ROTARY SPEED DETECTION DEVICE WITH ERROR MONITORING

Technical Field

The present invention is generally directed to speed and movement direction sensing in motion control systems (elevators, escalators, motor drives, etc) and more particularly, the present invention is directed to an improved, fault-tolerant, high reliability speed and movement direction sensing device having a self-test, error-monitoring and diagnosis features by using electronic components.

Background Art

The present invention is an improvement over the priori art and compared with high reliability speed and movement direction sensing is a cost effective solution.

Speed and movement direction sensing in case of motion control systems (elevators, escalators, motor drives) is usually performed using an incremental encoder (optical, magnetic, inductive, etc.), which generates two shifted pulses (with 90 electrical degrees), shown in FIG. 1. Measuring the frequency of the pulses, is possible to find out the rotation speed as well as traveling speed of elevator car or escalator. The direction of the movement can be detected using different approaches. One approach is: at the event generated by the falling edge of signal A (for example) check the state of the signal B. If signal B is 1 logic then the movement direction is clockwise (CW, i.e. forward). Another approach is to assign to each encoder state a decimal state (3, 1, 0 and 2) shown in FIG. 1. If the state transitions are: 3 to 1 to 0 to 2 as shown in FIG. 1. the movement direction is clockwise (i.e. forward or up). If the state transitions are opposite (see FIG. 1) the movement direction is counterclockwise (CCW, i.e. backward or down), such as disclose by U.S. Patent, No. 6,127,948: Bidirectional synthesis of pseudorandom sequences for arbitrary encoding resolutions.

The invalid transitions between different encoder states are also shown in FIG. 1, and can be used for error detection. However, the main disadvantage of the encoder with two pulses is that if one of the sensors fails, movement direction detection is no longer possible (two shifted signals are required for movement direction detection and one signal for speed measurement). Another disadvantage is: since there is no invalid state on current state, error detection based on current state is not possible. There are only invalid state transitions, which can be used for error detection.

Reliability of the speed and movement direction sensing is a key issue in motion control systems in general, in the elevator and escalator industry in particular. Furthermore, the current regulations related to elevators in several countries allow the use of electronic overspeed governor, however the imposed safety and integrity level requires systems with self-test and monitoring such as disclosed by: World Patent, No. WO2007123522: Rotary encoder with built-in-self-test and European Patent, No. EPl 186432: Pinter having fault tolerant encoder wheel. Another approach is to use systems with two channels or more with comparison. The reliability of the speed and movement direction sensing using the encoder having two shifted pulses (shown in FIG. 1) can be enhanced considering a dual-channel system with com arison additional to i is which detects s stem failure. A dual-channel s stem havin_ pplications for elevators is disclosed by U.S. Patent, No. 6,170,614: Electronic overspeed governor for elevators. However, such a system will require the mounting on the same shaft of two identical encoders, which will increase significantly the costs of the system. Furthermore, precise alignment of the encoders must be ensured.

Therefore, the sensing device proposed in this invention is going to overcome these disadvantages.

Summary of Invention

In accordance with a preferred first embodiment of the present invention, a speed and movement direction sensing device comprises an encoder, which generates signals for a speed signal generations section, a direction detections section, and encoder self-test section and which are interface with and elevator or escalator control unit.

The encoder has three sensors placed equidistantly at 120 electrical degrees, a disc with optic, magnetic or inductive asymmetry, which is connected mechanically to the elevator motor shaft, governor shaft or governor sheave or escalator motor shaft.

However, the shift between the pulses can be different from 120 (electrical) degrees as long as the states and states transitions associated to such an encoder are identical to the states and state transitions associated to and encoder with three pulses shifted with 120 (electrical) degrees. The states and states transitions for the encoder which has three sensors placed equidistantly at 120 electrical degrees are shown in FIG. 3 and FIG. 4. The speed signal generation section receives the encoder signals and generates a pulse signal, which frequency is equal with the frequency of the input signal. The direction detection section generates a direction signal based on the encoder pulses and the encoder self-test section monitors the encoder states and detects encoder error based on the encoder signals.

