Development of a control system for a surgical microscope stand

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Starting situation

Surgical microscopes are primarily used in ophthalmology and microsurgery and enable the surgeon to magnify anatomy with optimal illumination. The stand of a modern microscope holds heavy optical components and must be highly stable and rigid, while simultaneously ensuring full freedom of motion and positioning.

A manufacturer of surgical microscopes commissioned IMT to develop the motor control and positioning firmware for the stand of a new microscope. The deadline was tight—the job needed to be completed in one year.

Objective of the project

From the client’s standpoint, the focus was on the following requirements:

  • Secure positioning of the stand with 6 degrees of freedom
  • Easy operation with 2 fingers or with mouth switch
  • Motorization of selected axes
  • Reduction of undesirable vibrations following repositioning of the visualization system or after manipulation by the operator

From a technical standpoint, it was important to integrate the new firmware into the overall system via CAN bus communication. The client’s specific operating system must be used for this purpose.

Technical implementation

In consultation with the client, IMT decided to use the Dataflow Runtime software framework by IMT DATAFLOW, an IMT product. The framework is written in C++ and the associated tool suite supports developers in the systematic and efficient creation of high-quality embedded applications with minimal need for documentation.

Since the stand was to be freely positioned using six axes and different motors, one firmware application per axis was developed along with an overarching firmware application. This overarching firmware application communicates with each axis motor microcontroller and thus coordinates the axis movements. The axis motor control system was modeled using Matlab Simulink. “Hardware-in-the-loop” simulations were used to test the controls in real time on the target hardware during development to optimize the control of the motors. This also succeeded in optimizing the commutation of the DC motors for minimal current consumption.

The customer-specific CAN protocol generated by a CAN protocol generator (specified and developed by the client) was implemented in the control firmware for integration into the entire system. The client-specific operating system with the correspondingly adapted Dataflow framework was used in all firmware components.

Of course, IMT prepared the technical documentation (SW architecture, V&V test plans) and provided hands-on support to the client during system integration.

Results

The project was completed on schedule and to the full satisfaction of the client. The device has been successfully launched on the market. The device has been successfully launched on the market.

“The project was technically and schedule-wise very challenging, but it was a lot of fun for the whole team. We felt well integrated into the customer landscape and the intensive alignment successfully prevented potential disruptions in the project.”

Roger Millischer, Development Team Manager

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