walking beam

This sounds like a design issue rather than programming one. The approaches you tried are the only ones possible here, with all the caveats you have mentioned.

Other than that, someone would have to invest either in clutch/brake or in a servo. Or at least some kind of speed controller so you can run your WB a bit slower.

you can use diffential up or down in your program or you can change your construction.

nmk said:

I have a walking beam machine(new project), that has multiple stations; dwell and indexing stations.

1) has an encoder that can tell angle position, but no clutch/brake installed.

2) walking beam is being driven by a motor that has two internal momentarily switches start and stop coil contacts.

3) when the motor is pulsed to start, it starts and stays running till the stop contacts are energized or a fault occurs.


One of the dwell stations can not retract back fast enough before the walking beam trying to index.

Every cycle I get a fault that one of the dwell station did not fully retract far enough to clear the walking beam and assembly stops. I can not slow down the walking beam nor can speed up the dwell stations.

I do not know if any body has some constructive suggestions on the best way to program this part of the walking beam. At this time I tried the following approaches:

1. 1. Initiate the motor to stop at the beginning of the dwell cycle then after all stations finished working and retracted to their home position start the motor again. This might not be good for the motor to continuously starting and stopping.
   2. Keep the motor running, as long the dwell stations are not forward and clear the indexing walking beam pathway by not much. This works fine except the fear of walking beam might shear any of the dwell stations assembly keeps me on the edge.

Click to expand...

Having no idea what a walking beam is ( and very curious BTW), I still would definitely NOT use solution number two.

In most of my experiences, the motor/drive train is much cheaper and easier to replace than the often specialized working end of a machine.

Before you decide, answer for yourself (and us if you don't mind) the following question:

If there is a crash how expensive will it be to fix? Be sure to include the cost of downtime and labor as well as lost product.

IMHOO, If the motor/drive train is properly sized, it should survive a large number of normal stop cycles without failure. Still I am trying to envision a walking beam. . .so I may be way off in that okie opinion.

I don't know how large the drive system is or how sensitive it might be to frequent start/stop cycles. If a high inertia load exists that needs a soft start/stop, the cost of a VFD might be much cheaper than the loss of productivity you might suffer if you break something with too many hard start stop cycles. Yes, then you will have to do away with the motor mounted relay. And, I don't even know what kind of motor it is, so this may be way out in left field.

I would most likely implement solution number 1, and consider, possibly, a modified version of solution one in which you automatically clear and restart only after a fault occurs. Make it a cycle delay warning, protect the product and the machine, and minimize the excess strain on the drive train.

If there is a high inertia load attached, or any reason to avoid quickly restarting the motor, be sure to put in an off delay to ensure that the motor won't be regenerating when you start it again, and that you don't twist a shaft "in two" or shear drive components. As a matter of fact, add an off delay anyway, to keep from wearing out the contactor in a case of limit switch bounce, and especially if you "program"* it to auto restart.

*(If there is no PLC, substitute "re-wire")

If it is happening every cycle, then it won't make much difference from your 1st solution. To me it will give the chance to keep uptime to a maximum, not hide the fact that there is a problem, and let you work on finding the root cause.

Maybe you find you can adjust the ranges of your position feedback devices. If the mahcine is programmed to post a warning, rather than alarm (keep the same alarm if you wish, no HMI programming) and automatically restart, be sure to inform all hte personnel of the change (safety). Also, as soon as you find an adjustment that reduces the frequency of the hesitation, or eliminates it, then you will be done. You can leave the program as-is.

I am talking about adjusting the retract limit feedback device so that it "makes" (satisfies the "clear" condition) at the exact point where mechanical clearance is achieved. Also, you should see if it is possible to adjust the range in which the walking beam is checked for clearance, by adjusting it's limit window from its encoder.

Then, you must carefully scrutinize the cycle of events that causes this particular workstation to take too long.

I googled walking beam, and came up with too many widely varied devices. Is it like a crane on wheels on a track?

Hopefully Helpful,
Paul

I googled walking beam, and came up with too many widely varied devices. Is it like a crane on wheels on a track?

Click to expand...

Not exactly. It is rather a horizontal bar with vertical fingers that move up->forward->down->back. Pushing some product through a track during the forward stroke. There are many different designs and implementations but the basic idea is the same: providing reciprocating motion in two directions.

Not the exact same motion as a walking beam, but the same movement concept...



For nmk: Is there any way you can mechanically couple the walking beam drive to the dwell station's motion?



-Eric

Thanks, guys, I have never had to control one of those. . .

I WAS way out in left field after all, but i learned something.

PiEaCe!

Paul

LadderLogic said:

Not exactly. It is rather a horizontal bar with vertical fingers that move up->forward->down->back. Pushing some product through a track during the forward stroke. There are many different designs and implementations but the basic idea is the same: providing reciprocating motion in two directions.

Click to expand...

All of ours are do not have any verticle fingers. The movable horizontal supports lift the part off of other stationary horizontal supports then traverse lateraly then down to lower the part onto the stationary horizontal supports. The movable horizontal supports then will traverse back to a home position under the stationary horizontal supports. These are used to move 30' long 15 ton metal billets through a reheat furnace. Others are used to moved extruded rod from a press through a cooling spray zone. The parts are never pushed, only lifted and lowered in a different position. In the reheat furnace everything is done via hydraulic cylinders with Temposonic position transducers. The stroke is variable to accomodate various sized billets determined during loading.
Sounds like some mechanical guy didn't talk to the programmer. I've had that happen too many times.

John Soltesz said:

These are used to move 30' long 15 ton metal billets through a reheat furnace.

Click to expand...

That explains the difference in the implementation of the concept: our parts weigh less that an ounce.

Walking beam

See whether the attached example suits you.
Regards
Ranjith