Power Supply:
Failure in the power supply will cause mayor machine black outs.
If the input voltage is 3 ~ 208V, locate the terminals for power input: Set the meter for AC Voltage and range up to 1000 V. Measure 208 V between phase 1-2, 2-3 and 1-3. Check the phase against neutral or ground, which should be 110 to 120 AC. Some European machines require separate neutral and ground. wire, Neutral and ground have to be tied together, if there is no fifth wire. Color code of the wires will be different to meet IEC requirement.
If the input voltages are missing follow the power cable to the outlet. Check fuses in the switch box. Note, for most of the machines ( P&P, printer, conveyors ) 15 A fuses should be enough.
If Input voltages are o.k. we will require some circuit diagrams to find terminals in the path. Very likely there will be a three phase circuit breaker and several single phase circuit breakers. In the same area there may be a few single pole and triple pole relays turning power on and off for reasons like safety or emergency stop.
From here the voltage is supplied to individual DC power supplies.
5 VDC is used for computers and other logical electronic components. Most likely 5 V will not deviate by more than 10 %, However, directly at the power supply you may measure more than 5.5 V, because the Voltage will drop with cable length and diameter.
15 VDC +/- is used for digital and analog components. Position control systems like encoders and limit switches are using either 5 V or 15 V DC. Small motors can be driven directly with the same voltage than the analog components.
12 VDC is used for vision components, but because popular in automotive, small DC motors like conveyors or component feeders may operate on 12 V DC as well.
24 VDC is used for I/O devices, signal lights and solenoids. There could be a separate circuit for all input signals and output signals. Because this is also a control voltage for solenoids, which can activate very powerful air cylinder, the output voltage should be cut off in the e-stop mode.
30-60 VDC is used for servo motors. In most cases the vendor of the servo motor supplies the power supply for the motors and motor servos. It is no surprise to find this transformer somewhat away from the other power supplies and located closed to the servo cards.
Power On Switch:
Not all machine voltages can be switched on to the same time. In example, the 5 V logic has to be on before the 24 V output voltage is on, in order to re-set all memory flags to zero. Usually there is a main switch, which supplies the power to the transformers and DC power supplies and a start switch, which turns on the outputs and may also already initialize the axis motors.
Safety Interlocks:
Safety doors and light curtains protect the operator for injuries. When doors are opened the machine may continue to operate in slow speed. Some machines may have a key operated switch to allow slow axis movements with open doors.
The e-stop is activated in case of an emergency. It will take the power from the main axis motors and in most cases will cut off the output voltage which in turn shuts off the valves, solenoids and conveyor motors. The program may be lost and the machine has to be re-booted. The e-stop is latched and may turn off the entire machine.
Machine safety functions such as axis limit switches or anti crash switches will not turn of the power, but stop the function it attempted to execute.
All safety functions are usually looped together and switches are normal closed contact. In case of a bad contact or a broken wire, the particular machine function will not work.
These features are quite often operated with relay and other mechanical contacts, which also means the lifetime of these contacts is somewhat limited. A contaminated contact can draw too much current and blow a fuse.
Initialize Axis:
When the machine is powered up, the axis motors could be in any position. Most machines will require to move the axis manually out of any limit switch. When the start switch is activated, the axis moves slowly and sometimes in both directions searching for typical marks on the scale, proximity or micro switches. Once the position is found it may set a counter to zero. Sometimes this is more complicated and several different names come up for different positions of the axis.
Most of the scales, linear and rotary, have several marks in regular distances. The resolution of the scale is defined by the number of lines per mm, inch or per 360° . Additional lines are made for a Zero point .Some scales have half of the area black and the other clear. The two sections are made to determine in which direction the motor has to turn to find the zero position. The reader head has several windows in different locations to read the appropriate lines from the scale. Lets assume the axis motor searches for the pulse closest to the light/dark section. If the motor stops here, it will be somewhere in the machine, which does not make any mechanical sense. A correction factor is required to place the axis into a reference position.
The reference position is an axis position from the 0-pulse plus or minus a number of pulses ( digits ) on the scale. This could be the extreme outer position the axis can reach without hitting the limit switch, the Z-axis is of course in upper position. It makes sense to set the counter again to zero and reference all position to this position. Movements from reference are counted in positive directions.
