Exercise 7. Conveyors EXERCISE OBJECTIVE

Transcription

1 Exercise 7 Conveyors EXERCISE OBJECTIVE In this exercise, you will be introduced to conveyors. You will learn to use the Belt Conveyor, Model You will also learn to use the If-Else-Endif and While-Repeat task commands In the Procedure section, you will experiment with the various features of the Belt Conveyor, and you will detect these objects with a limit switch mounted on the conveyor chassis. You will use the TTL outputs of the Robot Controller to remotely control the Belt Conveyor. DISCUSSION Conveyor systems are needed when components or material must be moved from one station to another one along a fixed path. Most conveyor systems use an electrical or hydraulic power source to move their loads. However, when the receiver station is lower than that of the sender, the force of gravity is often used as power source. The most common types of conveyors are roller, belt and chain. Roller conveyors are popular in manufacturing. Tubes or rollers, over which the material flows, are connected to two ends of a fixed frame. They can use the force of gravity or be driven by mechanisms. Belt conveyors are another automated way to move materials. The belt moves in a continuous loop with the top half carrying the load to the next station, and the bottom half returning to its starting point. You have seen belt-type conveyors at the checkout counter of supermarkets and airport security checkpoints. Chain conveyors loop chains around sprockets at the ends of their pathways. They operate in the same way as bicycle chains. However, they use powered sprockets rather than manual force to drive the chain along channels supporting the flexible chain sections. 7-1

2 Belt Conveyor The Belt Conveyor of your training system is shown in Figure 7-1. It can be operated either by switches mounted on the control panel, or by control signals applied to its TTL inputs. The control signals are provided by the TTL outputs of the Robot Controller. Figure 7-1. Belt Conveyor, Model The control panel of the Belt Conveyor is shown in Figure 7-2. As the figure shows, the operating parameters that can be controlled from the control panel are the speed (SPEED), logic level of the TTL input (STOP) at which the conveyor stops, motor engage/disengage (MOTOR), and belt direction (DIRECTION). Figure 7-2. Control panel of the Belt Conveyor. 7-2

3 Speed The SPEED potentiometer controls the speed of the belt from Slow to Fast. At the Slow position, the belt of the conveyor is stopped. Stop The Logic switch is used to select the TTL level required at the input Stop to remotely stop the conveyor. When the Logic switch is set at High, the conveyor stops on a high level. Conversely, when the Logic switch is set at Low, it stops on a low level. Motor The Motor switch is used to select between three operating modes: Engage: In this mode, the motor of the Belt Conveyor is torqued and the conveyor runs if the settings of the Stop section correspond to a run condition. If the settings of the Stop section correspond to a stop condition the motor is stopped but remains torqued. Disengage: In this mode, the motor is stopped and freed (not torqued). Ext.: The operation is controlled remotely by a signal applied to the Ext. Input. When the level of the Ext. Input is high, the conveyor operates as in the Engage mode. Conversely, when the level is low, it operates as in the Disengage mode. Direction The Direction switch is used to select between three operating modes: Forward: In this mode, the belt of the conveyor goes from right to left (when facing the control panel). Reverse: In this mode, the belt of the conveyor goes from left to right. Ext.: The operation is remotely controlled by a signal applied to the Ext. Input. When the level of the Ext. Input is high, the direction of the belt is in the Forward mode. Conversely, when the level is low, it is in the Reverse mode. Limit Switch The Belt Conveyor is provided with a limit switch to detect the presence of parts on the belt. The limit switch is movable, and there are several sets of mounting positions found along both sides of the conveyor chassis. 7-3

