Production line monitoring and control

Challenges

The usage of conveyors is a typical manufacturing solution for mass production automation. Products are moved sequentially along the production line and stop at workstations. Cycle time as a parameter of the production line is a key performance indicator of the whole production. However (specifically for conveyors) this parameter is also a system input.

If the assembled product type may change in the production (modular production), then it’s a critical task to tune optimally the conveying cycle time. The easiest way is to keep it at an average value based on technological installation times, although substantial product variance can lead to losses (stand-by times, poor utilization).

If we have accurate information about each workpiece in the production line (position, product feature, technological times), then Sunstone has a specific product list. Thus which products (and associated technological times) belong to each workstation are known all the time. Based on these data, it is possible to determine the critical time, which is the optimal cycle time in the given step (Figure 1). Then the Sunstone system sends the critical times to the production line via the UWB radio interface. Any additional production line can extend the system.

Basic concept

Cycle time adjustment of conveyors depends on different production technologies. We distinguish three large groups:

  • Manually driven production lines without a buffer: in this case, either no physical conveyor built or there is a track driven manually (trolleys, workbenches moving in hollows). Instead of a motor drive that we could control, we set a timer for the cycle time. During this time the workers need to complete the installation of the product.
  • Intermittent Conveyor: in this case, the motor drive is directly controlled and each time when a new workpiece appears the cycle time gets adjusted according to the time required in the next cycle. Adjusted cycle time applied after the current step finished.
  • Continuous Conveyor: in this case, the motor drive is directly controlled too, but instead of cycle time, here we change the speed of the continuous movement itself at any moment. Thus as soon as a new workpiece gets on the line, its effect becomes immediately perceptible.

Installation and technological times are critical input parameters of the system. Production control is based on these parameters and an algorithm for the given process.
Production control with the Sunstone system works through a specially designed TAG via UWB communication. That TAG connects to the controller on one of the available interfaces (RS232, RS485, CAN, Bluetooth, e.g.).

Tracking semi-finished goods:

Product tracking on conveyors can happen two way:

  • manual scanner identification at the very first workstation of the line
  • on RTLS basis

The following product information is required:

  • time of the product placed on the line
  • the unique ID of the product
  • theoretical assembly time

System benefits

  • A reliable, well-maintained hardware element
  • Flexible infrastructure (system moves with the PLC controller)
  • Optional continuous monitoring and intervention
  • Optionally expandable without additional infrastructure costs