Patent Application
20220250260
The present invention relates to a brakes piloting system for a robotic device displaying one movable element or a chain of movable elements.
It is well known in the state of the art, that robotic devices, in particular medical devices, comprising movable elements, have to include position locking systems when the movable element reaches a determined target position, in order to prevent unwanted movement from said movable elements when a target position is reached.
Usually, the control in position as well as the holding at a target position of a movable element is carried out by a motor. However, motors are not always the optimal actuator to lock movable elements into a precise, stable, repeatable position. Motors may then present difficulties to maintain the target position.
To keep the target position of the movable element under a varying external effort or under its own weight, the control in position of motors needs short and high accelerations, resulting in a sudden increase of power consumption as well as the need for complex algorithms
Further, gear motors provide static or dynamic backlashes, meaning there is an unavoidable and often unpredictable error in the actual position of the moveable element, more precisely on the target position of the moveable element, which leads to reliability issues regarding the reach and the hold of the target position.
Aging is also an issue with gear motors since they comprise a lot of fragile moving parts that are subject to mechanical wear, the combination of wears leading to a decreased precision.
Another drawback of gear motors dimensioned to maintain a strong effort is their important dimensions and weight.
It is thus known from the state of art to use brakes in order to offload the gear motor. In the state of the art, brakes are thus generally used to lock a movable element at a certain position, without controlling the position of movable elements with precision and accuracy, especially during transition phases and once the target position has been reached. For example, in document U.S. Pat. No. 8,870 141 B2, brakes are used to lock the robotic arm into position when a user decides to lock it, without having a determined target position to reach.
The present invention aims at solving the here-above mentioned issues by using brakes instead of motors to lock robotic movable elements into a determined target position, as well as to control the brakes during transition phases.
This invention thus relates to a brake piloting system, said system comprising:
According to one embodiment, the microcontroller is configured so that whenever the movable element overcomes the predetermined activation position, the determined configuration of the at least one brake is an activated configuration. Advantageously this embodiment allows to guarantee a smooth convergence of the movable element through the target position as the brake is activated when the movable element is located between the predetermined activation position and the target position (i.e., the brake applies a force on the movable element so as to control and/or reduce the speed of the movable element). In this way, independently of the force and attention put by the surgeon in the manipulation of the robotic arm, hence the movable element, it will be ensured that the surgical tool (e.g., saw) approaches the target position with a limited and controlled speed.
According to one embodiment, the microcontroller is configured so that whenever the movable element is in the target position, the determined configuration of the at least one brake is a specific activated configuration wherein the movable element is immobilized. This embodiment allows an easy manipulation of the robotic arm as the surgeon only as to apply a force to the robotic arm through the direction of the target position to bring the robotic arm at stop in the configuration planned for at least one of the steps of the surgery (e.g., the robotic arm will be locked in the target position wherein the saw is positioned with respect to the bone so as to be used to perform one of the planned surgical actions).
According to one preferred embodiment, the microcontroller is configured so that:
This embodiment is particularly advantageous (with respect to the two features taken separately) as not only it allows to guide the robotic arm till the target position, where the movable element will be safely locked, but thanks to the activation of the brake when the movable element is located between the predetermined activation position and the target position, the present system also ensures a smooth and controlled approach of the movable element (i.e., and surgical tool) to the target locking position without demanding any kind of control or attention to the surgeon which is manipulating the robotic arm. As the control of the speed limitation and deceleration/lock of the robotic arm it is not left to the experience and current state of attention of the surgeon, but it is ensure by the system of the present invention, a high degree of safety during the surgery is obtained no matter what.
The brake control system according to the invention may comprises one or several of the following features, taken in isolation or combined with each other:
According to one embodiment, wherein the control unit comprising at least one mother microcontroller, wherein the instructions are stored, and at least one brake microcontroller connected to the at least one position sensor and to the at least one brake, said at least one brake microcontroller being configured to:
According to one embodiment, the brake microcontroller is further configured to monitor the real time speed of the movable element and further use the real time speed of the movable element to determine the configuration of the at least one brake so as to limit the speed of the movable element to a predetermined maximal speed value. According to one embodiment, whenever the movable element overcome the predetermined activation position, the predetermined maximal speed value is function of the distance between the real time position of the movable element and the target position of the movable element.
According to one embodiment, the brake microcontroller is further configured to receive from a current sensor a measure in real time of a current applied to the at least one brake and further use said real time current to determine the configuration of the at least one brake.
According to one embodiment, the at least one brake is an electromagnetic brake.
According to one embodiment, the at least one brake is a power-off type of brake.