4 Task Commands In this exercise, you will be introduced to the If - Else - Endif and While - Repeat task commands. If - Else - Endif If: This command evaluates an expression. If the expression is true, the execution of the task program continues normally on the next instruction line. If the expression is false, the execution continues after the next Else statement (if used) or Endif statement. The syntax and the parameters associated with the If command are as follows: IF <expression>. Example: IF INPUT(1) = HIGH Else: This command indicates the end of the instruction lines that are executed when the previous If statement has evaluated a true condition. The instruction lines that follow the Else statement are executed only when the previous If statement has evaluated a false condition. Endif: This command indicates the end of an If-Else-Endif block of codes and execution continues on the next instruction line. For each If command there must be one matching Endif statement. If there are multiple nested If statements, each statement must have a matching Endif statement. While - Repeat While: This command evaluates an expression. If the expression is true, the next instruction lines are executed up to the Repeat command. When the Repeat command is reached, the execution is returned to the While command where the expression will be evaluated repeatedly until the expression fails. The syntax and the parameters associated with the While command are as follows: WHILE <expression>. Example: WHILE INPUT(1) = HIGH. Procedure Summary In the first part of the exercise, Set-up, you will install and connect the equipment. In the second part, Direct Control of the Belt Conveyor, you will operate the conveyor using the switches on the control panel. In the third part, Remote Control of the Belt Conveyor, you will experiment with the remote control of the Belt Conveyor. You will control the operation from the Controller Status window of Robotics. In the fourth part, Additional Experiment - Simulation of a Quality Control Station, you will create a program that simulates a quality control station using the Gravity Feeder and the Belt Conveyor. You will create the position points using the Hand-Held Terminal and you will use Robotics to create the task program. In the last part of the exercise, Shutdown Procedure, you will shut down the system. 7-4

5 EQUIPMENT REQUIRED Refer to the Equipment Utilization Chart, in Appendix A of this manual, to obtain the list of equipment required to perform this exercise. PROCEDURE Set-up CAUTION! When you work with moving equipment, make sure you are not wearing anything that might get caught, such as a tie or jewelry. If your hair is long, tie it out of the way. G 1. Install the Servo Robot and the Belt Conveyor as shown on Figure 7-3. Note: Refer to the Equipment Layout shown in Figure E-1 in Appendix E. 7-5

6 Figure 7-3. Location of the equipment on the Work Surfaces. 7-6

7 G 2. Make sure the limit switch of the Belt Conveyor is located as shown in Figure 7-4. Relocate if necessary. Figure 7-4. Location of the limit switch on the Belt Conveyor. G 3. Make sure that the emergency stop button is released (in the up position) and easily accessible. G 4. Connect the equipment as shown in Appendix B. Refer to the User Guide of your training system for detailed instructions. Connect the Belt Conveyor to an AC power source. Direct Control of the Belt Conveyor G 5. On the control panel of the Belt Conveyor, set the controls as follows: SPEED FAST LOGIC LOW MOTOR DISENGAGE DIRECTION REVERSE 7-7

8 Turn the power on using the switch located on the left side of the control panel. G 6. Set the MOTOR switch at ENGAGE to start the motor. Familiarize yourself with the operation of the Belt Conveyor using the SPEED, LOGIC, MOTOR and DIRECTION controls. Place a film canister on the conveyor and observe its movement while operating each control. G 7. Indicate in Table 7-1 if the Belt Conveyor is stopped or running for each combination shown. LOGIC SWITCH POSITION STOP INPUT LEVEL (TTL) MOTOR SWITCH POSITION BELT CONVEYOR OPERATION High Low High 1 Low 2 High Low Engage Disengage Engage Disengage Engage Disengage Engage Disengage 1 The default level of the TTL inputs is high. 2 Short-circuit the input with a lead to set the level at low. Table 7-1. Direct control of the Belt Conveyor. G 8. Once your experiment is completed, turn off the power of the Belt Conveyor using the switch located on the left side of the control panel. Remote Control of the Belt Conveyor G 9. On the control panel of the Belt Conveyor, set the controls as follows: SPEED FAST LOGIC HIGH MOTOR EXT. DIRECTION EXT. 7-8

9 G 10. Connect TTL output 1 of the Robot Controller to the Stop Input of the Belt Conveyor as shown in Figure 7-5. Figure 7-5. TTL input/output connection diagram. Connect the common terminal of TTL output 1 to the common terminal of the Stop Input on the Belt Conveyor. Connect TTL output 2 to the Motor Ext. Input of the Belt Conveyor. Note: Since the common terminals are linked in the Belt Conveyor and Robot Controller, it is not required to connect the common terminal of the Direction Ext. Input and Motor Ext. Input. Connect TTL output 3 to the Direction Ext. Input of the Belt Conveyor. G 11. Turn the Belt Conveyor and Robot Controller on. G 12. Launch Robotics. G 13. Open the Controller Status window by selecting Controller Status in the Window menu. G 14. Click the appropriate LEDs for controlling the level of the TTL outputs to determine if the Belt Conveyor is stopped or running for the combinations shown in Table

