BOOK 2, CHAPTER 22: Synchronizing the Movement of the Cylinder (2023)

Synchronization of cylinder circuits

On some multi-cylinder machines, the cylinder strokes must be perfectly synchronized for the machine to function properly. If all the loads, line sizes and lengths, and the friction of the cylinders and machine elements are the same, they can all run at the same time and at the same speed. Although thread sizes and lengths and machine loading can be controlled to some extent, friction is constantly changing. Therefore, if cylinders need to work together, use a method to synchronize them.

One way to synchronize the cylinders is with external mechanical hardware. Some common mechanisms are racks and pinions, crankshafts, cables and pulleys, chains and sprockets. The accuracy of these methods depends on the resistance of the hardware and the location of the load. Mechanical methods are the most common way to accurately time air cylinders. An advantage of mechanical timing is that the cylinders can operate at any point in their stroke without losing phase. The accuracy of the mechanical time is approx.±0.005 to 0.010 inches. -- depending on load variation and resistance of mechanism used.

Hydraulic cylinders can be synchronized most precisely with servo valves. Servovalves control each cylinder independently with electronic position feedback, comparing each actuator's position to all others. This is the most expensive way to synchronize cylinders, but it is the most accurate. drive position inside±0.001 to 0.002 inches apart can be achieved with good servo practice. (This type of timing also works well with cylinders that never come home.)

This chapter describes ways of synchronizing cylinders with other hydraulic drive components. These circuits show how the components must be laid out to keep different cylinder positions close together. The simplest circuit just uses flow controls to create resistance to hold the cylinder in place. Flow control timing accuracy is moderate to poor. Some of the more complex shapes, like using tandem cylinders or a master-slave cylinder arrangement, keep the relative position as low as possible.±0.010 a 06 pol.

In order to use the hydraulic power components to synchronize the cylinders, all cylinders must reach positive dead center at the end of each cycle. Leaks at cylinder or valve seals cause small differences in position after each stroke. If all cylinders bottom or reach a positive level stop, the error cannot be accumulated for each cycle. This is the main reason for not using smooth power timing on cylinders that only run mid-stroke.

When testing cylinder control on a machine, always start the circuit with the cylinders disconnected from the machine. Bicycle cylinder without an attached load. This allows a safe time for venting and valve adjustment. Sudden or out-of-control movements do not affect machine limbs.

Synchronization with flow controls
The circuit in Figure 22-1 has no controls other than the directional control valve. If the pipes are all the same relative size and all the same length; when the load is centered; and if the friction of all parts were identical, the cylinders could travel exactly together. Some of these variables are controllable, but things like friction can change even during a single cycle. In the configuration of Figure 22.1, the cylinders actually move in sequence until they reach the end of their stroke or mechanically lock.

With the off-center load shown in Figure 22-2, the cylinder farthest from the load would extend until it was balanced or locked before the opposite cylinder began to operate.

Adding output flow regulators to each cylinder port, as shown in Figure 22-3, adds variable resistance for each cylinder. The additional resistance may need to be changed throughout the day as many factors affect cylinder movement.

The flow control timer circuits are driven by pneumatic or hydraulic cylinders. For air cylinders, the compressibility issue contributes to potential instability. However, without resorting to a mechanical or hydraulic option like the tandem cylinder shift described in Chapter 3, this is the only way to synchronize the air cylinders using hydraulic power alone.

With current controls, the cylinders stay reasonably in sync only when the position of the load does not change. As the load moves, the force on the cylinder must change to maintain synchronization. If the load position changes infrequently, resetting the flow control is an option.

The same goes for the hydraulics. Another problem with unequal loads is what happens when the cylinder doesn't move all the way. If the cylinder stops mid-stroke, as in Figure 22-4, oil from the filled cylinder can spill over to the opposite cylinder and pull the distributor plate. Figure 22-5 shows pilot operated check valves added to the end cap lines to prevent oil carryover during mid-stroke stops. With these check valves installed, oil cannot be transferred when the cylinders stop mid-stroke, allowing the cylinders to maintain their position.

Another issue with flow timing is maximum lifting power. With two identical cylinders placed parallel to each other, the plate must be able to lift twice the force of each cylinder. However, this only applies if the load is centered. With a double load on one cylinder, that cylinder would stop while the opposite cylinder tried to extend. When using timing for flow control, size each cylinder to carry the full load when the load can get off center.