According to one embodiment, the position sensor is an encoder.
According to one embodiment, the robotic device is a medical device.
According to one embodiment, the at least one brake, the at least one position sensor forms an independent functional module.
Another object of the present invention is a brake piloting method, said method being implemented by a system according to any one of the embodiments described above, the method comprising, within the at least one microcontroller of the control unit:
wherein the microcontroller activates in real time the at least one brake into said determined configuration.
According to one embodiment, the control unit comprises at least one mother microcontroller and at least one brake microcontroller according to any one of the embodiments described above, further comprising:
wherein monitoring the movement of the movable element and determining a corresponding configuration of the at least one brake, are performed by the at least one brake microcontroller;
and wherein the at least one brake microcontroller activates the at least one brake into the activated configuration.
According to one embodiment, the activation of the at least one brake comprises two phases:
According to one embodiment, the method comprised a third phase whenever the movable element precedes the predetermined activation position, wherein the third phase is a constant speed limitation phase during which the at least one brake microcontroller limits the speed of the movable element to a constant maximum speed value, said speed limitation phase chronologically precedes the transition phase.
According to one embodiment, the at least one brake card monitors the heat emitted by the at least one brake
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In the embodiment illustrated on
In the current invention, the term “robotic” is understood in its broadest way, including for example cobotic devices, which are robots intended for direct human-robot interaction within a shared space.
Each brake 16 can be activated from an open configuration to an activated configuration. In the present specification the term “configuration” with regards to brakes designates a “state” of the brake:
It is to be noted that each brake 16 only displays one open configuration, but can display a wide range of activated configurations. Each activated configuration displays a determined braking power that is applied to the corresponding movable element 14. A particular active configuration wherein the brake immobilizes the movable element 14 in a specific position is referred to as the locking configuration.
In one embodiment, the brakes 16 can be electromagnetic brakes, more precisely electromagnetic power-off brakes, meaning that the brakes are into their locking configuration when no electrical current flows through them. Advantageously, a permanent magnet inside each brake 16 ensures that it remains in its locking configuration when no current flows through it.
The position sensors 18 connected to each brake 16 and movable element 14 may, for example, be encoders, magnetic or optical, incremental or absolute.
The position of the movable elements 14 can be a relative position, for example a relative angular position of one movable element 14 with regards to another, or a relative linear position of one movable element 14 with regards to another, or an absolute position of the movable element 14 within the internal referential R.
The system 10 further comprises at least one control unit 20 comprising at least one microcontroller (22, 24) configured to store instructions comprising at least one given target position of the movable element 14. A microcontroller contains one or more CPUs (processor cores) along with memory and programmable input/output peripherals.
Therefore, the above-mentioned instructions are stored in the memory of the microcontroller.
Said predetermined target position of the movable element 14 is associated to a specific activated configuration of its corresponding brake 16. This specific activated configuration is preferably the locking configuration, wherein the movable element 14 is immobilized at the predetermined target position stored in the microcontroller (22,24). The predetermined target position(s) for each movable element is determined during a preparative stage. In this preparative stage, a planning of the actions is performed by the robotic device and translated into the corresponding target positions in which the robotic device has to be placed in order to accomplish the desired actions.
In the case of application of the system in the medical domain, more precisely for surgery, the predetermined target position is determined during a pre-operative stage. Indeed, for each surgery a preoperative planning is determined, said preoperative planning comprising a list of actions to be performed during the different surgical phases. For example, the actions may comprise the cutting of a portion of a bone and said preoperative planning will comprise the equations of the cutting planes in one referential that may be registered to the internal referential R. Then, one cutting plane may be used to determine the corresponding position of the saw used to cut the bone in the internal referential R, and from this determine the target position of each movable element 14 of the system 10 to reach said cutting plane.
In one embodiment, a predetermined activation position may be either stored into the microcontroller memory or calculated within the microcontroller as a function of the target position, for example.
Said at least one microcontroller (22, 24) is connected to the at least one position sensor 18 and to the at least one brake 16.
In particular the at least one microcontroller (22, 24) receives the real time position of the movable element 14 from the position sensor 18. Then, the microcontroller uses said real time position of the movable element 14, the predetermined activation position and the at least one given target position within the internal referential R to determine in real time a configuration for the at least one brake 16. This step of determining the configuration may be performed for each position of the movable element 14 transmitted by the position sensor (for example, sampling frequency of the sensor). For each iteration, the microcontroller compares the position of the movable element 14 to a predetermined activation position within the internal referential R. Notably, whenever the movable element 14 is in the target position, it sets the determined configuration into an activated configuration. This means that for each position of each movable element 14 within the referential R, the microcontroller determines a determined brake configuration of the corresponding brake 16.
