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use the lowest reasonable gain setting, and then adjust the damping to the lowest setting 
possible without ringing or overshoot. 
 
 

INTEGRAL COEFFICIENT 

 
The third element in a PID compensation loop is the integral gain coefficient. The gain is 
fixed for this component and is not adjustable by the user. The purpose of the integral 
coefficient is to “take up” or eliminate over time any remaining position error. There is 
always a position error that the proportional coefficient cannot remove because it becomes 
less effective as the position error decreases. 
 
The integral coefficient works by “integrating” over time any remaining position error. This 
means any residual error becomes multiplied over time, restoring the motor to the command 
position with zero error. The integral gain coefficient is not settable on the CN0182. 
 
The motor will be perfectly still when not commanded to move if sine-cosine encoders are 
used. This is because the integral coefficient reduces any position error to zero. 
 
If TTL encoders are used, the motor will bounce between two adjacent encoder count edges 
when not commanded to move. This is because there is not position feedback information 
between count edges. Any residual position error, no matter how small, is multiplied over 
time to a level sufficient to move the motor. The motor then moves until it reaches an 
encoder count edge, where it reverses direction until it hits the other constraining encoder 
count edge, repeating the process. 
 
Using the minimum Gain Trimpot setting for TTL encoders helps reduce bounce. The higher 
the gain the higher the Damping Trimpot setting, both of which contribute to how strongly 
and rapidly the motor will bounce between the adjacent encoder count edges. The stronger 
the motor bounces, the more torque is required. This results in unnecessary motor heating, 
vibration and audible noise. 
 
 

SERVO LOOP TUNING  
 

A DC servo drive must be "tuned" to the application to achieve optimum system stability. 
This consists of adjusting the Gain and Damping Trimpots to the correct values for the 
particular motor and load combination the CN0182 is driving. 
 
The tools needed are: 
 

•

  A STEP and DIRECTION pulse source or 2 FUNCTION GENERATORS 

•

  A 2 channel OSCILLOSCOPE with 10:1 probes 

•

  A small SCREWDRIVER 

 
Begin by connecting the power supply and the encoder to the CN0182. Do not connect the 
motor or pulse source yet. Jumper the Option Header for the type of encoder being used (pins 
9, 10) and the expected moment of inertia. The default is Low Inertia (pins 3, 4). 
 
Turn on the power supply. The Fault LED should light momentarily when power is applied. 

 

23

Summary of Contents for CN0182

Page 1: ...OPERATING MANUAL CN0182 SERVO DRIVE 3879 SOUTH MAIN STREET 714 979 6491 SANTAANA CALIFORNIA 92707 5710 U S A 0 M P A N Y ...

Page 2: ...0182 Servo Drive Centent and the Centent Company logo are trademarks of Centent Company Other trademarks tradenames and service marks owned or registered by any other company and used in this manual are the property of their respective companies Copyright 2019 Centent Company 3879 South Main Street Santa Ana CA 97207 All Rights Reserved ii ...

Page 3: ...up 12 Sine Cosine Encoders 14 TTL Encoders 14 Command Group 15 OPTION HEADER 17 System Inertia 17 Position Error 18 2 5V Reference 18 Current Monitor 18 Fault Output 19 Reset Input 20 12 Volt Test 20 Encoder Jumper 20 Ground 20 TUNING THE CN0182 SERVO DRIVE Current Trimpot 21 Gain Trimpot 22 Damping Trimpot 22 Integral Coefficient 23 Servo Loop Tuning 23 Interpreting Figure 12 Optimum Damping 27 P...

Page 4: ......

Page 5: ...s step motor to servo motor conversions since it is controlled by a step motor indexer pulse generator or motion controller like a step motor drive The servo motor exhibits holding torque velocity tracking incremental motion and no minimum operating speed while retaining the advantages of a DC servo motor such as increased high speed torque absence of vibration and low heating The upgrade from ste...

Page 6: ...drive just strip the wire insert and tighten the screw The motor power supply encoder and indexer interface are accessed through this connector The function of each terminal is printed on the cover adjacent to the screw Do not over tighten the screws a torque limit driver is recommended 4 OPTION HEADER The user must configure this header for encoder type and system inertia Position Error Fault out...

