Overview: • Create a sequential function chart for the Rail Welding Station Control and implement it in ladder logic on paper. Background: Rail Welding Station Control. Using the function chart approach, implement the program for the following station that welds railroad rails together. Process Narrative: Figure P6.1 shows the general layout of a station that welds 40-foot lengths of railroad rail into a 1/4-mile length of rail (called a string). In summary, individual rails are fed into a track, a ram pushes the rail into the welder, the robot welder welds the rail onto the current “string” of welded rail, and then the entire string is moved 40 feet to be in position to weld on the next piece. The operation is described in the following format; (hint…basic name for step, INPUTS_TRANSITION, OUTPUT__ACTION). 1. When initially started, assume there is a rail located in the String Wheel, check conditions are met so that piece is in position 1 in Figure P6. 1. Before continuing with the operation, two conditions must be verified: (1) There must be a rail piece in the feeder (sensed by PROX374); and (2) the WELD_ENABLE internal coil must be on. Both of these conditions must be met before the next step. 2. Then the rail piece can be pushed onto the welding track. To bring in the next 40-foot rail piece, the feed hydraulic ram control, FRAM_EXT s turned on to push a rail piece onto the welding track (sensed by PROX375). 3. Then the WRAM_EXT cylinder control is energized to extend the welding hydraulic ram to push the 40-foot rail piece into the welding position (sensed by PE377 off). 4. The welding ram cylinder controls are then turned off so the new rail piece is held in the welding position (butting against the end of the existing “string” of welded rail). The welding robot is then activated (with ROBOT_START) to actually produce the weld. The welding robot turns on the ROBOT_FINI input to the PLC to signal that the welding operation is complete. 5. The string of welded rail is then pulled forward by activating the STRING_FWD output. When the proximity sensor PE377 turns on, the string is in position to weld on the next 40-foot piece. 6. The WRAM_RET cylinder control is energized to move the welding hydraulic ram back into position, ready to push the next piece into the welder. The LS376 limit switch turns on when the ram is retracted. The operation then repeats (starting with verifying the two conditions). Details: The WELD_ENABLE internal coil signals that the current welded rail string is less than 1320 feet (1/4 mile) and thus the next 40-footpiece in the feeder can he welded onto the current string. When the string is 1320 feet long, the WELD_ENABLE internal coil is turned off and a new string is started by moving one rail into position 1. Your part of the ladder does not move this first rail piece into position. Another part of the PLC program does this part of the operation. The feeder area has two proximity sensors, PR0X374 and PR0X375. When PROX 374 is on, a 40-foot rail piece is present in the feeder. You are not concerned with the mechanism that places the piece into the feeder area. You just need to sense that the rail is present before activating the FRAM_EXT control to push the 40-foot rail piece into the weld track. PR0X375 is on when the rail has been pushed by the feed ram onto the welding rail. The weld position is sensed by the photoelectric eye, PE377. When the active end (end to be welded) of the welded string is moved into the proper position, PE377 transitions on. When the 40-foot piece is moved in to contact the active end, PE377 turns off. The feed ram is a single-action hydraulic cylinder, controlled by FRAM_EXT. Once the FRAM_EXT output is energized (on), the ram extends and pushes the 40-foot rail piece onto the welding track. When FRAM_EXT is off, the ram retracts. The ram retracts very quickly and so you may assume that when FRAM_EXT is turned off after the rail piece is placed onto the weld track, the ram has retracted sufficiently far so that it does not interfere with the weld ram. In normal operation, you do not need to detect that it has retracted (if the ram does not retract within a certain time period an alarm is activated, which is not part of the problem). However, during reset, you do need to detect when the feed ram is retracted. LS373 is on when the feed ram is retracted. The welding ram is a double-action hydraulic cylinder with two controls. While the WRAM_EXT control is energized the ram extends (moves out) as long as power is applied (WRAM_EXT is on). While the WRAM_RET control is energized, the ram retracts (moves in) as long as power is applied (WRAM_RET is on). The ram stops at its current position when either control is turned