Problem with the speed of the main motor of the printing machine ?

Problem with the speed of the main motor of the printing machine ?

Its an old printing machine it doesn't have the electronic controlling system ..... No electronics involve in it .........

The speed of the main motor (machine) is set manually with the pot (multi-turn pot of 10 K ohm resistance ) ......... and the output of the pot is directly connected to the inverter Mitsubishi Freqrol A 500 .........


The problem is that the speed of the main motor automatically decrease & sometimes automatically decreases (as compared to the set speed) ........ I have already checked & changed the pot but with no effect ........

The frequency on the inverter's panel keeps on increasing & decreasing for e.g : set at about 59 m/min and on the inverter's panel frequency keeps on changing between the range 27.32 to 27.47 Hz ......

What might be the cause of the problem ?
How to cure for this problem ?

thanks

If your pot is worn out replace the pot and try..

The frequency variation is is a relatively small ... about 0.5%

at first check has inverter supply voltage these variations too
do measuring in inverter input connectors

is motor frame and inverter frame connected , wire size is about same as phase wire.

when control panel ( -module ) is in monitor mode,
you can check voltage , current and frequency in inverter output

what is the size of the main motor

is speed control system principle open loop or closed loop
ie. is there any speed feedback from motor or main shaft .....

check is the variation periodically repeated or a completely random

if repeated, what is the cycle time for variation

if random, check is this maybe result of variation in web tension
or pressure settings in rollers , etc....

check is speed pot. wires connected with shielded cable and
ground connection done only on inverter side.

are all pot. wires connected only and directly to inverter

if speed feedback is used
- check cable for that signal too (like in speed pot.)
- check tachometer if used

there are no more pots ...... there's only one pot ........ no feedback is used ........ no tacho .......... the operator says that when he increases the speed to a certain point then the speed exceeded the set speed ........ and when he decreases the speed to a certain speed then the speed decreases more as compared to the set value

---------- Post added at 14:22 ---------- Previous post was at 14:21 ----------

the machine was working well before and this fault came across now ...........

---------- Post added at 14:29 ---------- Previous post was at 14:22 ----------

web tension is done with the help of tension controllers used with clutch brake system ........ air pressure regulators ....... load cells are also used ..........

What is the size of the main motor

and what is the model of the inverter ie. FR-A500-xxxK , power class xxx=?

Is the fault present throughout the control range or just a certain set values ?

Because the speed ​​feedback is not been used , motor load variations can cause thiskind of symptoms.
so check is there unwanted noticeable variations in the web tension , when speed is changed.

At first check has inverter supply voltage these variations too
and do these measurings in inverter input connectors ( phase to phase )

Suspect filter capacitors in inverter also.

About inverter :
Freqrol A-500
11KW
FR - A540 - 11K
Input : 43.8 A
Output : 23 A

Open loop , no feedback, no connections for tachometer or for encoder or for resolver inside the inverter
checked the voltages on the motor terminal and also the inputs R , S , T of the inverter & also measured the voltages U , V ,W the outputs of the inverter .......... when pot is rotated then about very little variations in the output voltages U , V , W of the inverter inside the inverter and also on the motor terminal ....... like 195 V to 198 V & 192 V then settle very quickly to the 195 V ......... i think this little variation in voltage for a very fractions of couple of second is due to non-feedback system (i.e. running in open loop) ..... Am i right, in this regard ?

thanks

Small voltage variation may be due to load variation. There is a certain pattern for frequency change for speed change Did you individually checked each phase.

In above post #8
TRANSISTORIZED INVERTER
FR-A540-0.4K to 55K(-NA)(-EC)
– INSTRUCTION MANUAL –


Page 174......
CHAPTER 5
PROTECTIVE FUNCTIONS

Always read the instructions before using the equipment.

Page 180..............

(3) Speed greatly differs from the setting.
· Check that the frequency setting signal is correct. (Measure the input signal level.)
· Check that the following parameter settings are proper: Pr. 1, Pr. 2, Pr. 902 to Pr. 905, Pr. 19.
· Check that the input signal lines are not affected by external noise. (Use shielded cables)
· Check that the load is not too heavy.

(4) Acceleration/deceleration is not smooth.
· Check that the acceleration and deceleration time settings are not too short.
· Check that the load is not too heavy.
· Check that the torque boost (Pr. 0, Pr. 46, Pr. 112) setting is not too large to activate the stall
function.


Page 181.............

(5) Motor current is large.
· Check that the load is not too heavy.
· Check that the torque boost (Pr. 0, Pr. 46, Pr. 112) setting is not too large.

(6) Speed does not increase.
· Check that the maximum frequency (Pr. 1) setting is correct.
· Check that the load is not too heavy. (In agitators, etc., load may become heavy in winter.)
· Check that the torque boost (Pr. 0, Pr. 46, Pr. 112) setting is not too large to activate the stall
prevention function.

(7) Speed varies during operation.
During operation under advanced magnetic flux vector control, the output frequency varies with load
fluctuation between 0 and 2Hz. This is a normal operation and is not a fault.
1) Inspection of load
· Check that the load is not varying.
2) Inspection of input signal
· Check that the frequency setting signal is not varying.
· Check that the frequency setting signal is not affected by induced noise.
3) Others
· Check that the settings of the applied motor capacity (Pr. 80) and the number of applied motor poles
(Pr. 81) are correct for the inverter and motor capacities in advanced magnetic flux vector control.
· Check that the wiring length is within 30m (98.42 feet) in advanced magnetic flux vector control.
· Check that the wiring length is correct in V/F control.

(8) Operation mode is not changed properly.
If the operation mode is not changed properly, check the following:
1. External input signal .............Check that the STF or STR signal is off.
When it is on, the operation mode cannot be changed.
2. Parameter setting .................Check the Pr. 79 setting.
When the setting of Pr. 79 "operation mode selection" is "0" (factory
setting), switching input power on places the inverter in the external
operation mode. Press the operation panel's [MODE] key three times
and press the [UP] key (press the [PU] key for the parameter unit
(FR-PU04)). This changes the external operation mode into the PU
operation mode. For any other setting (1 to 8), the operation mode is
limited according to the setting.


Pages 182...185
5.3 Precautions for Maintenance and Inspection

5.3.4 Insulation resistance test using megger
READ CAREFUL

5.3.5 Pressure test
in table READ CAREFUL .... column Method

Pages 188...189
5.3.8 Measurement of main circuit voltages, currents and power

Ps-
Is this the same inverter, in which the parameter was changed "by themselves" ???
if so ...then check parameters related to motor , motor control and power.

I don't know whether the parameter(s) changed or not ......... but i had the gut feeling that it might be the case ......

---------- Post added at 00:44 ---------- Previous post was at 00:43 ----------

yeah i individually checked & measure each phase