Dual-axis synchronous control method, control device and synchronous motion device

Abstract

The present invention provides a dual-axis synchronous control method, a control device and a synchronous motion device, which relate to the technical field of dual-axis synchronous control. The dual-axis synchronous control method of the present invention respectively obtains the torque data of the first motor and the second motor and performs feedback; calculates and obtains the torque difference data of the first motor and the second motor; if the torque difference data does not meet the preset conditions, then according to the torque difference data, controls the first motor and / or the second motor to operate with target operating parameters, so that the torque difference between the first motor and the second motor meets the preset conditions. Based on the technical solution of the present invention, the torque difference between the first motor and the second motor is controlled to meet the preset conditions, avoiding the situation of two-axis motion skew, forming a torque closed-loop control. Since the innermost ring of the three rings of the motor is the current / torque ring, it can respond first, the calculation is minimal, and the recovery speed is fast.

Description

Technical Field

[0001] The present invention relates to the technical field of dual-axis synchronous control, and in particular to a dual-axis synchronous control method, a control device and a synchronous motion device. Background Art

[0002] Traditional single-axis drive solutions are prone to vibration due to transient driving force, which reduces machining accuracy. Furthermore, they struggle to provide a sufficiently high or relatively low-cost driving force. To meet the requirements of high-speed, high-precision CNC machining, redundant gantry platforms offer greater thrust, structural rigidity, and control bandwidth compared to single-axis drive solutions. Furthermore, the symmetry of the dual-drive structure offsets the additional bending moments on the lead screw due to unbalanced loads, effectively suppressing high-speed machine vibration, extending lead screw life, improving system response, and increasing system rigidity. Although the transmission components on the two feed axes are identical, the redundant drive and strong mechanical coupling between the axes inevitably lead to inconsistent motion during high-speed operation, resulting in skewed moving parts. This is directly reflected in the fact that improper coordination mechanisms of the redundant motors often cause ball bearings to be squeezed and deformed, leading to asynchronous motion between the two actuators and impaired synchronization accuracy, which directly impacts the control accuracy of the redundant drive axes. Therefore, a gantry synchronization control method that ensures redundant gantry synchronization is crucial for ensuring machining accuracy.

[0003] A gantry control method discloses the following steps: first, dividing two groups of power mechanisms into a master power mechanism and a slave power mechanism; then connecting the frequency division output interface of the master drive and the full closed-loop interface of the slave drive, and connecting the full closed-loop interface of the master drive and the frequency division output interface of the slave drive; second, setting the master drive as a gantry synchronization master through a gantry controller, setting the frequency division output source of the master drive as a position instruction output; setting the slave drive as a gantry synchronization slave, setting the frequency division output source of the slave drive as a normal frequency division output, and setting the position instruction selection to a second encoder input; setting a position deviation threshold in the gantry controller; third, controlling the movement of the slave servo motor through a torque loop, and the master drive reading the position signal and speed signal of the master servo motor and the slave servo motor in real time, obtaining the position and speed difference between the master servo motor and the slave servo motor, and then outputting speed and torque compensation instructions.

[0004] A control method based on a laser displacement sensor is disclosed. The device comprises a dual-axis synchronous motion control device body, a displacement detection system, and a control component. The dual-axis synchronous motion control device body comprises a first drive mechanism, a second drive mechanism, a first linear motion platform, a second linear motion platform, and a laboratory table. The displacement detection system comprises a long-distance laser displacement sensor, a high-precision laser displacement sensor, a reflector, a workbench, a first indexing plate, and a second indexing plate. The control component is respectively connected to the first drive mechanism, the second drive mechanism, the long-distance laser displacement sensor, and the high-precision laser displacement sensor. The laser displacement sensor is used to measure motion position signals of the two axes, which are input into an industrial control computer. The obtained control signals are output to a servo driver to drive the motion of two servo motors, thereby achieving dual closed-loop control of the speed and position of the device.

[0005] A dual-axis control device and method includes a coaxial synchronous motion main body and a drive detection control part. A tension and pressure sensor and an acceleration sensor are used to detect the motion speed signals of the two axes, which are input into an industrial control computer. The obtained control signals are output to a servo driver to drive the movement of two servo motors, thereby realizing dual closed-loop control of the speed and position of the device.

[0006] The above technologies all provide closed-loop control of the speed and position loops of the servo motor. Compared with current loop feedback, they have inaccurate data, large driver calculations, and slow dynamic response. Summary of the Invention

[0007] In view of the fact that the dual-axis structure in the existing technology will inevitably have inconsistent movement during high-speed operation, which will cause the crossbeam to twist, the present application proposes a dual-axis synchronous control method, control device and synchronous motion device, which can accurately measure the dual-axis synchronization error, ensure the synchronization accuracy of the dual-axis drive, and avoid the twisting of the two-axis movement.

[0008] The dual-axis synchronous control method of the present invention comprises the following steps:

[0009] respectively obtaining torque data of the first motor and the second motor and providing feedback;

[0010] Calculating and obtaining torque difference data between the first motor and the second motor;

[0011] If the torque difference data does not meet the preset conditions, the first motor and / or the second motor are controlled to operate with target operating parameters according to the torque difference data so that the torque difference between the first motor and the second motor meets the preset conditions.

