Encoder with Backup Circuit

Abstract

This encoder, which includes a connector to which an external power source and an external battery for backup are connected, comprises: a backup circuit that is driven when power is not being supplied from the external power source; an internal battery for backup; and a power source switching circuit that selectively switches, in response to the voltage of the internal battery for backup, a power supply source for driving the backup circuit when power is not being supplied from the external power source, between the internal battery for backup and the external battery for backup.

Description

Technical Field

[0001] The present invention relates to an encoder having a backup circuit.

Background Art

[0002] An encoder is used to detect the rotational position information of a rotating body such as a rotating shaft of a motor provided in a machine tool or a robot, or a movable part of a robot. In an encoder (for example, an absolute encoder), in addition to a main circuit that receives driving power from the main power supply while the main power supply of the machine where the encoder is provided is on and performs high-precision rotational position detection, there is also a backup circuit that can detect the rotational position with low power consumption even while the main power supply is off. While the main power supply is off, the backup circuit is operated by receiving driving power from a backup external battery separate from the main power supply, and by detecting the rotational position information when the rotating body rotates due to an external force even while the main power supply is off, it prevents the origin information of the machine from being lost. An encoder that operates the backup circuit by receiving driving power from such a backup external battery may be referred to as a "battery backup type encoder".

[0003] In addition, an encoder is connected to the main power supply and an external backup battery of the machine on which the encoder is provided via a connector. While the main power supply and the external backup power supply are removed from the encoder during maintenance of the machine, there is no means to supply power to the backup circuit in the encoder. During this period, if the rotational position information of the rotating body rotated by an external force cannot be detected, the origin information of the machine on which the encoder is provided will be lost. Therefore, in order to operate the backup circuit even while the main power supply and the external backup power supply are removed from the encoder, an electric double layer capacitor is provided in the encoder as an internal power supply for the backup circuit. The backup electric double layer capacitor is charged while the main power supply of the machine on which the encoder is provided is on, and enables the operation of the backup circuit by the power stored in the electric double layer capacitor for a short time even while the main power supply and the external backup power supply are removed from the encoder.

[0004] For example, in a power supply device that supplies a main power supply and a backup power supply to storage means for storing an output signal of an encoder that detects the rotational position of a joint of a walking robot, a main battery and a spare battery respectively mounted on the walking robot, a first diode that connects the main battery to the supply circuit of the main power supply and prevents the backflow of current to the main battery side, a second diode that connects a backup circuit to the supply circuit of the backup power supply and prevents the backflow of current to the backup circuit side, a backup converter that adjusts the output voltage of the second diode to be lower than the output voltage of the first diode, a third diode that connects the main battery to the backup circuit and prevents the backflow of current to the main battery side, a fourth diode that connects the spare battery to the backup circuit and prevents the backflow of current to the spare battery side, and a battery converter that adjusts the output voltage of the fourth diode to be lower than the output voltage of the third diode. A power supply device for a joint encoder of a walking robot comprising the above is known (see, for example, Patent Document 1).

[0005] For example, there is known an encoder device having an encoder main body that measures the displacement amount of a measurement object and a backup power supply that supplies backup power when the main power supply that supplies power to the encoder main body is shut off, and having, outside the encoder main body, an auxiliary power supply that supplies backup power in place of the main battery when the main battery of the backup power supply is replaced (see, for example, Patent Document 2).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] In a battery backup type encoder, power is supplied from a backup external battery to a backup circuit while the main power supply to which the encoder is provided is off. The machine provided with the encoder may have its main power supply turned off for a relatively long time, such as about two days every weekend, and the power supply time by the backup external battery is long. For this reason, the backup external battery is consumed (deteriorated) quickly. When the backup external battery is consumed, it is necessary to replace it with a new backup external battery. The price of the backup external battery is high, and the replacement work of the backup external battery is also time-consuming. Therefore, in a battery backup type encoder, development of a technology for reducing the replacement frequency of the backup external battery is desired.

Means for Solving the Problems

[0008] According to one aspect of the present disclosure, an external power supply and a backup external battery are connected PossibleAn encoder having a connector includes a backup circuit that is driven when there is no power supply from an external power source, a backup internal battery, and a power supply switching circuit that selectively switches a power supply source for driving the backup circuit between the backup internal battery and a backup external battery according to the voltage of the backup internal battery when there is no power supply from the external power source. When there is no power supply from the external power source, the power supply switching circuit supplies the power for driving the backup circuit from the internal backup battery when the voltage of the internal backup battery is higher than the first threshold value, and supplies the power for driving the backup circuit from the external backup battery when the voltage of the internal backup battery is lower than the first threshold value. When the power for driving the backup circuit is supplied from the internal backup battery, if the voltage of the internal backup battery becomes lower than the second threshold value, the power for driving the backup circuit is supplied from the external backup battery. When the power for driving the backup circuit is supplied from the external backup battery because the voltage of the internal backup battery has become lower than the second threshold value, if the voltage of the external backup battery becomes lower than the third threshold value, the power for driving the backup circuit is supplied from the internal backup battery is provided.

Advantages of the Invention

[0009] According to one aspect of the present disclosure, in a battery backup type encoder, the replacement frequency of the backup external battery can be reduced, and the maintainability and economy are improved.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

DETAILED DESCRIPTION OF THE INVENTION

[0011] An encoder having a backup circuit will be described below with reference to the drawings. In each drawing, similar members are denoted by similar reference numerals. Also, for ease of understanding, the scales of these drawings are appropriately changed. The illustrated embodiments are merely examples for implementation and are not limited to these embodiments.

