electronic lead screw

RJSakowski said:
I would be concerned about a sudden spindle stop or reversal of direction causing high back emf in the stepper and triggering a driver error.
Click to expand...
Agree, RJ.
Another alternative, as you probably know,
But for the sake if others,
A less vicious brake can be a VSD braking power resistor. The higher the value, the slower the wind down, particularly towards the last few revs as the little amount of energy generated has a very small residual field current, - all assuming V bus is disconnected in the VSD (Coasting mode).
Well, that's my understanding of the brake mechanism.
DC injection is usually on bigger machines w very high inertial loads.
 
I received my encoder belt on Monday; the last item on my BOM. However, I also had carpal tunnel surgery that day and had to delay the mounting of the encoder. I managed to get the encoder mounted and connected everything together for a test run. I was disappointed in the available torque. I expected more from a 600 oz.-in stepper. Running the spindle at 175 rpm and the 12 tpi lead screw at .125"/rev. (8 tpi) , the stepper was turning at 262 rpm. I could make the motor lose steps with 40 lbs. of force applied to the carriage. I tried cutting a 7/16 -14 tpi thread and was able to cut the thread although the motor encoder kicked in to make up lost steps.

One obvious improvement would be to increase the supply voltage. I am running a 36 volt supply and the drive is capable of handling 48 volts. From the torque curve, this would give me about 20 - 30% more torque. A simple experiment would be to use the 602 gear box to do a 2:1 reduction, doubling the torque. This would be similar to Clough42's 3:1 motor pulley ratio. The concern is that the stepper motor has a relatively flat torque x rpm curve so very little is gained by using pulleys.
602 Torque x RPM Curve.JPG

Here is that curve for my motor, running at 36 volts, derived from the published specs.

Another possible issue is driver tuning. Supposedly, the driver has an autotune feature but this may be making compromises for torque for the sake of other features. StepperOnline is secretive about the tuning software but others have suggested that Leadshine's tuning software is the one to use. I'll have to make up the serial cable. It's been a long time since I've done any work with RS232 cables but as I recall, only RX, TX, and GND are needed and the RX and TX lines are crossed. (Someone please correct me if I'm wrong.)

I am using a setting of 1600 steps/rev on the driver and 200 steps and 8 microsteps in the Clough42 software. This gives me the correct spindle to lead screw ratio. However, other have used the motor encoder resolution of 1000 pulses in setting the driver and in the controller software. Is there possibly an impact on torque there?

As I recall, a stepper has its best torque output at full step positions. Would there be an advantage to decreasing the number of microsteps? So many questions to answer.:rolleyes:
 
Qtron said:
Agree, RJ.
Another alternative, as you probably know,
But for the sake if others,
A less vicious brake can be a VSD braking power resistor. The higher the value, the slower the wind down, particularly towards the last few revs as the little amount of energy generated has a very small residual field current, - all assuming V bus is disconnected in the VSD (Coasting mode).
Well, that's my understanding of the brake mechanism.
DC injection is usually on bigger machines w very high inertial loads.
Click to expand...
Both methods cause extra motor heating which with repetitive stopping, can become a problem
RJSakowski said:
I received my encoder belt on Monday; the last item on my BOM. However, I also had carpal tunnel surgery that day and had to delay the mounting of the encoder. I managed to get the encoder mounted and connected everything together for a test run. I was disappointed in the available torque. I expected more from a 600 oz.-in stepper. Running the spindle at 175 rpm and the 12 tpi lead screw at .125"/rev. (8 tpi) , the stepper was turning at 262 rpm. I could make the motor lose steps with 40 lbs. of force applied to the carriage. I tried cutting a 7/16 -14 tpi thread and was able to cut the thread although the motor encoder kicked in to make up lost steps.

One obvious improvement would be to increase the supply voltage. I am running a 36 volt supply and the drive is capable of handling 48 volts. From the torque curve, this would give me about 20 - 30% more torque. A simple experiment would be to use the 602 gear box to do a 2:1 reduction, doubling the torque. This would be similar to Clough42's 3:1 motor pulley ratio. The concern is that the stepper motor has a relatively flat torque x rpm curve so very little is gained by using pulleys.
View attachment 307253
Here is that curve for my motor, running at 36 volts, derived from the published specs.

Another possible issue is driver tuning. Supposedly, the driver has an autotune feature but this may be making compromises for torque for the sake of other features. StepperOnline is secretive about the tuning software but others have suggested that Leadshine's tuning software is the one to use. I'll have to make up the serial cable. It's been a long time since I've done any work with RS232 cables but as I recall, only RX, TX, and GND are needed and the RX and TX lines are crossed. (Someone please correct me if I'm wrong.)

I am using a setting of 1600 steps/rev on the driver and 200 steps and 8 microsteps in the Clough42 software. This gives me the correct spindle to lead screw ratio. However, other have used the motor encoder resolution of 1000 pulses in setting the driver and in the controller software. Is there possibly an impact on torque there?

As I recall, a stepper has its best torque output at full step positions. Would there be an advantage to decreasing the number of microsteps? So many questions to answer.:rolleyes:
Click to expand...
110,000 oz.INS/sec =776.7707 watts! Acc to a converter, pls check.
Thats enormous!
 
Qtron said:
Both methods cause extra motor heating which with repetitive stopping, can become a problem

110,000 oz.INS/sec =776.7707 watts! Acc to a converter, pls check.
Thats enormous!
Click to expand...
Whats the average current draw at 400 rpm?
 
Qtron said:
Both methods cause extra motor heating which with repetitive stopping, can become a problem

110,000 oz.INS/sec =776.7707 watts! Acc to a converter, pls check.
Thats enormous!
Click to expand...
There is actually a unitless factor of 2π, if I am not mistaken, so it more like 120 watts.
 
It actually doesn't as I am simply looking at torque times rpm to determine if there would be a benefit to gearing up or down. From the graph, it appears that I wouldn't. The y axis is proportional to power so a flat curve kind of makes sense.
 
RJSakowski said:
It actually doesn't as I am simply looking at torque times rpm to determine if there would be a benefit to gearing up or down. From the graph, it appears that I wouldn't. The y axis is proportional to power so a flat curve kind of makes sense.
Click to expand...
A while back Briney Eye was quoting huge forces on the saddle, 700 lb plus, for 8 tpi threads in harder steels,, He had received a torque gauge but dunno the outcome of measurements.
 
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