off. The ram will not move if both WRAM_EXT and WRAM_RET are energized simultaneously. There are mechanical stops to prevent extension or retraction beyond certain limits. The LS376 limit switch is on when the welding ram is fully retracted. The welding robot is a piece of equipment separate from the PLC. It is programmed separately to move a welding head along a programmed path and thus weld the two rail pieces together. The PLC only commands the welding robot to start its operation (with ROBOT_START) and receives an indication (ROBOT_FINI) that the welding operation is complete The ROBOT_START output must remain on during the robot’s operation (unless paused). If ROBOT_START is turned off the robot pauses its preprogrammed operation. The ROBOT_FINI input to the PLC is turned on when the welding robot has finished its operation. The STRING_FWD output commands a mechanism that moves the welded string (up to 1320’ long) to place the active end in a position where the next piece can be welded. You are not concerned about the details of the mechanism. It basically activates a roller conveyor to move the string. The STRING_FWD output must be on to move the welded rail string. When the start switch is pressed (turned on) for the first time only, the station assumes there is one 40-foot rail in position 1. When the stop switch is pressed (turned off) the operation should pause and all outputs (except STRING_FWD) must be turned off. Pressing the start switch while the operation of the station is paused causes the station to resume its suspended step. The STRING_FWD output must remain on if the station is paused in the step where the rail string is moved in order to accurately place the active end. With one exception, do not advance to the next step when paused. If the operation is paused when STRING_FWD is on, the welded rail string must continue to be moved into position and then advance to the next step when the string is in position. Make sure a separate reset switch, RESET_PB, is provided which resets any internal states so that when the start switch is pressed, no rails are assumed present in the station. Obviously, the operator must clear everything out of the welding area before resuming operation after a reset operation. Also, the reset operation should cause the welding and feed rams to retract and the reset operation is not complete until both rams are retracted. Make no assumption about which ram requires the longest time to retract. The reset switch should be ignored if the station is running or when the string is moving forward. The start switch should be ignored when the reset operation is in progress. If the station is paused and RESET_PB on, the operator must release the RESET_PB before the start pushbutton switch can be used to restart the station. Do not add any more timed steps to those explicitly stated in the problem. In other words, do not put a timer in a step unless it is stated that the step duration is a specific time. Assume the following physical inputs and outputs. DO NOT assign any more inputs!! Variable I/O Description START_PB In Start push button, N. O., on when starting. (input) STOP_PB In Stop push button, N. C., off when stopping. (input) RESET_PB In Reset push button, N. O., on when restoring station to initial state. (input) LS373 In Limit switch that closes (on) when feeder ram is retracted. (input) PROX374 In Proximity sensor, on (closed) when 40-foot rail piece in feeder area; off as rail is pushed onto weld rail or when no rail piece is present. (input) PROX375 In Proximity sensor, on (closed) when 40-foot rail piece on weld track, ready to be pushed into welder; off as rail is pushed into welder or when no rail piece is present. (input) LS376 In Limit switch that closes (on) when weld ram is retracted. (input) PE377 In Photo-electric eye that senses active end of welded rail. See above for description. (input) ROBOT-FINI In Indication from welding robot that is on when operation is complete. (input) WELD_ENABLE In Signals that the next 40-foot piece of rail can be welded onto current string. On when next 40-foot piece of rail can be welded onto current string. (input) FRAM_EXT Out Feed ram extend control, on to extend ram, off causes ram to retract. (output) WRAM_EXT Out Weld ram extend control, on to extend ram. (output) WRAM_RET Out Weld ram retract control, on to retract ram. (output) ROBOT_START Out Command to welding robot to start operation. Welding robot senses an off-to-on transition to start. It may remain on while welding is occurring. (output) STRING_FWD Out Welded string movement control, on to move welded string forward and down roller conveyor. (output) STEP1_LMP To STEP_N_LMP Out Lights up correspond lamp outputs per Lamp Box drawing. Create Internal Boolean bits: RUN, STEP#s, and RESET_INT. Please remember that STEP1 is a BOOL and STEP1_LMP is a hardwired output. They are NOT the same! It is your responsibility to fully design, document, debug, and test your program. Ensure that you have made effective use of both instruction and rung comments to clearly document your program. All I/O components referenced within your program should be clearly labeled, and rung comments should be employed to add additional clarity as required. Procedure: 1. Create a sequential function chart for the Rail Welding Station Control. 