Patent Description:
Conventional digital X-ray (DXR) Ceiling Suspension (CS) systems and tubestand subsystems use a mechanical method or an electrical brake to perform an auto-detent process. Most of the DXR systems use mechanical methods due to the existence of many different detent mechanical structures and their use on industrial products with a long history.

For a DXR system, there are two normal system structures. Wall stand and table systems are used to support a subject and an X-ray detector. CS and tubestand subsystems are used to support an X-ray source (tube). The distance between the source and detector impacts the quality of the X-ray image. There are some values of distances which are used often (e.g. <NUM>, <NUM> and <NUM>).

When using the mechanical method, mechanical parts (e.g. limit pins and limit holes) are activated to stop the systems at a target position. A few systems use an electrical brake method. When using the electrical brake method, an electric brake is activated when the CS/tubestand reaches a target position and the CS/tubestand stops after it slides an accepted distance. However, both the mechanical method and electrical brake method have disadvantages.

Mechanical methods may be relatively accurate and precise. However, the mechanical method requires the installation of additional parts (e.g. limit pins and limit holes). This make the CS/tubestand subsystem mechanical structure more complex. Additionally, the additional parts may increase the cost and installation time of the systems. The kinetic energy of the system may also be mostly cancelled out by vibration in the system, which may make a user uncomfortable.

Electrical brake methods do not require the additional mechanical parts, but they also have disadvantages. The detent position precision has a relatively large error when the mass of the subsystem is relatively large or when the velocity (before enabling the brake) is relatively large. Particular brake forces may need a larger braking distance to cancel out the kinetic energy. However, most CS/tubestand subsystems (especially in high performance systems) are heavy. Secondly, the brake needs to activated ahead of time as the CS system approaches the target position, and it is difficult to determine the suitable braking time. The braking force may also change with friction surface conditions or a change in the braking gap.

In addition, sometimes the braking forces are applied manually by operators, therefore, the value of the forces is hard to predict and varies by operators.

<CIT> introduced a detent control system for reducing position errors in the positioning of an X-Ray tube including how to calculate overshoot correction. However, the article fails to consider some factors, like errors caused by operators, also it does not give the effectiveness evaluation of the correction, or the re-calibration/adjustment condition for the correction during a braking operation process. Thus, there is a need for an improved detent process.

According to examples in accordance with an aspect of the invention, there is provided a detent method for a medical imaging system, the method comprising:.

The distance S moved by a moveable component of the medical imaging system when a brake is applied to the component may be defined as the difference between the braking position PB and the target position PT, such that S = |PT - PB|.

Using a braking function to determine a braking position enables the detent method to stop the component at (or at least near) the target position. The braking position defines the position at which the brake needs to be applied to the component in order to make the component stop at the target position. The method may further comprise:.

In this way, the method is, in essence, an auto-calibration method for an automatic detent process. The detent process enables the component to be positioned at particular pre-determined target positions on, for example, a railing system. The calibration (i.e. adjusting the braking function) ensures the component stops within a particular "detent window" (e.g. within ± <NUM>) from the pre-determined target position. If the component stops outside the detent window, then the latest movement data (i.e. the distance moved by the component and the velocity before braking begins) is used to re-calibrate the detent process.

The detent process is based on a braking function which defines how far the component moves when a brake is applied to the component relative to the velocity at which it was travelling when the brake is applied. This function may change over time (e.g. wear of the braking system) or based on outside parameters (e.g. temperature).

Thus, the inventors propose checking the function is performing correctly (i.e. the measured position similar to the target position) after a movement of the component and, if it is not performing correctly, adjusting the braking function based on the latest movement data.

The method does not require additional complex mechanical parts on the component which may wear over time and need to be installed on the component (and/or on a system associated with the movement of component). Additionally, mechanical detent processes usually generate vibrations on the component due to the sudden change in kinetic energy of the component.

Additionally, the method does not have a higher error when the measured velocity (before braking) is relatively high nor when the mass of the component is high, as often occurs with electronic detent processes.

The component is a moveable component. The component may be a moveable medical component such a DXR ceiling suspension subsystem or a tubestand subsystem.

The braking function F(S,V) may be a quadratic function where S ∝ V<NUM>. The inventors realized that the braking function can be approximated to a quadratic function based on the conservation of energy. The kinetic energy of the component is equal to <MAT>, where m is the mass of the component and V is the velocity of the component. The energy absorbed by the brake is approximately fTS, where fT is the total force acting on the component (e.g. including the braking force, forces due to friction and an operating force on the component) and S is the distance travelled by the component during braking.

The operating force may be manually applied by an operator (i.e. an operator moving the component). The value of the operating force is significantly harder to predict than some of the other forces. This is due to the behavior of operators being difficult to predict. For example, if the behavior of an operator varies significantly to the behavior of the worker who initially calibrated the breaking function, the breaking function may no longer be able to assure accuracy. Thus, it may be advantageous to adjust the breaking function after one or more movements of the component. This ensures that the breaking function gets used to particular behaviors of an operator.