Page 7: ...a power supply with a voltage equal to the motor s rated voltage and a current capability equal or greater than the application will require Turn the CN0182 Current Trimpot completely clockwise CW Turn the CN0182 Gain Trimpot to the 9 o clock position Turn the CN0182 Damping Trimpot to the 11 o clock position Jumper the CN0182 System Inertia pins on the Option Header to Low Inertia Connect the pow...

Page 8: ... U D COUNTER QUADRATURE X4 ANALOG SLOPE PROCESSOR ENCODER JUMPER 5V GAIN TRIMPOT OVER CURRENT DETECT CIRCUIT OVER TEMPERATURE DETECT CIRCUIT TO PWM TO PWM TO PWM TO PWM TO FETS MOSFET BRIDGE LEVEL SHIFT CIRCUIT 5V GENERATOR DAMPING TRIMPOT POSITION LIMIT CIRCUIT ERROR 3 2 2 1 4 12 11 10 10 5 5 6 6 7 7 8 9 9 Figure 2 MAIN ELEMENTS The Command Position U D Counter is updated by the Step and Directio...

Page 9: ...a form usable by the drive It accepts either TTL digital encoders or analog sine cosine encoders depending on the settings of the Encoder Jumper on the Option Header If a sine cosine encoder is selected the TTL Analog Processor also passes data to the Analog Slope Processor The Analog Slope Processor uses the sine and cosine waveforms to interpolate position between encoder counts The interpolatio...

Page 10: ...Header Pin 2 One example shown in Figure 4 multiplies the encoder line count by a factor of ten A 500 line sine cosine encoder has the equivalent resolution of a 5000 count digital encoder This results in 20 000 resolvable locations The user s U D Counter divides the Step count by 10 and acts as a low resolution D A Converter The full range output of the D A is scaled to equal a one count Position...

Page 11: ...r lengths short Use the encoder power supply ground Terminal 6 as a common for external circuitry Do not put any capacitors on the Position Error Pin Failure to follow these precautions will result in unstable operation and probable Fault Protect shutdown CURRENT LIMIT Motor current is sensed across a Current Sense resistor located at the power supply end of the MOSFET Bridge The Current Sense res...

Page 12: ...rent Detect trip point Over Temperature The Over Temperature Detect Circuit monitors the drive s temperature If the temperature of the drive exceeds 70 C the circuit sets the Fault Latch This might occur if the motor operates continuously at high currents the drive is poorly heat sunk or the ambient temperature is very high If the cause is high motor current consider the possibility the motor may ...

Page 13: ...rmation back to the CN0182 completing the loop Any malfunction in this loop will result in a position error and a protective shutdown Verify that the encoder connections to the drive are correct and that there are no breaks in the wiring or terminals 3 Insufficient Torque At High Speed DC motor torque is at a maximum at zero speed stall torque and linearly decreases to zero at the motor s maximum ...

Page 14: ...d motors have a laminated iron armature The drive requires a minimum inductance of 500 μH Pancake cup and other ironless armature motors have very low inductance less than 500 μH and consequently will have excessive ripple current This ripple current will cause considerable motor heating If these type motors are used insert a 500 μH inductor in series with the motor Make sure the inductor is rated...

Page 15: ...y with a current rating equal to the motor s stall current Most motors have a stall current ten times higher than the motor s continuous rated current The continuous rated current is based on the motor s ability to safely dissipate heat However for short periods of time while accelerating or decelerating the motor can handle much higher currents without harm The power supply must be rated to meet ...

Page 16: ...an be enough to cause the CN0182 go into Under Voltage Protect and reset This will then cause the motor to develop a Position Error Limit and Fault Output The result is the motor will have less performance than expected since it would have to be accelerated more slowly to avoid drawing this level of current IMPORTANT Power supply wires must be heavy 16 gauge maximum and as short in length as possi...