2. Implement your sequential function chart in ladder logic. Use the prescribed program naming convention. The last section of your program should use RUN to turn on RUN_LMP, STEP1 to turn on STEP1_LMP, etc. 3. Save your ladder logic program. STEP01 STEP02 STEP03 STEP04 STEP05 STEP06 STEP07 Rail Welding Station Control Operation: 1. Start with inputs @: LS373 ON PROX374 OFF PROX375 OFF LS376 ON PE377 ON ROBOT_FINI OFF WELD_ENABLE OFF 2. Press START_PB Program should transition to STEP1 3. Turn PROX374 (rail in feed area) and WELD_ENABLE ON Program should transition to STEP2 with FRAM_EXT ON 4. Turn LS373 OFF (to indicate that feed ram is no longer fully retracted), turn PROX374 OFF (to show that rail is pushed out of feed area), turn PROX375 ON (to show that rail piece is on weld track) Program should transition to STEP3 with WRAM_EXT ON 5. Turn LS373 ON (to show that the feed ram has automatically retracted), turn LS376 OFF (to show that the weld ram is no longer fully retracted), turn PROX375 OFF (to show that the weld ram has pushed the rail past this sensor), turn PE377 OFF (to show that the rail is in position to be welded) Program should transition to STEP4 with ROBOT_START ON 6. Turn ROBOT_FINI ON Program should transition to STEP5 with STRING_FWD ON Turn ROBOT_FINI OFF 7. Turn PE377 ON (to show that welded rail string has been pulled into position for next weld) Program should transition to STEP6 with WRAM_RET ON 8. Turn LS376 ON (to show that weld ram has fully retracted) Program should transition to STEP1 Pause – Program should pause during any step except STEP5 (with STRING_FWD ON) Reset – Program should not reset unless RUN is OFF Reset should turn WRAM_RET ON if LS376 is OFF. WRAM_RET should remain ON until LS376 is turned ON.
Overview: • Create a sequential function chart for the Rail Welding Station Control and implement it in ladder logic on paper. Background: Rail Welding Station Control. Using the function chart approach, implement the program for the following station that welds railroad rails together. Process Narrative: Figure P6.1 shows the general layout of a station that welds 40-foot lengths of railroad rail into a 1/4-mile length of rail (called a string). In summary, individual rails are fed into a track, a ram pushes the rail into the welder, the robot welder welds the rail onto the current “string” of welded rail, and then the entire string is moved 40 feet to be in position to weld on the next piece. The operation is described in the following format; (hint…basic name for step, INPUTS_TRANSITION, OUTPUT__ACTION). 1. When initially started, assume there is a rail located in the String Wheel, check conditions are met so that piece is in position 1 in Figure P6. 1. Before continuing with the operation, two conditions must be verified: (1) There must be a rail piece in the feeder (sensed by PROX374); and (2) the WELD_ENABLE internal coil must be on. Both of these conditions must be met before the next step. 2. Then the rail piece can be pushed onto the welding track. To bring in the next 40-foot rail piece, the feed hydraulic ram control, FRAM_EXT s turned on to push a rail piece onto the welding track (sensed by PROX375). 3. Then the WRAM_EXT cylinder control is energized to extend the welding hydraulic ram to push the 40-foot rail piece into the welding position (sensed by PE377 off). 4. The welding ram cylinder controls are then turned off so the new rail piece is held in the welding position (butting against the end of the existing “string” of welded rail). The welding robot is then activated (with ROBOT_START) to actually produce the weld. The welding robot turns on the ROBOT_FINI input to the PLC to signal that the welding operation is complete. 5. The string of welded rail is then pulled forward by activating the STRING_FWD output. When the proximity sensor PE377 turns on, the string is in position to weld on the next 40-foot piece. 