Mechatronics · Module 1 of 10
Introduction to Mechatronics and Measurement Systems
Mechatronics is the deliberate integration of mechanical, electronic, control, and computer engineering into one design. It begins with the measurement system: sense a quantity, condition the signal, and read it out, with the stages multiplying together.
Readiness check
This module opens the course. Tick only what you can do closed-notes.
- Multiply two numbers that carry different units.
- Recall that a sensor turns a physical quantity into an electrical signal.
- Recall the idea of gain as output divided by input.
- Distinguish an open loop from a closed loop.
- Read a simple block diagram left to right.
The core idea
A mechatronic system senses, decides, and actuates. The measurement subsystem turns a physical quantity into a usable signal through stages in series, so the overall sensitivity is the product of the stage sensitivities. Closing a loop trades raw forward gain for a stable, predictable closed-loop gain.
overall sensitivity = product of stage sensitivitiesopen loop: output = sensitivity × inputclosed loop: gain = G / (1 + GH)Mechatronics is not a new physics; it is the practice of designing mechanical, electronic, control, and software elements together so the whole behaves better than the parts. Almost every mechatronic system follows one shape: a measurement system observes the world, a controller decides, and an actuator changes the world. The measurement system itself is a chain of stages, a sensor followed by signal conditioning followed by a display or converter, and because the stages are in series their sensitivities multiply. A sensor of 8 mV/mm feeding an amplifier of gain 250 gives an overall 2 V/mm; you never add such numbers. When the output is fed back and compared to a target, the system is closed loop. Feedback replaces the raw forward gain G with the closed-loop gain G/(1 + GH), which is smaller but far less sensitive to changes in G, the property that makes closed-loop systems accurate and repeatable. The rest of this course builds each block in that sense, decide, actuate chain and then connects them.
The skills, taught in order
Five ideas set the vocabulary the whole course reuses.
1.1 What mechatronics integrates
Mechatronics combines mechanisms, sensors, actuators, analog and digital electronics, control theory, and embedded software. The value is in the integration: a cheaper motor with a smart controller can beat an expensive motor run open loop.
1.2 The measurement system
Every measurement system has a sensor stage that responds to the quantity, a signal-conditioning stage that scales and cleans the signal, and a display or data stage that presents or records it. Naming the stage a value belongs to keeps a design organized.
1.3 Sensitivity multiplies along a chain
Because the stages pass their output to the next stage's input, the overall sensitivity is the product of the individual sensitivities. This single rule sizes amplifiers and predicts the reading for any input.
| Stage | Sensitivity | Running product |
|---|---|---|
| Sensor | 8 mV/mm | 8 mV/mm |
| Amplifier | 250 (V/V) | 2000 mV/mm |
| Overall | 2 V/mm | 2 V/mm |
Stage sensitivities multiply, never add. The product is the overall system sensitivity.
1.4 Open loop versus closed loop
An open-loop system acts without checking the result; a closed-loop system measures the output and feeds it back to a comparator. Closed loop costs a sensor and a controller but buys accuracy, disturbance rejection, and repeatability.
1.5 The closed-loop gain
With forward gain G and feedback fraction H, the closed-loop gain is G/(1 + GH). When GH is large the gain approaches 1/H, set by the feedback path alone and almost independent of G, which is why feedback tames variable or drifting components.
Engineering connection: a robot joint uses a cheap, nonlinear motor, but an encoder and a feedback controller make the joint angle accurate and repeatable, exactly the 1/H behaviour.
Worked example 1: sizing a measurement chain
A displacement sensor produces 8 mV per millimetre. It feeds an amplifier of gain 250. Find the overall sensitivity and the output voltage for a 4 mm displacement.
- ProblemFind the overall sensitivity and the 4 mm output for the chain in Figure 1.
- Given / findSensor 8 mV/mm, amplifier gain 250. Find overall sensitivity and output at 4 mm.
- AssumptionsBoth stages are linear over the range, and loading between stages is negligible.
- ModelSeries stages multiply: overall = sensor × amplifier; output = overall × input.
- EquationsS = 8 mV/mm × 250V = S × x
- SolveS = 8 × 250 = 2000 mV/mm = 2 V/mm. At x = 4 mm, V = 2 × 4 = 8 V.
