The AcuBot robot includes three of the
previous robotic modules and adds a bridge support over the table
(Bridge Mount), and a linear pre-positioning stage (XYZ Stage):
AcuBot = Bridge Mount + XYZ Stage + Support Arm +
RCM + PAKY
The AcuBot's base (2) provides a bridge-like structure.
This attaches to the table of the imager (CT or fluoroscopy table)
with custom made table adapters (1). The needle (7) is held by the
needle driver (6), mounted in the RCM module (5), supported by a passive
arm (4), driven by the Cartesian stage (3). This serial link architecture
presents six degrees of freedom (DOF) configured for decoupled positioning,
orientation, and instrument insertion.
The needle driver (6) is responsible for the insertion
of the needle. The RCM module (5) performs needle orientation about
two directions coincident at the RCM point, thus allowing a pivoting
motion about that point. The RCM is supported by a passive positioning
arm (4) with 7 DOF. The arm can be positioned and rigidly locked from
a single lever. The base of the arm (4) is mounted in a 3 DOF Cartesian
stage (3). This stage is built within the bridge (2).
Needle Access Sequence:
The table adapter is initially mounted on the fluoroscopy table and
the robot is attached to it. The patient can be placed from either
side of the table by tilting the bridge on the opposite side. A sterile
needle driver and the procedure needle are mounted so that the tip
of the needle is at the RCM point. Percutaneous access is achieved
in four independent steps:
- The passive arm is manipulated so that the needle is in close
proximity of the intervention site and firmly locked.
- The tip of the needle is driven to the desired skin entry point
using the Cartesian stage. This is performed in two steps, starting
with a horizontal plane motion (TX, TZ) above the patient followed
by a vertical move (TY).
- The RCM module is used to orient the needle about this point
(RZ, RX).
- Finally, the needle is inserted (T) using the needle driver,
after proper targeting is confirmed by the physician.
Step number 3 is the only automated part of the procedure. The
other steps are performed by the physician under joystick control.
Safety through Motion Decoupling:
The four step sequence of the intervention is directly correlated
with the manipulator’s mechanical decoupling of motion and
the electronic grouping of axes enabling their independent activation.
With this, four separate mechanisms with independent controls are
used to perform horizontal and vertical positioning, orientation,
and instrument insertion. This safety feature allows the control
to sequentially enable groups of axes so that only the active mechanism
is enabled in each sequence. For example, this ensures that the
needle is not inadvertently inserted during the orientation step,
since in that step the XZ, Y, and needle driver axes are disabled.
Mechanically, all axes of the robot are highly geared thus presenting
minimal backdrivability. Vertical motion is gravity balanced ensuring
that the robot does not inadvertently plunge should an emergency,
computer crash, or even a power loss occur. Other safety features
are: 1) the robot has minimal mechanical power, 2) its high gearing
insures low maximum speeds, and 3) the workspace of the manipulator
is small yet sufficient for the intervention.
|