[0012] An encoder according to an embodiment of the present disclosure is attached to a rotating body such as a rotating shaft of a motor provided in a machine tool or a robot, or a movable part of a robot, and generates rotational position information such as the rotational position (rotation angle) and rotational speed of the rotating body. The encoder according to an embodiment of the present disclosure may be optical or magnetic.

[0013] FIG. 1 is a block diagram showing an encoder according to an embodiment of the present disclosure.

[0014] An encoder 1 according to an embodiment of the present disclosure includes a backup circuit 11, an internal battery 12 for backup, a power supply switching circuit 13, a position detection circuit 14, a connector 15, a voltage generation circuit 16, a voltage comparator 17, a charging circuit 18, and a main circuit 19.

[0015] A cable 20 is connected to an external power supply 2 and an external battery 3 for backup. The cable 20 has a first current path 20-1 for supplying the power of the external power supply 2 to the main circuit 19, the charging circuit 18, and the power supply switching circuit 13 in the encoder 1, and a second current path 20-2 for supplying the power of the external battery 3 for backup to the voltage generation circuit 16 in the encoder 1. The first current path 20-1 and the second current path 20-2 are electrically independent, but they are provided in the same cable 20.

[0016] When the cable 20 is connected to the connector 15, the encoder 1, the external power supply 2, and the backup external battery 3 are electrically connected. When the cable 20 is removed from the connector 15, the electrical connection between the encoder 1 and both the external power supply 2 and the backup external battery 3 is broken.

[0017] The external power supply 2 is the main power supply of the machine where the encoder 1 is installed, and may be referred to as a control power supply depending on the applicable machine. Examples of the external power supply 2 include, for example, the main power supply of a servo amplifier for driving a motor where the encoder 1 is installed, or the main power supply of a numerical control device of a machine tool having a motor where the encoder 1 is installed. A second current path 20-2 for supplying the power of the backup external battery 3 to the voltage generation circuit 16 in the encoder 1 passes through the servo amplifier and the numerical control device. Note that the voltage output by the external power supply 2 is, for example, 5V, but may be a voltage of other magnitudes. While the cable 20 is connected to the connector 15 and the external power supply 2 is on, driving power for operating the main circuit 19 that causes the position detection circuit 14 to perform high-precision rotation position detection is supplied from the external power supply 2 via the connector 15.

[0018] The backup external battery 3 is a battery provided outside the encoder 1 and is composed of, for example, a primary battery. The voltage output by the backup external battery 3 is, for example, 6V. While the backup external battery 3 is connected to the connector 15 and the external power supply 2 is off, when particularly meeting a predetermined requirement, driving power for operating the backup circuit 11 that causes the position detection circuit 14 to perform simple rotation position detection is supplied from the backup external battery 3 via the connector 15. Details of the requirements for the backup external battery 3 to supply driving power to the backup circuit 11 will be described later.

[0019] The backup circuit 11 is driven when there is no power supply from the external power supply 2, that is, when the external power supply 2 is off or when the cable 20 is removed from the connector 15.

[0020] Figure 2 is a block diagram showing a backup circuit provided in an encoder according to an embodiment of the present disclosure.

[0021] In FIG. 2, as an example, the case where the encoder 1 is configured as a transmissive optical encoder is shown. In this case, the position detection circuit 14 includes an LED (light emitting diode) 31, a rotary slit 32 to which the rotation axis of the rotating body is attached, and a light receiving element 33 composed of a photodiode. The rotary slit 32 rotates in accordance with the rotation of the rotating body. The light generated from the LED 31 is transmitted or blocked by the rotary slit 32 in accordance with the rotation of the rotary slit 32. Among the light emitted from the LED 31, the light transmitted through the rotary slit 32 is received by the light receiving element 33. The light receiving element 33 converts the received light into an analog electrical signal having an amplitude corresponding to the intensity of the received light and outputs it. Although not shown here, when the encoder 1 is configured as a reflective optical encoder, the LED and the light receiving element are arranged on the same plane, and a code wheel is provided above the LED and the light receiving element. Also, although not shown here, when the encoder 1 is configured as a magnetic encoder, a sensor gear to which the rotation axis of the rotating body is attached and a sensor head provided with a magnet and a magnetic sensor that converts the magnetic field generated by the magnet into an electrical signal are provided.

[0022] While the external power supply 2 connected to the connector 15 is on, driving power for operating the main circuit 19 that causes the position detection circuit 14 to perform high-precision rotation position detection is supplied from the external power supply 2 via the connector 15. The main circuit 19 is provided with a control unit that constantly lights the LED 31, and an AD converter that performs analog-digital conversion on the analog electrical signal output from the light receiving element 33 and outputs a digital electrical signal.

[0023] While there is no power supply from the external power source 2, that is, while the external power source 2 connected to the connector 15 is off or while the cable 20 is not connected to the connector, in order to prevent the origin information of the machine provided with the encoder 1 from being lost when the rotating body is rotated by an external force, it is necessary to continue the position detection process by the position detection circuit 14. The backup circuit 11 is a circuit that causes the position detection circuit 14 to perform simple rotation position detection of the rotating body with less power than the power from the external power source 2 when there is no power supply from the external power source 2, and is for intermittently operating the position detection circuit 14 with a clock for backup operation.