The braking function F(S,V) may be a quadratic function S = KV<NUM> between the distance moved by the component, S, and the velocity of the component, V, wherein K is a calibration constant and wherein adjusting the braking function S = KV<NUM> comprises adjusting the value of the calibration constant K.

The braking function may be defined as <MAT> if it is assumed that no other terms are relevant in the conservation of energy equation. The total force and the mass can be assumed to be constant and, thus, the braking function can be defined as a quadratic equation with one constant K = <MAT>. The constant K may be estimated based on estimated values of m and FT. Alternatively, the constant may be calculated based on measured values of S and V.

Using the equation S = KV<NUM> enables the braking function to be a linear relationship between S and V<NUM>. Thus, only two known pairs of values for S and V<NUM> are needed to determine a calibrated value for K. One of these pairs may be S = <NUM> and V<NUM>= <NUM>.

The braking function F(S,V) may be a quadratic function, S = aV<NUM> + bV + c, between the distance moved by the component, S, and the velocity of the component, V, wherein a, b and c are calibration constants and wherein adjusting the braking function S = aV<NUM> + bV + c comprises adjusting the values of one or more of the calibration constants a, b and c.

It may be beneficial to also consider other factors affecting the braking function. For example, there may be a time delay between the initiation of braking and the time at which the component begins braking. This would mean the braking function would be <MAT>, where Δt is the time delay between the initiation of braking and the component beginning to brake and can be approximated as being constant.

Additionally, the measured velocity may not be precise or the velocity sensor used to measure the velocity may have a bias. Thus, the braking function would be <MAT>, where AV is a bias or error in the velocity measurement and can be approximated as being constant.

Thus, the inventors realized that the braking function may be better approximated as the general quadratic function S = aV<NUM> + bV + c.

Determining a braking position PB may comprise determining a braking distance SB based on applying the measured velocity Vm to the braking function F(S,V) and determining the braking position PB based on the difference between the target position PT and the braking distance SB.

Obtaining the braking relationship F(S,V) may comprise obtaining at least two measured distances Sm travelled by the component when the brake is actuated, obtaining at least two measured velocities Vm corresponding to the velocity of the component when braking begins for the at least two measured distances Sm respectively and fitting a function F(S,V) for the at least two pairs [Sm , Vm].

The invention also provides a computer program product comprising computer program code which, when executed on a computing device having a processing system, cause the processing system to perform all of the steps of the detent method.

The invention also provides a system for performing a detent method for a medical imaging system, the system comprising a processor configured to:.

The processor may be further configured to obtain a measured position Pm of the component after the component stops moving and, if the measured position Pm does not fall within a detent window relative to the target position PT, adjust the braking function F(S,V) based on a distance S<NUM> between the braking position PB and the measured position Pm and the measured velocity Vm.

The braking function F(S,V) may be a quadratic function where S ∝ V<NUM>. For example, the braking function F(S,V) may be a quadratic function S = KV<NUM> between the distance moved by the component, S, and the velocity of the component, V, wherein K is a calibration constant and wherein the processor is configured to adjust the braking function S = KV<NUM> by adjusting the value of the calibration constant K.

The braking function F(S,V) may be a quadratic function, S = aV<NUM> + bV + c, between the distance moved by the component, S, and the velocity of the component, V, wherein a, b and c are calibration constants and wherein the processor is configured to adjust the braking function S = aV<NUM> + bV + cby adjusting the values of one or more of the calibration constants a, b and c.

The system may comprise one or more positioning rails, with the component placed on the positioning rails, a movement system configured to move the component along the positioning rails and a braking system configured to stop the component from moving.

The system may further comprise one or more of a position sensor configured to obtain the measured position Pm of the component and a velocity sensor configured to determine the measured velocity Vm of the component.

The invention provides a detent method for a medical imaging system. The method comprises obtaining a braking function F(S,V) between a distance S moved by a moveable component of the medical imaging system when a brake is applied to the component and a velocity V of the component and obtaining a measured velocity Vm of the component before the brake is applied. A braking position PB is determined based on a target position PT, the measured velocity Vm and the braking function F(S,V), wherein the brake is configured to be actuated when the component reaches the braking position PB.

<FIG> shows an illustration of a conventional DXR ceiling suspension (CS) system <NUM>. The CS system <NUM> is one example of a possible medical imaging system to which the invention may be applied. The CS system <NUM> comprises a scanner <NUM> suspended from the ceiling and movable via rails <NUM>. The CS system <NUM> also comprises a wallstand <NUM> movable via rails <NUM> and a table <NUM>. The table may also be movable. The current invention may be used to move the scanner <NUM>, the wallstand <NUM> and/or the table <NUM>.

