Problem description: A doubl double-a e-acti cting ng hydra hydrauli ulicc cylind cylinder er is used used to open open and and close close a furna furnace ce doo doorr. Inchin Inching g operation allows the door to be driven to any desired intermediate position. The cylinder is hydraulically clamped in all such position. The above process can be automated using electrohydraulics. The proposed (theoretical) hydraulics circuit is shown below (igure !):
Problems encountered by theoretical circuit: "ith the above circuit# both $% and $& has to be actuated to allow the piston to e'tend. If the cylinder is to be stopped during its forward stroe at any intermediate position between its end positons# $& is de-actuated. evertheless# during the return stroe# the piston could not be stopped at any an y intermediate position.
*oreover# pressure built up in the piloted non-return valve when $% was pressed and $& was not. This +ammed the non-return valve and thus compromised its use. The latter had to be depressurised using a pressure-relief tool. Therefore we redesigned and implemented another electrohydraulics circuit to mitigate all the above problems. The electrohydraulics circuit is shown below:
Figure 5: Implemented electrohydraulics circuit for door control
The typical price range of double-acting cylinders used in the practical (esto) Do you know the price of the equipment set for “Electrohydraulics Basic Leel !"#$%&? What is the purchase price of a hydraulic e'caator?
A typical hydraulic e'cavator used primarily for ditch cleaning and small e'cavating applications costs about 3&4ȫ which is about 1s 6.7millions in terms of local currency. The annual maintenance fee is about 365#555 which is about 1s/%7555.
Exercise 9 – Feed for drilling machine
Problem description: The feed of a drilling machine is to be automated. "hen carrying out drilling with large diameter drilling bits# it is necessary to achieve constant feed characteristic and a finelyad+ustable feed speed. The machine is therefore to be e8uipped with hydraulic feed# which must provide a rapid-traverse feed motion and a infinitely-ad+ustable woring feed motion. The return stroe is to be initiated by pressing a second pushbutton. uring this phase# the flow control valve is to be bypassed by means of a non-return valve. The above process can be automated using electrohydraulics. The proposed (theoretical) hydraulics circuit is shown below (igure 7):
It should be noted that the for the hydraulics circuit# only the components were given and therefore# the connections had to be done.
There is only one limitation with the proposed circuit (igure 7)# which is the unavailability of the &&-way spring-return# solenoid actuated valve. Therefore# the latter was replaced by a !/-way spring centred# solenoid actuated valve and the circuit was properly implemented and tested on the board. The redesigned circuit is shown below (igure 4):
Figure 7: Implemented electrohydraulics circuit for automation of feed for drilling machine
,omponents used: • • • • • • • •
ouble acting cylinder 9imit switches (roller lever valves) % and & Pressure gauge !/-way valve# spring centred# solenoid actuated ;ne-way flow control vale !& way valve# spring return# solenoid actuated *ain switch button# pushbuttons / and ! 1elay switches 2% and 2&
What is the purpose of the “(ydraulics )$$$& !ransparent models? What do these transparent models illustrate more clearly than the components mounted on the pro*le plate? (ae you worked with the “(ydraulics& electronic transparencies?
Exercise 12 – Assembly device
Problem description: An assembly device is used to press-fit a plastic bush into a steel worpiece. A screw is then inserted to secure the connection. "hen the TA1T pushbutton % is pressed# the vertical double-acting A presses the plastic bush into the steel worpiece. "hen the pressure in the piston chamber of the press cylinder reached !.< *Pa (!.T?1 pushbutton & is pressed# the press cylinder A retracts and the motor * stops. ome parameters to be respected:
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The cylinder must no slip when the hydraulic power pac is switched off. *easures must be taen to ensure that the motor cannot rotate clocwise under any
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circumstances. A visual indicator must show the position of the detended 1>T?1 pushbutton &. The
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visual indicator must not go out# allowing a restart# until the switch has been unloced. The above operation can be automated using electrohydraulics. igure @ below shows the designed and implemented electrohydraulics circuit. ,omponents used: • • • • • • • • • • •