The elevator or escalator control unit receives the speed, direction and encoder self-test signals, is interfaced to the external world via an input/output port and can activate the safety system in case of encoder/sensor failure.

The encoder of the present invention generates three shifted signals, which leads to six valid encoder states and two invalid encoder states. If the encoder self-test section, detects an invalid state, then reports encoder error to the elevator or escalator control unit. Based on elevator/escalator current state and received signals via the input/output port, the control unit decides if the elevator/escalator goes out of service, elevator moves safely to the next floor or the safety gear is activated.

The main advantage is that encoder self-test can be performed at zero speed too, before the elevator or escalator movement, since the self-test is based on the encoder current state and does not require the knowledge of the previous state.

Moreover, the encoder provides three shifted signals - since only two shifted signals are necessary for direction detection - a fault-tolerant speed and movement direction sensing is possible.

In accordance with a preferred second embodiment of the present invention, a fault-tolerant speed and movement direction sensing device comprises: - an encoder having three sensors placed equidistantly at 120 electrical degrees, a disc with optic, magnetic or inductive asymmetry, which is connected mechanically to the shaft of moving part (i.e. elevator or escalator motor shaft, governor shaft or governor sheave, motor drive shaft, etc.);

- an encoder self-test section (exactly as in the first embodiment of the present invention) which monitors the encoder states and detects encoder error based on the encoder signals;

- a speed signal generation section which receives the encoder signals and generates a pulse signal having a frequency proportional with the input signal; - a direction detection section which combines the encoder input signals and generates three direction signals;

- an error monitoring and diagnosis section, which detects the encoder signal failure and generates signals for direction signal selection (selection of the proper direction signal) and signals for selection of the proper frequency division factor, used in the frequency divider section;

- a direction signal selection section, which selects the proper direction signal, received from direction detection section, based on the information provided by the error monitoring and diagnosis section; - a frequency divider section, which outputs the speed signal after dividing the frequency of the signal from the speed signal generation section with a frequency division factor specified by the error monitoring and diagnosis section.

The shift between the pulses can be different from 120 (electrical) degrees as long as the states and states transitions associated to such an encoder are identical to the states and state transitions associated to and encoder with three pulses shifted with 120. (electrical) degrees.

If only one encoder signal failed the sensing device reports minor error and provides valid direction and speed signals (fault-tolerant for one encoder signal failure). If two or more signals failed, major error is reported in this case direction information is no longer valid and the speed information is valid only if two signals failed.

The main advantage of the fault-tolerant sensing device is that offers valid speed and direction information in case of minor error (one encoder signal failed) and allows the motion control system to continue or finish its task before the system goes out of service (i.e. the elevator system safely moves to the next floor, before going out of service due to encoder failure).

The above discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings. Brief Description of the Drawings

FIG. 1 is an illustrative diagram related to an encoder having two shifted pulses, showing encoder states and states transitions;

FIG. 2 is a block diagram of the speed and direction sensing device with self-test applied in elevators and escalators, illustrating the system components and interconnections;

FIG. 3 is a diagram illustrating the valid states and state transitions of an encoder having three sensors shifted with 120 (electrical) degrees;

FIG. 4 is a diagram illustrating the invalid state transitions of an encoder having three sensors shifted with 120 (electrical) degrees, in case of minor and major encoder error;

FIG. 5 is a logical function description of the encoder self-test section and is an illustrative example of its implementation using logical gates;

FIG. 6 is a block diagram of the fault-tolerant speed and direction sensing device with self-test, error monitoring and diagnosis, illustrating the system components and interconnections;

FIG. 7 is a diagram illustrating the speed signal generation section, the frequency divider section and the direction detection section, related to the fault-tolerant speed and movement direction sensing device; FIG. 8 is a diagram illustrating state transition trajectories, and a state machine description of the encoder error monitoring and diagnosis section used for direction signal selection; and

FIG. 9 is a diagram illustrating a state machine description of the encoder error monitoring and diagnosis section used for frequency division factor selection.

Description of embodiments

An illustrative example of the main states and state transitions of an encoder with two sensors (prior art), generating two pulses shifted with 90 has been described in the background of the invention and is shown in FIG. 1.

