Challenges
Conveyors are 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 process. However (specifically for conveyors) this parameter is also a system input.
If the assembled product type can change in production (modular production), then it is critical to tune the conveying cycle time optimally. The easiest way to achieve this is by keeping it at an average value based on technological installation times, although substantial product variance can lead to losses (stand-by times, poor utilization).
If accurate information about each workpiece in the production line (position, product feature, technological times) is available, then Sunstone has a specific product list. As a result, the products (and associated technological times) at each workstation are known at all times. Based on this 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 has been built or there is a track driven manually (trolleys, workbenches moving in hollows). Instead of a motor drive that the system could control, a timer is set 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 a new workpiece appears the cycle time is adjusted according to the time required in the next cycle. Adjusted cycle time is applied after the current step has been finished.
- Continuous Conveyor: in this case, the motor drive is directly controlled, but instead of cycle time, here the speed of the continuous movement itself is changed at any moment. Thus, as soon as a new workpiece is placed 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. The 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 in two ways:
- manual scanner identification at the very first workstation of the line
- based on RTLS
The following product information is required:
- the time when the product was 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