DMM Tec Servos

[Al_The_Man]

Originally Posted by lgalla I have used this formula posted by Marris of GECKO Drive on motor sizing. Pick the weight of the heaviest item you are pushing around. If it weighs 40lbs, use 40lbs. multiply it by the IPM you want. Say that's 1,000 IPM. Divide the result by the magic number "531". The answer is 75.3 Watts so use a step motor. Eq: Watts = IPM * Lbs / 531 Would the answer be in peak or continuous watts??? Larry

The characteristics are different for steppers and servo's.
Steppers operate at one continuous torque (current), whether they are moving with no load, under load or at stop.
If the load increases to too high a value, the drive does not know this and the stepper current is not increased and the stepper can stall or miss steps because of this.

With a servo, the systems aim is to maintain a position by virtue of the PID feedback loop, this aim is to keep the servo motor within so many position counts known as following error, as following error increases, the current (torque) Increases Proportionately, this increase in current attempts to reduce this margin of error.
If the motor load causes too large an error, a couple of things can happen if the system does not turn the drive off, the current will climb according to the degree of error (load), this can place the motor current into the intermittent range, which in turn will cause heating of the motor.
If the drive is allowed to because of too high a current limit setting, it will keep the motor in this range until the load and following error decreases.
In this event, the only other way to protect the motor is if the motor is fitted with a thermal sensor, which many are.
Al.

[lgalla]

Al if the powersupply voltage is doubled with the 900Watt peak servo in question...correct me if am wrong.The RPM goes up but the torque remains the same?It was stated in a previous post that the torque would increse as well
Thanks Al
Larry

[ihavenofish]

Originally Posted by lgalla Al if the powersupply voltage is doubled with the 900Watt peak servo in question...correct me if am wrong.The RPM goes up but the torque remains the same?It was stated in a previous post that the torque would increse as well Thanks Al Larry

the speed goes up with voltage, and the wattage goes up.

torque stays the same, as its based on current.

[hub]

I agree Al.
Peak torque is peak torque It means the system can take it for a brief moment; But, it won't run at peak torque for a long time without damage.
You can't use peak torque in design calculations. Use constant torque & wattage required for constant running and PSU requirement calculations.
~Hub

Originally Posted by Al_The_Man The characteristics are different for steppers and servo's. Steppers operate at one continuous torque (current), whether they are moving with no load, under load or at stop. If the load increases to too high a value, the drive does not know this and the stepper current is not increased and the stepper can stall or miss steps because of this. With a servo, the systems aim is to maintain a position by virtue of the PID feedback loop, this aim is to keep the servo motor within so many position counts known as following error, as following error increases, the current (torque) Increases Proportionately, this increase in current attempts to reduce this margin of error. If the motor load causes too large an error, a couple of things can happen if the system does not turn the drive off, the current will climb according to the degree of error (load), this can place the motor current into the intermittent range, which in turn will cause heating of the motor. If the drive is allowed to because of too high a current limit setting, it will keep the motor in this range until the load and following error decreases. In this event, the only other way to protect the motor is if the motor is fitted with a thermal sensor, which many are. Al.

[Al_The_Man]

A simplification is that voltage potentially allows higher RPM. As to torque, if you look at some typical servo torque curves, the Potential torque starts to fall off at a certain rpm, so this is considered the useful range of the servo.
Torque is dependent on current, so increasing the PWM voltage to the drive not only increases the potential maximum rpm, it allows the drive to reach the desired current limit that much sooner.
Remember, the value of torque required comes into play as need or required by the load, this torque is directly proportional to the current and proportional to the existing following error.
Al.

[Al_The_Man]

Originally Posted by hub I agree Al. Peak torque is peak torque It means the system can take it for a brief moment; But, it won't run at peak torque for a long time without damage. You can't use peak torque in design calculations. Use constant torque & wattage required for constant running and PSU requirement calculations. ~Hub

If you allow the servo to take advantage of peak torque, what element is controlling this use of peak torque and how much is a brief moment?
The idea of a servo loop is to always be in control and the only way a servo knows this is by the feedback element and the degree of error between the commanded position and the actual position.
A servo cannot or should not take off into a area that can cause damage to the servo as if this occurs, it means the servo system has lost control, (excess following error).
It is like saying it took off to where it should not go but it will be back!
Al.

[hub]

Higher end servo drives have current sensing & will fault if they have to "push too much". Without, I'm guessing a servo could run for quite a while (probably minutes) overload until it would break.

A servo is only a motor with an encoder attached to a servo drive as far as I know. It does not 'know' if it's pushing too hard. The drive has control & decides how much power & speed & direction.

Originally Posted by Al_The_Man If you allow the servo to take advantage of peak torque, what element is controlling this use of peak torque and how much is a brief moment? The idea of a servo loop is to always be in control and the only way a servo knows this is by the feedback element and the degree of error between the commanded position and the actual position. A servo cannot or should not take off into a area that can cause damage to the servo as if this occurs, it means the servo system has lost control, (excess following error). It is like saying it took off to where it should not go but it will be back! Al.

[Al_The_Man]

Originally Posted by hub Higher end servo drives have current sensing & will fault if they have to "push too much". Without, I'm guessing a servo could run for quite a while (probably minutes) overload until it would break. A servo is only a motor with an encoder attached to a servo drive as far as I know. It does not 'know' if it's pushing too hard.

Exactly, there are two common setting that detect when a servo is not performing as it should, one is excess following error, set by parameter, the other is servo drive current limit, and a often a third element which is a thermal sensor embedded in the motor windings, All Fanuc servo's have these and are monitored by the drive.
Al.

[iknowyoudo]

Counting the days till the new drivers are released.

[azam1959]

Hi,

Few weeks ago I did ask number of questions about control box and got more help then expected. I am very thank full for the help and as you can see from picture my control box is influenced by couple of samples posted here to help me. I did not account for parallel port cable plug size during layout phase and to accommodate this mistake I have to reverse breakout board placement, oh well .... (this is the first time I am attaching the picture, hope it will show up).

Still in the process of checking the wires etc. and have not turned on the power yet.

During the learning process I also got a teacher/mentor I met here and this gentleman is helping me to select right type of wires, connectors, tools etc.

Originally Posted by azam1959 quick question about your cabinet ... i am also working very slowly to put four motor kit in the cabinet. Wires on the left of the cabinet in the picture going from driver to encoder, how did you mange to put them so nicely on the side? Did you use some kind of cutter to make right size rectangles in the cabinet? Can you post a close up of that part. I am using a second hand enclosure which already had few holes which make my life easy. I do have to make couple of holes for the wires and screws and each hole take few minutes on hand drill and my weak hands can not make too many holes from hand drill. If there is a good tool to cut cabinet, it will help. thanks

[azam1959]

Thanks Eric.

I was able to control the motor through SW (without any smoke). DMM can improve on documentation but system is pretty easy to setup. I was worried about my lack of knowledge about physical interfaces between different components but kit has all the necessary wires and connections. For newbie like me this was a big help. Nobody bribed me to write this post, just trying to help folks like me who are still deciding.

I am hearing that my XZero machine is shipped. Once I have the machine, I may have to change three parameters based on load, inertia, etc. Changing the parameters is a simple process (and hopefully need to be done only once). There was some discussion and anticipation about new generation of smart drivers which can automatically set itself based on load. Now I understand ... but will I pay for smart driver if I need to change three parameters only once. I must be missing something. Oh well, lot to learn ....

Cheers

Originally Posted by iknowyoudo azam1959, Looking good so far. Eric

[lgalla]

Anyone having trouble.I can not get past post #5 on this thread.Seem to have PM trouble also
Larry