[0012] In one embodiment, before controlling the first motor and / or the second motor to operate at target operating parameters, the rotation angle and speed of the first motor and the rotation angle and speed of the second motor are respectively obtained, and the rotation angle and speed of the first motor and the rotation angle and speed of the second motor are respectively adjusted to the target parameters based on the torque difference data. In this embodiment, closed-loop control of the speed loop is achieved by obtaining the rotation angle and speed of the first motor and the second motor and controlling the rotation angle and speed of the first motor and the second motor so that the torque difference between the first motor and / or the second motor meets a preset condition.

[0013] In one embodiment, the target operating parameter includes at least a rotational speed. In this embodiment, the rotational speeds of the first motor and the second motor are controlled so that the torque difference between the first motor and the second motor reaches a preset value.

[0014] In one embodiment, the preset condition is that the torque difference between the first motor and the second motor is zero. This embodiment allows the first motor and the second motor to maintain perfect synchronous motion. When the ends of the crossbeam are respectively mounted on the transmission structures of the first and second motors, the crossbeam exerts zero lateral squeezing force on the first and second motors. This prevents the crossbeam from squeezing the transmission structure and affecting its service life, while ensuring smooth operation of the crossbeam.

[0015] In one embodiment, a pulse control signal is generated based on the torque difference data to control the first motor and / or the second motor to operate at the target operating parameters. In this embodiment, a pulse signal is generated based on the acquired torque difference data, and the target parameters of the first motor and the second motor are controlled by the pulse signal to achieve preset conditions, thereby achieving a rapid response effect.

[0016] The dual-axis synchronous control device of the present invention comprises:

[0017] a torque data acquisition module, configured to acquire torque data of the first rotating shaft and the second rotating shaft respectively;

[0018] a torque difference data acquisition module, configured to calculate, based on the torque data, torque difference data of a first motor and a second motor connected to the first rotating shaft and the second rotating shaft, respectively;

[0019] A motor control module is used to control target operating parameters of the first motor and / or the second motor according to the torque difference data so that the torque difference between the first motor and the second motor meets a preset condition.

[0020] The dual-axis synchronous motion device of the present invention includes a drive assembly, which includes a first drive unit and a second drive unit, wherein the first drive unit includes a first rotating shaft and a first motor connected to each other, and the second drive unit includes a second rotating shaft and a second motor connected to each other;

[0021] a torque detection assembly comprising a first torque sensor and a second torque sensor respectively disposed on the first rotating shaft and the second rotating shaft;

[0022] The motor drive component includes a first driver and a second driver respectively provided on the first motor and the second motor. The motor drive component is used to drive the motor to operate according to target operating parameters determined by the torque data obtained by the torque detection component.

[0023] Through this embodiment, the first torque sensor and the second torque sensor respectively obtain torque information of the first rotating shaft and the second rotating shaft, with high measurement accuracy and good stability. It has the advantages of measuring static and dynamic torque, no need for repeated zeroing, continuous measurement of positive and negative torque, high sampling frequency, and fast dynamic response.

[0024] In one embodiment, the system further includes a main controller electrically connected to the torque sensor in the torque detection assembly and the driver in the motor control assembly. In this embodiment, the controller processes information from the first and second torque sensors and outputs signals to control the operation of the first and second motors, thereby achieving closed-loop control.

[0025] In one embodiment, a signal converter assembly is further included, comprising a first signal converter disposed in the electrical connection loop between the first torque sensor and the main controller, and a second signal converter disposed in the electrical connection loop between the second torque sensor and the main controller. In this embodiment, the signal converter assembly is provided to convert analog signals from the first and second torque sensors into digital signals, which are then output to the controller for processing.

[0026] In one embodiment, an encoder assembly is further included, comprising a first encoder and a second encoder, respectively disposed on the first motor and the second motor. In this embodiment, the encoder assembly can be used to obtain rotational angle and speed information of the first motor and the second motor, and in response to zeroing the torque difference between the first motor and the second motor, a control signal can be fed back to the first driver and the second driver via the encoder assembly.

[0027] The above technical features can be combined in various suitable ways or replaced by equivalent technical features, as long as the purpose of the present invention can be achieved.

[0028] The dual-axis synchronous control method, control device, and synchronous motion device provided by the present invention have at least the following beneficial effects compared with the prior art:

[0029] The torque data of the first and second rotating shafts are obtained, and the torque difference between the first motor and the second motor is controlled to meet the preset conditions to avoid the twisting of the two-axis movement, thereby forming a torque closed-loop control. Since the innermost loop of the three motor loops is the current / torque loop, it can respond first, with the smallest calculation and the fastest recovery speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention will be described in more detail below based on embodiments and with reference to the accompanying drawings, wherein:

[0031] Figure 1 Shows a schematic structural diagram of the dual-axis synchronous motion device of the present invention;

[0032] Figure 2 A schematic top view of the dual-axis synchronous motion device of the present invention is shown;

[0033] Figure 3 This is the motor three-loop control schematic;

[0034] Figure 4 This is the geometric principle diagram for measuring the change in relative displacement of synchronous motion.

