Actuators and Control, Part 3 Grant Agreement No LLP UK-LEONARDO-LMP Project acronym: CLEM Project title: Cloud services for E-Learning in Mechatronics Technology

Control A Control System is a device, or set of devices to manage, command, direct or regulate the behavior of other device(s) or system(s); may be applied to the essentially manual controls that allow an operator, for example, to close and open a hydraulic press; There are two common classes of control systems: logic or sequential controls; feedback or linear controls. Hydraulic valves function is to control pressure, control flow or direct flow in response to external commands.

Valve is a basic component In industrial systems; is mechanical device which regulate either the flow or the pressure of the fluid; can be stopping or starting the flow; control flow rate; divert flow; prevent back flow; control pressure, or reliev pressure; is an assembly of a body with connection to the pipe and some elements with a sealing functionality; can be complemented with several devices such as positioners, transductors, pressure regulators, etc. ; directional control valves start, stop or change the direction of flow in compressed air applications. Control

Categories of Valves: 1. spool–bonded and lapped; use an elastomer to seal against pressure; are tolerant of dirt and compressor varnish and when lubricated properly, will cycle for millions of operations; are available in 3-way and 4-way configurations 2. poppet; use a large poppet seal and operate much the same way as a home water faucet; is fast, rugged, and known for their ability to operate under adverse conditions; are made in 2-way, 3-way, and 4-way configurations; 3. a combination of spool and poppet; 4. sliding seal; 5. rotary and diaphragm. Control Fig. 25 Example of three-way valve applied to a spring return cylinder.

Control Fig. 26 Example of speed control on cylinder extension. Fig.27 Example of two-way-two-position valve.

On/Off Control Digital circuits are composed of logic gates. Logic gates are elementary electronic circuits operating in only two states; can realize every logical and arithmetical operation; operations are performed in combinational circuits. The automata can be constructed from standard ICs containing logic gates; more complex combinational logic blocks and registers; counters; memories; and other standard sequential ICs assembled on a printed circuit board. Types 1.combinational logic; 2.sequential logic. A digital circuit converts digital inputs into digital outputs.

Combinational Logic Combinational logic devices are “static” where the present inputs completely (and uniquely) determine the present outputs, without using any past information (history) or memory. The purpose of a digital circuit might be to turn on or off a device depending on some logical conditions For example, turn the light on or off in a room depending whether there are people in it or not. A digital device can perform such numerical functions using the binary number system: 0 or 1.

Logic gates are the basic circuit elements found in IC circuits that are used in digital systems. A logic gate has one or more logical inputs and only one logical output: true (represented by the binary digit 1) false (represented by the binary digit 0). The three main ways of specifying the function of a combinational logic circuit are: 1.Boolean Algebra – This forms the algebraic expression showing the operation of the logic circuit for each input variable either True or False that result in a logic "1" output. 2. Truth Table – A truth table defines the function of a logic gate by providing a concise list that shows all the output states in tabular form for each possible combination of input variable that the gate could encounter. 3. Logic Diagram – This is a graphical representation of a logic circuit that shows the wiring and connections of each individual logic gate, represented by a specific graphical symbol that implements the logic circuit. Combinational Logic

Fig. 28 Examples of basic logic gates formed using switches: a) AND gate; b) AND truth table; c) OR gate; d) OR truth table. a) b) c) d)

Combinational Logic: Example n.1 A + indicates that the piston rod of the cylinder A extends; A – indicates that the piston rod of the cylinder A retracts; B + indicates that the piston rod of the cylinder B extends; B – indicates that the piston rod of the cylinder B retracts; a0a0 a1a1 b0b0 b1b1 A+A B+B A−A− 0101 B−B− 1001 Fig. 29 Displacement-set diagram. Table 1 - The combinational relations between sensors and displacement-set diagram. a 0 indicates the switching-on of the end- stroke a 0 of cylinder A at its instroke position; a 1 indicates the indicates switching-on of the end-stroke a 1 of cylinder A at its extend position; b 0 indicates the indicates switching-on of the end-stroke b 0 of cylinder B at its instroke position; b 1 indicates switching-on of the end-stroke b 1 of cylinder B at its extend position. The automatic pneumatic system is composed by two pneumatic actuators named as A and B.

Combinational Logic: Example n.1 two pneumatic double-acting cylinder; two 5/2 double-solenoid valves; four 3/2-way roller-lever valves; one push-button. Fig.30 Pneumatic circuit for a combinational cycle. The combinational pneumatic circuit which is composed by:

Combinational Logic: Example n.1 A + command is active only when both signals m and b 0 are switched-on; A + is given by the AND logic gate because the Boolean function A + = m*b 0 ; B + command is given when a 1 is switched-on through the Boolean function B + = a 1 ; A − command is given when b 1 is switched-on through the Boolean function A − = b 1 ; B − command is given when a 0 is switched-on through the Boolean function B − = a 0. Fig. 31 Pneumatic circuit: A + Command. Fig. 32 Pneumatic circuit: B + Command.

Combinational Logic: Example n.1 Fig. 33 Pneumatic circuit: A - Command. Fig. 34 Pneumatic circuit: B _ Command. Initial position: double-acting cylinders A and B are supposed to be at the retracted position.

Sequential Logic Examples of sequential logic devices: flip-flops, are bi-stable devices because they can assume two and only two stable output states (0 or 1); latches, are flip-flop that are able to latch onto a binary state; shift registers, counters, –“Up-counters” generate a binary number sequence where each number is generated by incrementing the previous number by 1 –“down-counters” generate a binary number sequence in the consecutive descending order. and trigger devices with memory. Integrated circuits (IC) are used to perform important functions such as data storage (memory) and processing (ALU) in a microcomputer.

Sequential Logic: Example n.2 A lay-out of the proposed on/off system. The automatic machine is provided of four pneumatic cylinders A, B, C and D in order to perform the automatic cycle through suitable on/off displacements. Fig. 35 Lay-out of the electro-pneumatic circuit. Fig. 36 Displacement-set diagram. The automatic machine works as an event-based system in on/off environment

Sequential Logic: Example n.2 Fig.37 The sequential pneumatic circuit. Fig. 38 Grafcet diagram for the automatic cycle. 4 pneumatic double-acting cylinders; 4 bi-stable pneumatic valves; 4 mechanically actuated; 1 3/2 pneumatic push-button, 8 3/2-way pneumatic end- strokes valve; 7 AND valves; 6 OR valves; 2 sequential batteries. The sequential pneumatic circuit is composed by:

Sequential Logic: Example n.2 Referring to the Grafcet and the Sequential pneumatic circuit, In the first phase the cylinders A and B are extended, because of the signals A+ and B+, because the input of the first sequencer is an AND gate of a 1 and b 1 feed-back signals that come from the sensor system; In the second phase, both cylinders C and D are extended, because of the signals C+ and D+, respectively, and cylinder A retracts, because of the signal A-. The input of the second sequencer is an AND gate of a 0, c 1 and d 1 feed-back signals that come from the end-strokes; In the third phase, cylinder D retracts, because of the signal D-. The input of the third sequencer is d 0. In the fourth phase, cylinder A returns at starting instroke position and the input of the fourth sequencer is a 1. In the fifth phase, B and C retract, respectively, while D extends. The input of the fifth sequencer is given by AND of b 0, c 0 and d 1. In the sixth phase, cylinder C is extended, while D is retracted. The input of the sixth sequencer is given by AND of c 1 and d 0. In the seventh phase, cylinders A and C retract in order to start a new loop.