6. The WRAM_RET cylinder control is energized to move the welding hydraulic ram back into position, ready to push the next piece into the welder. The LS376 limit switch turns on when the ram is retracted. The operation then repeats (starting with verifying the two conditions). Details: The WELD_ENABLE internal coil signals that the current welded rail string is less than 1320 feet (1/4 mile) and thus the next 40-footpiece in the feeder can he welded onto the current string. When the string is 1320 feet long, the WELD_ENABLE internal coil is turned off and a new string is started by moving one rail into position 1. Your part of the ladder does not move this first rail piece into position. Another part of the PLC program does this part of the operation. The feeder area has two proximity sensors, PR0X374 and PR0X375. When PROX 374 is on, a 40-foot rail piece is present in the feeder. You are not concerned with the mechanism that places the piece into the feeder area. You just need to sense that the rail is present before activating the FRAM_EXT control to push the 40-foot rail piece into the weld track. PR0X375 is on when the rail has been pushed by the feed ram onto the welding rail. The weld position is sensed by the photoelectric eye, PE377. When the active end (end to be welded) of the welded string is moved into the proper position, PE377 transitions on. When the 40-foot piece is moved in to contact the active end, PE377 turns off. The feed ram is a single-action hydraulic cylinder, controlled by FRAM_EXT. Once the FRAM_EXT output is energized (on), the ram extends and pushes the 40-foot rail piece onto the welding track. When FRAM_EXT is off, the ram retracts. The ram retracts very quickly and so you may assume that when FRAM_EXT is turned off after the rail piece is placed onto the weld track, the ram has retracted sufficiently far so that it does not interfere with the weld ram. In normal operation, you do not need to detect that it has retracted (if the ram does not retract within a certain time period an alarm is activated, which is not part of the problem). However, during reset, you do need to detect when the feed ram is retracted. LS373 is on when the feed ram is retracted. The welding ram is a double-action hydraulic cylinder with two controls. While the WRAM_EXT control is energized the ram extends (moves out) as long as power is applied (WRAM_EXT is on). While the WRAM_RET control is energized, the ram retracts (moves in) as long as power is applied (WRAM_RET is on). The ram stops at its current position when either control is turned off. The ram will not move if both WRAM_EXT and WRAM_RET are energized simultaneously. There are mechanical stops to prevent extension or retraction beyond certain limits. The LS376 limit switch is on when the welding ram is fully retracted. The welding robot is a piece of equipment separate from the PLC. It is programmed separately to move a welding head along a programmed path and thus weld the two rail pieces together. The PLC only commands the welding robot to start its operation (with ROBOT_START) and receives an indication (ROBOT_FINI) that the welding operation is complete The ROBOT_START output must remain on during the robot’s operation (unless paused). If ROBOT_START is turned off the robot pauses its preprogrammed operation. The ROBOT_FINI input to the PLC is turned on when the welding robot has finished its operation. The STRING_FWD output commands a mechanism that moves the welded string (up to 1320’ long) to place the active end in a position where the next piece can be welded. You are not concerned about the details of the mechanism. It basically activates a roller conveyor to move the string. The STRING_FWD output must be on to move the welded rail string. When the start switch is pressed (turned on) for the first time only, the station assumes there is one 40-foot rail in position 1. When the stop switch is pressed (turned off) the operation should pause and all outputs (except STRING_FWD) must be turned off. Pressing the start switch while the operation of the station is paused causes the station to resume its suspended step. The STRING_FWD output must remain on if the station is paused in the step where the rail string is moved in order to accurately place the active end. With one exception, do not advance to the next step when paused. If the operation is paused when STRING_FWD is on, the welded rail string must continue to be moved into position and then advance to the next step when the string is in position. Make sure a separate reset switch, RESET_PB, is provided which resets any internal states so that when the start switch is pressed, no rails are assumed present in the station. Obviously, the operator must clear everything out of the welding area before resuming operation after a reset operation. Also, the reset operation should cause the welding and feed rams to retract and the reset operation is not complete