Advanced Hydraulic Motion Control Design Practices High-performance hydraulic motion Good Design Practices Overview Affect of system components on control Compensating for design deficiencies Know where design can be modified to meet design requirements Good Valve Hard Piping Accumulato r Feedbac k Cylinder Pump Controller Reservoi r Good Design is Simple! Good Design Provides… • Excellent Control! – Accuracy < 0.001 inch, even while moving – Complex motion profiles – Synchronization (no flow dividers) • Smooth startup • Less maintenance • Less tech support • Higher Initial Cost (not always) • May not be possible Real-life design pressures • Cost – Valve: good valves are much more expensive – Feedback: high resolution is more expensive – Larger cylinder  larger valve  larger pump • Availability – Linear valves may have longer lead times (Rexroth) • Special requirements – Space constraints: valve location – Environment: valve location Real-life design pressures Understanding control features Meet Design Requirement s Closed-Loop Control Review Control Review Target Position Control Signal (V) Actual Position Control Review Each PID gain contributes to the control output signal • Proportional Gain • Integral Gain • Differential Gain • Velocity Feed Forward • Acceleration Feed Forward 10 Cylinders 45 Remote Valve is similar to Narrow Cylinder Cylinders Sizing is Difficult Large Bore Small Bore Stiffness Energy Savings Force Cost Savings Cylinder size affects: • System Response • Valve size • HPU size 46 Cylinders VCCM Equation Enhanced VCCM v(t)  Sizing Calculation Methods • Good for calculating steady state speed • Enhanced for motion dynamics • Produces acceleration times c0 * ( c12  * c0 * c2  c1) * (e c12 4*c0*c2*t 1) c1* c12  * c0 * c2  * c0 * c2 * (e c12 4*c0*c2*t 1)  c12 47 Thanks to George Keller, Jack Johnson, Peter Nachtwey Controlling Sloppy Systems Low Natural Frequency Forc Spring absorbs e energy during acceleration, then releases it 48 Mass Low Natural Frequency Mass Velocity Feed Forward Jerk Feed Forward Provides extra boost during beginning of acceleration, pulls back during end of deceleration Target Accel Acceleration Feed Forward Jerk Feed Forward 49 Jerk Feed Forward Low Natural Frequency Mass Double Differential Gain Low Natural Frequencies require extra control f the acceleration Double Differential Gain Target Accel Actual Accel 50 Low Natural Frequency Mass 51 Double Differential Gain Quantization Noise Low Natural Frequency Observer Calculates actual acceleration based on the mathematical system model Mass This Actual Acceleration is very clean, allowing the double differential gain to be used Output Filter is also possible It filters the result of the Double Differential Gain, does not filter actual acceelration 52 Low Natural Frequency Mass Prerequisites to using Double-Differential Gain • High resolution feedback • High response, linear valve 53 Cylinders 54 Real-Life Cylinder Example Sawmill • A number of years ago, sawmill OEM needed assistance tuning during new sawmill startup • Delta suggested increasing cylinder bore to achieve proper stiffness • OEM replaced cylinders Cost: Several $100,000 • Now, with advanced tuning, it is possible to control smaller cylinders • Higher-order tuning is complex, so should be approached with caution Cylinders 55 Real-Life Cylinder Example Sheet metal brake • Customer designed brake with one cylinder on either end, one valve in middle Approx ft hose to each • Customer requested assistance tuning • After hours of tuning, met specs This required Double-differential gain • Pros: customer achieved competitive machine price • Cons: Difficult tuning, maintenance tuning requires great expertise Cylinders 56 Real-Life Cylinder Example Radioactive cell • Hydraulic cylinder in a radioactive cell • Due to radiation, valve needed to be outside of cell, resulting in long length of hose • Higher-order tuning was successful Cylinders 57 Real-Life Cylinder Example Large Pool • In House of Dancing Waters in Macau, hydraulic cylinders were in large pool • Valves needed to be outside of pool, resulting in long length of hose • Higher-order tuning was successful Summary Proper hydraulic design saves time and money 58 Real-life demands may require compromise Modern motion controller features compensate for design deficiencies Summary • Undersized Cylinder or remote valve • Poor Valve • Noisy Feedback 59 Problem Many Problems [...]... D Gains operate only if an error exists PID-only will not follow target exactly Feed Forwards eliminate error 18 Control Review Important! Gains and feed forwards are linear equations! Therefore, The hydraulic system should be as linear as possible! 19 How Components Affect Control 20 Critical Components Accumulator • Size • Type • Size • Close to cylinder Valve Feedback • High resolution Cylinder... algorithm 28 Appears linear to PID and feed forwards Good Control Valve Single-Knee Spool  Historically, lower gain section used for low flow, higher gain used for high flow  Modern high resolution of motion controllers and valves make this reason nearly obsolete Auto-tuning non-linear valves is difficult because system exhibits two different gains Unfortunately , single-knee spools may be more available... One Solution: Turn of integrator during move Won’t track well, but will not overshoot and will hold final position 31 Overshoot Valve Overlapped Spools (deadband) Doesn’t accurately reach position No motion until Control Output reaches deadband value Spool travel delay causes more problems 32 Valve Deadband Compensation Always add positive or negative Deadband value to Control Output Deadband value ...High-performance hydraulic motion Good Design Practices Overview Affect of system components on control Compensating for design deficiencies Know where design can be modified to meet design requirements... Cylinder Pump Controller Reservoi r Good Design is Simple! Good Design Provides… • Excellent Control! – Accuracy < 0.001 inch, even while moving – Complex motion profiles – Synchronization (no flow... Space constraints: valve location – Environment: valve location Real-life design pressures Understanding control features Meet Design Requirement s Closed-Loop Control Review Control Review Target