Patent Description:
A surgical robot is generally used for guidance during orthopedic surgery, and the precision of a guide element has a significant influence on the path planning precision. Deformation and wear of the guide element caused in the transportation, storage, sterilization or using process will affect the path planning accuracy or precision. In addition, due to the fact that the deformation and wear of the guide element are unperceivable, the guide element cannot accurately move to a preset position of a wound of patients during the surgery, which in turn affects the control precision of the whole surgical robot.

In view of this, there is a need for a novel probe device, precision detection method, precision detection system, and positioning system.

<CIT> provides a method to operate an imaging system using a contact imaging probe to generate imaging of a body. A robotic actuator may be controlled to position the contact imaging probe at a first location on a surface of the body such that the contact imaging probe is in a first radial alignment with an imaging isocenter. The robotic actuator may then be controlled to position the contact imaging probe at a second location on the surface of the body such that the contact imaging probe is in a second radial alignment with the imaging isocenter. Moreover, the first and second radial alignments may be different.

<CIT> provides a method for verifying the positional accuracy of a tracking reference device. The tracking reference device is attached to a bone. The bone is then registered with respect to a coordinate frame of the tracking reference device. A verification mark on the bone is then created where the position of the verification mark is recorded, by way of a tracking system, with respect to the tracking reference device. The positional accuracy of the tracking reference device is verified by instructing an end-effector of a robotic-assisted surgical device to align with the verification mark on the bone, and wherein if the end-effector does not align with the verification mark, the positional accuracy of the tracking reference device is compromised. A surgical system for performing the computerized method is also provided.

The objective of the invention is to improve the precision of a guide element by providing a probe device, a precision detection method, a precision detection system, and a positioning system.

The probe device of the invention includes the positioning part and the guide detection part, three or more non-collinear positioning elements are arranged on the support of the positioning part, and the guide detection part has a first preset positional relation with the positioning elements, so that the spatial position of the guide detection part can be figured out according to the positioning elements; the guide detection part is matched with the guide element through the cylindrical outer contour, so that the actual position of the guide element can be figured out according to the positional relation between the guide element and the guide detection part, and the precision of the guide element can be determined by comparison of the actual position and the first set position of the guide element. The precision of the guide element can be accurately detected, so that the control precision of the surgical robot is effectively improved. The probe according to the invention also comprises a contact ball arranged at the end of the contact tip and away from the positioning part and has a radius greater than or equal to <NUM> and smaller than or equal to <NUM>.

Those skilled in the art can have a better understanding of other characteristics, objectives, and advantages of the invention by reading the following detailed description of non-restrictive embodiments with reference to the accompanying drawings, wherein identical or similar reference signs in the drawings represent identical or similar characteristics.

The characteristics and illustrative embodiments of the invention are detailed below. For a comprehensive understanding of the invention, many details are given in the following description. However, it is obvious for those skilled in the art to implement the invention without certain ones of these specific details. These illustrative embodiments in the following description are used for a better understanding of the invention. At least part of well-known structures and techniques are not shown in the accompanying drawings and the following description to avoid a fuzzy comprehension of the invention. In addition, for the sake of a clear illustration, the sizes of part of the structures are amplified. Moreover, the characteristics, structures, and properties in the following description can be appropriately integrated in one or more embodiments.

In the description of the invention, unless otherwise noted, "multiple" refers to two or more; and the directional or positional relations indicated by the terms "upper", "lower", "left", "right", "inner", and "outer" are used for facilitating and simplifying the description of the invention, and do not indicate or hint that devices or elements referred to must have specific directions or must be configured or operated in specific directions, and thus, these terms should not be interpreted as limitations on the invention. Moreover, the terms such as "first" and "second" are only for the purpose of description, and do not indicate or hint the relative importance of devices or elements referred to.

All directional terms involved in the following description refer to directions shown in the drawings and are not intended to limit the specific structures of the embodiments of the invention. What should to be pointed out is that unless otherwise explicitly specified or limited, the terms "install" and "connect" should be broadly appreciated. For instance, the term "connect" may refer to "fixed connection", "detachable connection", "integral connection", "direct connection", or "indirect connection". Those ordinarily skilled in the art can appreciate the specific meanings of these terms in the invention as the case may be.

For a better understanding of the invention, a detailed description of the probe device, the precision detection method, the precision detection system, and the positioning system of the embodiments of the invention is given below with reference to <FIG>.