until both rams are retracted. Make no assumption about which ram requires the longest time to retract. The reset switch should be ignored if the station is running or when the string is moving forward. The start switch should be ignored when the reset operation is in progress. If the station is paused and RESET_PB on, the operator must release the RESET_PB before the start pushbutton switch can be used to restart the station. Do not add any more timed steps to those explicitly stated in the problem. In other words, do not put a timer in a step unless it is stated that the step duration is a specific time. Assume the following physical inputs and outputs. DO NOT assign any more inputs!! Variable I/O Description START_PB In Start push button, N. O., on when starting. (input) STOP_PB In Stop push button, N. C., off when stopping. (input) RESET_PB In Reset push button, N. O., on when restoring station to initial state. (input) LS373 In Limit switch that closes (on) when feeder ram is retracted.
(input) PROX374 In Proximity sensor, on (closed) when 40-foot rail piece in feeder area; off as rail is pushed onto weld rail or when no rail piece is present. (input) PROX375 In Proximity sensor, on (closed) when 40-foot rail piece on weld track, ready to be pushed into welder; off as rail is pushed into welder or when no rail piece is present. (input) LS376 In Limit switch that closes (on) when weld ram is retracted. (input) PE377 In Photo-electric eye that senses active end of welded rail. See above for description. (input) ROBOT-FINI In Indication from welding robot that is on when operation is complete. (input) WELD_ENABLE In Signals that the next 40-foot piece of rail can be welded onto current string. On when next 40-foot piece of rail can be welded onto current string. (input) FRAM_EXT Out Feed ram extend control, on to extend ram, off causes ram to retract. (output) WRAM_EXT Out Weld ram extend control, on to extend ram. (output) WRAM_RET Out Weld ram retract control, on to retract ram. (output) ROBOT_START Out Command to welding robot to start operation. Welding robot senses an off-to-on transition to start. It may remain on while welding is occurring. (output) STRING_FWD Out Welded string movement control, on to move welded string forward and down roller conveyor. (output) STEP1_LMP To STEP_N_LMP Out Lights up correspond lamp outputs per Lamp Box drawing. Create Internal Boolean bits: RUN, STEP#s, and RESET_INT. Please remember that STEP1 is a BOOL and STEP1_LMP is a hardwired output. They are NOT the same! It is your responsibility to fully design, document, debug, and test your program. Ensure that you have made effective use of both instruction and rung comments to clearly document your program. All I/O components referenced within your program should be clearly labeled, and rung comments should be employed to add additional clarity as required. Procedure: 1. Create a sequential function chart for the Rail Welding Station Control. 2. Implement your sequential function chart in ladder logic. Use the prescribed program naming convention. The last section of your program should use RUN to turn on RUN_LMP, STEP1 to turn on STEP1_LMP, etc. 3. Save your ladder logic program. STEP01 STEP02 STEP03 STEP04 STEP05 STEP06 STEP07 Rail Welding Station Control Operation: 1. Start with inputs @: LS373 ON PROX374 OFF PROX375 OFF LS376 ON PE377 ON ROBOT_FINI OFF WELD_ENABLE OFF 2. Press START_PB Program should transition to STEP1 3. Turn PROX374 (rail in feed area) and WELD_ENABLE ON Program should transition to STEP2 with FRAM_EXT ON 4. Turn LS373 OFF (to indicate that feed ram is no longer fully retracted), turn PROX374 OFF (to show that rail is pushed out of feed area), turn PROX375 ON (to show that rail piece is on weld track) Program should transition to STEP3 with WRAM_EXT ON 5. Turn LS373 ON (to show that the feed ram has automatically retracted), turn LS376 OFF (to show that the weld ram is no longer fully retracted), turn PROX375 OFF (to show that the weld ram has pushed the rail past this sensor), turn PE377 OFF (to show that the rail is in position to be welded) Program should transition to STEP4 with ROBOT_START ON 6. Turn ROBOT_FINI ON Program should transition to STEP5 with STRING_FWD ON Turn ROBOT_FINI OFF 7. Turn PE377 ON (to show that welded rail string has been pulled into position for next weld) Program should transition to STEP6 with WRAM_RET ON 8. Turn LS376 ON (to show that weld ram has fully retracted) Program should transition to STEP1 Pause – Program should pause during any step except STEP5 (with STRING_FWD ON) Reset – Program should not reset unless RUN is OFF Reset should turn WRAM_RET ON if LS376 is OFF. WRAM_RET should remain ON until LS376 is turned ON..
