Stopping time for a cycloidial dial table

In summary, the Risk Assessment for this dial table states that the indexer will stop in 0.86 seconds, worst case. If power is disconnected from the motor driving the indexer, the stop time will be based on the system response time. The contactor will rule under the operator protection scenario. The indexer has two positions, and the move profile is sinusoidal.
  • #1
Jonesy
2
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I am working on a Risk Assessment for a dial table, the manufacturer states that the indexer will stop in 0.86 sec, worst case. Since the indexer is cam driven the speed varies throughout its motion. That being said I expect stop times to be highest at 90 and 270deg, while lowest at 0 and 180deg. My thinking is to multiply the SIN(r)*θ. Am I on the right path, or off on a tangent.
 
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  • #2
Welcome to PF.

Jonesy said:
That being said I expect stop times to be highest at 90 and 270deg, while lowest at 0 and 180deg.
Please give a diagram of the cam mechanism. What is the reference direction relative to the cam?

Jonesy said:
My thinking is to multiply the SIN(r)*θ
You cannot take the Sin(r) of a dimensioned radius, only of a dimensionless angle. Sin(θ)*r would make more dimensional sense.
 
  • #3
Jonesy said:
I am working on a Risk Assessment for a dial table, the manufacturer states that the indexer will stop in 0.86 sec, worst case. Since the indexer is cam driven the speed varies throughout its motion. That being said I expect stop times to be highest at 90 and 270deg, while lowest at 0 and 180deg. My thinking is to multiply the SIN(r)*θ. Am I on the right path, or off on a tangent.

What kind of risks? Risks that the workpiece will be ruined for some reason, or risks that the operator can be hurt?

When you say the indexer will stop in 0.86s worst case, that's 0.86s from what?
 
  • #4
It sounds like the manufacturer quoted you the time to disable power to the driving motor and engage the motor brake. If no brake, then stoppage occurs due to cam motion friction between the mechanical components.

If they did their engineering sizing calculations properly, the motor is matched to the specified rotating payload mass & inertia on the dial table. So it follows that the brake is properly matched also. On ESTOP, cut power to motor and clamp on the brake...rotation stops in 0.86 seconds. Seems reasonable. But the cost to do that is likely damage to the mechanical components if the rotational mass payload is spinning at max speed.
 
  • #5
Thank you all for prompt reply.

Baluncore,
The move profile is sinusoidal, this type of indexer is common in the manufacturing industry, it give a nice slow start/stop at the pitch, this system has two positions. Thanks for correcting my math.

Berkeman.

Risks in my business is prioritized to people, tooling, part. I am assuming the .86 represents from max velocity, since the profile is sinusoidal, ithink the velocity varies throughout the index cycle, at this point I assume at 90 deg intervals.

Tigerdawg.

The stop time is based on power disconnection from the motor driving the thing, the time to disable is the system response time. This includes the actuation of the stop signal, fieldbus (Ethernet) transport time, processor input update time, logic execution time, I/O faults within the system, output update time, and contactor opening time (power removal). Under normal stopping conditions the drive (VFD) supplies regenerative braking, when the dial is in dwell. Under the operator protection scenario, the contactor rules.

I am reasonably sure the calculations are correct, this is a common system, and the technology has been around for a long time. Braking is common, and works just like the brakes on your car, no damage unless you hit something.

All,

I am using worst case .86 seconds for stop time, but my intellectual curiosity always overpower me and I have to know more. Interestingly enough I find the response time of a contactor with an integral diode, is faster that one with an external diode. The diodes are used to 'snub' counter EMF. Does anyone have an explanation? Maybe some additional inductance, or slower field collapse?
 

Related to Stopping time for a cycloidial dial table

1. What is a cycloidal dial table?

A cycloidal dial table is a type of mechanical device that is used to measure time. It consists of a circular table with a cycloidal-shaped track on its surface, along which a ball can roll. The time can be measured by the position of the ball on the track.

2. How does stopping time for a cycloidal dial table work?

To stop time on a cycloidal dial table, a lever or brake is used to hold the ball in place on the track, preventing it from rolling. This allows for an accurate measurement of time at that specific moment.

3. What is the purpose of stopping time for a cycloidal dial table?

The purpose of stopping time on a cycloidal dial table is to accurately measure and record the time at a specific moment, rather than relying on continuous motion of the ball on the track. This can be useful in scientific experiments or industrial applications where precise timing is necessary.

4. Can the time be restarted after it has been stopped on a cycloidal dial table?

Yes, the time can be restarted on a cycloidal dial table by releasing the lever or brake that is holding the ball in place. The ball will then resume its motion along the track, allowing for continuous measurement of time.

5. Are there any limitations to stopping time for a cycloidal dial table?

One limitation of stopping time on a cycloidal dial table is that it can only measure time in short intervals, typically ranging from seconds to minutes. Additionally, the accuracy of the measurement may be affected by external factors such as friction or imperfections in the track or ball.

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