Thanks for clearifying, Frederick and Phaedrux!
I really think I got confused about the different techniques there..
Ok, so what I am trying do accomplish is to have my printer automatically level the bed as far as possible.
My printer has two independent Z-motors to lift the bed, one on each side.
Homing is done using two independent Z-limit-switches (mounted close to the corresponding motor leadscrew), and both switches still allow for about 1mm of moving further up (at least physically), once they trigger.
In order to get the bed as level as possible, slightly offset to the nozzle a ir-probe is mounted and should be used for the fine-tuning, I guess.
The complete config.g of mine:
; General preferences
G90 ; send absolute coordinates...
M83 ; ...but relative extruder moves
M550 P"My 3D Printer" ; set printer name
M669 K1 X1:0:0 Y0:1:0 Z0:0:1 ; set CoreXY mode
; Network
M552 S1 ; enable network
M586 P0 S1 ; enable HTTP
M586 P1 S0 ; disable FTP
M586 P2 S0 ; disable Telnet
; Drives
M569 P0 S1 R0 ; physical drive 0 is disabled (R0)
M569 P1 S1 R0 ; physical drive 1 is disabled (R0)
M569 P2 S1 R0 ; physical drive 2 is disabled (R0)
M569 P3 S1 ; physical drive 3 goes forwards (E0)
M569 P4 S0 ; physical drive 4 goes backwards (E1)
M569 P5 S1 R1 T5.05:5.05:0.5:0.5 ; physical drive 5 goes forwards (E2 on Expansion Header, X)
M569 P6 S1 R1 T5.05:5.05:0.5:0.5 ; physical drive 6 goes forwards (E3 on Expansion Header, Y-Left)
M569 P7 S0 R1 T5.05:5.05:0.5:0.5 ; physical drive 7 goes backwards (E4 on Expansion Header, Y-Right)
M569 P8 S1 R1 T5.05:5.05:0.5:0.5 ; physical drive 8 goes forwards (E5 on Expansion Header, Z-Left)
M569 P9 S1 R1 T5.05:5.05:0.5:0.5 ; physical drive 9 goes forwards (E6 on Expansion Header, Z-Right)
M584 X5 Y6:7 Z8:9 E3:4 ; set drive mapping
M350 X16 Y16 Z16 E16 I0 ; configure microstepping with interpolation
M92 X855.00 Y420.00 Z6316.00 E837.00 ; set steps per mm (X = 20T, Y = 60T, Z = M8:1.25)
M566 X600.00 Y300.00 Z50.00 E820.00 ; set maximum instantaneous speed changes (mm/min)
M203 X6000.00 Y6000.00 Z1500.00 E1200.00 ; set maximum speeds (mm/min)
M201 X500.00 Y500.00 Z1000.00 E250.00 ; set accelerations (mm/s^2)
M906 X800 Y800 Z800 E1000 I30 ; set motor currents (mA) and motor idle factor in per cent
M84 S30 ; Set idle timeout
; Axis Limits
M208 X0 Y0 Z0 S1 ; set axis minima
M208 X284 Y333 Z370 S0 ; set axis maxima
; Endstops
M574 X1 S1 P"xstop" ; configure active-high endstop for low end on X via pin xstop
M574 Y1 S1 P"ystop+exp.e2stop" ; configure active-high endstop for low end on Y via pin ystop / exp.e2stop
M574 Z1 S1 P"zstop+exp.e3stop" ; configure active-high endstop for low end on Z via pin zstop / exp.e3stop
; Opposite Side Limit Switches
M950 J1 C"^exp.e4stop" ; create input J1 on pin exp.e4stop
M581 P1 S0 T3 C0 ; configure active-high X/Y/Z-Axis Upper Limit switch (S0 = falling edge)
; Magnetic Filament Monitor
M591 D0 P4 C"exp.e5stop" S1 A0 ; configure Filament monitoring for E0 on pin exp.e5stop
M591 D1 P4 C"exp.e6stop" S1 A0 ; configure Filament monitoring for E1 on pin exp.e6stop