When controlling hydraulic cylinders it is best to use pressure compensated flow controllers. Pressure compensated flow regulators maintain constant flow when load differentials cause the pressure drop to change.

Double piston cylinder in series

Figure 22-7 shows a very precise way of synchronizing cylinders with synchronized cylinders connected in series. The directional valve oil extends the first cylinder, the top port of the first cylinder supplies oil to extend the second cylinder, and the top port of the second cylinder is connected to the other directional valve port. With this arrangement, oil trapped between the cylinders must have a way of being refilled or drained. As this circuit operates, leakage from the cylinder seal will either decrease or increase the trapped volume. Both situations adversely alter synchronization.

Figure 22-7. Distribution circuit with double-piston cylinders in series, idling when the pump is running.

In Figure 22-7, if the spring-centered, tandem-centered, single-solenoid, 2-position air suspension valveDis de-energized, allows oil to flow out of the cylinder (A)for cylinder (MI)🇧🇷 The valve is deactivated while the cylinders extend and retract to work. (Figure 22-10 shows how the cylinders are leveled at the end of a cycle.)

closing magnetA1of the main directional control valve, as shown in figure 22-8, supplies oil to the cylinder (A), causing it to spread. Oil from opposite end of cylinder (A)flows through the air suspension valve (D)to the axial end of the cylinder (MI)🇧🇷 Oil from the opposite end of the cylinder (MI)flows through the main directional control valve into the tank. When the trapped volume is completely full and all seals are tight, the cylinders are almost perfectly synchronized regardless of the load position.

Energize solenoid to retract cylinderB1of the main directional control valve as in Fig. 22-9. This supplies oil to the retract side of the cylinder (MI)🇧🇷 Oil from the opposite end of the cylinder (MI)flows through the air suspension valve (D)to the top of the cylinder (A)🇧🇷 Oil from the opposite end of the cylinder (A)flows into the tank via the counterbalance valve and the main directional control valve.

Figure 22.10 shows how the cylinders stay in sync as they rotate. As the board approaches the ground, it makes contact with the limit switchesBjF🇧🇷 If the switches are pressed at the same time, no leveling takes place. If one limit switch works before the other, the cylinders are obviously asynchronous, so the magnetC1at the air suspension valve is energized. with solenoidsB1jC1energized, pump oil flows to the retracting sides of the cylinders (A)y (MI), forcing them to retreat completely. cylinder (A)y (MI)It can be retracted as the extended sides of both cylinders have a direct path to the tank. When both limit switches are activated, the leveling valve and retract solenoids are deactivated. (This leveling circuit also works with horizontally mounted cylinders.)

With in-line cylinder control, the location of the load is not important. Cylinders remain level regardless of loading position or weight. The only thing that can cause severe off-center loading is more seal leakage or oil volume changes due to compressibility.

It is important to note that since the cylinders are connected in series, each must be able to lift the full load. No matter where the load is or how many cylinders are connected in series, everyone must be able to lift the full load. At the same time, when calculating the pump flow, only the volume of one cylinder is taken into account.

Other ways to use cylinders in series
Use the circuit in Figure 22-11 to save cost, reduce potential leakage from additional rod seals, and eliminate the space required for the second rod. The cylinders in this circuit face each other, so one extends while the other retracts. This is a way of synchronizing cylinders with a piston rod in a series connection. Mating identical piston rod volumes allows series synchronization in the same manner as double rod end cylinders. Clearance for the top cylinder can be a problem on some machines, so the circuit in Figure 22.12, while more expensive, works just as well. (Use the same tandem mid-valve timing circuit as in Chapter 21, Figures 7-10 to align the cylinders after each stroke.)

The assembly is more conventional, using three coated cylinders with a piston rod, as shown in Figure 22-12. The sole purpose of the cylinder (B)is to connect equal areas. This design is still cheaper than two synchronous cylinders and has one less leak source. This circuit requires return valves that operate the cylinder (C)retract, cylinder (A)retract without cavitation, and the cylinder (B)to fall if the other two do not reach the starting position at the same time.