<FIG> shows an illustration of a conventional tubestand system <NUM>. The tubestand system <NUM> is another example of a possible medical imaging system to which the invention may be applied. The tubestand system <NUM> comprises a scanner <NUM> which may be moved vertically via rails <NUM>. The scanner <NUM> may also be configured to move horizontally via additional rails on the floor. The tubestand system <NUM> also comprises a wallstand <NUM> movable via rails <NUM> and a table <NUM>. The table may also be movable. The current invention may be used to move the scanner <NUM>, the wallstand <NUM> and/or the table <NUM>.

Other medical imaging systems (e.g. X-ray scanners, ultrasound scanners, CT scanners etc.) which comprise moving components may also be used.

<FIG> shows a flow chart for a detent method according to the claims. During factory debugging or during field installation debugging, a calibration may be performed to derive an initial relationship F(S,V) between a brake distance S and the measured velocity Vm before enabling a brake.

An algorithm (according to the flow chart) will, in real-time, determine in step <NUM> the measured velocity Vm of a moveable component based on, for example, the data of position sensor (e.g. a potential meter or absolute encoder) or a velocity sensor. A target position PT is also obtained in step <NUM> defining where the user wants the component to stop (i.e. a detent position). The velocity Vm is input in step <NUM> into the initial relationship F(S,V) to calculate the needed brake distance S<NUM> and thus the braking position PB can be determined in step <NUM> based on the difference between the brake distance S and the target position PT.

Once the component is detected to be at the braking position PB, the brake is enabled <NUM> to make the component stop. The component will naturally decelerate to zero due to the brake and should stop at the target position PT.

The position Pm at which the component actually stops may also be measured in step <NUM>. If the measured position Pm is outside a pre-defined detent window (e.g. ± <NUM>cm) <NUM>, the braking function F(S,V) may need to be adjusted in step <NUM> based on the measured velocity Vm and the braking distance S between the braking position PB and the measured position Pm.

Adjusting the braking function F(S,V) in step <NUM> may preferably be based on one or more rules to trigger re-calibration (e.g. two continuous failures to stop within the detent window). In some cases, a particular movement of the component may be accidental or particularly different to common behaviors for manually moving the component (e.g. an operator losing control of the movement). Thus, triggering the re-calibration step (i.e. box <NUM>) may comprise a more complex set of rules to avoid adjusting the breaking function F(S,V) based on accidental data. One particular rule may be to only adjust the breaking function F(S,V) after two consecutive movements which fall outside the pre-defined detent window.

Adjusting <NUM> the braking function F(S,V) is, in essence, a re-calibration of the braking function F(S,V). If the algorithm performs the afore-mentioned checks for each movement of the component, the algorithm is, in essence, an automatic re-calibrating algorithm which maintains detent precision.

It will now be explained how the form of a braking function may be obtained. Firstly, the following set of variables will be defined (with example values for a tubestand system <NUM> as shown in <FIG>):.

An initial equation can be obtained based on the conservation of energy by equating the kinetic energy of the component to the energy of the forces applied to the component: <MAT>.

The initial equation can be modified by considering the time delay Δt between the brake being enabled and the braking action beginning: <MAT>.

The initial equation can also be modified by considering that the braking force fB needs time to stabilize and reach a maximum value. Thus, the braking force fB can be modified to an average braking force fB: <MAT>.

The user may also change the operating force frequently. The operating force is a manually exerted force by a user and is typically unpredictable. In general, the operating force may vary based on the particular user, the physical condition of the user (e.g. injuries etc.) or even on the time of day (e.g. user may be tired at the end of the day and apply less force).

Thus, the operating force fo can be modified in the initial equation to an average operating force fO : <MAT>.

Similarly, the friction force may also be different at different positions. Thus, the braking force ff can be modified to an average braking force ff: <MAT>.

Additionally, the measured velocity may not be fully accurate and thus a velocity error (or velocity bias) ΔVm may be considered such that the initial equation is modified to: <MAT>.

Thus, by considering all of the above possible modifications to the initial equation, a modified equation may be constructed such that: <MAT>.

Where fT is the total sum of all the (average) forces applied to the component. Clearly this is a quadratic equation. The braking distance S can be defined as the distance between the target position PT and the braking position PB. Thus, a general equation may be constructed: <MAT>.

Where a, b and c are constants based on the modified equation above.