Please refer to <FIG>, wherein <FIG> is a structural diagram of the probe device <NUM> in the first embodiment of the invention, and <FIG> is a cooperative structural diagram of the probe device <NUM> and a guide element <NUM>. The probe device <NUM> is used for a surgical robot positioning system which generally includes a guide element <NUM>, a position finder, a calibrator <NUM>, and the like. The probe device <NUM> includes a positioning part <NUM> and a guide detection part <NUM>, wherein the positioning part <NUM> is provided with a support having three or more non-collinear positioning elements <NUM> installed thereon, and the guide detection part <NUM> is connected with the support, has a first preset positional relation with the positioning elements <NUM>, and has a cylindrical outer contour matched with the guide element <NUM> of the positioning system.

Wherein, the number of the positioning elements <NUM> on the support is not limited and can be three, four, or more. For instance, as shown in <FIG>, four positioning elements <NUM> are configured, and at least three of the four positioning elements <NUM> are not collinear, so that the position finder can accurately figure out the spatial position of the guide detection part <NUM> according to the three or more positioning elements <NUM>.

The specific configuration of the positioning elements <NUM> is not limited. For instance, the positioning elements <NUM> are infrared reflection balls capable of reflecting infrared rays to be recognized by the position finder; or, the positioning elements <NUM> are infrared emitters capable of emitting infrared rays, and the position finder can recognize the infrared rays so as to recognize the positioning elements <NUM>. Other configurations are also feasible as long as the positioning elements <NUM> can be recognized by the position finder.

The probe device <NUM> of the invention includes the positioning part <NUM> and the guide detection part <NUM>, wherein three or more non-collinear positioning elements <NUM> are installed on the support of the positioning part <NUM>, and the guide detection part <NUM> has a first preset positional relation with the positioning elements <NUM>, so that the spatial position of the guide detection part <NUM> can be figured out according to the positioning elements <NUM>; the guide detection part <NUM> is matched with the guide element <NUM> through the cylindrical outer contour, so that the actual position of the guide element <NUM> can be figured out based on the positional relation between the guide element <NUM> and the guide detection part <NUM>; and the precision of the guide element <NUM> can be determined by comparison of the actual position and the set position of the guide element <NUM>. In this way, the probe device in this embodiment can accurately detect the precision of the guide element <NUM>, and thus, the control precision of the surgical robot is effectively improved.

In the using process of the probe device <NUM> and the surgical robot positioning system, the positioning system can control the guide element <NUM> to move to a preset position; when the guide detection part <NUM> is matched with the guide element <NUM>, the actual position of the guide element <NUM> can be figured out according to the spatial position of the guide detection part <NUM>; and the precision of the guide element <NUM> can be determined by comparison of the actual position and the set position of the guide element <NUM>. The probe device <NUM> of the invention can detect the precision of the guide element <NUM>, so that the situation that the control precision of the surgical robot is affected due to poor precision of the guide element <NUM> is prevented.

The guide detection part <NUM> can be matched with the guide element <NUM> in various ways. For instance, the guide detection part <NUM> is attached to the guide element <NUM>, and in this case, in order to make sure that the guide detection part <NUM> can be matched with the guide element <NUM> more tightly, the guide detection part <NUM> and the guide element <NUM> are matched in a sleeved manner. Particularly, one of the guide detection part <NUM> and the guide element <NUM> is a cylindrical body, and the other one is a sleeve matched with the cylindrical body.

The guide element <NUM> is usually a guide cylinder, and in this case, the guide detection part <NUM> is cylindrical and has an outer circumferential surface matched with the guide cylinder, so that the guide detection part <NUM> can be matched with the guide element <NUM> through the outer circumferential surface.

The surgical robot positioning system usually further includes a calibrator <NUM> used for auxiliary positioning of the surgical robot. The precision of the calibrator <NUM> is an important factor of the planning precision of a surgical path, and the deformation and wear of the calibrator <NUM> caused in the transportation, storage, sterilization, and using process will affect the path planning accuracy or precision. In view of this, a mark point <NUM> is set on the calibrator <NUM>, wherein the position of the mark point <NUM> is known or is measured, for instance, through a tracer in a positional relation with the mark point <NUM> particularly in such a manner: the positioning system can acquire the position of the tracer through the position finder so as to acquire the spatial position of the mark point <NUM>, and then the set position of the mark point <NUM> is obtained.