[0024] The backup circuit 11 includes a backup clock 21 composed of a power supply IC, an LSI (Large Scale Integration) 22, and a comparator 23. The backup clock 21 can select several clock frequencies so as not to miscount even when the rotary slit 32 is rotating at high speed. The backup clock 21 receives the drive power from the power supply switching circuit 13 and intermittently drives the LSI 22 based on the clock frequency for the intermittent drive specified by the LSI 22. The LED 31 is always lit while the external power supply 2 is connected to the connector 15 and the external power supply 2 is on, but the LED 31 blinks intermittently under the control of the LSI 22 while the backup circuit 11 is operating (i.e., while there is no power supply from the external power supply 2). The light from the intermittently lit LED 31 is transmitted or blocked by the rotary slit 32 in accordance with the rotation of the rotary slit 32. Among the light emitted from the intermittently lit LED 31, the light transmitted through the rotary slit 32 is received by the light receiving element 33. The light receiving element 33 converts the received light into an analog electrical signal having an amplitude corresponding to the intensity of the received light and outputs it. The comparator converts the analog electrical signal output from the light receiving element 33 into a digital electrical signal. The intermittent lighting of the LED 31 and the generation of the digital signal by the comparator 23 consume less power than the constant lighting of the LED 31 and the analog-digital conversion by the AD converter. Thus, when there is no power supply from the external power supply 2, the backup circuit 11 operates with low power consumption, enabling the position detection circuit 14 to simply detect the rotational position of the rotating body.

[0025] The drive power of the backup circuit 11 is supplied by the internal backup battery 12 or the external backup battery 3.

[0026] The internal backup battery 12 is composed of a secondary battery that can be repeatedly used by charging. Examples of the internal backup battery 12 include, for example, all-solid-state batteries, lithium-ion batteries, and nickel-cadmium batteries. In particular, all-solid-state batteries can be mounted on the printed circuit board in the encoder 1, and since there is no electrolytic solution inside, they have high safety and reliability, so they are suitable as the internal backup battery 12. While the external power supply 2 is connected to the connector 15 and is on, the power supplied from the external power supply 2 through the connector 15 is input to the charging circuit 18, and the charging circuit 18 charges the internal backup battery 12. Also, the voltage of the internal backup battery 12 is input to the voltage comparator 17.

[0027] The voltage generation circuit 16 steps down the voltage supplied from the external backup battery 3 through the connector 15 to an arbitrary value and outputs it. The voltage generation circuit 16 outputs the voltage when the external backup battery 3 is connected to the connector 15, and does not output the voltage when the external backup battery 3 is not connected to the connector 15. When the voltage output by the external backup battery 3 is, for example, 6V, the voltage generation circuit 16 steps it down to, for example, 4V and outputs it. The voltage output from the voltage generation circuit 16 is input to the power supply switching circuit 13 and is used for the comparison process in the voltage comparator 17.

[0028] The power supply switching circuit 13 selectively switches the power supply source for driving the backup circuit 11 when there is no power supply from the external power supply 2 between the internal backup battery 12 and the external backup battery 3 according to the voltage of the internal backup battery 12.

[0029] When there is no power supply from the external power supply 2, the voltage comparator 17 compares the voltage of the backup internal battery 12 with the first threshold value. The first threshold value is used to determine whether the backup internal battery 12 is sufficiently charged. In an embodiment of the present disclosure, the first threshold value is set to the voltage output from the voltage generation circuit 16, for example. Conventionally, when an external power supply and an external backup battery are connected to an encoder, in order to prevent the external backup battery from being consumed when the external power supply is on, the voltage supplied from the external backup battery is stepped down by a voltage generation circuit. On the other hand, in an embodiment of the present disclosure, the voltage stepped down and output by the voltage generation circuit 16 is used as the first threshold value for determining whether the backup internal battery 12 is sufficiently charged. As an alternative example, the first threshold value may be set to a fixed value. In this case, if the first threshold value, which is a fixed value, is stored in a rewritable storage unit (not shown), the first threshold value can be changed to an appropriate value as needed even after it is once set.

[0030] The determination result by the voltage comparator 17 is transmitted to the power supply switching circuit 13. When there is no power supply from the external power supply 2, the power supply switching circuit 13 that has received the determination result by the voltage comparator 17 supplies the power for driving the backup circuit 11 from the backup internal battery 12 when the voltage of the backup internal battery 12 is higher than the first threshold value (for example, when it is equal to or higher than the first threshold value), and supplies the power from the backup external battery 3 when the voltage of the backup internal battery 12 is lower than the first threshold value (for example, when it is less than the first threshold value). By operating the power supply switching circuit 13 in this way, when there is no power supply from the external power supply 2, if the backup internal battery 12 is sufficiently charged, the backup internal battery 12 is selected and the backup circuit 11 is driven by the backup internal battery 12. If the backup internal battery 12 is not sufficiently charged, the backup external battery 3 is selected and the backup circuit 11 is driven by the backup external battery 3. According to an embodiment of the present disclosure, when there is no power supply from the external power supply 2 and the backup internal battery 12 is sufficiently charged, the backup circuit 11 is driven by the backup internal battery 12 instead of the backup external battery 3. Therefore, the power supply time by the backup external battery 3 can be shortened, and the consumption (deterioration) of the backup external battery can be suppressed. That is, in a battery backup type encoder, the replacement frequency of the backup external battery can be reduced, and the maintainability and economy are improved.

