSE TO THE RESET COIL. THE PRE-DETERMINED VALUE IS MAINTAINED WHEN THE COUNTER IS RESET. DOWN COUNTER SAFETY OPERATION DIRECT CONTROL OF SINGLE ACTING CYLINDER INDIRECT CONTROL OF SINGLE ACTING CYLINDER INDIRECT CONTROL OF SINGLE ACTING CYLINDER