What is chordal action or the polygon effect?
We often receive questions concerning the chordal action, also known as the polygon effect. Today we will try to break down the meaning of this action and suggest a couple ways to reduce its effect.
Polygon means ‘multi-angle’. Module and chain links moving around the radius of the sprocket causes the linear belt speeds to vary. The pivot rod travels on the pitch diameter of the sprocket while the module moves through the smaller chordal radius causing a horizontal rise and fall of the module. This polygon effect is typical of all modular belt systems. The magnitude of speed variation is dependent on the number of sprocket teeth.
Sprocket diameter
Sprockets with a low number of teeth show a high speed variation (5 teeth up to over 14%). This is why we advise using a sprocket with a minimum of 12 teeth in order to limit the polygon effect. As the graph shows, more teeth will further reduce the effect. By the way, this not only effects the sprockets. You will find the same result among all idler-, transfer- or support rollers. To minimize this effect, choose the diameter for the roller based on the nominal pitch of a 12 teeth sprocket of the belt series that you prefer.
In general, we suggest designing the conveyor with the biggest possible diameter in mind and taking care that the distance between the center of the rollers is not a multiple of the belt pitch.
If you have any further questions regarding the polygoneffect,downloadourHabasitLINK Engineering Guide or contact us!
In “The Complete Guide to Chain” it says that:
In addition to the number of teeth, if the shaft center distance is a common multiple of the chain pitch, chordal action is small. On the other hand, if shaft center distance is a multiple of chain pitch + 0.5 pitch, chordal action increases.
Your blog post seems to say the opposite:
In general, we suggest designing the conveyor with the biggest possible diameter in mind and taking care that the distance between the center of the rollers is not a multiple of the belt pitch.
Is this an error?
Polygone effect you have explained but when my chain is travelling at and angle spiral way than chain needs some more play in the pin dia? Can we calculate how much play will be ok as per angular raise in the chain.