[0031] When the backup circuit 11 is driven by the internal backup battery 12 in the absence of power supply from the external power source 2, the voltage of the internal backup battery 12 gradually decreases. Therefore, when the backup circuit 11 is driven by the internal backup battery 12 in the absence of power supply from the external power source 2, the voltage comparator 17 compares the voltage of the internal backup battery 12 with a second threshold value. The second threshold value is for leaving power that enables short-term backup in order to use the internal backup battery 12 as an emergency power source to prevent the loss of origin information when replacing the external backup battery 3 for backup or when the cable 20 is disconnected or detached from the connector 15. The second threshold value is set to an arbitrary value according to the discharge characteristics of the battery used as the internal backup battery 12. The second threshold value is stored in a storage unit (not shown), and by making the storage unit rewritable, the second threshold value can be changed to an appropriate value as needed even after it is once set.

[0032] The determination result by the voltage comparator 17 is transmitted to the power supply switching circuit 13. When the power supply switching circuit 13 that has received the determination result by the voltage comparator 17 is supplying power for driving the backup circuit 11 from the internal backup battery 12, if the voltage of the internal backup battery 12 becomes lower than the second threshold value (for example, less than the second threshold value), it switches to supply power for driving the backup circuit 11 from the external backup battery 3 for backup. By operating the power supply switching circuit 13 in this way, when the backup circuit 11 is driven by the internal backup battery 12 in the absence of power supply from the external power source 2, if the internal backup battery 12 is not fully charged, the external backup battery 3 for backup is selected and the backup circuit 11 is driven by the external backup battery 3 for backup. As described above, the internal backup battery 12 is charged while the external power source 2 is connected to the connector 15 and the external power source 2 is on.

[0033] Thus, in one embodiment of the present disclosure, the backup circuit 11 is driven by the backup external battery 3 when there is no power supply from the external power source 2 only when the voltage of the backup internal battery 12 becomes lower than the second threshold while the power for driving the backup circuit 11 is supplied from the backup internal battery 12. However, when the backup circuit 11 is driven by the backup external battery 3 when there is no power supply from the external power source 2, the voltage of the backup external battery 3 may drop below the minimum voltage required to drive the backup circuit 11. Also, when the backup circuit 11 is driven by the backup external battery 3 when there is no power supply from the external power source 2, the backup external battery 3 may be removed from the connector 15 during maintenance of the machine. In these cases, it is necessary to switch the power supply source for driving the backup circuit 11 from the backup external battery 3 to the backup internal battery 12. Therefore, the voltage comparator 17 compares the voltage of the backup external battery 3 with the third threshold when the power for driving the backup circuit 11 is supplied from the backup external battery 3 because the voltage of the backup internal battery 12 has become lower than the second threshold. The third threshold is provided to monitor whether the backup external battery 3 can maintain the voltage required for backup. If the voltage required for driving the LSI 22 cannot be supplied, the LSI 22 may malfunction and the origin information may be lost. Therefore, the third threshold is provided to monitor the voltage of the backup external battery 3. The third threshold is set to a value slightly higher (e.g., 3.7 V) with a margin from the minimum voltage (e.g., 3.5 V) at which the backup circuit 11 can be driven. The third threshold is stored in a storage unit (not shown), and by making the storage unit rewritable, the third threshold can be changed to an appropriate value as needed even after it has been set once.

[0034] The determination result by the voltage comparator 17 is transmitted to the power supply switching circuit 13. When the power supply switching circuit 13 that has received the determination result by the voltage comparator 17 is supplying power for driving the backup circuit 11 from the backup external battery 3 because the voltage of the backup internal battery 12 has become lower than the second threshold value, when the voltage of the backup external battery 3 becomes lower than the third threshold value (for example, less than the third threshold value), it switches to supply the power for driving the backup circuit from the backup internal battery 12. By operating the power supply switching circuit 13 in this way, when the voltage of the backup internal battery 12 has become lower than the second threshold value and the power for driving the backup circuit 11 is being supplied from the backup external battery 3, if the backup external battery 3 is removed from the connector 15 for some reason such as maintenance of the machine, the power supply source for driving the backup circuit 11 is switched to the backup internal battery 12 and the backup circuit 11 is driven.

[0035] Figure 3 is a flowchart showing the operation flow of the encoder according to an embodiment of the present disclosure.

[0036] While the external power supply 2 connected to the connector 15 is on, the power from the external power supply 2 is supplied to the main circuit 19, the charging circuit 18, and the power supply switching circuit 13 via the connector 15. The main circuit 19 causes the position detection circuit 14 to perform high-precision rotational position detection. The charging circuit 18 charges the backup internal battery 12.

[0037] When the power supply from the external power supply 2 to the encoder 1 stops, the backup operation by the backup circuit 11 starts.

[0038] In step S101, the voltage comparator 17 compares the voltage of the internal backup battery 12 with the first threshold value, and determines whether the voltage of the internal backup battery 12 is equal to or higher than the first threshold value. The determination result by the voltage comparator 17 is transmitted to the power supply switching circuit 13. If the voltage of the internal backup battery 12 is equal to or higher than the first threshold value, the process proceeds to step S102; if the voltage of the internal backup battery 12 is less than the first threshold value, the process proceeds to step S104.

[0039] In step S102, the power supply switching circuit 13 selects the internal backup battery 12 as the power supply for driving the backup circuit 11. The backup circuit causes the position detection circuit 14 to perform simple rotation position detection of the rotating body with low power consumption based on the power supplied from the internal backup battery 12.

[0040] When the backup circuit 11 is being driven by the internal backup battery 12, the voltage of the internal backup battery 12 gradually decreases. In step S103, the voltage comparator 17 compares the voltage of the internal backup battery 12 with the second threshold value, and determines whether the voltage of the internal backup battery 12 is less than the second threshold value. The determination result by the voltage comparator 17 is transmitted to the power supply switching circuit 13. If the voltage of the internal backup battery 12 is less than the second threshold value, the process proceeds to step S104.