Also referring to <FIG>, in embodiments according to the invention, the probe device <NUM> further includes a contact tip <NUM>, wherein the contact tip <NUM> is connected with the positioning part <NUM>, has a second preset positional relation with the positioning elements <NUM>, and is able to make contact with the mark point <NUM> on the calibrator <NUM> of the positioning system to acquire position information of the mark point <NUM>.

In these embodiments according to the invention, the contact tip <NUM> has a second preset positional relation with the positioning elements <NUM>, so that the spatial position of the contact tip <NUM> can be figured out according to the spatial positions of the positioning elements <NUM>; and the contact tip <NUM> is able to make contact with the mark point <NUM>, so that the actual position of the mark point <NUM> can be figured out according to the spatial position of the contact tip <NUM>. The precision of the mark point <NUM>, namely the precision of the calibrator <NUM>, can be determined by comparison of the actual position and the set position of the mark point <NUM>. In these optional embodiments, the precision of the calibrator <NUM> can be detected through the contact tip <NUM>.

Also referring to <FIG>, the contact tip <NUM> can make contact with the mark point <NUM> in various ways. In embodiments according to the invention, a contact ball <NUM> is arranged at the top of the contact tip <NUM>, and the contact tip <NUM> makes contact with the mark point <NUM> through the contact ball <NUM>. In order to reduce the detection error, the radius of the contact ball <NUM> is greater than or equal to <NUM> and is smaller than or equal to <NUM>.

In any one of the above embodiments, the relative positions of the contact tip <NUM> and the guide detection part <NUM> are not limited. For instance, the contact tip <NUM> and the guide detection part <NUM> are respectively arranged on two sides of the positioning part <NUM>; or, as shown in <FIG>, the contact tip <NUM> and the guide detection part <NUM> are located on one side of the positioning part <NUM>, and the contact tip <NUM> is connected with the positioning part <NUM> through the guide detection part <NUM>.

In certain optional embodiments, the probe device <NUM> further includes a handle <NUM>, and the probe device <NUM> can be operated and held through the handle <NUM>. The configuration position of the handle <NUM> is not limited. In certain optional embodiments, the handle <NUM> is connected between two adjacent positioning elements <NUM>, so that the size of the probe device <NUM> can be effectively reduced, and the structure of probe device can be simplified.

Also referring to <FIG>, the second embodiment of the invention provides a precision detection method for a surgical robot positioning system. The positioning system includes a guide element <NUM> used for guiding the surgical needle, and a calibrator <NUM>. The precision detection method is based on the probe device <NUM> in the first embodiment and includes the following steps:.

S01: a first set position of the guide element <NUM> is acquired.

The positioning system usually includes a host computer used for controlling a mechanical arm to move along a planned path so as to drive the guide element <NUM> to move. The position of the guide element <NUM> is prestored in the host computer, or is measured, for instance, through a tracer in a preset positional relation with the guide element <NUM> particularly in such a manner: the position of the tracer is acquired by the position finder, and then the position of the guide element <NUM> is acquired.

S02, a position parameter of the guide detection part <NUM> in the case where the guide detection part <NUM> is matched with the guide element <NUM> is acquired.

The guide detection part <NUM> is made to be matched with the guide element <NUM>, and then the position parameter of the guide detection part <NUM> can be figured out according to the positioning elements <NUM> and the first preset positional relation.

S03, the precision of the guide element <NUM> is determined according to the first set position of the guide element <NUM> and the position parameter of the guide detection part <NUM>.

Wherein, the guide element <NUM> is matched with the guide detection part <NUM>, so that the actual position of the guide element <NUM> can be figured out according to the position parameter of the guide detection part <NUM>, and then the precision of the guide element <NUM> can be determined by comparison of the actual position and the first set position (theoretical position) of the guide element <NUM>. In this way, the precision of the guide element <NUM> is determined according to the position parameter of the guide detection part <NUM> and the first set position.

According to this embodiment, in S01, the first set position of the guide element <NUM> is acquired; in S02, the position parameter of the guide detection part <NUM> is figured out according to three or more positioning elements <NUM> and the first preset positional relation in the case where the guide detection part <NUM> is matched with the guide element <NUM>; and in S03, the precision of the guide element <NUM> is determined by comparison of the first set position of the guide element <NUM> and the position parameter of the guide detection part <NUM>. In this way, the precision of the positioning system is determined.

