Conveyor Belt

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svaurez

Member
Location
California
I have a question for some of the motor control guys here.I have a small conveyor belt about 6 feet long and 4 inches wide.I want to be able to start the conveyor belt with a foot switch and when one of the objects on the belt falls off the end I want the belt to stop moving immediately.

Foot switch=on
Object leaving belt=off

I have no idea what kind of motor to use to do this.

Any suggestions?
 

sdbob

Senior Member
Re: Conveyor Belt

Originally posted by svaurez:


I have no idea what kind of motor to use to do this.

Any suggestions?
Electric? :D

Seriously, your question is how is the control circuit wired and what will tell the circuit that a box has fallen.

Does one press of the foot-switch start the motor or does the foot-switch have to be closed constantly to move the conveyor?

How does a box "fall off" a conveyor? It seems like a conveyor design failure vs. an electrical control issue.

Optical sensors? Limit switches? Magic carpets? :eek: (just kidding)

This dilemma is gonna be real tough to solve via a BBS.
 

svaurez

Member
Location
California
Re: Conveyor Belt

It will be one press of the foot switch to start the motor.The conveyor belt will hold drinking glasses.When a glass comes to the end of the conveyor belt it will slide down a ramp.I want the belt to stop as soon as a glass leaves the belt.Maybe a limit switch at the end.I think the motor would have to have a slow speed so as to not jolt the glasses and make them fall.

I appreciate your input.
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
Re: Conveyor Belt

I think the first thing you need to figure out is how fast the belt has to go. A slower belt speed means you are waiting longer for the glass to fall. A faster speed means more problems not knocking over glasses, and you may have problems with the belt coasting to a stop. (Any reason why the belt has to stop immediately, or does it just have to stop before the next glass falls. You may even want it to run until the next glass is just about to fall. Then you have less wait time for the next one to fall).

I would think about optical or proximity sensors. Maybe 2. One to slow the belt down, and one to stop it. A VFD would also be helpful to ramp the speed up and down (you would get faster speeds without tipping over the glasses).

Steve
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
Re: Conveyor Belt

I can?t draw pictures and post them, but here is a basic description of the control circuit you have in mind:
</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">Let the foot switch be a ?momentary contact type.? That is, the switch is closed only when your foot is on the pedal.</font>
<font size="2" face="Verdana, Helvetica, sans-serif"></font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">Place that momentary contact switch in series with a control relay.</font>
<font size="2" face="Verdana, Helvetica, sans-serif"></font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">Place one ?a contact? of the relay in parallel with the momentary contact switch. That way, once you hit the switch with the foot pedal, the relay will energize, and the ?a contact? that is in parallel with the foot switch will close. This will keep the relay energized, even after you lift your foot from the pedal. It is called a ?seal in? feature.</font>
<font size="2" face="Verdana, Helvetica, sans-serif"></font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">Place another ?a contact? in series with the starting coil for the motor. Thus, when the relay is energized by the action of the foot pedal, the motor will start running.</font>
<font size="2" face="Verdana, Helvetica, sans-serif"></font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">Now you will need some type of sensor, such as those suggested by sdbob and steve66, to detect the fact that the item has left the belt. All you need to do is to have a ?b contact? from that sensor in series with the relay I mentioned above. When the sensor sees the bottle leave the belt, the ?b contact? opens, the relay no longer has power, and the motor stops.</font>
<font size="2" face="Verdana, Helvetica, sans-serif"></font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">Note also that the action of the ?b contact? removes the ?seal in? feature, so that the system is ready to start up again the next time you hit the foot pedal.</font>
<font size="2" face="Verdana, Helvetica, sans-serif">
SIDE NOTE:
I used the terms ?a contact? and ?b contact.? Some of you would know these instead by the terms ?normally open contact? and ?normally closed contact.? It is a personal preference, but I seriously dislike the ?NO? and ?NC? terms. They tend to open the doors to miscommunication. For example, if a motor is intended to be run 24 hours a day, 7 days a week, and 365.2475 days a year (i.e., including all the Feb 29 days), would you say that its main contactor is ?normally? closed, on the basis that the normal condition of the system has that contactor closed? I would not. That contact is ?normally open.? To avoid that confusion, I would call the contactor by the name ?a contact.?
 
Re: Conveyor Belt

Finally a question I can answer! Being an electrician and an automation controls engineer in the material handling business, we (I) do this kind of thing all the time. I would be happy to discuss your application privately via the provisions of this BB service if you would like. Most likely this will invlove a simple relay based control method and a photo-eye sensor. A variable frequency drive to control the accel and decel of the belt may also be warranted.
 

texelec

Member
Re: Conveyor Belt

A standard three wire Stop-start circuit with the foot switch as the start and a sensor (Photoeye located at the discharge end) as the stop switch would solve the start/stop problem. As for the motor to stop immediately you can add a motor brake on the conveyor drive. With only a six foot conveyor, trying to ramp up belt speed using a VFD to avoid tipping the glass over would be a little of a overkill. Suggest that you slow the conveyor down until you have the stability you need.
 

electricman2

Senior Member
Location
North Carolina
Occupation
Retired Electrical Contractor
Re: Conveyor Belt

quote by charlie b
It is a personal preference, but I seriously dislike the ?NO? and ?NC? terms.
As you say, it is a matter of personal preference but I learned these terms 30 years ago and having worked with control systems this long I have got used to them. No use to change this late in the game. :D
 

svaurez

Member
Location
California
Re: Conveyor Belt

This is more of an invention type project than a manufacturing one so the expensive vfd drives and stepping motor drives are out of the question.The replies have been very helpful as far as the control circuits.

How do I control the speed of a motor?
What kind of motor should I buy?

Ive been an electrician for about 6 years but this kind of automation design is completely foreign to me.

Thanks Again
 
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