**3. Bone drilling process execution**

The successful realization of drilling manipulation depends on normal functioning of the whole system components – motors, force sensor, controllers, buttons, etc. That means the components have to be tested before the start of manipulation. A procedure 'Self Test' is developed which starts immediately after the power is switched on. The 'Self Test' procedure passes through the following testing steps:


The force sensor test reports the ability of transferring the data for resistant force at free translation motion forth and back as well as an average value for normal motion which confirms a previously defined and known criterion.

The decision whether the component works right or wrong is taken according to criteria downloaded in the program. The 'Self Test' procedure confirms safe working the whole system. When some differences from the criteria incorporated in the software are registered then the message "Self TEST ERR" appears on the display. The robot cannot be used until the corresponding reasons are eliminated. The message confirming the positive result of the procedure is "Self TEST OK" on the display.

The next step is to set the working mode. Additionally another parameter in [mm] ( *B*max ) is set which is connected with the patient's safety and it is related to each specific patient. The hole depth cannot exceed *B*max . This parameter depends on the specific task, for example - it can be taken from the x-ray image of the bone before operation. During the drilling at every discretization time interval " *k* " the current position is compared with *B*max and then the decision for going on or stop the process is taken.

**141**

*Orthopedic Bone Drilling Robot ODRO: Basic Characteristics and Areas of Applications*

The drilling process (**Figure 9**) is running when the button of the executive module (start button) is pressed and is held continuously by the surgeon. He can stop the manipulation aiming to set a new working regime or to prevent a drilling error. The manipulation execution goes on after the start button is pressed again and is held until the drilling ends automatically and the drill bit returns to its home (reference) position. During the operation the surgeon must keep firm contact with the bone all the time. When performing the drilling process, the selected drilling

The control algorithms are realized in the specialized program language (Trinamic Motion Control Language – TMCL) specific for the TMCM (Trinamic Motion Control Module) controllers in the program environment TMCL-IDE. The execution of commands start immediately after the input (direct regime) or the program can be downloaded for autonomous execution in the controller (standalone regime). The user is also allowed to input different axes and global parameters which enrich the control algorithms results and make its realization easier. The main control program is structured in separate states - State Search for Contact, State Contact Found, State Drilling, State Check for Missing Steps, State not Contact Found, State Ready etc. In Stand-alone regime the program recognizes the current state for every cycle and executes the corresponding algorithm, taking a decision for

going to the next state in dependence on preliminary determined criteria.

, *ik k* =− … ( ) 4 ,, ,, ;

The translation motion control during the drilling is based on the force feedback. A modified PI control law (Eq. (1)) is used to calculate the new position, or the "next target position", (number of steps *<sup>k</sup>* ∆*s* where *k* is the time interval discretization), which the linear motor as well as the drill bit, respectively, must

> *k P k Ik* ∆= + *s K KI* ε

*KP* and *KI* - feed-back coefficients of the proportional and the integral compo-

*Fr* - reference force which must be maintained following the created algorithm during the drilling process. The value of *Fr* is calculated for drilling of each specific (individual) bone and depends on features of the patients, for example health

Considering our specific task the following comments have to be done. The registration of far cortex from inside the bone and the breakthrough detection depends on the evaluation of the bone density in the current drilling zone. Because of that an integral component *ds I* (Eq. (2)) is formed as a sliding window in the same

drilling zone. By this integral component information is obtained for the change of bone density:

( ) *<sup>k</sup>*

the bone density which corresponds to Reference Force *Fr* .

In the last expression " *n* " is the dimension of *ds I* in the sense of sample discretization. Its value is updated after every *n* sample. Decreasing of *ds I* shows higher bone density and its increasing – drilling in lower bone density in comparison with

*ds i I I i kn k* =∑ = − … ,, , (2)

, (1)

*DOI: http://dx.doi.org/10.5772/intechopen.96768*

Then the drilling process can begin.

mode was indicated on the display.

reach in a given interval of time ∆*t*.

ε

*<sup>k</sup> Fact* - actual thrust force (measured);

*k*

*k r act* = − *F F* ; *k i I* = ∑

nent in the control low;

status, age, sex, etc.

where:

ε

#### *Orthopedic Bone Drilling Robot ODRO: Basic Characteristics and Areas of Applications DOI: http://dx.doi.org/10.5772/intechopen.96768*

Then the drilling process can begin.

