denise01

G5 Servo Motor Too Slow

17 posts in this topic

Hello, I am new to Servo Control so need advise. I an using a single axis NC71 TO CONTROL A r88d-KN4-ML2 Servo Drive. The Encoder is the Incremental Type. I have used the Function Blocks from the Omron Library and have managed to connect the Comms, Enable the Servo and have done a Relative Move. My problem is that I cant get the Servo to move fast enough for my application. The Motor is 3000 RPM and I have got the maximum MOVL setting for the Velocity but it is no where near 3000RPM. The motor is connected to a SMC Electric Actuator but I have disconnected the motor from the Actuator and still slow. I have got a Regenative Resistor connected not sure if that is hindering the speed.The PLC is CJ1M. I have looked at the parameters via CX Motion and everything looks okay. Any advice would be appreciated. Regards

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The NC71 operates in positioning pulses. There are electronic gear parameters in the servodrive, defining the positioning pulses per motor turn. Are they set correctly for your application?

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Will check Sergei, I really want the motor to run at 3000 RPM I think the default is 1:1 but not sure what would be the ideal setting. You would have thought the default would give you the highest possible speed and then you just alter the Velocity rate. Regards

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Sergei, I have just looked at parameter Pn 200 the default is 1000 so I gues that if I raise this then I should get some more speed out of the moto?

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Read the Manual. There is a formula to calculate electronic gear for the motor encoder resolution and desired positioning pulses per motor turn. The default setup is NOT for the fastest possible motor speed at certain frequency. Edited by Sergei Troizky

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Thanks Sergei, Do you happen to know what parameter this is. Also the section in the Controller manual. Regards

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Pn009 and Pn010 are the electronic gear ratio numerator and denominator respectively. They combine to translate your user units (mm, degrees whatever) into the motor's encoder resolution. If you have an incremental encoder G5 motor, you have 2^20 encoder edges per rev (1048576 pulses). You need to know the distance, in units, that the axis moves for this motor rev. For instance, if you have a 5mm ballscrew the numbers would be 1048576 and 5. Caveat: the ratio must be between 1/1000 and 1000. The high res encoder means that this combination is illegal, so rather than mm, your units could end up as hundredths of mm or even microns. Using my 5mm ballscrew, I'd go for 1048576 and 5000 to achieve a micron resolution (better than the ballscrew, certainly!) The numbers that you poke at the axis for position and velocity are now in microns and microns/sec respectively, so you need some big numbers to get the axis moving at speed. You can now think in length units, not rpm. The position and speed parameters are DINTs, so there's plenty to go at. Pp Edit: Section 6-6 of the manual explains the electronic gear ratio perfectly. Edited by ParaffinPower

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The Lead Pitch of the Ball Screw that I programming is 20mm and so I have set Pn009 to 1048576 and Pn 10 to 20000 his has made the Ball Screw move faster I need to move the Ball Screw 320 mm so for my Position Input I have set the DINT to 320000 but the higest I can set the Velocity DINT is 1650000. Anything higher than that causes the NC71 to alarm

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1650000 translates to 82.5 revs per sec of the motor, or 4950 rpm. Without an error code I'm guessing here, but the max motor speed (not rated speed) is 5000 rpm. You'll have some loss of torque at this speed so this could cause trouble, or to close the loop the servo may need to go in excess of 5000 rpm and it won't want to do this. 1.65m/s sounds pretty quick for a ballscrew. What's its max? Pp

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The problem I have got really is that I need to match the speed of our existing Clutch/Brake Unit that runs at 50Hz. I am trialling this Ball Screw on the fact that it will be more accurate and have far more cycles than the Clutch/Brake that does approx 2 million. The error code I get is 94 which is a Data Setting Error, I guess I will have to live with this limit or even reduce the Velocity slightly. The figure of 1.65m/s is roughly what was advertised. Would a larger Servo Motor give more speed and better Torque?

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More speed- no. Probably, its speed limit will be even less. For more speed you will need to switch from the motor directly driving the ball screw to some transmission. More torque- yes. This is what a motor is made larger for. However, the ball screw will be in more danger in a case of jam or collision.

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I have been told today by one of the technical guys at SMC that the Ball Screw should be capable of a speed of 320mm in 0.6 seconds. I dont understand why I cant achieve that speed. Will try again tomorrow

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Sorry the maximum speed of the Ball Screw is 600 mm/s. So in theory I should be able to move it 320 mm in 0.5 seconds. Are there any more Parameters that I need to look at?

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The max speed quoted for the ballscrew is a mechanical constraint. Your figure have neglected accel and decel. You haven't provided a follo up to the fact you were asking for 82.5 rps earlier. See one of my earlier responses. To achieve 300 mm/s, the speed command needs to be 300,000 (assuming units are as previously discussed) What result does this give? The drive itself applies the accel and decel. The drive will triangulate the motion profile if the position command you request is too short to achieve your speed with the drive's accel and decel. These are parameters pn811 and pn814 in the drive. This is detailed in manual w426. The accel and decel will have been determined during sizing. Pp

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I have increased the acceleration slightly. I timed our existing clutch/brake assembly yesterday using PLC Timing and was approx 0.4 seconds to cover 320mm and so I have to more or less match that.I dont think increasing the Velocity from 300 000 would give me any more speed so will have to fit on to line and see what happens.

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This is not possible. It is not a limit of the servo that makes it a problem however, but the ball screw. The servo can drive the ball screw at 600 mm / s as that is 30 revs / s (600 / 20), which is only 1800 rpm. Even if you could have instantaneous acceleration and deceleration, the servo could only travel 300 mm in 0.5s with a max velocity of 600 mm / s. If you used a triangular move with a max velocity of 600 mm / s, it would take about 1.06s. You could increase the acceleration and deceleration from there, but would never complete the move in 0.5s.

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Hi Denise01   You are saying wrong because servo motor work is very good and depend its features. I have servo motor here given below  features...... Standard size digital servo with plastic gears 25T servo, 2BB. Torque motor,12bit Digital PCB. Operating Voltage: 4.8V~6V. Dead band width: 2usc. Interface: (JR) Wire length: 30cm. Thanks Xolbrin

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