From here all other positions may be reached. There may be a home, waiting , machine zero and other positions.
For trouble shooting purpose it is important to know, that all axis positions are counted from the reference position. If this point is changed for any reason all other machine position will change with it. If a motor is changed which has its own rotary scale than the shaft may stay in any position when the motor coupling is tightened. The new reference position has to be determined and changed in the machine data.
If all axis move to reference position, we can assume they will perform all other position functions as well.
Machine Data:
Machine data are usually password protected. Upon start up, the machine controller downloads some information to the axis control cards. These data contain information about motor drive mode, how the motor accelerates, max. speed and position information of each axis. Other information are required in order to calculate the positions of a placement program like calibration factors of cameras and machine specific positions.
The machine vendor should supply a test software, capable of calibrating cameras and machine positions and updating the machine data.
Keep at least one copy of machine data in a safe place.
Motor Servo Control:
DC Motors have usually a tachometer attached to it. The encoder is either rotary or linear.
AC Motors do not require a tachometer, but an encoder.
Stepper Motors do not require a tachometer or an encoder.
Two electronic cards control speed, direction and position of the motor.
The Axis Control card controls the position and the direction of the motor, using the information from the machine controller or computer and the encoder. The signal is amplified in the
Servo card with a speed feed back signal from the tachometer. For trouble shooting purpose it is important to know that the signals from the encoder can be measured on the axis card and the analog signal from the tachometer at the servo card. It is very important to know that the speed of DC servo motors is controlled with the tachometer generated voltage. If this feedback signal is missing, the motor will go full speed into a limit switch.
I do prefer to have some LED?s indicating the status of the axis on the control card. There may be also LED?s on the servo card ( over load, limit switch ).
If the purpose of the LED?s is not labeled or in the manual, I would put a label on.
You should be able to measure the track signals A and B from the encoder with an oscilloscope. Two signals are required to determine in which direction the axis is moving. The signal offset is 90° . Assuming the motor can travel at 3 m/s and there are 100 pulses per 1 mm, then the control card has to process 300,000 pulses per second. There may be test pins for the zero pulse, the nominal output and offset. Although all axis cards look alike, there may be an address switch in or outside for each axis. The X-axis could have address 0, Y 1, Z 2 a.s.f. It is very common to store certain axis parameter on an EPROM located on the card. If cards are exchanged, make sure they have the same EPROM.
On the servo card, locate the input signals from the axis card, the tachometer and the cable going to the motor. If none of the terminals can be reached from the front side, you may need an adapter card for serious trouble shooting.
Axis control and servo cards have usually a long lifetime. If anything than the power MOS-FET on the servo card die and most likely the motor dies first.
Problem Possible Cause Resolution
Motor (axis) does not make any movements Axis in limit switch Move axis manually
Z-axis not in reference Check Z-axis problem
Motor supply voltage missing Check on motor terminals
Defective axis control card Swap with other card
Defective servo card Swap with other card
Defective Motor Replace motor (Note, motors usually give up slowly, make either noise or oscillating movements)
Safety interlocks open
Close doors, unlock e-stop
Axis moves into limit switch during reference run Counting error of encoder Clean scale, if accessible
Limit switch too close to reference and motor oscillates Defective motor or servo
Motor turns full speed Defective tachometer Check output voltage of tachometer when machine is turned off and axis moved manually
Axis moves in one direction and stops Defective servo card Swap or re-place card
Axis drifts in one direction Defective servo card Swap or re-place card
Motor oscillates Defective motor Replace
Defective servo Replace
Motor Control Board:
Some motors in the machine do not require a servo control. If a motor operates a device for example a board conveyor all three types of motors could be used DC, AC and stepper. At simplest the motor is turned on and off with an I/O card output operating a relay or a transistor.
AC and stepper motor card require a driver board. Quite possible stepper motor and driver board come from the same vendor.
Look for fuses on these boards. Also look for test pins or terminals for input signals and output to the motors.
If the board contains potentiometers, they may have the purpose to control the motor speed. I recommend to put a label on pot?s, terminals and test pins.
STEERING-INC