Finally, the microcontroller activates in real time the at least one brake 16 into said determined configuration, which may be an open configuration or activated configuration, notably a locking configuration when the movable element 14 had reached the target position.
In one example, the predetermined activation position and the target position stored are one unique value, corresponding to the target position. In this case the brakes will be always associated to an open configuration (except for the target position) and will be only activated into the locking configuration once the movable element 14 will reach the target position.
According to one embodiment, the control unit 20 comprises a unique microcontroller, for example connected by wires to the brakes 16 and the position sensors 18 (not represented).
In one alternative embodiment, illustrated in
The brake microcontroller 24 is configured to receive the instructions from the mother microcontroller 22 and real time information from the position sensor 18. Each brake microcontroller 24 can also send, in real time, feedbacks and information to the mother microcontroller 22.
Each brake microcontroller 24 is further configured to determine in real time, for each received real time position of the movable element 14, a corresponding configuration of the at least one brake 16 using said real time position of the movable element 14, the predetermined activation position and the target position; wherein, whenever the movable element 14 is in the target position, the determined configuration is an activated configuration.
In this embodiment, it is each brake microcontroller 24 that is thus configured to activate each corresponding brake 16 into the determined configuration.
Each brake microcontroller 24 is configured to pilot its corresponding brake(s) 16 whereas mother microcontroller 22 is configured for the global control of the system 10.
In one embodiment, the mother microcontroller 22 is further configured to implement a state machine, which is a mathematical computation model which provides an output based on the actual state of the system and other inputs. The outputs of this state machine may be sent to each brake microcontroller 24 according to the workflow of a preoperative planning and the state of progress of the surgery. These outputs of the state machine may be stored in the mother microcontroller 22 as instruction and comprise the predetermined target position of the movable element 14 of the robotic device 12. The brake microcontroller 24 sends feedback to the mother microcontroller 22 regarding the position of the movable element 14 and the corresponding configuration of its associated brake 16, notably when one target position is reached.
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According to one embodiment, the brake microcontroller 24 is also configured to perform the monitoring and limitation of the speed in real time whenever the movable element 14 is farther than a second predefined activation position. This embodiment advantageously allows to limit the speed of the movement allowed to the movable element when the surgeon put the robotic arm far from the normal perimeter of use (i.e., slow the movement of the robotic arm when the surgical tool is too far from the one or more target positions according to the surgical plan). The brake microcontroller 24 may also configured to lock the brake when the movable element exceeds a limit predefined position, beyond which the movable element cannot be moved (i.e., physical limits of the system).
According to one embodiment, the brake microcontroller 24 is further configured to receive from a current sensor 26 a measure in real time of a current applied to its corresponding brake 16 and further use this measured real time current of the movable element 14 to determine the configuration of the at least one brake 16. This advantageously allows a finer control of the brake.
For most of the positions of each movable element 14, the corresponding configuration of the brake 16 is the open configuration. However, for at least one first real time determined activation position of the movable element 14, the corresponding configuration of the associated brake is an activated configuration. Thus, when the movable element 14 is set into motion and reaches said first real time determined activation position, the associated brake 16 is activated by its corresponding brake microcontroller 24. This brake activation leads the brake 16 to change from its former configuration, the open configuration, to a first determined activated configuration. When the movable element 14 further reaches a second determined activation position, the associated brake 16 is activated by its corresponding brake microcontroller 24 and changes from its former configuration, the first real time determined activated configuration, to a second determined activated configuration. There can be an infinite number of activation positions, depending on the movement imposed to the movable element 14. The activation level of the brake 16 depends on the real time position of the movable element 14. In some embodiments, the activation level of the brake 16 also depends on the real time speed of the movable element 14. Depending on the embodiments, the first determined activation position of the movable element is either speed induced, position induced, or both.
In other words, the piloting of the brake 16 configuration is mainly position driven: when a movable element 14 is set into motion and reaches the predetermined target position within the internal referential R, its corresponding brake 16 is activated by the corresponding brake microcontroller 24, the brake 16 configuration changes into its locking configuration and the movable element 14 is immobilized.