In FIG. 1 to each encoder state is assigned i.e. a decimal state (3, 1, 0 and 2). If the state transitions are: 3 to 1 to 0 to 2 as shown in FIG. 1, then the movement direction is clockwise (CW), i.e. forward or up. If the state transitions are opposite (see FIG. 1) the movement direction is counterclockwise (CCW), i.e. backward or down.

Invalid transitions between different states are also shown in FIG. 1 and can be used for error detection (prior art). However, the main disadvantage is that since there is no invalid state on current state, error detection based on current state is not possible (is possible only based on invalid state transitions). To facilitate error detection based on current encoder state, speed and direction sensing device with self-test is described in greater detail below.

Referring now to FIG. 2, a block diagram of the speed and direction sensing device with self-test, illustrating the system components and interconnections is shown. An encoder 10, having three sensors 11, 12 and 13 placed equidistantly at 120 electrical degrees and a disc 14, (with optic, magnetic or inductive asymmetry) is connected mechanically via connection link 15, to the elevator or escalator motor shaft, governor shaft or governor sheave 70. The encoder 10 generates three pulses 1, 2 and 3 shifted for example to 120 electrical degrees, which are received by the speed signal generation section 20, encoder self-test section 30 and direction detection section 40.

The speed signal generation section 20 generates the speed signal 21 (the output signal 21) based on the pulse signals 1, 2 and 3. Since one signal is enough for speed measurement, section 20 passes one of the input signals (1 or 2 or 3), in this case the frequency of the speed signal 21, will be equal with the frequency of the input signal. Another realization of section 20, to generate the speed signal 21, is to combine the input signals using or exclusive logic (XOR), i.e. if all three input signals 1, 2 and 3 are combined using XOR logic then the frequency of the speed signal 21, will three times the frequency of the input signal. If only two signals are combined using XOR logic the frequency of the speed signal 21 (the output signal 21), will two times the frequency of the input signal. The encoder self-test section 30 receives the input signals (1, 2 and 3) and monitors the encoder states and detects encoder error. The encoder error signal 31 (the output signal 31), is generated i.e. according to negative logic: is 0 logic if is an encoder error and 1 logic if is no encoder error.

Direction detection section 40 selects, based on the three shifted pulse signals, two of the pulse signals, and generates a movement direction signal of the rotary body based on the state transitions of the selected pulse signals.

Therefore, the direction detection section 40, combines two encoder input signals (i.e. signal 1 and signal 2) and generates the direction signal 41.

The elevator or escalator control unit 50 receives the speed signal 21, the encoder error signal 31 and the direction signal 41. Based on elevator/escalator current state and received signals via the input/output port 52, the control unit 50 decides if the elevator/escalator goes out of service, elevator moves safely to the next floor or activates via signal 51 the safety gear 60.

The input/output port 52 facilitates software up-dates, initialization, operational status, alarm conditions and monitoring features between the control unit 50 and external devices.

In order to describe the encoder self-test section, first the valid and invalid state and state transitions of the encoder 10, are described at great detail below and are shown in FIG. 3 and FIG.4.

Referring to FIG. 3, the diagram illustrates the valid states and state transitions of encoder 10. The six valid states of encoder 10, are coded as Sl, S2, S3, S4, S5 and S6. If the state transitions are: Sl to S2 or S2 to S3 and so on, the movement direction is clockwise (i.e. forward or up). If the state transitions are opposite (see FIG. 3) the movement direction is counterclockwise (i.e. backward or down).

Referring to FIG. 4, it illustrates the invalid states and the invalid state transitions of encoder 10. The two invalid states are coded SO (000) and S7 (111) and invalid state transitions are shown toward to invalid state SO (similar transitions can be described toward state S7).

Transitions from state S 1 to SO, from state S3 to SO, from state S5 to SO are associated with one signal failure. Transitions from state S2 to SO, from state S4 to SO, from state S6 to SO are associated with two simultaneous signals failures.

In the illustrative example, we assume that the encoder sensors have pnp output, normally open (the pnp transistor switches the output high). In case of sensor failure, transistor failure or power failure the output will be switched to low and will stay low. Similar transitions can be defined for sensors having pnp output normally closed, npn output, normally open or close.

