1. Briefly describe the meaning of the term mechatronics both in terms of the 'systems approach' and the technology involved.
2. State the elements that are common to all mechatronic systems and state their purpose.
3. Compare regulatory control with follow-up control. In which form of industrial control is each of these two control modes generally found? Give an example of each.
4. FIGURE 1 shows a level control system in which the level is controlled by regulating the inlet flow of liquid into the vessel.
Draw a block diagram which represents the level control loop.
5.
Derive the closed loop transfer functions for the system shown in FIGURE 2 and show that for large values of G the value of Vo/Vi approaches unity.
6. FIGURE 3 shows a closed loop system with a variable gain element G in the feedback path.
(a) Derive an expression for y/x.
(b) Show that for large values of K1 and K2, the value of y/x can be varied directly by changing the gain of the feedback element G.
7. The curve in FIGURE 4 shows the response of a bare thermocouple which has been subjected to a step change in temperature from 50°C to 10°C. Assuming that the bare thermocouple behaves as a single transfer lag system, determine the mathematical relationship between the temperature (T) and time (t).
8. In order to prevent greenhouses becoming too hot in sunny weather, an automatic window can be installed. This opens automatically if the temperature reaches a pre-determined value. The higher the temperature, the greater the opening becomes. Other than the heat produced by the sun, there is no external power source.
(a) Research and describe how this mechanism works.
(b) State whether this is open or closed loop control, give reasons for your answer.
(c) Represent the system with a block diagram.
9. A direct acting proportional pressure controller has a gain of 3, a range of 0-40 bar and is set to control at 25 bar. When the measured value and the desired value are equal, the output signal is 60%. Determine the input pressure required to produce controller output values of 10% and 90%.
10. The mass M shown in FIGURE 5 is to be held in position by two hydraulic pistons (A and B) which exert forces F1 and F2, (respectively) onto the mass. The total for FT (where FT = F1 + F2,) is to be controlled at a constant value.
The force F2, is uncontrolled, it is set at a nominal value however this may vary due to changes in the pressure of the hydraulic fluid supplying piston B.
A control loop is to be used to maintain the total applied force FT by controlling the magnitude of F1.
(a) Draw a block diagram for a proportional control system (with bias) to control FT.
(b) Derive a relationship between the actual total force (FT) and:
- Force F2
- Bias B
- Controller gain C
- Desired value Dv
- Feedback gain G
(c) If the desired value (for FT) is 5 kN, F., is set nominally to 3 kN and the controller and feedback gains are 1, determine a suitable value for the bias.
(d) If the desired value remains 5 kN, using the bias you calculated and the values set out in part (c) determine the value of the offset produced if F, increases to 4 kN.
11. In order to reduce offset in the control loop in Question 10 integral action is introduced into the controller and the bias removed.
(a) Show how this can be represented by a block diagram
(b) The control loop with integrator has the following initial conditions :
Desired value (Dv) = 5 kN
F2 = 3 kN
I = 2 kN (I is the output from the Integrator)
Error (e) = 0
Controller gain (C) = 0.2
Integrator gain (Ki) = 0.8
Total measured force (FT) = 5 kN
Feedback gain (G) =1
While at the above conditions F2, suddenly increases to 3.5 kN. Show that the control system will eliminate the offset. Continue your calculations until the actual value of force (FT) is within 0.5 % of the desired value for two successive calculations.