Figures 22-13 through 14 show how to achieve adequate time with a set of compensating flow regulators on stock single rod end cylinders. The cylinders are extended in Figure 22-13. Oil from the directional control valve flows through the needle valve (C)to the end of the head (B)How to control your speed. At the same time, some tapping oil flows from the directional control valve through the needle valve (D)to the end of the head (A)🇧🇷 Adjust the needle valve (D)to compensate for the decrease in oil volume as it flows from the rod end of the cylinder (B)to the end of the head (A)🇧🇷 Without needle valve (D), cylinder (A)it would delay each cycle and get out of sync. Flow change in the needle valve (C)means readjustment of the needle valve (D)What else. Both needle valves work best when they are pressure compensated. This is a problem in this circuit as there is bi-directional flow. See Chapter 10, Figure 10-4 for a pressure-compensated needle valve connected for bi-directional flow.

To retract the cylinders, the directional valve shifts as shown in figure 22-14, drawing oil into the rod end of the cylinder (A). as cylinder (A)retracted, oil is transferred from the cap end to the rod end of the cylinder (B)🇧🇷 Cylinder excess oil volume (A)goes through the needle valve directly into the tank (D)🇧🇷 Needle valve (C)controls the ascent and descent speed of the plate.

Each cylinder in a series connection must have enough power to lift the entire load. When the position of the load changes, due to the resulting change in pressure drop across the needle valve (D)🇧🇷 An off-center load too heavy for a cylinder to lift still allows oil transfer through the needle valve (D), which keeps the deck asynchronous. Add Pilot Operated Check Valves (MI)whether the cylinders must stop mid-stroke. Without these pilot operated controls, the oil transfer through the needle valve (D)Allows cylinders to be moved.

Double pump and valve control circuit

Figures 22-15 through 18 illustrate a common method of synchronizing cylinders. Many designers use this circuit and consider it one of the best ways to synchronize cylinders. It's fairly accurate, but can cause cylinders to drift under certain conditions.

The two pumps in Figure 22-15 have identical flow rates. They are connected to two spring centered double solenoid valves connected to two equal cylinders. Both pumps have a relief valve set to the same maximum pressure. Because both pumps have the same flow rate and both cylinders use the same volume, the cylinders move at roughly the same speed.

The cylinders are shown extended in Figure 22-16. closing magnetA1jA2at the directional control valves simultaneously causes the cylinders to extend evenly. If a cylinder's charge needs more pressure, the pump on that side will continue to deliver nearly the same flow until the relief valve exhausts.

Energize the solenoids to retract the cylindersB1jB2on both directional control valves at the same time, as in Figure 22-17. The cylinders retract at the same speed.

If the cylinders are out of phase, Figure 22-18 shows how to reprogram them. Because each cylinder is controlled by a separate pump and valve, separate limit switches de-energize the retract solenoids after the cylinders are at rest. This leveling occurs automatically with each cycle, so position errors do not accumulate.

A major problem with this timer is the difficulty of finding two identical bombs. Even pumps manufactured at the same time often have slightly different flow rates. Any fluctuation in pump flow will cause the cylinders to be out of phase. Another issue is efficiency. As pressure increases, pump efficiency allows more oil to flow, valves leak more, and some cylinder seals deviate more. All of these losses lead to poor performance, especially when the cylinders have long strokes.

Also, what if a solenoid is slow or not working? This causes a cylinder to start late or not at all. A late start will cause the cylinders to be out of phase; If you do not start at all, the machine could be damaged.

This circuit has the same performance problem as a flow control timing circuit. Each cylinder must be able to lift the entire load. If the load in this circuit is too high for a cylinder, its pump is unloaded via the unloader valve and the cylinder stops. Here, too, the other cylinder continues to extend until it damages itself or the machine.

Improved dual pump and valve timing circuit
The circuit modifications shown in Figure 22-19 solve most of the problems mentioned in Figures 22-5 through 18. Instead of using two cylinders as before, use two or more pairs of cylinders. Connect half of the cylinders to each pump/valve combination. pipe connectionONEdirectional valve(MI)for cylinder heads(ONE)j(C)🇧🇷 HakenanschlussBdirectional valve(MI)for cylinder doors(B)j(D).pipe holderONEdirectional valve(F)to the end of the cylinder head(B)j(D)with theirBConnection hooked to the connecting rod cylinder connections(ONE)j(C).When the circuit is piped in this way, one pump and valve are used to extend two cylinders while the same valve retracts the cylinders extended by the other pump and valve.