*Latest Developments in Medical Robotics Systems*

*Information displayed after "Cortex II Full" drill mode.*

**Figure 7.**

**Figure 8.**

**3. Bone drilling process execution**

*Information displayed after "Cortex II Find" mode.*

• start button reliability (switch on and switch off)

• ability to receive the force sensor data

• check the rotational motion

• ability to find out the initial position (Reference position)

• check the translation motion of the step motor (going forth and back the

The force sensor test reports the ability of transferring the data for resistant force at free translation motion forth and back as well as an average value for normal

The decision whether the component works right or wrong is taken according to criteria downloaded in the program. The 'Self Test' procedure confirms safe working the whole system. When some differences from the criteria incorporated in the software are registered then the message "Self TEST ERR" appears on the display. The robot cannot be used until the corresponding reasons are eliminated. The message confirming the positive result of the procedure is "Self TEST OK" on the display. The next step is to set the working mode. Additionally another parameter in [mm] ( *B*max ) is set which is connected with the patient's safety and it is related to each specific patient. The hole depth cannot exceed *B*max . This parameter depends on the specific task, for example - it can be taken from the x-ray image of the bone before operation. During the drilling at every discretization time interval " *k* " the current position is compared with *B*max and then the decision for going on or stop

working zone, free motion resistance, check for missing steps)

motion which confirms a previously defined and known criterion.

The successful realization of drilling manipulation depends on normal functioning of the whole system components – motors, force sensor, controllers, buttons, etc. That means the components have to be tested before the start of manipulation. A procedure 'Self Test' is developed which starts immediately after the power is switched on. The 'Self Test' procedure passes through the following testing steps:

**140**

the process is taken.

The drilling process (**Figure 9**) is running when the button of the executive module (start button) is pressed and is held continuously by the surgeon. He can stop the manipulation aiming to set a new working regime or to prevent a drilling error. The manipulation execution goes on after the start button is pressed again and is held until the drilling ends automatically and the drill bit returns to its home (reference) position. During the operation the surgeon must keep firm contact with the bone all the time. When performing the drilling process, the selected drilling mode was indicated on the display.

The control algorithms are realized in the specialized program language (Trinamic Motion Control Language – TMCL) specific for the TMCM (Trinamic Motion Control Module) controllers in the program environment TMCL-IDE. The execution of commands start immediately after the input (direct regime) or the program can be downloaded for autonomous execution in the controller (standalone regime). The user is also allowed to input different axes and global parameters which enrich the control algorithms results and make its realization easier. The main control program is structured in separate states - State Search for Contact, State Contact Found, State Drilling, State Check for Missing Steps, State not Contact Found, State Ready etc. In Stand-alone regime the program recognizes the current state for every cycle and executes the corresponding algorithm, taking a decision for going to the next state in dependence on preliminary determined criteria.

The translation motion control during the drilling is based on the force feedback. A modified PI control law (Eq. (1)) is used to calculate the new position, or the "next target position", (number of steps *<sup>k</sup>* ∆*s* where *k* is the time interval

discretization), which the linear motor as well as the drill bit, respectively, must reach in a given interval of time ∆*t*.

$$
\Delta \mathfrak{s}\_k = K\_P \mathfrak{s}\_k + K\_I I\_k \, , \tag{1}
$$

where:

$$\varepsilon\_k = F\_r - F\_{\text{act}}^k \; ; \; I\_k = \sum \varepsilon\_i \; , \; \left\lceil i = (k-4) \right\rceil , ... , \& \text{\textquotedblleft} \right\rceil ;$$

*KP* and *KI* - feed-back coefficients of the proportional and the integral component in the control low;

*<sup>k</sup> Fact* - actual thrust force (measured);

*Fr* - reference force which must be maintained following the created algorithm during the drilling process. The value of *Fr* is calculated for drilling of each specific (individual) bone and depends on features of the patients, for example health status, age, sex, etc.

Considering our specific task the following comments have to be done. The registration of far cortex from inside the bone and the breakthrough detection depends on the evaluation of the bone density in the current drilling zone. Because of that an integral component *ds I* (Eq. (2)) is formed as a sliding window in the same

drilling zone. By this integral component information is obtained for the change of bone density:

$$I\_{ds}^k = \sum I\_{\iota}, \left[ i = (k - n), \dots k \right], \tag{2}$$

In the last expression " *n* " is the dimension of *ds I* in the sense of sample discretization. Its value is updated after every *n* sample. Decreasing of *ds I* shows higher bone density and its increasing – drilling in lower bone density in comparison with the bone density which corresponds to Reference Force *Fr* .

**Figure 9.** *Bone drilling process.*

The parameter *ds* ∆*I* is formed as a difference between two consecutive values. It gives information for tissue density deviation in current drilling area. The higher the *ds* ∆*I* the bigger is bone density deviation in the current zone in comparison with the zone drilled just before.

Next, the comparison of the value *ds* ∆*I* with some appropriately chosen reference value allows taking a decision for the breakthrough detection of second cortex as well as the far cortex registration. The dimension of *ds I* from view point of number of subtractions ( *<sup>k</sup>* ε *k r act* = − *F F* ) assures the accurate monitoring the tendency of increasing or decreasing the bone density and in the same time minimizes the "not typical force sensor data" in the drilling area.

The dimension of *ds I* from view point of number of samples of discretization is in connection with the extent of the drill bit penetration when it starts moving in low density area.

Once the drilling process is completed according to the selected operating mode, the result of the operation is presented on the display.
