Possible to adjust Bed Heater Power on the Fly?

totalitarian

So, my printer has an issue with the bed expanding and contracting if I give the bed too much power. (I suspect the issue is the way the bed it mounted but we'll not get into that here)

I have managed to resolve the issue by running my bed PID at less than half power

[c]M307 H0 A15.6 C85.1 D5.7 S0.40 B0[/c]

The main issue with this workaround is that it takes a long time to get the bed to the initial temperature.

Is it possible to heat the bed at full power from cold and once there, reduce the power back to half?

dc42

You could set up a macro to do that, and invoke it from your slicer start script.

totalitarian

What would the macro look like?

dc42

M307 H0 S1
M140 S100 ; set the bed temperature you want here, or perhaps 10deg below it
M116
M307 H0 D0.4

However, as you are using PID control of the bed, if your heater model parameters are about right then the power should remain much lower than 1.0 when the temperature is stable anyway. Does the bed temperature oscillate instead of remaining steady? Your M307 parameters look very unusual. Have you tuned the bed heater?

deckingman

@totalitarian
Could you describe your bed configuration. By that I mean, what it physically consists of. I might have an idea.

totalitarian

@deckingman:

@totalitarian
Could you describe your bed configuration. By that I mean, what it physically consists of. I might have an idea.

It's a sheet of 4mm glass with a stick on heater pad, (there is no aluminium bed plate like most printers I've seen)

The glass is clipped on 2 thin metal strips that run along the edges of the glass. These strips have 2 screws/springs for adjusting the height. The bed is fixed and the print head moves. On my phone now so can't take a pictures but if you Google east 3d gecko corexy you should get an idea
Basically the bed design is flawed as under full power (24v) the glass flexes up and down 0.1mm. The designer is confident he can come up with a solution soon but in the mean time, I find than ticking the bed with heat seems to work better than blasting it. If that makes sense?