Page 17: ...r on the Option Header pins 9 10 selects between digital and analog encoder operation With no jumper in place the inputs must be TTL level signals with a jumper present the inputs are analog For analog sine cosine encoders the CN0182 requires the channel outputs to be 1 volt in reference to ground Encoders that do not comply will require external amplification or attenuation to interface to the CN...

Page 18: ...ith the CN0182 This is by no means a complete list of acceptable encoders SINE COSINE ENCODERS COMPUTER OPTICAL PRODUCTS DYNAMICS RESEARCH CORP MODEL CP 800 5000 F T23DA4EDB2V 1000 LINES 5000 20 000 counts rev 1000 4000 counts rev CN0182 ENCODER LEAD WIRE ENCODER LEAD WIRE Terminal 5 WHITE BROWN stripe BLUE Terminal 6 GRAY WHITE stripe BLACK Terminal 7 WHITE ORANGE stripe WHITE Terminal 8 BLUE WHI...

Page 19: ...puts have rise and fall times under 50 nano seconds to avoid false steps and erratic operation The opto isolator driver current sink capability must be at least 16 mA This requirement is easily met with standard TTL or 74HC bus drivers IMPORTANT Do not run the Command Group wires in a common wiring harness with the Motor Group wires Doing so will result in erratic motor behavior because capacitive...

Page 20: ...mmand Group is shown in Figure 10 5 VOLTS DC SUPPLY STEP PULSE OUTPUT DIRECTION OUTPUT SHIELDED CABLE INDEXER CN0182 GROUND DIRECTION STEP PULSE 5 VOLTS DC 10 11 12 Figure 10 If power supply voltages higher than 5 VDC must be used the Step Pulse and Direction inputs will each require external series resistor to limit the current to the opto isolators to a maximum of 10 milliamps Do not connect a s...

Page 21: ...ted on the face of the drive Pins 1 2 3 4 and 9 10 are designed as pairs for jumper blocks Pins 2 and 3 also have discrete functions Pins 5 8 have discrete functions do not use jumper blocks for these pins The following section describes each function and its pin assignment HIGH INERITIA 1 2 3 4 5 6 7 8 9 10 LOW INERTIA 3 4 5 6 7 8 9 10 SYSTEM INERTIA PINS 1 2 PINS 3 4 1 2 A shorting bar supplied ...

Page 22: ...ther the motor is turning or not Only a change in load conditions such as an abrupt speed command change a change in the direction command while the motor is turning or a suddenly applied or removed load will cause a transient deviation from this value Once the motor adjusts itself to the new conditions the voltage will return to 1 25 volts The stability of the servo can be determined by observing...

Page 23: ...ns are 1 UNDER VOLTAGE Power supply voltage below 18 VDC 2 OVER TEMPERATURE Case temperature in excess of 70 C 3 OVER CURRENT Motor current in excess of 20 amps 4 POSITION ERROR An error of more than 128 counts The Fault LED provides a visual indication of a fault Over temperature over current and position error faults are latched faults The Fault Output stays low the CN0182 remains shut down The ...

Page 24: ...eader Pin 9 or Terminal Block Terminal 6 for Ground when monitoring the 12 VDC supply 3 4 5 6 9 10 2 1 7 8 ENCODER JUMPER PINS 9 10 3 4 5 6 9 10 2 1 7 8 3 4 5 6 2 1 7 8 9 10 DIGITAL ANALOG To operate the CN0182 with a motor equipped with an analog sine cosine encoders jumper Pin 9 to Pin 10 The CN0182 will extract additional position information from the encoder signals in this configuration For d...

Page 25: ... proportional to motor current Setting a current limit below what the motor can carry will limit the motor s torque and its ability to drive a load If a motor cannot drive the load a rapidly increasing position error will develop leading to a premature Position Error fault shutdown Motors that have a stall current less than 20 amps should draw no more than their rated stall current in normal opera...

Page 26: ... severely under damped the oscillations will increase rapidly in amplitude until they exceed the Position Error Limit and the CN0182 shuts down An over damped system will take longer than necessary to return to the command position after a disturbance Excessive damping also causes greater motor heating and noise since any position disturbance is responded to over aggressively A properly damped sys...