Overview:
- Create a sequential function chart for the Rail Welding Station Control and implement it in ladder logic on paper.
Background:
Rail Welding Station Control. Using the function chart approach, implement the program for the following station that welds railroad rails together.
Process Narrative:
Figure P6.1 shows the general layout of a station that welds 40-foot lengths of railroad rail into a 1/4-mile length of rail (called a string). In summary, individual rails are fed into a track, a ram pushes the rail into the welder, the robot welder welds the rail onto the current “string” of welded rail, and then the entire string is moved 40 feet to be in position to weld on the next piece. The operation is described in the following format; (hint…basic name for step, INPUTS_TRANSITION, OUTPUT__ACTION).
- When initially started, assume there is a rail located in the String Wheel, check conditions are met so that piece is in position 1 in Figure P6. 1. Before continuing with the operation, two conditions must be verified: (1) There must be a rail piece in the feeder (sensed by PROX374); and (2) the WELD_ENABLE internal coil must be on. Both of these conditions must be met before the next step.
- Then the rail piece can be pushed onto the welding track. To bring in the next 40-foot rail piece, the feed hydraulic ram control, FRAM_EXT s turned on to push a rail piece onto the welding track (sensed by PROX375).
- Then the WRAM_EXT cylinder control is energized to extend the welding hydraulic ram to push the 40-foot rail piece into the welding position (sensed by PE377 off).
- The welding ram cylinder controls are then turned off so the new rail piece is held in the welding position (butting against the end of the existing “string” of welded rail). The welding robot is then activated (with ROBOT_START) to actually produce the weld. The welding robot turns on the ROBOT_FINI input to the PLC to signal that the welding operation is complete.
- The string of welded rail is then pulled forward by activating the STRING_FWD output. When the proximity sensor PE377 turns on, the string is in position to weld on the next 40-foot piece.
- The WRAM_RET cylinder control is energized to move the welding hydraulic ram back into position, ready to push the next piece into the welder. The LS376 limit switch turns on when the ram is retracted. The operation then repeats (starting with verifying the two conditions).
Details:
The WELD_ENABLE internal coil signals that the current welded rail string is less than 1320 feet (1/4 mile) and thus the next 40-footpiece in the feeder can he welded onto the current string. When the string is 1320 feet long, the WELD_ENABLE internal coil is turned off and a new string is started by moving one rail into position 1. Your part of the ladder does not move this first rail piece into position. Another part of the PLC program does this part of the operation.
The feeder area has two proximity sensors, PR0X374 and PR0X375. When PROX 374 is on, a 40-foot rail piece is present in the feeder. You are not concerned with the mechanism that places the piece into the feeder area. You just need to sense that the rail is present before activating the FRAM_EXT control to push the 40-foot rail piece into the weld track. PR0X375 is on when the rail has been pushed by the feed ram onto the welding rail.