Having defined the encoder valid and invalid states the encoder self- test section 30, is described in detail below.

Referring to FIG. 5, is a logical function description of the encoder self-test section 30. Invalid encoder states are reported as encoder error. The encoder error signal 31 (i.e. considering negative logic) is: 1 logic in case of valid encoder states (no encoder error) and 0 logic in case of invalid encoder states (encoder error). The logic function described above can be implemented using logical gates and circuits, an illustrative example is shown in FIG. 5. Moreover, the output signal can be stored in a D-latch if it is required.

Therefore, the first embodiment of present invention describes a speed and movement direction sensing device with self-test connected to an elevator or escalator control unit. Encoder 10 generates 3 signals shifted with 120 electrical degrees, since only two signals are necessary for movement direction sensing and only one signal is necessary for speed sensing, the realization of a fault-tolerant speed and movement direction sensing device is possible and is described in detail in the second embodiment of the present invention.

Referring to FIG. 6, is a block diagram of the second embodiment of the present invention, a fault-tolerant speed and direction sensing device with self-test, error monitoring and diagnosis, illustrating the system components and interconnections.

The components and the interconnections of the second embodiment of the present invention is described in details below.

The encoder 10, as in the first embodiment of the invention, generates pulse signals (1, 2 and 3) shifted to 120 electrical degrees, which are received by the speed signal generation section 22, encoder self-test section 30 (as in the first embodiment of the invention), direction detection section 42 and error monitoring and diagnosis section 80.

The speed signal generation section 22 generates the output signal 23

(signal F) by combing the input signals (1, 2 and 3) by XOR logic.

The encoder self-test section 30 generates exactly as in as in the first embodiment of the invention the output signal 31.

The direction detection section 42, combines encoder input signals in pairs (i.e. 1 and 2, 2 and 3, 3 and 1) and generates three direction signals denoted by Dl, D2, D3.

The error monitoring and diagnosis section 80 receives inputs from the encoder section 10, and based on current encoder state denoted by S(n) and previous encoder states denoted by S(n-l), S(n-2) and S(n-3), generates output signals (81, 82, 83 and 84) denoted by Pl, P2, P3 and Major Error. Signal 81 (Pl) and signal 82 (P2) selects via the direction signal section 43, the proper direction signal 41. Signal 83 (P3) monitors invalid state transitions in case of one signal failure and the signal 84 (denoted Major Error) monitors major encoder error (two or more encoder signals failures).

The direction signal selection section 43 generates the direction output signal 41 by selecting (multiplexing) one of the input signals (Dl, D2 or D3), function on signal 81 (Pl) and signal 82 (P2) generated by the error monitoring and diagnosis section 80 The frequency divider section 24 receives the input signal 23, from speed signal generation section 22 and divides the frequency of the input signal with a constant factor, depending on the encoder error state. The constant division factor is defined by the signals 83 (P3) and (84) Major Error. If there is no encoder error (no signal failure) then divides the frequency of the input signal with the factor of 3 (three). If minor encoder error occurred (one signal failed) then the frequency of the input signal is divided by a factor of 2 (two). If a major encoder error occurred (two or more signals failed) then the frequency of the input signal is left unchanged.

Signal 33 (Minor Error) according to the second embodiment of the current invention is generated by section 32 as a logical AND combination between signal 31 and signal 83 (P3), combing static error monitoring (section 30) and dynamic error monitoring (section 80). The static error monitoring is related to the encoder current state and the dynamic error monitoring is related to encoder state transition.

Speed signal generation section 22, direction detection section 42 and the frequency divider section 24 are described in more detail below.

Referring to FIG. 7, is a diagram illustrating the speed signal generation section 22, where the output signal 23 is generated as an XOR combination of the input signals 1, 2 and 3. The output signal 23 is received by the frequency divider section 24, which divides the frequency with a frequency division factor 1 (one) , 2 (two) or 3 (three) selected by signals 83 (P3) and signal 84 (Major Error) and then generates the output speed signal 21. The direction detection section 42, combines encoder input signals in pairs (i.e. 1 and 2, 2 and 3, 3 and 1) such in an encoder with two shifted pulses and using known direction detection logic denoted by Ll and generates three direction signals denoted by Dl ₅ D2, D3.

