Method and system for evaluating a play
The invention relates to a method of evaluating the play between two threaded components, a first component comprising an internal thread, and a second component comprising an external thread that corresponds to the internal thread of the first component, the components are engaged with each other the method comprising the steps of: applying a torque from a motor to said components such that a first side of the internal thread is in contact with an opposing first side of the external thread wherein the two components are mutually rotated, which mutual rotation yields a mutual translation movement of the two threaded components; fixing the components with respect to each other, such that no mutual translation movement is allowed, whereas mutual rotation is still allowed; withholding the applied torque to one of said components, until a second side of the internal thread is in contact with an opposing second side of the external thread, monitoring the applied torque during the above steps by determining the power input to the motor and the rotational speed of the motor in order to identify a first point in time when the first side of the internal tread loses contact with the opposing first side of the external tread and a second point in time when the second side of the internal tread meets the opposing second side of external tread, calculating from the identification of the first and second points in time a play (a) between the internal tread and the external tread evaluating the play (a) by comparing the play (a) with a reference play. The invention further relates to an evaluation system for evaluating the play between the two threaded components.
1. A method of evaluating the play between two threaded components, a first component comprising an internal thread, and a second component comprising an external thread that corresponds to the internal thread of the first component, the components are engaged with each other, the method comprising the steps of:
applying a torque from a motor to said components such that a first side of the internal thread is in contact with an opposing first side of the external thread wherein the two components are mutually rotated, which mutual rotation yields a mutual translational movement of the two threaded components;
fixing the components with respect to each other, such that no mutual translational movement is allowed, whereas mutual rotation is still allowed;
withholding a torque to said components, until a second side of the internal thread reaches contact with an opposing second side of the external thread,
monitoring the applied torque during the above steps by determining the power input to the motor and the rotational speed of the motor in order to identify a first point in time t 1 when the first side of the internal thread loses contact with the opposing first side of the external thread and a second point in time t 2 when the second side of the internal thread meets the opposing second side of the external thread,
calculating from the identification of the first and second points in time a play (a) between the internal thread and the external thread
evaluating the play (a) by comparing the play (a) with a reference play.
2. Method according to claim 1 , further comprising the step of monitoring the mutual rotational movement of the two threaded components, wherein the play (a) is calculated from the comparison of the torque and the mutual rotational movement of the components over time.
3. Method according to claim 2 , comprising the step of determining said rotational movement by measuring an angle rotation between the components by means of an angle rotation sensor.
4. Method according to claim 3 , comprising determining a rotation angle f i being the obtained rotational difference between said first point in time and said second point of time, whereby said play (a) is determined by calculating a=f i /360·G, where G is the pitch of the threads of said components.
5. Method according to claim 1 , wherein the step of monitoring the torque comprises measuring said torque applied by a motor by a torque sensor.
6. Method according to claim 1 , wherein the step of monitoring the torque comprises measuring a motor current I and a motor voltage U of a motor applying said torque, and deriving an angular frequency ω and the torque from the measured signals.
7. Method according to claim 1 , wherein the step of monitoring the torque comprises measuring a motor current I, a motor voltage U and an angular frequency ω of a motor applying said torque.
8. An evaluation system for evaluating the play between two threaded components, a first component comprising an internal thread, and a second component comprising an external thread that corresponds to the internal thread of the first component, the components are engaged with each other, the system comprises a control unit configured to send control signals (r) to a motor applying a torque to the components, such that
the components are first fixated with respect to each other, such that no mutual translational movement is allowed, and a first side of the internal thread is in contact with an opposing first side of the external thread wherein the two components are mutually rotated, which mutual rotation yields a mutual translation movement of the two threaded components;
a torque is withheld to said components, until a second side of the internal thread reaches contact with an opposing second side of the external thread;
the evaluation system further comprises an evaluation unit configured to monitor said torque applied to at least one of said components, said monitoring comprises determining the power input to the motor and the rotational speed of the motor and a processing unit, wherein the evaluation unit further is configured to
from the monitored torque, identify a first point in time t 1 when the first side of the internal thread loses contact with the opposing first side of the external thread and a second point in time t 2 when the second side of the internal thread meets the opposing second side of the external thread;
calculate from the identification of the first and second points in time a play (a) between the internal thread and the external thread; and to
evaluate the play (a) by comparing the calculated play (a) with a reference play.
9. Evaluation system according to claim 8 , wherein the evaluation unit is configured to monitor the rotational movement of the two threaded components, to compare the torque and the rotational movement of the components over time, and to calculate the play (a) from the comparison.
10. Evaluation system according to claim 9 , comprising an angle rotation sensor configured to measure a rotational movement between the components.
11. Evaluation system according to claim 10 , wherein the evaluation unit is configured to determine a rotation angle f i being the obtained rotational difference between said first point in time and said second point of time, and to determine said play (a) by calculating a=f i /360·G, where G is the pitch of the threads of said components.
12. Evaluation system according to claim 8 , comprising a torque sensor configured to measure said torque applied by a motor.
13. Evaluation system according to claim 8 , comprising sensors configured to measure a motor current I and a motor voltage U of a motor applying said torque, whereby the evaluation unit is configured to derive an angular frequency ω and the torque from the measured signals.
14. Evaluation system according to claim 8 , comprising sensors configured to measure a motor current I, a motor voltage U and an angular frequency ω of a motor applying said torque, whereby the evaluation unit is adapted to calculate a torque from the sensed signals.
15. Evaluation system according to claim 8 , wherein said components are a screw and nut in a control rod assembly.
16. A non-transitory computer readable medium storing computer program code for performing the steps of the method according to claim 1 , when running on a processor associated with a control unit.