what will be best oscillating mechanism for Oscillating granulator

best and very simple mechanism for this case is that make motor shaft unbalance .for this purpose you should increase the mass of one side of motor shaft something like phone vibrate. another case is using pneumatic tools .because with pneumatic system you can change the amount of vibration.another case is cam and shaft mechanism .but whole of everything that i told you is depend of amount of your space .because for oscillating we have many mechanism like changing rotation to linear movement .another important point is that how much you need accuracy