Encoder error monitoring and diagnosis is done in section 80, where the output signals 81 (Pl) and 82 (P2) for direction signal selection are generated according to the state machine described in details below.

Referring to FIG. 8, is a diagram illustrating a state machine description of the encoder error monitoring and diagnosis section 80, used for direction signal selection according to the second embodiment of the present invention. Based on current and previous encoder state transitions, as shown in FIG. 8, is possible to detect which encoder signal failed. The state of the encoder signal (no failure or failure) is coded into the output signals 81 (P 1) and 82 (P2) according to FIG 8, which are used to select the direction signal, and represents selection signals for the direction signal selection section 43. Valid transitions and invalid transitions associated with minor error (one encoder signal failed) are shown in the state transition table. Since at least two valid encoder signals are required for direction detection, in case of major error (two or more signals failed), direction detection is no longer possible.

The frequency division factor is specified by signals 83 (P3) and signal 84 (Major Error), which represents the output signals of section 80. In case of no error, the frequency division factor should be 3 (three), in case of minor error (one encoder signal failed) it should be 2 (two), and in case of major error (two or more encoder signals failed) it should be 1 (one). The error detection and diagnosis as well as generation of signal 83 (P3) and signal 84 (Major Error) is described in details below using a state machine description.

FIG. 9 is a diagram illustrating a state machine description of the encoder error monitoring and diagnosis section 80, used for frequency division factor selection according to the second embodiment of the present invention. Current and previous encoder state transitions (shown in the state transition table) are used to detect encoder signal failure. One encoder signal failure is monitored by the output signal 83 (P3), two encoder signal failure is monitored by signal 84 (Major Error). According to the speed signal generation section 22, if there is no encoder signal failure the frequency of the output signal 23 will be three times the frequency of the input signals (signals 1, 2 and 3 have same frequencies). If one encoder signal fails, the frequency of the output signal 23 will be two times the frequency of the input signals. If two encoder signals failed the frequency of the output signal 23 will be equal with the frequency of the input signal.

Therefore, the frequency division factor (shown in FIG. 9) selected by the signals 83 (P3) and 84 (Major Error) should be 3 in case of no error, should be 2 in case of minor error (one signal failed) and should be 1 in case of major error (two signals failed).

The output signals 21 (Speed), 41 (Direction), 33 (Minor Error) and

84 (Major Error) generated by the fault-tolerant speed and movement direction sensing device can be sent to a motion control unit. The first embodiment of the present invention discloses a speed and movement direction sensing device with self-test for elevators and escalators. The sensing device includes an incremental encoder, which generates three pulses shifted with 120 (electrical) degrees. However, the shift between the pulses can be different from 120 (electrical) degrees as long as the states and states transitions associated to such an encoder are identical to the states and state transitions associated to and encoder with three pulses shifted with 120 (electrical) degrees.

A speed signal generation section receives the encoder signals and generates a pulse signal, which frequency is proportional with the frequency of the input signal.

The encoder self -test section monitors the encoder states and detects encoder error based on the encoder signals and a direction detection section generates a direction signal based on the encoder pulses.

The speed signal, the encoder self-test signal and the direction signal are sent to the elevator or escalator control unit. The sensing device allows encoder self-test even in case of zero speed. The encoder error (fault) can be detected before the elevator or escalator movement, which represent an advantage compared with the prior art.

The second embodiment of the present invention discloses a fault- tolerant encoder with self-test, monitoring and diagnosis for speed and movement direction sensing. In case of minor encoder error (one encoder signal failed) the sensing device provides correct speed and movement direction information. In case of major encoder error (two or more encoder signals failed) the sensing device reports major error and can provide correct speed information if two encoder signals failed.

The fault-tolerant speed and movement direction sensing device offers a higher reliability than the prior art and can be applied in motion control systems where high safety and integrity level is required.