If a solenoid fails, as in Figure 22-19, the platen will not move because the cylinders(ONE)j(C)may attempt to spread, oil from rod end fittings cannot flow back through valve to tank(F).Also, blocked intake flow to the cylinders(B)j(D)on the valve(F)prevents them from moving even though they leak through the spool into the valve(F)may allow minor movements.

After both directional control valves move and the cylinders operate as shown in Figure 22-20, the pairs of cylinders try to stay level. yes bomb(GRAMM)produces a larger flow, cylinder(ONE)j(C)try to run ahead. why cylinder(B)between them, it will hold or be pulled by the other cylinders. The plate must be strong enough to transfer this differential cylinder load without flexing.

This circuit is less load sensitive since the load is always on a pair of cylinders operated by different pumps. Both pumps unload the tank before the cargo stops moving. However, lightly loaded cylinders can advance in terms of plate stiffness and spacing between cylinders.

Only use a limit switch with this cylinder arrangement. To phase the cylinders, change both directional control valves to send the cylinders to their home position. A relief valve diverts fluid until the lagging cylinders hit the positive stop.

Shifter type current divider synchronization circuit

Power divider in the form of a snakeSplit the flow of a single conductor into two separate flows. The split flows can be at different rates if needed, but for cylinder timing they are usually the same. Spool flow dividers basically consist of two pressure-compensated flow regulators in one housing. With this arrangement, the pressure drop from each flow control modifies the opposite flow output. Because these flow controllers are constantly analyzing each other's pressure drop, they split the flow relatively well. (Most manufacturers say so±5%, depending on the pressure difference at the outlets.)

A problem with coil-type flow dividers is that they do not allow reverse flow. Even if they did, there would be no guarantee of an even flow. A spool-type flow splitter/combiner allows both forward and reverse flow and equally divides or combines the two flows. Typically, a flow divider/combiner is the component of choice in cylinder distribution circuits. Figure 22-21 shows a control circuit for a coil-type flow divider/combiner. It is similar to a dual pump circuit but uses only one pump and one valve. The volume flow is divided behind the one-way valve.

In Figure 22-22, the cylinders are extended. shift magnetA1in the directional valve directs oil to the flow divider, which directs half of the pump flow to each cylinder. Even with a pressure difference in the cylinders, the flow rates are almost the same. Even with off-centre loads, the cylinders extend at about the same speed. Each cylinder must develop enough force to lift the load above it. If one cylinder hits its performance limit and stalls, the opposite cylinder will try but not fully stop due to internal leakage in the flow divider spool. (Figure 22-24 shows the condition of the flow divider when the cylinder(B)stops when entering.)

Figure 22-23 shows the circuit after energizing the solenoid.B1on the 4-way valve. Oil flows to the piston rod ends of the cylinder while fluid from the cylinder head ends is evenly combined in the flow divider and flows into the tank. The flow divider holds back the extending cylinder and thus maintains synchronization. When the cylinders bottom out, they roll back automatically if the directional control valve is left in down mode long enough. An internal leak in the flow divider spool allows the retarded cylinder to continue its stroke. (Some brands of flow dividers have built-in bypasses that operate when the pressure difference reaches a preset limit.)

Because the flow divider shares a common path internally, fluid can flow between the end cap ports. When cylinders must stop mid-stroke, always use pilot operated check valves.(C)prevent oil transfer. Control overload with a counterbalance valve(MI)between flow divider and directional control valve.

Slider type current dividers waste energy. Observe the reading on each cylinder when extended,PG2indicates 800psi while PG3 indicates 300psi. In this situation, measurePG1The pump reads 800 psi. The 500 psi drop on the right side of the flow divider generates heat as the cylinders extend.

Slider current dividers only divide the current into two outputs. It would require three coil-type flow splitters to split the flow in four directions.

Motor type flux divider timing circuit
Motor type flow dividerThey don't waste energy and are more versatile. A motor-type flow divider can split the flow of a pump and drive two or more cylinders together. In addition, they offer multiple exits, up to ten or more, to be able to pass irregular flows if necessary.