The first set position of the guide element <NUM> can be any position of the guide element <NUM> meeting the requirement for figuring out the spatial position of the guide element <NUM>. The guide element <NUM> is generally cylindrical. In certain optional embodiments, the first set position includes center positions of two opposite axial end faces of the guide element <NUM>, so that the first set position can be accurately searched out and located. Wherein, a connection line between the centers of the two end faces is defined as a mark axis.

The position parameter of the guide detection part <NUM> can be the spatial position of a specified axis of the guide detection part <NUM>. Due to the fact that the guide element <NUM> is in a cooperative positional relation with the guide detection part <NUM> when matched with the guide detection part <NUM>, the position of mark axis has a cooperative positional relation with that of the specified axis.

Generally, the guide detection part <NUM> and the guide element <NUM> are matched in a sleeved manner, in this case, the central axis of the guide detection part <NUM> theoretically coincides with the central axis of the guide element <NUM>, so, if the specified axis of the guide detection part <NUM> is set as the central axis of the guide detection part <NUM>, the position of the central axis is the actual position of the mark axis. In this way, the comparison process can be simplified, and the precision of the guide element <NUM> can be determined more easily according to the positional relation of the two axes.

The support and the guide detection part <NUM> can be in any positional relations as long as the first preset positional relation is presented between the positioning elements <NUM> and the guide detection part <NUM>, and the invention has not limitation in this aspect. Preferably, the specified axis of the guide detection part <NUM> (such as the central axis of the guide detection part <NUM>) and the support are coplanar, so that the relative positional relation between the support and the specified axis of the guide detection part <NUM> can be determined easily.

In the case where the guide detection part <NUM> is matched with the guide element <NUM>, the position parameter of the guide detection part <NUM> can be determined in various ways. In certain optional embodiments, S02 includes the following steps:.

Wherein, the four or more fitting data can be fitted in various ways to form the fitted axis data. For instance, the four or more fitting data are fitted through a least square method to form the fitted axis data.

In these optional embodiments, if the guide detection part <NUM> and the guide element <NUM> cannot be entirely attached due to wear or deformation of the guide element <NUM>, the guide detection part <NUM> will rotate within the guide element <NUM>, multiple different position parameters of the guide detection part <NUM> may be acquired, and in view of this, n axis data are acquired. With reference to the fitted axis data formed by fitting four or more of the n axis data, the detection error can be reduced, and the detection result can be more accurate.

The distance from the specified axis of the guide detection part <NUM> to the two ends of the guide element <NUM> should meet a detection deviation value. Thus, in order to further improve the precision of the detection result, S021 includes the following step:
In the case where the guide detection part <NUM> and the guide element <NUM> are sleeved and attached together, n axis data, meeting a first detection deviation value, corresponding to the specified axis of the guide detection part <NUM> at the multiple rotation positions, which are formed when the guide detection part <NUM> rotates on the guide element <NUM>, are acquired.

Wherein, meeting the detection deviation means the distances from the actual positions of the specified axis of the guide detection part <NUM> at the multiple rotation positions determined according to the positioning elements <NUM> to two endpoints of the first set position of the guide element are smaller than or equal to the first detection deviation value. The first detection deviation value is not limited and can be, for instance, <NUM>, <NUM>, and <NUM>.

The guide element <NUM> is generally cylindrical, has a preset length in the axial direction, and is used for providing a spatial path for a guide pin, and thus, the position of the axis of the guide element <NUM> directly reflects the precision of the guide element <NUM>. Due to the fact that the first set position is a theoretical measurement position of the guide element <NUM>, the first set position is usually set as the axis of the guide element <NUM>; and if the first set position includes the center positions of the two opposite end faces of the guide element <NUM>, the two endpoints of the first set position are the centers of the two opposite end faces of the guide element <NUM>.

Invalid data, having the distances to the centers of the two opposite end faces of the guide element <NUM> being too large, may exist in all the axis data corresponding to the specified axis at the multiple rotation positions due to detection errors. In this embodiment, the n axis data, having the distances to the two endpoints of the first set position being smaller than the first detection deviation value, are selected from all the axes, and invalid axes are removed, so that the detection precision of the guide element <NUM> is further improved.