[0041] In step S104, the power supply switching circuit 13 selects the external backup battery 3 as the power supply for driving the backup circuit 11. The backup circuit causes the position detection circuit 14 to perform simple rotation position detection of the rotating body with low power consumption based on the power supplied from the external backup battery 3.

[0042] In step S105, the voltage comparator 17 compares the voltage of the external backup battery 3 with the third threshold value, and determines whether the voltage of the external backup battery 3 is less than the third threshold value. The determination result by the voltage comparator 17 is transmitted to the power supply switching circuit 13. If the voltage of the external backup battery 3 is less than the third threshold value, the process proceeds to step S106.

[0043] In step S106, the power supply switching circuit 13 selects the internal backup battery 12 as the power supply source for driving the backup circuit 11. The backup circuit causes the position detection circuit 14 to perform simple rotation position detection of the rotating body with low power consumption based on the power supplied from the internal backup battery 12. In addition, if it is determined in step S105 that the voltage of the external backup battery 3 is less than the third threshold value, the backup circuit 11 is driven by the internal backup battery 12 in step S106. Therefore, it is also possible to perform maintenance such as replacing the external backup battery 3 or removing the external power supply 2 from the connector 15.

[0044] In step S107, the voltage comparator 17 compares the voltage of the external backup battery 3 with the third threshold value, and determines whether the voltage of the external backup battery 3 is greater than or equal to the third threshold value. The determination result by the voltage comparator 17 is transmitted to the power supply switching circuit 13. If the voltage of the external backup battery 3 is greater than or equal to the third threshold value, the process returns to step S104.

[0045] During the backup operation period of steps S101 to S107, if the external power supply 2 connected to the connector 15 is turned on, the backup operation by the backup circuit 11 ends. Based on the power supplied from the external power supply 2, the main circuit 19 causes the position detection circuit 14 to perform high-precision rotation position detection, and the charging circuit 18 charges the internal backup battery 12.

[0046] Subsequently, several specific operation examples of the encoder 1 according to an embodiment of the present disclosure will be listed.

[0047] FIG. 4 is a diagram (part 1) illustrating a timing chart of the operation of the encoder according to an embodiment of the present disclosure.

[0048] Time t 1 When the external power supply connected to the connector 15 is turned on at time t, based on the power supplied from the external power supply 2, the main circuit 19 causes the position detection circuit 14 to perform high-precision rotation position detection, and the charging circuit 18 charges the backup internal battery 12. The voltage of the backup internal battery 12 gradually rises and becomes fully charged after exceeding the first threshold value. At time t 2 When the external power supply is turned off at time t, the backup operation by the backup circuit 11 is started. Also at time t 2 since the voltage of the backup internal battery 12 is equal to or higher than the first threshold value at this point (Yes in step S101), the power supply switching circuit 13 selects the backup internal battery 12 as the power supply source for driving the backup circuit 11, and the backup circuit 11 is driven by the power supplied from the backup internal battery 12 (step S102). When the backup circuit 11 is driven by the power supplied from the backup internal battery 12, the voltage of the backup internal battery 12 gradually decreases. At time t 3 when the voltage of the backup internal battery 12 falls below the second threshold value at time t (Yes in step S103), at that point the power supply switching circuit 13 selects the backup external battery 3 as the power supply source for driving the backup circuit 11. After time t 3 the backup circuit 11 is driven by the power supplied from the backup external battery 3 (step S104). When the backup circuit 11 is driven by the power supplied from the backup external battery 3, the voltage of the backup external battery 3 gradually decreases. At time t 4 when the voltage of the backup external battery 3 falls below the third threshold value at time t (Yes in step S105), at that point the power supply switching circuit 13 selects the backup internal battery 12 as the power supply source for driving the backup circuit 11. At time t 4Thereafter, the backup circuit 11 is driven by the power supplied from the internal backup battery 12 for backup (step S106). Time t 5 When the external power supply 2 is turned on at time t, the backup operation by the backup circuit 11 ends, and based on the power supplied from the external power supply 2, the main circuit 19 causes the position detection circuit 14 to perform high-precision rotation position detection, and the charging circuit 18 charges the internal backup battery 12 for backup. After the voltage of the internal backup battery 12 for backup gradually rises and exceeds the first threshold value, it becomes a fully charged state. Time t 6 When the external power supply is turned off at time t, the backup operation by the backup circuit 11 is started, and also at time t 6 since the voltage of the internal backup battery 12 for backup is equal to or higher than the first threshold value at this time (Yes in step S101), the power supply switching circuit 13 selects the internal backup battery 12 for backup as the power supply source for driving the backup circuit 11, and the backup circuit 11 is driven by the power supplied from the internal backup battery 12 for backup (step S102).

[0049] FIG. 5 is a diagram (part 2) illustrating a timing chart of the operation of the encoder according to an embodiment of the present disclosure.