A motorized flow divider consists of two or more hydraulic motors in one housing. The motors have a common shaft. So when one motor spins, all motors spin. The motors share a common input but have separate outputs. The pump liquid enters all motors simultaneously and rotates together. If the engines are the same size, the power of each section is an equal share of the incoming oil. Since a mechanical motor divides the flow instead of an orifice, there is no energy loss due to different outlet pressures. Figure 22-25 shows a motor-type flow divider synchronizing two cylinders. The flow divider is installed between the directional control valve and the cylinders of this circuit.

In figure 22-26 solenoidA1is energized to turn on the 4-way directional control valve. This directs oil to the flow divider, which sends equal amounts to each cylinder. The accuracy of motorized flow dividers depends on the pressure difference at the outlets. Engines have internal slip that increases as the pressure drop increases. The greater the pressure differential, the greater the flow differential and loss of synchronization.

In Figure 22-27, the cylinders are retracting. Energizing the B1 solenoid on the directional control valve draws oil from the pump to the rod ends of the cylinders. As the cylinders retract, oil flows from the ends of the heads through the flow divider into the tank. The flow divider adjusts the cylinder flows and maintains synchronization when the cylinders are free to move.

When a cylinder stalls and stops moving, as in Figure 22-28, all of the pump oil flows into the free-moving cylinder. The section of the flow divider not receiving oil from the stationary cylinder continues to rotate and cavitates, causing the free cylinder to retract at double the speed. If the cylinders are likely to clog, install an engine-type flow divider on both ends of the cylinders. A flow divider at the end of the rod forces the connecting cylinder to synchronize or stop both.

The inherent slippage of engine flow dividers is usually sufficient to balance the cylinders. Another option is integrated relief valves that allow fluid to bypass an engine at a predetermined adjustable pressure.

As mentioned, one advantage of motorized flow dividers is that they consume little energy. Note the counter values ​​in Figure 22-26. The left cylinder requires 900 psi while the right cylinder only requires 300 psi. Under these conditions, the inlet pressure to a spool flow divider should be 900 psi. With a motor flow divider, the input pressure should only be 600 psi. Since the motor-type flow divider is mechanically connected via a common shaft, the transfer of energy between the sections reduces the required inlet pressure.

Another advantage is that motorized flow dividers with two, three, even ten or more outlets are common. Instead of stacking spool style manifolds with two outlets, for many circuits use only one motor flow divider with multiple outlets.

A word of caution: engine-type flow dividers increase output pressure when in operation. (See Chapter 11 for an explanation of engine-type flow divider step switching.) On a 2-port equal-sized flow divider, if the relief valve pressure is greater than half the maximum pressure rating of a driven component, install a relief valve on each output. 🇧🇷 Outlet relief valves protect cylinders, valves and lines from over pressure.

Synchronization circuit for master and slave cylinders
Figures 22-29 through 32 show one of the most accurate ways to hydraulically synchronize cylinders. Figure 22.29 shows the circuit at rest. cylinder(C)- mechanically connected to two cylinders(D)-- Provides the driving force. That(D)Cylinders have the same bore, stroke and rod as the power cylinders(ONE)j(B).a cylinder(D)connects to the cylinder(ONE),while the other cylinder(D)connects to the cylinder(B).In the event of external leakage, equalizing non-return valves(H)Allow oil to enter the dead areas of the cylinders(ONE),(B),j(D)at low pressure A 75 psi check valve in the tank line provides sufficient pressure to ensure the trapped volume of oil remains full. level control valves(J)through the(METRO)Retract cylinders to home position if out of phase. limit switch(F)j(GRAMM)indicate the starting positions of the cylinders and actuate counterbalance valves when the cylinders lose synchronization. counterbalance valve(MI)prevents the cylinders from deflecting when retracting.

cylinder power(C)Just do the whole operation yourself. This cylinder generates all the power and transfers it to the slave cylinder.(D),then to the working cylinders(ONE)j(B).

The location of the cargo on deck affects the time only slightly. The master/slave transmission moves the same amount of oil regardless of the pressure. cylinder(ONE)it operates at twice the pressure at a peak load than at a mid-load. To protect cylinders from over-pressurization, set the relief valve to no more than half the cylinder's rated pressure.

