An apparatus comprising: a needle ; a positioning device configured to position said needle at a first vertical position in response to control signals; a sealing member having a passage with a first opening at a first end for receiving a tip of said needle , wherein positioning said needle at said first vertical position causes: contact between inner sidewalls of the first opening of said sealing member with surfaces of said tip of said needle , and application of a force against said inner sidewalls of said first opening of said sealing member by surfaces of said tip of said needle causing vertical downward movement of said sealing member toward a spring engaged with said sealing member which, responsive to application of said force, is compressed a distance proportional to said force; a force sensor coupled to the spring , said force sensor measuring said force; and a computing device electrically connected to said force sensor and said positioning device, said computing device configured to receive a signal from said force sensor indicating said force measured by the force sensor , to determine an adjustment to said first vertical position of said needle in accordance with whether said force measured by said force sensor is at a desired force setting, and configured to send control signals to said positioning device causing said positioning device to vertically position said needle in accordance with said adjustment. a needle ; a positioning device configured to position said needle at a first vertical position in response to control signals; a sealing member having a passage with a first opening at a first end for receiving a tip of said needle , wherein positioning said needle at said first vertical position causes: contact between inner sidewalls of the first opening of said sealing member with surfaces of said tip of said needle , and application of a force against said inner sidewalls of said first opening of said sealing member by surfaces of said tip of said needle causing vertical downward movement of said sealing member toward a spring engaged with said sealing member which, responsive to application of said force, is compressed a distance proportional to said force; contact between inner sidewalls of the first opening of said sealing member with surfaces of said tip of said needle , and application of a force against said inner sidewalls of said first opening of said sealing member by surfaces of said tip of said needle causing vertical downward movement of said sealing member toward a spring engaged with said sealing member which, responsive to application of said force, is compressed a distance proportional to said force; a force sensor coupled to the spring , said force sensor measuring said force; and a computing device electrically connected to said force sensor and said positioning device, said computing device configured to receive a signal from said force sensor indicating said force measured by the force sensor , to determine an adjustment to said first vertical position of said needle in accordance with whether said force measured by said force sensor is at a desired force setting, and configured to send control signals to said positioning device causing said positioning device to vertically position said needle in accordance with said adjustment. <EOS>