10 LOGIC SWITCH POSITION STOP INPUT LEVEL (TTL) MOTOR EXT. INPUT LEVEL (TTL) BELT CONVEYOR OPERATION High Low High Low High Low Low High Low High Low High Low High Table 7-2. Remote control of the Belt Conveyor. G 15. Set a combination for which the conveyor is running, and determine if the belt is in the Forward or Reverse mode when the level of the Direction Ext. Input is high. G 16. Once your experiment is completed, turn off the Belt Conveyor. Remove the leads connected on the front panel of the Robot Controller. Additional Experiment - Simulation of a Quality Control Station Program Description You will create a task program which is a section of a more complex production process. In this program, a robot picks production parts and transfers them via a belt conveyor to a quality control station for examination. If a part is already present at the quality control station, the robot transfers the parts in a temporary container. You will use the Gravity Feeder to feed the Servo Robot with parts, and the Belt Conveyor to move the parts to the quality control station. You will use the limit switches mounted on the Gravity Feeder and Belt Conveyor to detect the presence of parts, and you will use a TTL output of the Robot Controller to control the operation of the Belt Conveyor. You will also use the task commands If and While to determine which actions to perform. 7-10

11 Program Flow Chart The flow chart for this program is shown in Figure 7-6. Figure 7-6. Flow chart for the quality control station program. 7-11

12 Suggested Connections When many input/output connections are required by a program, it is of good practice to use a table where all connections are grouped. Table 7-3 shows the suggested connections for the quality control station program. Gravity Feeder Belt Conveyor EXTERNAL DEVICES Limit Switch NO contact Limit Switch NC contact Limit Switch NO contact Stop TTL input ROBOT CONTROLLER TTL INPUT TTL OUTPUT Table 7-3. Input/output connection table. Program Set-up G 17. Install the Gravity Feeder and metallic can as shown in Figure 7-3. G 18. Fill the Gravity Feeder with 2 parts. G 19. Make the connections shown in Figure 7-7. Note: Since the connection table shown in Figure 7-1 and connection diagram shown in Figure 7-7 contain the same information, both methods can be used to illustrate the connections. G 20. On the control panel of the Belt Conveyor, set the controls as follows: SPEED middle position between SLOW and FAST LOGIC HIGH MOTOR ENGAGE DIRECTION REVERSE Turn the power on using the switch located on the left side of the control panel. 7-12

13 Figure 7-7. TTL input/output connection diagram. G 21. Execute a hard home positioning. Note: In this part of the exercise, you will save the position points using the Hand-Held Terminal. Once all position points required by the program are saved, you will transfer them in the Task Editor window of Robotics where they will be associated with task commands to create a task program. Creation of the Position Points G 22. Using the Hand-Held Terminal, pick a part from the Gravity Feeder and place it in the detection zone (shown in Figure 7-4) of the Belt Conveyor. Save all required points as PCONV01 to PCONV. Do not forget to reduce the speed when necessary. G 23. Using the Hand-Held Terminal, pick a part from the Gravity Feeder and drop it in the metallic can. Save all required points as PCONT01 to PCONT. Do not forget to reduce the speed when necessary. G 24. Once your points are saved, select Online in the Robot menu of Robotics to transfer the control to Robotics. 7-13

14 Writing of the Task Program G 25. Select New Task Editor in the sub-menu Upload to of the Robot menu of Robotics to transfer the points in the Task Editor window. In the Program Information window, enter your name in the Author field and the date in the Date field, then click the OK button. G 26. Enter the HOME command in the Task Editor window to execute the step [Home positioning] in the flow chart shown in Figure 7-6. Note: The expressions shown in brackets correspond to the steps in the flow chart of the program. G 27. Enter the OUTPUT(1) HIGH instruction to execute the step [Stop the conveyor]. This will ensure that the conveyor is stopped at the beginning of the program (as determined by the position of the Logic switch on the control panel of the Belt Conveyor). G 28. Enter the WHILE INPUT(1) = LOW instruction to execute the step [Part in the feeder?]. The instruction lines that follow will be repeated as long as the statement is true. If the statement is false, the program will continue with the instruction line that follows the associated REPEAT command. G 29. Enter the IF INPUT(2) = LOW instruction to execute the step [Part at the quality control station?]. If the statement is true, the program will continue on the next instruction line. If the statement is false, the program will continue with the instruction line that follows the ELSE command. G 30. Transfer the position points named PCONV01 to PCONV from the right to the left column of the Task Editor window to execute the step [Pick a part from the feeder and place it on the conveyor]. Note: Press the Ctrl key during the dragging to automatically add the MOVETO command to each point. G 31. Enter the WHILE INPUT(3) = HIGH instruction to execute the step [Part at the quality control station?]. As long as the statement is true, the instruction lines between the WHILE and associated REPEAT commands will be repeated. If the statement is 7-14