[0050] Time t 1 When the external power supply connected to the connector 15 is turned on at time t, based on the power supplied from the external power supply 2, the main circuit 19 causes the position detection circuit 14 to perform high-precision rotation position detection, and the charging circuit 18 charges the internal backup battery 12 for backup. Before the internal backup battery 12 for backup becomes fully charged after the voltage of the internal backup battery 12 for backup gradually rises and exceeds the first threshold value, at time t 2 When the external power supply is turned off at time t, the backup operation by the backup circuit 11 is started, and also at time t 2At this time, since the voltage of the backup internal battery 12 is equal to or higher than the first threshold value (Yes in step S101), the power supply switching circuit 13 selects the backup internal battery 12 as the power supply source for driving the backup circuit 11, and the backup circuit 11 is driven by the power supplied from the backup internal battery 12 (step S102). When the backup circuit 11 is driven by the power supplied from the backup internal battery 12, the voltage of the backup internal battery 12 gradually decreases, and at time t 3 when the voltage of the backup internal battery 12 falls below the second threshold value at 3 (Yes in step S103), at that time, the power supply switching circuit 13 selects the backup external battery 3 as the power supply source for driving the backup circuit 11, and at time t 3 thereafter, the backup circuit 11 is driven by the power supplied from the backup external battery 3 (step S104). When the backup circuit 11 is driven by the power supplied from the backup external battery 3, the voltage of the backup external battery 3 gradually decreases, and at time t 4 when the voltage of the backup external battery 3 falls below the third threshold value at 4 (Yes in step S105), at that time, the power supply switching circuit 13 selects the backup internal battery 12 as the power supply source for driving the backup circuit 11, and at time t 4 thereafter, the backup circuit 11 is driven by the power supplied from the backup internal battery 12 (step S106). At time t 5 when the external power supply 2 is turned on, the backup operation by the backup circuit 11 ends, and based on the power supplied from the external power supply 2, the main circuit 19 causes the position detection circuit 14 to perform high-precision rotational position detection, and the charging circuit 18 charges the backup internal battery 12. The voltage of the backup internal battery 12 gradually increases, but before the backup internal battery 12 is fully charged, at time t 6 when the external power supply is turned off, the backup operation by the backup circuit 11 is started. At time t 6At this point, since the voltage of the backup internal battery 12 is less than the first threshold value (No in step S101), the power supply switching circuit 13 selects the backup external battery 3 as the power supply for driving the backup circuit 11 (step S104). However, since the voltage of the backup external battery 3 is less than the third threshold value (Yes in step S105), the power supply switching circuit 13 reselects the backup internal battery 12 as the power supply for driving the backup circuit 11, and the backup circuit 11 is driven by the power supplied from the backup internal battery 12 (step S106).

[0051] FIG. 6 is a diagram (part 3) illustrating a timing chart of the operation of the encoder according to an embodiment of the present disclosure.

[0052] Time t 1 When the external power supply connected to the connector 15 is turned on at time t, based on the power supplied from the external power supply 2, the main circuit 19 causes the position detection circuit 14 to perform highly accurate rotation position detection, and the charging circuit 18 charges the backup internal battery 12. The voltage of the backup internal battery 12 gradually rises, and at the time t before the backup internal battery 12 exceeds the first threshold value 2 When the external power supply is turned off at time t, the backup operation by the backup circuit 11 is started, and also at time t 2 At this point, since the voltage of the backup internal battery 12 is less than the first threshold value (No in step S101), the power supply switching circuit 13 selects the backup external battery 3 as the power supply for driving the backup circuit 11, and the backup circuit 11 is driven by the power supplied from the backup external battery 3 (step S104). When the backup circuit 11 is driven by the power supplied from the backup external battery 3, the voltage of the backup external battery 3 gradually decreases, and at time t 3 When the voltage of the backup external battery 3 falls below the third threshold value at time t (Yes in step S105), at that point the power supply switching circuit 13 selects the backup internal battery 12 as the power supply for driving the backup circuit 11, and at time t3 Thereafter, the backup circuit 11 is driven by the power supplied from the internal backup battery 12 (step S106). When the backup circuit 11 is driven by the power supplied from the internal backup battery 12, the voltage of the external backup battery 3 gradually decreases. However, at time t 4 when the external power supply 2 is turned on, the backup operation by the backup circuit 11 ends. Based on the power supplied from the external power supply 2, the main circuit 19 causes the position detection circuit 14 to perform high-precision rotation position detection, and the charging circuit 18 charges the internal backup battery 12. After the voltage of the internal backup battery 12 gradually rises and exceeds the first threshold value, at time t 5 when the external power supply is turned off, the backup operation by the backup circuit 11 is started. At time t 5 since the voltage of the internal backup battery 12 is equal to or higher than the first threshold value at this point (Yes in step S101), the power supply switching circuit 13 selects the internal backup battery 12 as the power supply source for driving the backup circuit 11, and the backup circuit 11 is driven by the power supplied from the internal backup battery 12 (step S102).

[0053] FIG. 7 is a diagram (part 4) illustrating a timing chart of the operation of the encoder according to an embodiment of the present disclosure. In this example, it is assumed that the voltage of the external backup battery 3 is always below the third threshold value.