In some embodiments, the piloting of the brake 16 is also speed driven: when a movable element 14 is set into motion at a too high speed with respect to a maximum speed value (which may dependent or not from the predetermined target position), the brake card 24 may also induce a change in the corresponding brake 16 configuration and thus inducing either a deceleration of the movable element 14 or a limitation of the speed of the movable element 14 to a constant speed value. Thus, several types of activation positions can be defined:
Independently of any speed limitation, the real time determined activation positions are generally defined spatially, within the internal referential R, surrounding the predetermined target position. This leads each brake 16 to be activated progressively, stepwise or gradually, up to its locking configuration. In other words, this means that, as the movable element 14 is moved from one real time determined activation position to the next one, each brake 16 is activated progressively until the locking configuration is reached. The more a brake 16 is activated, the more intense the deceleration. This progressive activation of the brakes 16 defines a transition phase: this way, the closer the movable element 14 gets to its specific predefined target position, the more difficult it becomes to set said movable element 14 into motion. This transition phase may inform a user that the specific predefined target position of the movable element 14 is soon to be reached.
In some embodiments, each brake microcontroller 24 is able to monitor the heat emitted by its corresponding brake 16, in particular when the brake 16 is maintained in an activated configuration. This advantageously allows to avoid any degradation of the brake and any risk of burning the user.
A data bus 28 allows the communication between the motherboard 22 and each of the brake microcontroller 24.
To monitor the position of the movable elements 14 and to monitor and pilot the real time configuration of the brakes 16, each brake microcontroller 24 uses three pieces of information:
As illustrated in the embodiment of
More precisely, the brake microcontroller 24 continually applies a cascade control loop comprising a position control loop, a velocity limitation loop and a current control loop, wherein the current control loop is the inner loop. Advantageously a cascade control loop allows to respond quickly to position, speed and/or current disturbance and so considerably reduce the fluctuations that would have occurred with a single loop control system.
In one embodiment, each control loop 30, 32, 34 is managed by a proportional-integral-derivative corrector (PID) 38. A PID corrector is commonly known in automation and widely used in industrial control systems. A PID corrector continuously applies a correction based on the difference between the desired setpoint and the actual physical value.
The current control loop 30 enables the brake microcontroller 24 to finely control the configuration of its corresponding brake 16 by calculating the voltage to apply at its terminal.
The current control loop optimizes the velocity control by decreasing the response time of the brakes. The current control loop also allows feedback regarding the effort exerted by the brakes 16.
The present invention further relates to a brake piloting method being implemented by a system 10 according to any one of the embodiments hereabove.
The method uses the microcontroller (22,24) of the control unit 20 to perform the following steps:
The microcontroller (22,24) activates in real time the at least one brake 16 into said determined configuration.
According to the embodiment wherein the control unit 20 comprises at least one mother microcontroller 22 and at least one brake microcontroller 24, the method further comprises sending, by means of the mother microcontroller 22, at least one target position of the movable element 14 to the at least one brake microcontroller 24. In this embodiment, the steps of the method 1 and 2 cited above (i.e. monitoring the movement of the movable element and determining a corresponding configuration of the at least one brake) are performed by the at least one brake microcontroller 24. Finally, it is the at least one brake microcontroller 24 that activates the at least one brake 16 into the activated configuration
As previously mentioned, the activation of the brakes 16 comprises two phases following each other:
The transition phase starts when the movable element 14 overcomes the predetermined activation position and the locking phase starts when the movable element 14 reaches its predetermined target position. The start of the locking phase corresponds to the end of the transition phase.
As already mentioned, in some embodiments, the brake microcontroller 24 monitors the real time speed of the movable element 14 and in those embodiments, each brake 16 is activated proportionally to the speed of its corresponding movable element 14 when the movable element 14 is at the corresponding real time determined activation position. This allows the user of the device 10 to feel that the predetermined target position is soon to be reached and leads thus to a quicker and more precise positioning of the movable element 14.
In the embodiments in which the device 10 includes a maximal allowed speed limit, each brake microcontroller 24 limits the speed of the movable element 14, independently from the position of the movable element 14. In those embodiments, the brake activation comprises a third phase whenever the movable element 14 precedes the predetermined activation position, wherein the third phase is a constant speed limitation phase during which the at least one brake microcontroller 24 limits the speed of the movable element 14 to a constant maximum speed value, said speed limitation phase chronologically precedes the transition phase. This advantageously guarantee a smooth motion so that the user is never surprised by a brutal speed limitation, this feature enables to increase comfort of manipulation of the robotic device, which is particularly interesting in the case of a surgical robotic device during operation.
The present invention is thus about a control in position of one or several brakes connected to movable elements, said movable elements being positioned with precision and accuracy within an internal referential. As the movable elements are displaced by one or several external forces, such as human efforts, the brakes controlled in position aim at reaching a final target configuration and maintaining the movables elements in this position. It allows a fine control of the decelerations and a strong locking at the target position.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21305161.8 | Feb 2021 | EP | regional |
