TP 6 · Chapter 6
Capstone project
Take a machine from a written specification to a commissioned PLC program: resource allocation without conflicts, approved GRAFCET, commissioning record and an oral defence.
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Objectives
- Take a machine from a written functional specification to a commissioned PLC program, following the design method of Chapter 6.
- Allocate the trainer's resources without conflict, including the points that several modules share.
- Prove the machine safe with a planned commissioning and fault-injection test, and defend the design orally.
Organisation
Each group chooses one of the four projects below at the end of TP 5. The first session is spent on the specification, the resource allocation and the GRAFCET, which the instructor approves before any programming; the second on programming, commissioning and the demonstration. A group may propose another machine of comparable difficulty, provided it uses only the PLC-200 trainer and is approved before the first session.
Project A: drilling station
A part is clamped, drilled to depth and released.
- Spindle: the DC motor, switched through a relay (common RC2 → 24 V+, RQ0.2 → M+, M− → 24 V−); rotation proven by the proximity sensor on I1.1.
- Quill feed: the stepper (Q0.0 DIR, Q0.1 CK) with the encoder on HSC0 (mode 9): rapid approach, slow feed to depth, dwell, rapid return; homing on a toggle switch that simulates the quill top position.
- Required functions: clamp before the spindle starts; spindle proven before feed; feed stops and the quill returns if the spindle stops during drilling (broken drill); part counter; depth selectable between two values.
Project B: soap marking machine
Soap bars on an indexing conveyor are stopped under a stamp, marked and moved on.
- Indexing conveyor: the DC motor through a relay, as in Project A; one revolution (one proximity pulse) is one index.
- Stamp: the stepper, which moves down a set number of steps, dwells and returns; the encoder checks that it has returned before the conveyor may index.
- Required functions: bar-present input; no stamping without a bar; conveyor overshoot measured and compensated (stop command given before the sensor); count of marked bars; stamp jam detected by the encoder.
Project C: traffic intersection with pedestrian call and pre-emption
- Lamps: the traffic-light module (SW3) on Q0.0–Q0.5; audible pedestrian signal on the buzzer through RQ0.6 (SW7).
- Required functions: fixed-time cycle with all-red clearance; side-road vehicle detector that extends the side green up to a maximum; pedestrian call served at the next cycle; emergency-vehicle pre-emption from either road that ends the current green safely (through amber and all-red); flashing amber on a lamp-fault input.
- Compare your SCR program with manual Exercise 5-2 and justify every change.
Project D: batch mixing station
- Tanks: the tank device (SW4); ingredient A and B tanks with the level simulation of TP 2, lamps L6–L9 on Q0.6–Q1.1.
- Mixer: the DC motor on PWM (Q0.0), rotation proven by the proximity sensor; mixing time counted in revolutions, not seconds.
- Required functions: recipe ratio A:B set by potentiometer SMB28; fill A, fill B, mix, drain; the mixer never runs below the minimum level; batch aborted and drained on a mixer fault; batch counter.
Preparation tools
Control byte
Tick the bits you need; the value to move into the control byte appears below. Check each bit against the manual (Table 10-1.1).
MOVB 16#00, SMB67 (2#00000000 = 0)
Multi-segment PTO profile
Each segment starts at a cycle time and changes it by a fixed number of µs per pulse. Enter the frequencies and pulse counts of your segments; the tool gives the table values and the travel time.
| # | Start (Hz) | End (Hz) | Pulses | Start cycle (µs) | Δ per pulse (µs) | Last pulse (Hz) | Time (s) | |
|---|---|---|---|---|---|---|---|---|
| 1 | 20000 | 0 | 50.0 | 1.920 |
96 pulses · 1.920 s
MOVB 1, VB500 MOVW +20000, VW501 MOVW +0, VW503 MOVD +96, VD505
The frequency does not change linearly: the cycle time does. Word values above +32767 are written in hexadecimal (16#…). Check the table layout against the manual before you use it.
Timer choice
The S7-200 timer number fixes its type and resolution. Enter a duration to see the preset of every group.
| Type | Resolution | Timer numbers | Preset | |
|---|---|---|---|---|
| TON/TOF | 1 ms | T32, T96 | +1000 | exact |
| TON/TOF | 10 ms | T33–T36, T97–T100 | +100 | exact |
| TON/TOF | 100 ms | T37–T63, T101–T255 | +10 | exact |
| TONR | 1 ms | T0, T64 | +1000 | exact |
| TONR | 10 ms | T1–T4, T65–T68 | +100 | exact |
| TONR | 100 ms | T5–T31, T69–T95 | +10 | exact |
Deliverables
| Deliverable | Content |
|---|---|
| Functional specification | One page: what the machine does, its operating modes, and its hazards with the safe state of each output. |
| Resource allocation | The I/O table, the enable switches ON and OFF, the patch leads, and an explicit check against the shared points. |
| GRAFCET | Normal sequence, stop and fault handling, approved before programming. |
| Program | SCR-structured ladder with symbol table and one comment per network. |
| Commissioning record | The I/O check (every input and output tested and signed), then the functional tests and a fault-injection table with at least five tests. |
| Oral defence | Ten minutes: demonstration, then questions to each member of the group. |
In the group report, section 1 (Preparation) holds the specification, one row per item: what the machine does, each operating mode, each hazard with the safe state of its outputs. Section 2.1 holds the I/O table; in it, or in the resources table (2.3), write the enable switch of every module whose points you use, ON or OFF (for example “SW3 OFF”), and the thumbwheel setting 0000.
Assessment
The project is marked out of 20 with the usual criteria (preparation 3, program 6, bench demonstration 6, report 5), the oral defence replacing the report questions. A fault-injection test that does not fail safe costs the whole bench-demonstration mark for that function.
Questions for the oral defence
- Which of your outputs must go to the safe state when the CPU goes to STOP, and how did you verify it?
- Which hazard in your machine would need a hard-wired safety function on a real installation, rather than the PLC program alone? Refer to the required integrity level of Chapter 6.
- Which function of your specification could the trainer not reproduce faithfully, and how would it behave on the real machine?
Group report
One report per group, handed in here. Groups are 2 or 3 students; working alone or in a group of 4 needs your teacher's agreement. Everyone edits the same report, each member signs off what they did, then any member hands it in.
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