<FIG> shows a component <NUM> moving at a velocity Vm on a rail <NUM>. The target position PT and the corresponding braking position PB are shown. A detent window <NUM> is also shown. A user will push a button to disable the brake and manually move the component <NUM> to a pre-defined position (i.e. the target position PT). An algorithm will then actuate the brake at the braking position PB and record the measured position Pm at which the component <NUM> stops. If the component <NUM> stops within the detent window <NUM>, then there may be no need to re-calibrate the braking function (e.g. adjusting the constant a, b and c in the general equation above). However, if the component <NUM> does not stop within the detent window <NUM>, the constants of equation may need to be adjusted/re-calibrated to improve the accuracy/precision of the equation. The re-calibration may be based on a set of rules (e.g. two consecutive movements falling outside of detent window, time-period between two consecutive movements less than a pre-determined time e.g. one hour etc.).

The movement is likely begun by an operating force. The operating force may or may not continue to be applied when the break is engaged based on many different factors. One of the most significant factors is the particular behaviors/habits of different users (i.e. operators).

Some operators may continue to apply the operating force until the component <NUM> has completely stopped. This kind of behavior is typical of users who are confident in the accuracy of the detent. Other operators may stop applying the force as soon as the break is first applied, which will reduce the average operating force. The operating force is usually small relative to the mass of the component <NUM>. However, due to the variations in the operating force, the breaking function may have to be adjusted (i.e. re-calibrated) whenever a different operator is using the system.

The component <NUM> in <FIG> is shown as moving vertically. However, it will be appreciated that the component <NUM> could be moving horizontally (or even at an angle, if required). When moving vertically, a constant breaking force may be applied to the component <NUM> to counteract the force due to gravity.

<FIG> shows a quadratic curve <NUM> which may be used to find the braking function. In order to initially calibrate the braking function, the brake may be activated at a target position PT. The corresponding velocity Vm and the distance Sm from the target position PT at which the component stops could then be measured. This is then repeated at least three times for three different velocities. The three calibration measurement <NUM> can then be plotted and fitted to a quadratic curve <NUM> in order to obtain the constants a, b and c. In some cases, the constants b and/or c may be assumed to be negligible and thus only two (or even one) measurements may be necessary.

<FIG> shows an exemplary relationship between the braking distance S and the square of the measured velocity Vm. A linear function between S and the square of Vm may be used instead of the complex function according to equation (<NUM>) by assuming the constants b and c of equation <NUM> are negligible: <MAT>.

The real value of the constant K is shown in line <NUM>. The lines <NUM> and <NUM> show functions with alternate values of the constant K which are close to the real value of K. The thick line <NUM> shows the change in velocity of the component as the brake is applied for two different values of the constant K. When a function corresponding to line <NUM> is used as the braking function, the corresponding braking position is PB<NUM>. As soon as the component reaches the braking position PB<NUM> the brake is enabled and the velocity of the component begins to drop with time. The rate at which the velocity begins to fall corresponds is based on the real value of K and thus the thick line <NUM> is parallel to the line <NUM> which corresponds to the real value of K. As the braking function used (corresponding to line <NUM>) is not completely accurate, the position at which the component completely stops Pm1 will not be at the exact same position as the target position PT. However, the measured position Pm<NUM> does fall within the detent window <NUM> and thus there is no need to re-calibrate.

A similar situation occurs when a function corresponding to line <NUM> is used as the braking function. When the component reaches the braking position PB<NUM>, the velocity begins to drop at a rate dictated by line <NUM> and stops at a position Pm<NUM>, which is slightly after the target position PT. The measured position Pm<NUM> is within the detent window <NUM> and thus no re-calibration would be needed.

Thus it is clear that the accuracy of the braking function may depend on the size of the detent window <NUM> which is chosen.

The skilled person would be readily capable of developing a processor for carrying out any herein described method. Thus, each step of a flow chart may represent a different action performed by a processor, and may be performed by a respective module of the processor.

As discussed above, the system makes use of processor to perform the data processing. The processor can be implemented in numerous ways, with software and/or hardware, to perform the various functions required. The processor typically employs one or more microprocessors that may be programmed using software (e.g., microcode) to perform the required functions. The processor may be implemented as a combination of dedicated hardware to perform some functions and one or more programmed microprocessors and associated circuitry to perform other functions.

Claim 1:
A detent method for a medical imaging system, the method comprising:
(<NUM>) obtaining a braking function F(S,V) between a distance S moved by a moveable component (<NUM>, <NUM>, <NUM>) of the medical imaging system when a brake is applied to the component and a velocity V of the component;
(<NUM>) obtaining a measured velocity Vm of the component before the brake is applied; and
(<NUM>) determining a braking position PB based on a target position PT, the measured velocity Vm and the braking function F(S,V), wherein the brake is configured to be actuated when the component reaches the braking position PB
(<NUM>) obtaining a measured position Pm of the component after the component stops moving; and if a braking function re-calibration rule is triggered, adjusting the braking function F(S,V) based on:
a distance S<NUM> between the braking position PB and the measured position Pm; and
the measured velocity Vm
wherein, the braking function re-calibration rule includes that the measured position Pm does not fall within a detent window relative to the target position PT.