- CheckThe sensor alone gives 8 × 4 = 32 mV; amplified by 250 that is 8 V, matching the product route.
- ConclusionThe chain reads 2 V per millimetre, so a 4 mm move produces a clean 8 V signal, well matched to a typical converter input.
Worked example 2: closing the loop
A position system has forward gain G = 100 and a feedback fraction H = 0.09. Find the closed-loop gain and comment on its sensitivity to G.
- ProblemFind the closed-loop gain for the loop in Figure 2 and judge its dependence on G.
- Given / findG = 100, H = 0.09. Find G/(1 + GH) and compare with 1/H.
- AssumptionsLinear blocks, negative feedback, steady operating point.
- ModelClosed-loop gain = G/(1 + GH); for large GH it approaches 1/H.
- Equationsgain = G / (1 + GH)GH = 100 × 0.09 = 9
- Solvegain = 100/(1 + 9) = 100/10 = 10. For comparison 1/H = 1/0.09 = 11.1.
- CheckIf G doubled to 200, the gain becomes 200/(1 + 18) = 10.5, only a 5% change for a 100% change in G. Open loop it would have doubled.
- ConclusionFeedback fixes the gain near 10 and makes it almost independent of the forward gain, the defining benefit of closing the loop.
Misconceptions and diagnostics
| Mistake | Symptom | Diagnostic question | Correction |
|---|---|---|---|
| Adding stage gains | Sensitivity far too small | "Are the stages in series?" | Series stages multiply their sensitivities. |
| Quoting open-loop gain for a closed loop | Predicted output much too large | "Is there feedback?" | Use G/(1 + GH) once a loop is closed. |
| Ignoring units in the chain | Volts and millimetres mixed up | "Do the units cancel to the output unit?" | Carry units through every stage. |
| Thinking mechatronics is just electronics | Mechanism and control ignored | "What moves, and what decides?" | Design mechanism, electronics, and control together. |
Practice ladder
A sensor of 5 mV per degree Celsius feeds an amplifier of gain 200. What is the overall sensitivity, and what is the output at 30 degrees Celsius above reference?
Show answer
Overall = 5 × 200 = 1000 mV/degree = 1 V/degree. At 30 degrees, output = 30 V.
A loop has G = 50 and H = 0.2. Find the closed-loop gain, then find it again if G rises to 80.
Show answer
50/(1 + 10) = 4.55; 80/(1 + 16) = 4.71. A 60% rise in G moves the gain about 4%.
A chain has a 12 mV/mm sensor, an amplifier of gain 40, and a 0.5 V per volt attenuator at the display. Find the overall sensitivity and the reading at 2 mm.
Show answer
Overall = 0.012 × 40 × 0.5 = 0.24 V/mm. At 2 mm, reading = 0.48 V.
Sketch a temperature-controlled soldering iron as a sense, decide, actuate loop. Name the sensor, the controller, the actuator, and where feedback is taken.
What good work looks like
Thermocouple or thermistor sensor, a comparator and controller (often a microcontroller) as the decision, a heating element as the actuator, and feedback taken from the tip temperature back to the comparator, giving closed-loop temperature control.
Working with AI, and proving it yourself
Use AI as an examiner, not a solver
Portfolio task
Take a device you own, break it into sense, decide, and actuate blocks, and estimate the sensitivity of its measurement chain.
Retrieval and spaced review
Closed notes. Answer out loud, then reveal.
1. What three things does a mechatronic system do?
It senses, decides, and actuates.
2. How do sensitivities combine along a chain?
They multiply, because the stages are in series.
3. Write the closed-loop gain.
G/(1 + GH), which approaches 1/H for large GH.
4. Why close a loop at all?
For accuracy, disturbance rejection, and repeatability despite a variable forward gain.
5. Name the three stages of a measurement system.
Sensor, signal conditioning, and display or data stage.
Textbook mapping
This module follows William Bolton, Mechatronics, 6th edition. Use these references to read further.
| Topic in this module | Where to read more |
|---|---|
| What mechatronics integrates | Bolton, Chapter 1, Introduction to mechatronics |
| Measurement systems and stages | Bolton, Chapter 1, Measurement systems |
| Open and closed-loop control | Bolton, Chapter 1, Control systems |
Chapter numbers refer to Bolton's Mechatronics, 6th edition. Any edition with the same chapter titles is equivalent for study.