Allow slower minimum movement speed

adarshsimon

@dc42 Im using the duet on a project that requires extremely low speeds. For example I need to move 0.00005mm in 60 seconds. I have set lower speeds with M203 as mentioned in the documentation, however the move is completed in half the time. I have tried the same setup for longer distances and it works fine. Basically i need the movement to complete exactly at set times. Thank you for any input.

Big fan of Duet products.

dc42

Currently, if you use a M203 I parameter below 0.6 mm/min (0.01mm/sec), it will set the minimum movement speed to 0.01mm/sec. Looks like you need much less than that. However, if you really can move with a resolution better than 0.00005mm then I guess you have a very small machine. Have you considered changing your units so that what RRF thinks is mm is actually nm?

adarshsimon

@dc42 Thank you for the quick reply. I will try out your recommendation.

adarshsimon

@dc42 Hello, your solution works. Thank you!

dc42

@adarshsimon, I'm glad to help! Can you tell me a little more about the project?

adarshsimon

@dc42 sure, we are developing an electro spinning machine which requires very low material to be dispensed. We use a syringe to hold the material that is to be dispensed and the lowest dispensing rate is about 0.05ml/hour. Hence the low speed requirement. We are using duet because we also need 3 axis movement of the syringe.

adarshsimon

@dc42 Hello, I think i need some more help. The system we are designing has a single axis movement setup which moves 70mm . I have changed the steps per mm setup to allow for the slow speeds we require.

The translation stage is however supposed to move at relatively higher speeds (eg. 100mm/min). We need the translation stage to reach the speed with the highest acceleration possible. I have set the acceleration and other settings to reflect the change in steps per mm , however the stage always accelerates when starting a move and decelerates when stopping.

This is affecting our timing. Is there a limit to max instantaneous speed change?.

My config file

; General preferences
G90                                   ; send absolute coordinates...
M83                                   ; ...but relative extruder moves
M550 P"PICO"                          ; set printer name

; Network
M552 S1 P192.168.1.2                  ; enable network and acquire dynamic address via DHCP
M586 P0 S1                            ; enable HTTP
M586 P1 S1                            ; disable FTP
M586 P2 S0                            ; disable Telnet

; Drives
M569 P0 S1                            ; physical drive 0 goes forwards
M569 P1 S1                            ; physical drive 1 goes forwards
M569 P2 S1  
M569 P3 S1 
M569 P4 S1                            ; physical drive 4 goes forwards
M584 X0 Y1 Z2 U3 V4                   ; set drive mapping
M350 X256 Y256 Z256 U256 V256 I0      ; configure microstepping without interpolation
M92 X102.4 Y512 Z512 U102.4 V512              ; set steps per mm
M566 X1000000.00 Y1000000.00 Z1000000.00 U1000000.00 V1000000.00    ; set maximum instantaneous speed changes (mm/min)
M203 X1000000 Y1000000 Z1000000 U1000000 V1000000 I0.0001	; set maximum speeds (mm/min) 
M201 X1000000.00 Y1000000.00 Z1000000.00 U1000000.00 V1000000.00         ; set accelerations (mm/s^2)
M906 X1000 Y1000 Z1000 U1000 V1000 I30            ; set motor currents (mA) and motor idle factor in per cent
M84 S30                               ; Set idle timeout

; Axis Limits
M208 X0 Y0 Z0 U0 V0 S1                      ; set axis minima
M208 X70 Y80 Z80 U80 V300 S0                   ; set axis maxima

; Endstops
M574 X1 Y1 Z1 U1 V1 S0                      ; set active low and disabled endstops

; Z-Probe
M558 P0 H5 F120 T6000                 ; disable Z probe but set dive height, probe speed and travel speed
M557 X0:70 Y0:80 S20                  ; define mesh grid

; Heaters
M140 H-1                              ; disable heated bed

; Fans

; Tools

; Custom settings are not defined

dc42

There are minimum values for M201 and M566, but not maximum values. You can run M201 and M566 without parameters to see what values RRF is using.

I suspect that you are hitting the maximum step pulse rate. You are using x256 microstepping, which we do not recommend because it results in very high step pulse rates. Increasing microstepping beyond x16 rarely improves resolution. Try changing it to x16 with interpolation.

bot

I think, since you're commanding a single move, that "instantaneous speed change" (aka jerk) is not being applied. Jerk is normally only applied between two moves of print movement.

If you set M566 P1, you will enable "jerk policy 1" which replicates Marlin-style jerk. With this form, jerk is applied to every start and stop motion, regardless if there is another print move connected to it.

With M566 P1 enabled, the print moves will always start at the "jerk" speed, as set in M566.

adarshsimon

@dc42 I will try this and update . Thanks for the reply

adarshsimon

@bot I will try this also and update. Thank you for the reply.

adarshsimon

@dc42 @bot both suggestions were right. The movement timing is predictable now . Thank you!.

@bot "two moves of a print movement" means two axis have to move or two movement commands of a single axis would do?. Thanks in advance.

dc42

@adarshsimon said in Allow slower minimum movement speed:

@bot "two moves of a print movement" means two axis have to move or two movement commands of a single axis would do?. Thanks in advance.

If you did two consecutive printing commands along the same axis but at different speeds, jerk would be applied between them, even though it could be avoided.