Figure 22-30 shows the solenoidA1on the 4-way valve offset to the extending cylinder(C).cylinder(C)pressure cylinder(D),and oil from the tops of their heads(D)flows evenly to the ends of the cylinder head(ONE)j(B)🇧🇷 Cylinder ball joint oil(ONE)j(B)returns to the sides of the cylinder rod(D). cylinder(ONE)j(B)extend together when the cylinder(C)It has enough energy to get the job done. If one working cylinder stops, both stop.

To retract the power cylinders, energize solenoid B1 on the 4-way valve as shown in Figure 22-31. cylinder(C)then retract both slave cylinders and pull(D)back and forces the working cylinders(ONE)j(B)also withdraw.

If the work rolls lose synchronization, the circuit diagram in Fig. 22-32 shows how they level off. While solenoid B1 remains energized on the 4-way directional valve, energize solenoids A2 through A5 on the 4-way valves.(J)through the(METRO)🇧🇷 This directs oil from the pump to the sides of the cylinder rod.(ONE),(B)j(C),and on the sides of the cover of both(D)Cylinder. At the same time oil from the sides of the cylinder head(ONE),(B)j(C)and connecting rod sides of both cylinders(D)flows into the tank. In this state, the pump forces all cylinders to their home positions, ready for the next cycle.

This circuit is an accurate but expensive way to synchronize the cylinders. An advantage is that the master and slave cylinders can be located remotely, making the work area less cluttered. In addition, the power transmission minimizes the required cylinder size and still handles off-center loads.

Tandem cylinder synchronization circuit

Figure 22.-3 shows another very precise method of synchronizing the cylinders. The tandem cylinders of this circuit must meet in the middle even if the forces are unequal.

Tandem cylinders consist of two cylinders in one housing. They have four ports and the rear cylinder has a single rod end while the front cylinder has a double rod end. Because the front cylinder has a double-rod end, it has equal areas and volumes on both sides of the piston.

Note that the 4-way valve feeds piston rod cylinders conventionally. For twin piston cylinders, the front left cylinder port is connected to the rear right cylinder port and the front right cylinder port is connected to the rear left cylinder port.

Tandem cylinders move in unison and transmit power because the hydraulic flow brings them together. If one of the cylinders stops, both cylinders stop. Before the cylinders stop, energy is transferred through the tandem cylinders, trying to force the lagging cylinder to do its work. The lagging cylinder can see up to double the force before locking.

The two check valves(C),Driven by a 75 psi back pressure check valve in the tank line, allows the makeup oil to enter the trapped volume of the tandem cylinders. The pump compensates for leaks in the enclosed volume using non-return valves(C).The boost pressure is equal on both sides of both cylinders, so 75 psi has no effect on them. Always provide vent holes on both ends of tandem cylinders to release trapped air.

2-way valve, normally closed(D) between the tandem cylinder connecting lines opens to level the cylinders at one end of the stroke. Leaks in the cylinder piston seals can cause the cylinders to go out of phase. Valve(D) opens at limit switch(MI) j(F) Do not do this at the same time as the cylinders are retracting. If a limit arrives first, the valve(D) opens and allows fluid transfer from one end of the piston rod cylinder to the other until both limits are reached.

In figure 22-34 solenoidA1of the 4-way valve is energized and the cylinders extend. When extending, the oil transfer in the tandem cylinders remains almost perfectly synchronized. If one of the cylinders tries to overrun, power is hydraulically transmitted through the cylinder banks in tandem to keep them in unison. If the load is too great for both cylinders, they stop.

Figure 22-35 shows the retraction of the cylinders. closing magnetB1The 4-way directional control valve directs fluid to the rod ends of cylinders with a piston rod. When the cylinders are retracted, the cross tubes of the piston rod cylinders keep the machine in sync just as much as when they are extended.

As the cylinders near their starting location, they are leveled or ground as needed, as shown in Figure 22-36. limit switch(MI) j(F) both must center the 4-way valve. When a limit switch moves forward, the magnetC12-way valve(D)is energized, allowing the retarding cylinder to transfer oil until it reaches its limit switch.

This timing circuit works equally well with air as the power source for single rod end cylinders. Use oil in tandem cylinders as it does not compress. Oversized oil flow lines to 2-4 fps to maintain reasonable speed. Install a spare oil tank with check valves to supply the tandem cylinders when needed.