The weld position is sensed by the photoelectric eye, PE377. When the active end (end to be welded) of the welded string is moved into the proper position, PE377 transitions on. When the 40-foot piece is moved in to contact the active end, PE377 turns off.
The feed ram is a single-action hydraulic cylinder, controlled by FRAM_EXT. Once the FRAM_EXT output is energized (on), the ram extends and pushes the 40-foot rail piece onto the welding track. When FRAM_EXT is off, the ram retracts. The ram retracts very quickly and so you may assume that when FRAM_EXT is turned off after the rail piece is placed onto the weld track, the ram has retracted sufficiently far so that it does not interfere with the weld ram. In normal operation, you do not need to detect that it has retracted (if the ram does not retract within a certain time period an alarm is activated, which is not part of the problem). However, during reset, you do need to detect when the feed ram is retracted. LS373 is on when the feed ram is retracted.
The welding ram is a double-action hydraulic cylinder with two controls. While the WRAM_EXT control is energized the ram extends (moves out) as long as power is applied (WRAM_EXT is on). While the WRAM_RET control is energized, the ram retracts (moves in) as long as power is applied (WRAM_RET is on). The ram stops at its current position when either control is turned off. The ram will not move if both WRAM_EXT and WRAM_RET are energized simultaneously. There are mechanical stops to prevent extension or retraction beyond certain limits.
The LS376 limit switch is on when the welding ram is fully retracted.
The welding robot is a piece of equipment separate from the PLC. It is programmed separately to move a welding head along a programmed path and thus weld the two rail pieces together. The PLC only commands the welding robot to start its operation (with ROBOT_START) and receives an indication (ROBOT_FINI) that the welding operation is complete The ROBOT_START output must remain on during the robot’s operation (unless paused). If ROBOT_START is turned off the robot pauses its preprogrammed operation. The ROBOT_FINI input to the PLC is turned on when the welding robot has finished its operation.
The STRING_FWD output commands a mechanism that moves the welded string (up to 1320’ long) to place the active end in a position where the next piece can be welded. You are not concerned about the details of the mechanism. It basically activates a roller conveyor to move the string. The STRING_FWD output must be on to move the welded rail string.
When the start switch is pressed (turned on) for the first time only, the station assumes there is one 40-foot rail in position 1. When the stop switch is pressed (turned off) the operation should pause and all outputs (except STRING_FWD) must be turned off. Pressing the start switch while the operation of the station is paused causes the station to resume its suspended step. The STRING_FWD output must remain on if the station is paused in the step where the rail string is moved in order to accurately place the active end.
With one exception, do not advance to the next step when paused. If the operation is paused when STRING_FWD is on, the welded rail string must continue to be moved into position and then advance to the next step when the string is in position.
Make sure a separate reset switch, RESET_PB, is provided which resets any internal states so that when the start switch is pressed, no rails are assumed present in the station. Obviously, the operator must clear everything out of the welding area before resuming operation after a reset operation. Also, the reset operation should cause the welding and feed rams to retract and the reset operation is not complete until both rams are retracted. Make no assumption about which ram requires the longest time to retract. The reset switch should be ignored if the station is running or when the string is moving forward. The start switch should be ignored when the reset operation is in progress. If the station is paused and RESET_PB on, the operator must release the RESET_PB before the start pushbutton switch can be used to restart the station.
Do not add any more timed steps to those explicitly stated in the problem. In other words, do not put a timer in a step unless it is stated that the step duration is a specific time.