15 false, the program will continue with the instruction line that follows the associated REPEAT command. G 32. Enter the OUTPUT(1) LOW instruction to execute the step [Start the conveyor]. G 33. Enter the REPEAT command to return the execution of the program to the associated WHILE command (WHILE INPUT(3) = HIGH). G 34. Enter the OUTPUT(1) HIGH instruction to execute the step [Stop the conveyor]. G 35. Enter the HOME command to execute the step [Home positioning]. G 36. Enter the ELSE command. If the statement IF INPUT(2) = LOW is false the program will continue with the instruction line that follows the ELSE command. G 37. Transfer the position points named PCONT01 to PCONT from the right to the left column of the Task Editor window to execute the step [Pick a part from the feeder and place it in the container]. G 38. Enter the HOME command to execute the step [Home positioning]. G 39. Enter the ENDIF command to indicate the end of the IF INPUT(2) = LOW instruction. The execution of the program will continue with the next instruction line. G 40. Enter the REPEAT command to return the execution of the program to the associated WHILE command (WHILE INPUT(1) = LOW). G 41. Enter the END command to execute the step [End]. This will end the execution of the task program. 7-15

16 Formatting the Task Program G 42. Format your task program as shown to facilitate the reading HOME 0002 OUTPUT(1) HIGH 0003 WHILE INPUT(1) = LOW 0004 IF INPUT(2) = LOW 0005 MOVETO PCONV MOVETO PCONV02 (*)... MOVETO PCONV WHILE INPUT(3) = HIGH OUTPUT(1) LOW REPEAT OUTPUT(1) HIGH HOME ELSE MOVETO PCONT01 MOVETO PCONT02... MOVETO PCONT HOME ENDIF REPEAT END (*) From this line, the line numbers depend on the number of points saved. Note: You will learn in the next exercises how to add commentaries to the instruction lines to facilitate the understanding of the program. G 43. Save your program as EXE_7_A. Program Testing G 44. Fill your Gravity Feeder with two parts. G 45. Execute your program. G 46. Did the Servo Robot place the first part on the Belt Conveyor and the second one in the metallic can, then stop at the home position? If not, verify your program, and ask your instructor if necessary. 7-16

17 G 47. Remove the parts from the Belt Conveyor and metallic can, then fill your Gravity Feeder with five parts. G 48. Execute your program. While the Servo Robot is moving to the metallic can to drop the second part, remove the part from the belt conveyor (manually). G 49. Did the Servo Robot place the third part on the Belt Conveyor to feed the quality control station, then the fourth and fifth parts in the metallic can? If not, verify your program, and ask your instructor if necessary. G 50. What will happen if the program is launched without parts in the Gravity Feeder? Explain. Shutdown Procedure G 51. Make sure that there is nothing inside the gripper. G 52. Clear the area around the Servo Robot so that it will not hit anything when it moves. G 53. Execute a hard home positioning. G 54. Turn off the Robot Controller and Belt Conveyor by setting their power switch at the O (off) position. G 55. Disconnect the system and return the equipment to its storage location. 7-17

18 CONCLUSION In this exercise, you were introduced to conveyors. You learned that the conveyor of your training system is a belt conveyor, one of the most common types of conveyors. You learned to control the Belt Conveyor from the control panel and remotely using the TTL outputs of the Robot Controller. To obtain precise movements and facilitate the programming, you have used the Hand-Held Terminal to create the position points and Robotics to program. REVIEW QUESTIONS 1. Name three types of conveyors. 2. Describe the required settings for the Belt Conveyor to run in the reverse direction (direct control). 3. Name three parameters that can be remotely controlled on the Belt Conveyor. 4. To program the Simulation of a Quality Control Station, explain why it is best to use the Hand-Held Terminal to create the position points. 5. What is the use of the Else command in a If-Else-Endif block of codes? 7-18