; Z-Probe
M558 P1 C"zprobe.in+zprobe.mod" H5 F120 T3000 ; set Z probe type to modulated and the dive height + speeds
G31 P400 X21.6 Y34.15 Z1.83 ; set Z probe trigger value, offset and trigger height
M557 X45:301 Y35:336 S30 ; define mesh grid
; Dual Z-Motor bed levelling
M671 X34.6:291.1 Y:174.15:174.15 S0.75 ; define the two Z leadscrew test-positions (right: 13/140, left:269.5/140) and max correction of 0.75
; Heaters
M308 S0 P"bedtemp" Y"thermistor" A"Heated-Bed" T100000 B4138 ; configure sensor 0 as thermistor on pin bedtemp
M950 H0 C"bedheat" T0 ; create bed heater output on bedheat and map it to sensor 0
M307 H0 B0 S1.00 ; disable bang-bang mode for the bed heater and set PWM limit
M140 H0 ; map heated bed to heater 0
M143 H0 S145 ; set temperature limit for heater 0 to 145C
M308 S1 P"e0temp" Y"pt1000" A"E0-Temperature" ; configure sensor 1 as PT1000 on pin e0temp
M950 H1 C"e0heat" T1 ; create nozzle heater output on e0heat and map it to sensor 1
M307 H1 B0 S1.00 ; disable bang-bang mode for heater and set PWM limit
M143 H1 S360 ; set temperature limit for heater 1 to 360C
M308 S2 P"e1temp" Y"pt1000" A"E1-Temperature" ; configure sensor 2 as PT1000 on pin e1temp
M950 H2 C"e1heat" T2 ; create nozzle heater output on e1heat and map it to sensor 2
M307 H2 B0 S1.00 ; disable bang-bang mode for heater and set PWM limit
M143 H2 S360 ; set temperature limit for heater 2 to 360C
; Additional Temperature Sensors
M308 S3 P"exp.thermistor3" Y"thermistor" A"X-Motor" T100000 B4138 ; configure sensor 3 as thermistor on pin exp.thermistor3
M308 S4 P"exp.thermistor4" Y"thermistor" A"Y-Motor (Right)" T100000 B4138 ; configure sensor 4 as thermistor on pin exp.thermistor4
M308 S5 P"exp.thermistor5" Y"thermistor" A"Y-Motor (Left)" T100000 B4138 ; configure sensor 5 as thermistor on pin exp.thermistor5
M308 S6 P"exp.thermistor6" Y"thermistor" A"Z-Motor (Right)" T100000 B4138 ; configure sensor 6 as thermistor on pin exp.thermistor6
M308 S7 P"exp.thermistor7" Y"thermistor" A"Z-Motor (Left)" T100000 B4138 ; configure sensor 7 as thermistor on pin exp.thermistor7
; Fans
M950 F0 C"fan0" Q500 ; create fan 0 on pin fan0 and set its frequency
M106 P0 S1 H-1 ; set fan 0 value. Thermostatic control is turned off
M950 F1 C"fan1" Q500 ; create fan 1 on pin fan1 and set its frequency
M106 P1 S1 H-1 ; set fan 1 value. Thermostatic control is turned off
; Tools
M563 P0 S"Main Extruder" D0 H1 F0 ; define tool 0
G10 P0 X0 Y0 Z0 ; set tool 0 axis offsets
G10 P0 R0 S0 ; set initial tool 0 active and standby temperatures to 0C
M563 P1 S"Support Extruder" D1 H2 F1 ; define tool 1
G10 P1 X0 Y0 Z0 ; set tool 1 axis offsets
G10 P1 R0 S0 ; set initial tool 1 active and standby temperatures to 0C
M200 D1.75 ; set filament diameter for all extruders to 1.75mm
; Miscellaneous
M575 P1 S1 B57600 ; enable support for PanelDue
T0 ; select first tool
; Heater settings
M307 H0 A143.3 C694.4 D1.3 B0 ; PID settings for bed heate
M307 H1 A390.2 C250.5 D11.7 B0 ; settings for heater 1
M307 H2 A663.8 C218.7 D4.7 B0 ; settings for heater 2