An electro hydro web aligner is an edge guide that reads the web edge with a photocell and corrects it with a hydraulic cylinder fed by a power pack. Krishna Engineering Works builds the electro hydro web aligner in Ahmedabad with a photocell sensor, an electrical panel board, an AC motor, a hydraulic cylinder, an adjuster and an oil pipe.
What is an electro hydro web aligner?
An electro hydro web aligner is a guiding unit in which the signal is electrical and the muscle is hydraulic. A beam of light measures where the web edge is, an electrical panel turns that measurement into a command, and oil under pressure moves the reel stand or steering frame.
It is the sister of the air sensing unit. Both use the same kind of power pack and the same kind of cylinder. The difference is the path between the web and the valve: a cable and a panel in place of an air pipe and a diaphragm. That one change decides which webs each unit reads well and which surroundings each one tolerates.
What does the electro-hydro unit include?
The electro-hydro web aligner (power pack) unit is made up of six named items. The table lists them with the job each one does.
| Item | What it does |
| Photocell sensor | Reads the position of the web edge with light |
| Adjuster | Carries the sensor and lets the operator set the guide point |
| Electrical panel board | Operates the complete unit: motor, sensor signal and guiding modes |
| AC motor | Drives the pump of the power pack |
| Hydraulic cylinder | Moves the stand or frame sideways |
| Oil pipe | Links the power pack to the cylinder |
The motor, pump, tank and valve sit together in the power pack. Each of those parts is explained on the hydraulic power pack page, which also gives the published flow, pressure and force figures of the standard models. The stand, slides or frame that the cylinder pushes belong to the machine.
How does photocell edge sensing work?
A photocell senses the edge by measuring how much light the web blocks. The description below is general to guides of this type.
- A light source and a receiver face each other across a gap, usually in a fork that sits astride the web edge.
- The web edge covers part of the beam. The further the web moves in, the less light reaches the receiver.
- The receiver turns the light it sees into a small electrical signal that rises and falls with the edge position.
- A cable carries the signal to the panel, where it is compared with the set point, the half covered position.
- The difference, called the error, is amplified and sent to the electrically operated valve on the power pack.
- The valve sends oil to one side of the cylinder, the stand moves, and the edge returns to the half covered position.
A photoelectric sensor reacts almost instantly, and an electrical signal travels along a cable without delay. This means the sensor can stand a long way from the power pack with no loss of response, which is the main practical gain over an air signal in a pipe.
How does the electrical signal become movement?
The panel and the valve turn a signal of a few volts into a force of hundreds of kilograms. The power for that comes from the oil, not from the signal.
The pump runs all the time and holds the pressure line ready. The valve acts as a tap that the panel opens one way or the other. When it opens, oil flows into the cylinder and the piston moves at a speed set by the flow. When the error has gone, the valve closes and the trapped oil holds the load rigidly in place. This is the working principle of every servomechanism: a weak signal steers a strong source of power, and the result is measured and fed back.
Because the cylinder holds its position on trapped oil, the stand does not creep when the web pulls on it. That stiffness is the reason hydraulic correction is kept for heavy reels, even when the sensing is electronic.
Electro hydro web aligner or hydro-pneumo web aligner?
Choose by the web and the surroundings, because the oil side of both units does the same work. The table compares the two on the points that usually decide the matter.
| Point | Electro-hydro unit | Hydro-pneumo unit |
| Sensing medium | Light, read by a photocell | Low pressure air jet |
| Signal path | Cable to an electrical panel | Air pipe to the power pack |
| Clear and translucent film | Needs care, since light passes through the web | Reads well, the film blocks the jet |
| Open, porous and net like webs | Reads well if the web blocks enough light | Weak signal, air passes through |
| Dusty paper and fibre | Lens needs regular wiping | Outflowing air keeps the ports clear |
| Distance from sensor to pack | Long cable runs are practical | Pipe length slows the signal |
| Solvent vapour at the sensor | Electrical parts must suit the area | No electrical signal at the sensor |
| Operator controls | At the panel | At the adjuster and the unit |
| Fault finding | Electrical checks plus oil checks | Mechanical checks only |
In short, the electro-hydro unit is the natural choice for opaque and porous webs, for long distances between the guide and the pack, and where the operator wants the controls on a panel. The hydro-pneumo web aligner remains the simpler answer for clear films, dusty paper and solvent areas.
Where does an electro hydro web aligner fit?
It fits the same positions as any other aligner: the unwind, the rewind and, with a steering frame, the middle of the machine. What changes is the kind of web and layout it handles best.
- Opaque and printed webs. Paper, board, foil, metallised film and coated fabric block the beam fully and give a strong, clean signal.
- Open and textured webs. Non wovens, woven sacks and open fabrics that let an air jet leak through still cast a usable shadow.
- Wide machines and long lines. The sensor cable can run the length of the machine, so the power pack can stand where it is easy to reach.
- Machines with a central control desk. The panel board brings the guide controls to the operator instead of leaving them at the reel stand.
- Heavy unwind stands. The hydraulic side moves a full reel smoothly and holds it between corrections.
At the unwind the cylinder shifts the reel stand. At the rewind the sensor travels with the stand, so the reel follows the web. In mid machine the cylinder tilts a tracking roller assembly. These three arrangements are set out on the web guiding system page, and typical machines are listed under power packs by machine.
Limits to know before you choose
An optical sensor reads light, so anything that changes the light changes the reading. The points below are common to photocell guides in general.
- Clear film. A transparent web lets most of the beam through. Some sensing arrangements cope with it, but say plainly in the enquiry if the web is clear.
