The PCR (Primary Charge Roller) erases the printed image from the drum and prepares the drum for the next print job.
The PCR has both an AC and DC charge. The DC charge helps prep the drum to receive the image from the laser and toner from the Developer Roller.
Here is a close-up of the OPC Drum and PCR interacting during the printing process. The AC charge from the PCR removes the latent image from the OPC Drum during rotation.
Each PCR undergoes more than 30 different tests. Since the PCR can be one of the noisiest components within a cartridge, each one undergoes a noise test to ensure it is quiet within the cartridge. Other tests include exposure, voltage, resistance, circularity, adhesion, resilience and hardness.