[0054] At time t 1 when the external power supply connected to the connector 15 is turned on, based on the power supplied from the external power supply 2, the main circuit 19 causes the position detection circuit 14 to perform high-precision rotation position detection, and the charging circuit 18 charges the internal backup battery 12. After the voltage of the internal backup battery 12 gradually rises and exceeds the first threshold value, it reaches a fully charged state. At time t 2 when the external power supply is turned off, the backup operation by the backup circuit 11 is started, and also at time t 2At this time, since the voltage of the backup internal battery 12 is equal to or higher than the first threshold value (Yes in step S101), the power supply switching circuit 13 selects the backup internal battery 12 as the power supply for driving the backup circuit 11, and the backup circuit 11 is driven by the power supplied from the backup internal battery 12 (step S102). When the backup circuit 11 is driven by the power supplied from the backup internal battery 12, the voltage of the backup internal battery 12 gradually decreases. At time t 3 at, the voltage of the backup internal battery 12 falls below the second threshold value (Yes in step S103), and the power supply switching circuit 13 selects the backup external battery 3 as the power supply for driving the backup circuit 11 (step S104). However, since the voltage of the backup external battery 3 is less than the third threshold value (Yes in step S105), the power supply switching circuit 13 reselects the backup internal battery 12 as the power supply for driving the backup circuit 11, and the backup circuit 11 is driven by the power supplied from the backup internal battery 12 (step S106). At time t 4 when the external power supply 2 is turned on, the backup operation by the backup circuit 11 ends, and based on the power supplied from the external power supply 2, the main circuit 19 causes the position detection circuit 14 to perform high-precision rotation position detection, and the charging circuit 18 charges the backup internal battery 12. After the voltage of the backup internal battery 12 gradually rises and exceeds the first threshold value, at time t 5 when the external power supply is turned off, the backup operation by the backup circuit 11 is started, and also at time t 5 at this time, since the voltage of the backup internal battery 12 is equal to or higher than the first threshold value (Yes in step S101), the power supply switching circuit 13 selects the backup internal battery 12 as the power supply for driving the backup circuit 11, and the backup circuit 11 is driven by the power supplied from the backup internal battery 12 (step S102).

[0055] FIG. 8 is a diagram (part 5) illustrating a timing chart of the operation of the encoder according to an embodiment of the present disclosure.

[0056] Time t 1 When the external power supply 2 connected to the connector 15 is turned on at time t, based on the power supplied from the external power supply 2, the main circuit 19 causes the position detection circuit 14 to perform high-precision rotation position detection, and the charging circuit 18 charges the backup internal battery 12. The voltage of the backup internal battery 12 gradually rises and becomes fully charged after exceeding the first threshold value. Time t 2 When the cable 20 is removed from the connector 15 at time t, the backup operation by the backup circuit 11 is started, and also at time t 2 At this point, since the voltage of the backup internal battery 12 is equal to or higher than the first threshold value (Yes in step S101), the power supply switching circuit 13 selects the backup internal battery 12 as the power supply source for driving the backup circuit 11, and the backup circuit 11 is driven by the power supplied from the backup internal battery 12 (step S102). When the backup circuit 11 is driven by the power supplied from the backup internal battery 12, the voltage of the backup internal battery 12 gradually decreases. Before the voltage of the backup internal battery 12 drops below the second threshold value at time t 3 When the cable 20 is connected to the connector 15 at time t, and further at time t 4 When the voltage of the backup internal battery 12 drops below the second threshold value at time t (Yes in step S103), at that point, the power supply switching circuit 13 selects the backup external battery 3 as the power supply source for driving the backup circuit 11, and at time t 4 Thereafter, the backup circuit 11 is driven by the power supplied from the backup external battery 3 (step S104). When the backup circuit 11 is driven by the power supplied from the backup external battery 3, the voltage of the backup external battery 3 gradually decreases, and at time t 5 When the voltage of the backup external battery 3 drops below the third threshold value at time t (Yes in step S105), at that point, the power supply switching circuit 13 selects the backup internal battery 12 as the power supply source for driving the backup circuit 11, and at time t 5Thereafter, the backup circuit 11 is driven by the power supplied from the internal backup battery 12 (step S106).

[0057] FIG. 9 is a diagram (part 6) illustrating a timing chart of the operation of the encoder according to an embodiment of the present disclosure.

[0058] Time t 1 When the external power supply 2 connected to the connector 15 is turned on at time t, based on the power supplied from the external power supply 2, the main circuit 19 causes the position detection circuit 14 to perform high-precision rotation position detection, and the charging circuit 18 charges the internal backup battery 12. The voltage of the internal backup battery 12 gradually rises and becomes fully charged after exceeding the first threshold value. At time t 2 When the external power supply 2 is turned off at time t, the backup operation by the backup circuit 11 is started. Also at time t 2 since the voltage of the internal backup battery 12 is equal to or higher than the first threshold value at this point (Yes in step S101), the power supply switching circuit 13 selects the internal backup battery 12 as the power supply source for driving the backup circuit 11, and the backup circuit 11 is driven by the power supplied from the internal backup battery 12 (step S102). When the backup circuit 11 is driven by the power supplied from the internal backup battery 12, the voltage of the internal backup battery 12 gradually decreases. At time t 3 When the voltage of the internal backup battery 12 falls below the second threshold value at time t (Yes in step S103), at that point, the power supply switching circuit 13 selects the external backup battery 3 as the power supply source for driving the backup circuit 11, and at time t 3 thereafter, the backup circuit 11 is driven by the power supplied from the external backup battery 3 (step S104). When the backup circuit 11 is driven by the power supplied from the external backup battery 3, the voltage of the external backup battery 3 gradually decreases, and at time t 4Disconnect the cable 20 from the connector 15, perform some maintenance work on, for example, the machine to which the encoder 1 is connected, and when the voltage of the backup external battery 3 drops below the third threshold (Yes in step S105), at that time, the power supply switching circuit 13 selects the backup internal battery 12 as the power supply source for driving the backup circuit 11, at time t 4 After that, the backup circuit 11 is driven by the power supplied from the backup internal battery 12 (step S106). Further, at time t 5 When the cable 20 is connected to the connector 15, at time t 5 Since the voltage of the backup external battery 3 exceeds the second threshold at time t (No in step S107), the power supply switching circuit 13 selects the backup external battery 3 as the power supply source for driving the backup circuit 11, and the backup circuit 11 is driven by the power supplied from the backup external battery 3 (step S104). At time t 6 When the external power supply 2 is turned on at time t, the backup operation by the backup circuit 11 ends, and based on the power supplied from the external power supply 2, the main circuit 19 causes the position detection circuit 14 to perform high-precision rotation position detection, and the charging circuit 18 charges the backup internal battery 12.