- Dust and ink mist on the lens. A dirty lens looks like a web that has moved in. Wipe the sensor at each reel change in dusty areas.
- Strong stray light. Direct sunlight or a bright lamp shining into the receiver can upset the signal. Shield the fork if needed.
- Fluttering edges. A web that flaps in the gap gives a noisy signal. Mount the sensor close after a roller, where the web is supported.
- Hazardous areas. The photocell, cable and panel are electrical. Beside solvent based inks and coatings they must meet the safety rules for that area.
Setting up the electrical side and the oil side
Set up the oil side first, then the electrical side, then close the loop. A guide whose hydraulics are sound needs very little adjustment at the panel.
- Check by hand that the stand or frame moves freely over its full travel, and pin the cylinder to it at mid stroke.
- Fill the tank, start the motor briefly and confirm the direction of rotation.
- Using the manual controls, stroke the cylinder end to end several times to clear air from the oil.
- Mount the adjuster and photocell on a rigid part of the fixed frame, close after the roller that moves with the guided stand.
- Route the sensor cable away from motor cables and drives, and secure it so that it cannot be pulled by the moving stand.
- Thread the web at running tension and slide the sensor until the edge covers about half of the beam.
- Switch to automatic. The cylinder should settle near mid stroke and follow a gentle push on the web edge without swinging.
- Reduce the sensitivity if the stand hunts from side to side, and raise it if the response is lazy.
If the stand runs the wrong way when the guide is switched to automatic, the sense of the loop is reversed. That is a connection or panel setting matter, and it is put right before any tuning is tried.
Looking after an electro-hydro unit
An electro-hydro unit needs a clean lens, sound connections and clean oil. The checks are few, and most take seconds.
| Interval | Electrical side | Oil side |
| Every reel change in dusty areas | Wipe the photocell lens | No action |
| Every shift | Check that the web runs centrally in the sensor | Glance at the oil level |
| Weekly | Look at the cable and plug for damage | Look for weeping joints, note oil colour |
| When response slows | Check the sensor signal at the panel | Check the oil filter and the oil grade |
| After any repair | Confirm the direction of correction | Bleed the cylinder and top up |
These are intervals of general practice, and a hot or dusty plant will need shorter ones. Filters, pipes, cylinders and other wearing items are covered on the web aligner spare parts page. A unit that cleaning and adjustment can no longer bring back can go to the repairs and servicing department.
Related units in the range
The electro-hydro unit is one of three ways the same power pack is supplied. The web aligner unit page describes the standard kit with its pipes, filters and cylinder. Where a machine has two or three guides, double and triple hydraulic power units carry a servo valve for each guide on one reservoir.
Guiding by sensor type and actuator type is covered on the client’s web guide system site. The full range on this site is listed on the hydraulic power pack products page.
What to send for an electro hydro web aligner quotation
Send the details of the web, the load and the layout, and the unit is matched to them. Every unit is made in the company’s own factory in Ahmedabad and is given a continuous trial before dispatch.
- Machine type and the guide position: unwind, mid machine or rewind
- Web material, and whether it is opaque, clear, metallised, printed or porous
- Web width range, and whether you guide to one edge or to the centre
- Line speed
- Heaviest reel and the type of stand or frame to be moved
- Distance from the sensor to the place where the power pack and panel can stand
- Electrical supply at the machine
- Conditions near the sensor: dust, solvent vapour, heat, strong light
- Make and model of any unit being replaced
Send the enquiry through the contact page.
Frequently Asked Questions
What is the difference between an electro hydro and a hydro pneumo web aligner?
The difference is the sensing method. An electro hydro web aligner reads the web edge with a photocell and passes an electrical signal through a panel to the valve. A hydro pneumo web aligner reads the edge with a low pressure air jet and passes an air signal along a pipe. Both correct with the same kind of hydraulic cylinder.
Can a photocell sensor guide transparent film?
Not easily. A plain photocell depends on the web blocking light, and clear film lets most of the beam through, so the signal is weak. Some optical arrangements are made for clear webs, but air sensing is the more usual answer. State clearly in the enquiry that the web is transparent, so the right sensing method is proposed.
What does the electrical panel board of the unit do?
The electrical panel board operates the complete unit. It starts and stops the motor of the power pack, receives the signal from the photocell, and gives the operator the controls for the guide. In guides of this type the panel normally offers automatic guiding and manual movement of the cylinder, which is used for threading and for bleeding air.
How far can the photocell be from the power pack?
Much further than an air sensor can. An electrical signal travels along a cable without the delay that an air signal has in a pipe, so the sensor can sit at the guide while the pack stands some distance away. The oil pipes still matter: keep them short, because long oil runs slow the cylinder.
Is an electro hydro web aligner suitable for non woven and open fabrics?
Yes, in most cases. Webs that are too open for an air jet still block enough light to give a photocell a clear edge. Very thin or very open materials can let light through as well, so describe the web and its weight in the enquiry. A sample of the material settles the question quickly.
Why does the stand run to one end when I switch to automatic?
The stand runs to one end when the photocell does not see the edge or the loop is connected in the wrong sense. Check that the web edge is inside the sensor, that the lens is clean, and that the cable is plugged in. If the stand moves away from the edge instead of towards it, the direction of correction must be reversed.
Does the electro-hydro unit use the same oil as other KEW power packs?
It uses a hydraulic power pack of the same family, so the same care applies: a light hydraulic oil of the grade named for the unit, filled clean and kept clean. Confirm the oil grade for your unit when you order, do not mix grades, and change the filter element whenever the oil is changed.