In other optional embodiments, in order to further improve the accuracy of the detection result, S02 includes the following steps:.

The standard axis data corresponds to the maximum value of m, this means that there are the largest number of detection data having the distances to the standard axis data meeting the first preset distance threshold and having the angles with the standard axis data meeting the preset angle threshold value, and in this case, the standard axis data is closest to the actual position of the guide element <NUM>. With reference to the standard axis data, few errors will be caused, and the accuracy of the detection result is further improved.

For instance, as shown in <FIG>, when used for detecting the guide element <NUM>, the method specifically includes the following steps:.

Also referring to <FIG>, in certain optional embodiments, the probe device <NUM> further includes a contact tip <NUM> connected with the calibrator <NUM> and having a second preset positional relation with the positioning elements <NUM>, and in this case, the method further includes following steps:.

Due to the fact that the contact tip <NUM> directly makes contact with the mark point <NUM>, the spatial position of the contact tip <NUM> can be considered as the actual position of the mark point <NUM>. Thus, the precision of the calibrator <NUM> can be accurately determined by comparison of the second set position and actual position of the mark point in S03'.

In certain optional embodiments, in order to improve the accuracy of the detection result, S02' includes the following steps:.

Wherein, the distances from some of the multiple spatial positions acquired at the multiple contact positions to the center, namely the second set position, of the mark point <NUM> are greater than or equal to a second detection deviation value, and in order to further improve the accuracy of the detection result, the spatial positions not meeting the second detection deviation value should be removed after the spatial positions of the contact tip <NUM> at multiple contact positions are determined, and only p spatial position data meeting the second detection deviation value are reserved. Thus, in certain optional embodiments, S021' includes the following step:.

p spatial position data having distances to the second set position being smaller than the second detection deviation value are acquired from all the spatial position data of the contact tip <NUM> and the mark point <NUM> at the multiple positions.

The second detection deviation value can be set in various ways. For instance, the second preset distance value is <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or the like.

In order to further improve the accuracy of the detection result, S02' includes:.

When the number of detection points corresponding to the virtual ball is large, it indicates that the virtual ball is close to the actual position of the mark point <NUM>. The virtual ball corresponding to the maximum value qmax is used as the standard ball, and the spatial position of the contact tip <NUM> is set as the spatial position of the standard ball, so that the accuracy of the detection result is further improved.

Wherein, the virtual ball can be formed in various ways. For instance, the four or more fitting point data are fitted through a least square method to form the virtual ball.

For instance, as shown in <FIG>, when used for detecting the calibrator <NUM>, the method includes the following detection steps:.

The third embodiment of the invention provides a precision detection system for a surgical robot positioning system including a guide element <NUM> and the calibrator <NUM>. The precision detection system includes: any of the probe device <NUM> in the first embodiment;.

The precision detection system in this embodiment adopts any of the probe devices <NUM> in the first embodiment. The probe device <NUM> includes a positioning part <NUM> and a guide detection part <NUM>, wherein three or more non-collinear positioning elements <NUM> are installed on a support of the positioning part <NUM>, and the spatial position of the support can be figured out according to the three or more positioning elements <NUM>. The acquisition device can acquire the first preset position of the guide element <NUM>, namely the preset position of the guide element <NUM>; the position finder can acquire the position parameter of the guide detection part <NUM>; the guide detection part <NUM> can be matched with the guide element <NUM> through a cylindrical outer contour of the guide detection part <NUM>, so that the actual position of the guide element <NUM> can be figured out according to the positional relation of the guide detection part <NUM>; and the calculation device can determine the precision of the guide element <NUM> by comparison of the first set position of the guide element <NUM> and the position parameter of the guide detection part <NUM>, namely the preset position and the actual position of the guide element <NUM>. Thus, the precision of the guide element <NUM> can be accurately detected automatically, and the control precision of the surgical robot is effectively improved.

In certain optional embodiments, the probe device <NUM> further includes a contact tip <NUM>, and the contact tip <NUM> is connected with the positioning part <NUM> and has a second preset positional relation with the positioning elements <NUM>. The acquisition device is also used for acquiring a second set position of a mark point <NUM> on the calibrator <NUM>, the position finder is also used for acquiring the spatial position of the contact tip <NUM> in the case where the contact tip <NUM> makes contact with the mark point <NUM>, and the calculation device is also used for determining the precision of the calibrator <NUM> according to the second set position and the spatial position of the contact tip <NUM>. Thus, in these optional embodiments, the probe device <NUM> can also detect the precision of the calibrator <NUM>.

