Generating POs automatically based on a contract

Hi Experts,

With reference to a service procurement, I want to know the possibility of configuring a process in a manner that automatically generates POs periodically based on a contract created for a predefined time period(eg. 6 Months). I wonder if there is a scheduling mechanism in built  in SAP that can be used for this.

Note: The cost of the procurement and the vendor are fixed for the time period.

Thank you in advance.