Assume the following physical inputs and outputs. DO NOT assign any more inputs!!
| Variable | I/O | Description |
| START_PB | In | Start push button, N. O., on when starting. (input) |
| STOP_PB | In | Stop push button, N. C., off when stopping. (input) |
| RESET_PB | In | Reset push button, N. O., on when restoring station to initial state. (input) |
| LS373 | In | Limit switch that closes (on) when feeder ram is retracted. (input) |
| PROX374 | In | Proximity sensor, on (closed) when 40-foot rail piece in feeder area; off as rail is pushed onto weld rail or when no rail piece is present. (input) |
| PROX375 | In | Proximity sensor, on (closed) when 40-foot rail piece on weld track, ready to be pushed into welder; off as rail is pushed into welder or when no rail piece is present. (input) |
| LS376 | In | Limit switch that closes (on) when weld ram is retracted. (input) |
| PE377 | In | Photo-electric eye that senses active end of welded rail. See above for description. (input) |
| ROBOT-FINI | In | Indication from welding robot that is on when operation is complete. (input) |
| WELD_ENABLE | In | Signals that the next 40-foot piece of rail can be welded onto current string. On when next 40-foot piece of rail can be welded onto current string. (input) |
| FRAM_EXT | Out | Feed ram extend control, on to extend ram, off causes ram to retract. (output) |
| WRAM_EXT | Out | Weld ram extend control, on to extend ram. (output) |
| WRAM_RET | Out | Weld ram retract control, on to retract ram. (output) |
| ROBOT_START | Out | Command to welding robot to start operation. Welding robot senses an off-to-on transition to start. It may remain on while welding is occurring. (output) |
| STRING_FWD | Out | Welded string movement control, on to move welded string forward and down roller conveyor. (output) |
| STEP1_LMP To STEP_N_LMP |
Out | Lights up correspond lamp outputs per Lamp Box drawing. |
Create Internal Boolean bits: RUN, STEP#s, and RESET_INT.
Please remember that STEP1 is a BOOL and STEP1_LMP is a hardwired output. They are NOT the same!
It is your responsibility to fully design, document, debug, and test your program. Ensure that you have made effective use of both instruction and rung comments to clearly document your program. All I/O components referenced within your program should be clearly labeled, and rung comments should be employed to add additional clarity as required.
Procedure:
- Create a sequential function chart for the Rail Welding Station Control.
- Implement your sequential function chart in ladder logic. Use the prescribed program naming convention. The last section of your program should use RUN to turn on RUN_LMP, STEP1 to turn on STEP1_LMP, etc.
- Save your ladder logic program.
| INITIAL |
STEP01
STEP02
STEP03
STEP04
STEP05
STEP06
STEP07
Rail Welding Station Control Operation:
- Start with inputs @:
| LS373 | ON |
| PROX374 | OFF |
| PROX375 | OFF |
| LS376 | ON |
| PE377 | ON |
| ROBOT_FINI | OFF |
| WELD_ENABLE | OFF |
- Press START_PB
Program should transition to STEP1 - Turn PROX374 (rail in feed area) and WELD_ENABLE ON
Program should transition to STEP2 with FRAM_EXT ON - Turn LS373 OFF (to indicate that feed ram is no longer fully retracted), turn PROX374 OFF (to show that rail is pushed out of feed area), turn PROX375 ON (to show that rail piece is on weld track)
Program should transition to STEP3 with WRAM_EXT ON - Turn LS373 ON (to show that the feed ram has automatically retracted), turn LS376 OFF (to show that the weld ram is no longer fully retracted), turn PROX375 OFF (to show that the weld ram has pushed the rail past this sensor), turn PE377 OFF (to show that the rail is in position to be welded)
Program should transition to STEP4 with ROBOT_START ON - Turn ROBOT_FINI ON
Program should transition to STEP5 with STRING_FWD ON
Turn ROBOT_FINI OFF - Turn PE377 ON (to show that welded rail string has been pulled into position for next weld)
Program should transition to STEP6 with WRAM_RET ON - Turn LS376 ON (to show that weld ram has fully retracted)
Program should transition to STEP1
Pause –
Program should pause during any step except STEP5 (with STRING_FWD ON)
Reset –
Program should not reset unless RUN is OFF
Reset should turn WRAM_RET ON if LS376 is OFF. WRAM_RET should remain ON until LS376 is turned ON.
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