In certain optional embodiments, in order to fulfill full-automatic precision detection, the acquisition device includes a tracer, and the tracer is used for acquiring the set positions of the guide element <NUM> and the calibrator <NUM> in cooperation with the position finder.

In these optional embodiments, the tracer in a preset positional relation with the guide element <NUM> or the calibrator <NUM> is configured, and the position finder acquires the set positions of the guide element <NUM> and the calibrator <NUM> by acquiring the position of the tracer.

In the using process of the precision detection system, the tracer is in a preset positional relation with the guide element <NUM> and/or the calibrator <NUM>; when the guide element <NUM> and/or the calibrator <NUM> are/is worn or deformed, the preset positional relation between the tracer and the guide element <NUM> and/or the calibrator <NUM> will change, the position finder can acquire the set position of the guide element <NUM> and/or the calibrator <NUM> through the tracer and can also acquire the spatial position of the guide detection part <NUM> and/or the contact tip <NUM>, and the spatial position of the guide detection part <NUM> and/or the contact tip <NUM> are/is the actual position of the guide element <NUM> and/or the calibrator <NUM>; and the calculation device can accurately measure the precision of the guide element <NUM> and/or the calibrator <NUM> by comparing the set position and the actual position of the guide element <NUM> and/or the calibrator <NUM>.

The fourth embodiment of the invention provides a positioning system. The positioning system includes a surgical robot, a host computer, a position finder, a guide element <NUM>, a calibrator <NUM>, and a probe device <NUM> in any of the embodiments mentioned above.

During orthopedic surgery, the guide element <NUM> and the calibrator <NUM> are used for auxiliary guidance and positioning of the surgical robot, the host computer is used for controlling the surgical robot to drive the guide element <NUM> and the calibrator <NUM> to move, the position finder is used for acquiring the set positions of the guide element <NUM> and the calibrator <NUM> and is also used for recognizing three or more positioning elements <NUM> and determining the spatial position of a support according to the three or more positioning elements <NUM>, and then the spatial position of the guide detection part <NUM> is figured out.

The position finder can be configured in various ways. For instance, the position finder is an infrared receiver used for receiving an infrared signal emitted by the tracer in a preset positional relation with the positioning elements <NUM>; or, the position finder includes an infrared receiver and an infrared emitter, the tracer is an infrared reflector, the infrared emitter emits an infrared signal, the tracer reflects the infrared signal, and the infrared receiver receives the infrared signal reflected by the positioning elements <NUM>.

The calibrator <NUM> can be configured in various ways. In certain optional embodiments, a mark point <NUM> is set on the calibrator <NUM>, a body of the calibrator <NUM> is made from materials pervious to X-rays, and the mark point <NUM> is made from materials not pervious X-rays, so that the position of the mark point <NUM> on an image can be figured out during image registration.

In addition, a position calibrator (such as a tracer) is further arranged on the calibrator <NUM> and has a preset positional relation with the mark point <NUM>, so that the position finder can determine the target position of the mark point <NUM>, namely the spatial coordinates of the mark pint <NUM>, by acquiring the spatial position coordinates of the position calibrator.

Claim 1:
A probe device (<NUM>), configured to be used for detecting precision of a surgical robot positioning system, characterized in that the device comprises:
a positioning part (<NUM>), provided with a support supporting three or more non-collinear positioning elements (<NUM>);
a guide detection part (<NUM>), connected with the support, having a first preset positional relation with the positioning elements (<NUM>), and having a cylindrical outer contour matched with a guide element (<NUM>) of the positioning system; and
a contact tip (<NUM>), wherein the contact tip (<NUM>) is connected with the positioning part (<NUM>), has a second preset positional relation with the positioning elements (<NUM>), and is used for making contact with a mark point (<NUM>) on a calibrator (<NUM>) of the positioning system to acquire position information of the mark point (<NUM>);
wherein a contact ball (<NUM>) is arranged at an end, away from the positioning part (<NUM>), of the contact tip (<NUM>) and has a radius greater than or equal to <NUM> and smaller than or equal to <NUM>.