Is Your Servo Feeder Actually Hitting Rated Speed?

Rated Speed Is a Cycle Time, Not a Number on a Plate

At 300 SPM the full press cycle is 200 milliseconds. The feed has to happen inside part of that, and the rest belongs to the press doing work.

Pilot release and pilot engagement bound the window. If the die requires 90 degrees of crank rotation for the feed, that is 50 milliseconds of a 200-millisecond cycle.

A feeder that needs 70 milliseconds to complete a 350 mm feed physically cannot run in a 50-millisecond window, whatever the plate says.

So the first question is not how fast the feeder is. It is how much of the cycle the die actually leaves available.

Measure the Feed Window Before Blaming the Feeder

Two measurements do most of the work: the crank angle at which the feed starts and the crank angle at which it must be complete.

A proximity switch on the crank plus a marker on the strip gives both without instrumenting the drive.

Convert degrees to milliseconds using the actual running speed, not the rated speed, because the window shrinks as speed rises.

Then compare that window against the feeder's acceleration profile at the feed length in use. The difference is the real answer.

Most plants find the window is 20 to 35 percent smaller than they assumed, and that the feeder is being asked to do in 50 milliseconds what it was designed to do in 70.

A speed complaint usually arrives without data, so the first job is to create some. Crank angle and feed completion time are enough.

Two hours of logging beats two weeks of opinion, and it usually shows the feeder doing exactly what it was told.

Cause One: The Press Interlock Steals the Window

A die protection interlock that holds the feed until a sensor confirms strip presence consumes part of the window before the feed even starts.

That confirmation can take 15 to 25 milliseconds if the sensor is slow or the input filter is set conservatively.

It is the most common hidden cost in a line that never reaches its rated speed, and it is invisible in a feeder fault log.

Check the input filter setting on the die protection module. Many are shipped at 20 milliseconds and never revisited.

Die protection modules vary in input filter from 1 to 30 milliseconds, and the difference is invisible until the line nears rated speed.

Ask the controls engineer what the filter is set to, then ask why. Most have never changed it from the shipped value.

Cause Two: Acceleration Limits Set by Roll Grip

A servo feeder can only accelerate strip as fast as the rolls can grip it. Beyond that limit the strip slips and the feed goes short rather than fast.

Roll grip depends on pressure, roll surface condition and the coefficient of friction of the strip, which changes with lubricant.

A line that runs fine at 240 SPM and shows short feeds at 280 is usually at the grip limit rather than the torque limit.

Increasing motor size will not fix it. Increasing roll pressure slightly, cleaning the rolls and reviewing lubricant application will.

Measure the limit rather than guessing. Run the line at increasing speed and log at what speed the first short feed appears.

Roll surface condition matters more than operators believe. A polished roll grips less than a freshly ground one at identical pressure.

Lubricant film thickness changes with temperature, so a line reaching 280 SPM in winter may only reach 260 in summer.

Cause Three: The Drive Is Running in a Derated Mode

Servo drives derate for temperature, for input voltage sag and for a mismatched motor parameter set. All three reduce available acceleration.

Voltage sag on press start is the most common. A 10 percent dip during the stroke reduces the drive's available torque by roughly the same proportion.

All four rows look like the same complaint from the press floor. None of them has the same fix.

Read drive torque utilisation during a stroke. Sustained above 90 percent, derating is happening and the cause sits upstream of the drive.

A line reactor is often the cheapest answer to voltage sag, at a fraction of the cost of a larger motor.

Log voltage and current together for one full shift. The correlation between the two during a stroke tells you which limit you are against.

Where Rated Speed Was Never Available

A feeder rated at 300 SPM at a 100 mm feed length will not deliver 300 SPM at 600 mm. The rating is a feed-length-dependent figure.

Rated speed also assumes a die that leaves a normal window. A die with tight pilots and a long release angle can halve the available window at any speed.

And it assumes a strip the rolls can accelerate. Wide heavy strip changes the acceleration profile more than most specifications admit.

Read the rated speed as a maximum under favourable conditions, and measure your own line's ceiling before treating the difference as a fault.

Some dies cannot support rated speed at all. A long pilot engagement angle shrinks the window regardless of what is behind the machine.

Measure the die before buying a faster feeder. The die sets the ceiling and the feeder only reaches it.

A die with 30 degrees of pilot engagement is not a candidate for 300 SPM, whatever the machine behind it can do.

Ask the tool room for the pilot engagement angle before the speed target is agreed. It is a number that already exists in the die drawing.

A Four-Step Speed Audit

• Log the crank angle at feed start and feed complete, then convert to milliseconds at the running speed.
• Measure the die protection input filter and subtract it from the window before blaming the feeder.
• Find the speed at which the first short feed appears, then check roll pressure and surface before touching the drive.
• Compare commanded feed time against actual feed time at that speed. The gap is the control lag, and it should be under 5 milliseconds.

Four steps, one afternoon, and the answer is usually a setting rather than a capital request.

The press feeder range publishes rated speed against feed length, which is the honest way to compare two models.

That table settles most speed arguments before a machine is ordered, and it belongs with any quotation.