[0059] Thus, according to an embodiment of the present disclosure, in order to supply the driving power for the backup operation by the backup circuit 11 that is executed when there is no power supply from the external power supply 2, the backup internal battery 12 is preferentially selected over the backup external battery 3 as much as possible as the power supply source, thereby shortening the power supply time by the backup external battery 3. Also, by configuring the backup internal battery 12 with a secondary battery, it can be charged with the power supplied from the external power supply 2 via the connector 15. As a result, in a battery backup type encoder, it is possible to suppress the consumption (deterioration) of the backup external battery and reduce the replacement frequency of the backup external battery, thereby improving maintainability and economy.

[0060] An arithmetic processing unit (processor) is provided in the encoder 1 described above. Examples of the arithmetic processing unit include an IC, LSI, CPU, MPU, DSP, etc. The backup circuit 11, power supply switching circuit 13, voltage generation circuit 16, voltage comparator 17, and main circuit 19 may be configured by a combination of an analog circuit and an arithmetic processing unit, or may be configured by only the arithmetic processing unit, or may be configured by only the analog circuit. Examples of the arithmetic processing unit that can configure the backup circuit 11, power supply switching circuit 13, voltage generation circuit 16, voltage comparator 17, and main circuit 19 include an IC, LSI, CPU, MPU, DSP, etc. For example, when constructing the backup circuit 11, power supply switching circuit 13, voltage generation circuit 16, voltage comparator 17, and main circuit 19 in the form of a software program, the functions of the backup circuit 11, power supply switching circuit 13, voltage generation circuit 16, voltage comparator 17, and main circuit 19 can be realized by operating the arithmetic processing unit according to this software program. Alternatively, a semiconductor integrated circuit or storage medium in which a software program for realizing the functions of the backup circuit 11, power supply switching circuit 13, voltage generation circuit 16, voltage comparator 17, and main circuit 19 is written may be constructed.

Explanation of Signs

[0061] 1 Encoder 2 External power supply 3 Backup external battery 11 Backup circuit 12 Backup internal battery 13 Power supply switching circuit 14 Position detection circuit 15 Connector 16 Voltage generation circuit 17 Voltage comparator 18 Charging circuit 19 Main circuit 20 Cable 20-1 First current path 20-2 Second current path 21 Backup clock 22 LSI 23 Comparator 31 LED 32 Rotating slit 33 Light receiving element

Claims

1. An encoder having a connector to which an external power supply and an external backup battery can be connected, a backup circuit that is driven when power supply from the external power supply is not available, a backup internal battery, a power supply switching circuit that selectively switches the power supply source for driving the backup circuit between the backup internal battery and the backup external battery according to the voltage of the backup internal battery when power supply from the external power supply is not available, comprising, the power supply switching circuit, when power supply from the external power supply is lost, supplies power for driving the backup circuit from the backup internal battery when the voltage of the backup internal battery is higher than a first threshold value, and supplies power for driving the backup circuit from the backup external battery when the voltage of the backup internal battery is lower than the first threshold value, when supplying power for driving the backup circuit from the backup internal battery, if the voltage of the backup internal battery becomes lower than a second threshold value, supplies power for driving the backup circuit from the backup external battery, when supplying power for driving the backup circuit from the backup external battery due to the voltage of the backup internal battery becoming lower than the second threshold value, if the voltage of the backup external battery becomes lower than a third threshold value, supplies power for driving the backup circuit from the backup internal battery, the encoder.

2. The encoder according to claim 1, wherein the backup internal battery is a secondary battery.

3. The encoder according to claim 2, wherein the secondary battery is an all-solid-state battery.

4. comprising a position detection circuit for detecting the rotational position of a rotating body, The backup circuit is a circuit that causes the position detection circuit to detect the rotational position of the rotating body with power less than the power from the external power supply when power supply from the external power supply is not available. The encoder according to any one of claims 1 to 3.

5. Comprising a position detection circuit for detecting the rotational position of a rotating body, The backup circuit intermittently operates the position detection circuit with a clock for backup operation when there is no power supply from the external power source. The encoder according to any one of claims 1 to 4.

6. The position detection circuit includes an LED, a rotary slit to which the rotation axis of the rotating body is attached, and a light receiving element. The backup circuit includes a backup clock that receives driving power from the power supply switching circuit, an LSI, and a comparator. The encoder according to claim 5.

7. The backup clock intermittently drives the LSI based on the clock frequency for intermittent driving specified by the LSI while there is no power supply from the external power source to the backup circuit. The LED intermittently lights up under the control of the intermittently driven LSI. The light from the intermittently lit LED is transmitted or blocked by the rotary slit according to the rotation of the rotary slit. Among the light emitted from the intermittently lit LED, the light transmitted through the rotary slit is received by the light receiving element. The light receiving element converts and outputs an analog electrical signal having an amplitude corresponding to the intensity of the received light. The comparator converts the analog electrical signal output from the light receiving element into a digital electrical signal. The encoder according to claim 6.

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