As described above, according to the first embodiment of the present invention, there is provided an encoder for outputting a pulse signal which repeats ON/OFF every 180 electrical degrees, as three kinds of pulse signals shifted with 120 electrical degrees. With this configuration, eight encoder states are generated based on the three shifted pulse signals. Further, the eight encoder states are categorized into six valid encoder states and two invalid encoder states (see FIGS. 3 and 4).

Accordingly, the encoder self-test section 30 (corresponding to the static error diagnosis section) monitors, based on the three shifted pulse signals, the occurrence of the two invalid encoder states (corresponding to the states of SO and S7 in FIG. 4), to thereby statically detect an encoder error state (see FIGS. 4 and 5).

The speed signal generation section 20 selects, based on the three shifted pulse signals, one of the pulse signals, and generates a pulse signal having a frequency proportional to the frequency of the selected pulse signal, as a speed signal (see FIG. 3).

The direction detection section 40 selects, based on the three shifted pulse signals, two of the pulse signals, and generates a movement direction signal of the rotary body based on the state transitions of the selected pulse signals (see FIG. 3).

Alternatively, as described above, according to the second embodiment of the present invention, based on the three shifted pulse signals, the current states of the three pulse signals and previous state transitions to reach the current states are subjected to monitoring, thereby identifying one of the three pulse signals as a pulse signal in which the state transition is not effected, in other word, in which it is recognized that there is a transition erroφee FIGS. 8 and 9).

Accordingly, the error monitoring and diagnosis section 80 (corresponding to the dynamic error diagnosis section) monitors, based on data obtained from records of the current state and three previous states of the signals, the state transitions of the three pulse signals, to thereby dynamically detect a second encoder error state (see FIGS. 6, 8, and 9). Also, it is possible to identify, among the three pulse signals, a pulse signal having an error occurring therein. Further, it is possible to output a major encoder error signal in which two or more pulse signals fail and a minor encoder error in which only one pulse signal fails, in a manner that the major encoder error signal and the minor encoder error signal can be distinguished from each other (see FIG. 9). The computing section 32 generates a minor encoder error as a logical AND combination between the error detection result obtained by the encoder self-test section 30 (corresponding to the static error diagnosis section) and the error detection result obtained by the error monitoring and diagnosis section 80 (corresponding to the dynamic error diagnosis section), and outputs the minor encoder error (see FIG. 6).

The speed signal generation section 22 and the frequency divider section 24 select, based on the detection result of the encoder error state which includes the major encoder error signal and the minor encoder error both output from the error monitoring and diagnosis section 80, one of the three pulse signals which is in normal operation, to thereby generate a pulse signal having a frequency proportional to the frequency of the selected pulse signal, as a speed signal (see FIGS. 6 and 9).

The speed signal generation section 22 obtains a combined signal as an exclusive OR combination of the three pulse signals (see FIG. 7). Then, the frequency divider section 24 generates, based on the detection result of an encoder error state obtained by the error monitoring and diagnosis section 80, a speed signal, by following the three procedures described below (see FIGS. 7 and 9).

(1) In a case when the encoder error state signal is not received, the speed signal is generated based on the combined signal by dividing the frequency of the combined signal by a factor of 3.

(2) In a case when the minor encoder error signal is received, the speed signal is generated based on the combined signal by dividing the frequency of the combined signal by a factor of 2.

(3) In a case when the major encoder error signal is received, the speed signal is generated based on the combined signal without dividing the frequency of the combined signal.

The direction detection section 42 generates, based on the three shifted pulse signals, three kinds of pairs of signals (see FIG. 7). Further, the direction signal selection section 43 selects, based on the detection result of the encoder error state which includes the minor encoder error signal output from the error monitoring and diagnosis section 80, one pair of the three kinds of pairs of signals, as the pair of signals which include two signals in normal operation, to thereby generate a movement direction signal (see FIGS. 6 and 8).

It should be noted that the three shifted pulse signals are not necessarily shifted with 120 electrical degrees. The signals may be shifted with any electrical degrees other than 120 electrical degrees, as long as the signals allow the static error detection, the dynamic error detection, the speed signal detection, and the movement direction detection to be performed according to the method described above.