Page 27: ...s Any residual position error no matter how small is multiplied over time to a level sufficient to move the motor The motor then moves until it reaches an encoder count edge where it reverses direction until it hits the other constraining encoder count edge repeating the process Using the minimum Gain Trimpot setting for TTL encoders helps reduce bounce The higher the gain the higher the Damping T...

Page 28: ...h Function Generators to the square wave setting and adjust the outputs to a 5 volt amplitude One generator will drive the Direction Input while the other will drive the Step Input Set the Direction generator output to about 1 Hz Set the Step generator to a frequency range setting that will turn the motor about five revolutions per second full scale This frequency depends on the encoder line count...

Page 29: ...er Slope setting on the oscilloscope If the servo is tuned correctly the scope display should look like Figure 12 on page 26 If the oscilloscope display looks more like Figure 13 the servo loop needs more damping Either turn the Damping Trimpot slightly clockwise or turn the Gain Trimpot counter clockwise until the display most closely matches Figure 12 Turning the Damping Trimpot up will increase...

Page 30: ...CN0182 PULSE INCREMENTAL SERVO DRIVE Figure 12 optimum damping Figure 13 under damping Figure 14 over damping 26 ...

Page 31: ...s the bottom of the Position Error notch 0 6 volt amplitude 01 volts per increment of motion x 09 per encoder count 5 4 From 3 mS to 7 mS the motor catches up to the moving command position In Figure 12 this is the upward slope from the bottom of the notch until it crosses the 1 25 volt level From 7 mS to 10 mS the motor slightly overshoots by 36 degrees and then returns to match the moving comman...

Page 32: ...Equation 3 4 161 8 24 Terminal Resistance 0 89 Ohms Equation 4 24 26 97 No Load Speed 3500 RPM 2 x 1750 T as acceleration or deceleration While this motor is delivering 161 8 Watts to the load it is also dissipating the same amount as heat A motor this size would soon overheat if it were required to deliver this power continuously The continuous torque rating of the motor must be observed which ty...

Page 33: ...m resistor a reasonable value in series it now very closely resembles a real motor It will still draw a current proportional to torque but now the current passes through this resistor as well The maximum current the motor can draw is now limited by Ohm s law to 10 amps and is called the stall current Motor torque is also limited to the stall current times the torque constant and is called the stal...

Page 34: ...motor that is converted to mechanical power the rest is dissipated as heat As seen above the motor delivers maximum output power at one half of its stall current At this point the series resistor has half of the power supply voltage across it leaving the other half for the ideal motor Since the same current flows through both half the power is converted to heat This means the real motor efficiency...

Page 35: ...OUNTS Signal Level TTL encoder 0 5 VOLT DC analog encoder 1 1 VOLT DC Supply Current 5 Volt Supply 100 mA 5 Volt Supply 50 mA ENVIRONMENTAL Operating temperature 20 75 C 4 167 F Humidity 0 100 Shock 100 G MECHANICAL Weight 17 19 ounce 482 539 gram Terminal Screw Torque 4 5 lb in Size LxWxH 4 75 x 4 00 x 0 85 inch 121 x 102 x 22 millimeter Mounting hole centers 3 625 x 3 625 inch 92 x 92 millimeter...

Page 36: ... 625 92 1mm 4 0 101 6mm 4 5 114 3mm 3 625 92 1mm 0 85 21 5mm 0 125 3 2mm 3 25 82 6mm 0 186 4 7mm 0 20 5 1mm 0 7 17 8mm 330 330 INTERNAL MAX 115 OF MOTOR RATED VOLTAGE 50 mA MAX BRUSH TYPE DC SERVO MOTOR 100 mA MAX D A M P I N G G A I N C U R R E N T OPTION HEADER 1 2 3 4 5 6 7 8 9 10 1 2 3 4 2 3 5 6 7 8 9 9 10 ON OFF ANALOG DIGITAL HIGH INERTIA LOW INERTIA POSITION ERROR 2 5V REFERENCE CURRENT MON...

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