[0035] In the drawings, like reference numerals are used for like parts, but the drawings are not necessarily true to scale.

[0036] Reference numerals:

[0037] 11 - first rotating shaft, 12 - first motor, 13 - first torque sensor, 21 - second rotating shaft, 22 - second motor, 23 - second torque sensor. DETAILED DESCRIPTION

[0038] The present invention will be further described below with reference to the accompanying drawings.

[0039] Example 1

[0040] The dual-axis synchronous control method of the present invention comprises the following steps:

[0041] S10 respectively obtains torque data of the first motor 12 and the second motor 22 and provides feedback;

[0042] S20 calculates and obtains torque difference data between the first motor 12 and the second motor 22 ;

[0043] S30 If the torque difference data does not meet the preset condition, the first motor 12 and / or the second motor 22 are controlled to operate with target operating parameters according to the torque difference data so that the torque difference between the first motor 12 and the second motor 22 meets the preset condition.

[0044] Example 2

[0045] S00 obtains the rotation angle and speed of the first motor 12 and the rotation angle and speed of the second motor 22 respectively, and adjusts the rotation angle and speed of the first motor 12 and the rotation angle and speed of the second motor 22 to target parameters according to the torque difference data.

[0046] Specifically, the first motor 12 and the second motor 22 are equipped with a first encoder and a second encoder, respectively, which are photoelectric encoders. The rotation angle and speed signals of the first motor 12 and the rotation angle and speed of the second motor 22 obtained in S00 are respectively output to the controller through the first driver and the second driver, and the motion control card.

[0047] S10 respectively obtains torque data of the first motor 12 and the second motor 22 and provides feedback;

[0048] S20 calculates and obtains torque difference data between the first motor 12 and the second motor 22; specifically, the first torque sensor 13 and the second torque sensor 23 obtain torque data of the first rotating shaft 11 and the second rotating shaft 21, and the torque data is output by the first dynamic torque tester and the second dynamic torque tester to the first A / D conversion card and the second A / D conversion card to convert the converted digital signal into a digital signal, which is then input into the industrial control computer for processing;

[0049] If the torque difference data does not meet the preset condition, the first motor 12 and / or the second motor 22 are controlled to operate at the target operating parameters according to the torque difference data so that the torque difference between the first motor 12 and the second motor 22 is zero.

[0050] Specifically, the rotation angle and speed of the first motor 12 and the second motor 22, as well as the torque difference data are input into the industrial control computer and processed using a set algorithm. The generated torque difference is compensated to the drive shaft of the first motor 12 and / or the second motor 22 to ensure that the torque values of the first rotating shaft 11 and the second rotating shaft 21 are the same, and a pulse signal for controlling the first motor 12 and the second motor 22 is generated. The pulse signal passes through the motion control card, the first driver and the second driver respectively, and is processed by the first driver and the second driver and then output to the first motor 12 and the second motor 22, thereby realizing dual closed-loop control of the torque and speed of the two motors, so that the two drive mechanisms move synchronously.

[0051] The torque of the first motor 12 and the second motor 22 are measured respectively by the first torque sensor 13 and the second torque sensor 23 to ensure that the torque difference between the two motors is zero. The above signal is fed back to the driver through the encoder, thereby obtaining dual closed-loop control of the torque and speed of the two drive mechanisms. The torque sensor has high measurement accuracy and good stability, and has the advantages of measuring static and dynamic torque, no need for repeated zero adjustment, continuous measurement of positive and negative torque, high sampling frequency, and fast dynamic response. It can dynamically measure the torque value of the two motor shafts, thereby making the dual-drive synchronous movement more accurate and responsive.

[0052] In the prior art, dual-drive synchronous motion uses displacement sensors or tension and compression sensors, combined with photoelectric encoders to detect the angular displacement of the drive device, forming a dual closed-loop control of position and speed. While the system is controlling speed and position, it is also controlling current / torque to achieve corresponding control of speed and position. The current loop must be used in any mode. The current loop is the innermost loop and is the basis of control. The present invention uses a torque sensor to measure the torque of the motor shaft and directly controls it through the inner loop. The torque value of the two motor shafts can be quickly obtained. In the torque mode, the driver's calculation is minimal and the response is fastest. In this mode, the system can achieve synchronous motion stably, accurately, and quickly, and can restore synchronization more quickly when interference causes asynchronous motion.

[0053] Compared with the prior art which requires setting a zero point for both axes as a reference point for movement, installing a photoelectric switch between the zero point and the signals of two adjacent points, and performing zero return and error analysis before the start of dual-axis movement, the present invention is not affected by the dual-axis movement range, does not require zero return and calibration operations through a fixed detection device, and can avoid zero point setting and error analysis.

[0054] Example 3

[0055] like Figure 4 As shown, T1 and T2 are the torques of the dual-drive shafts, which can be measured by torque sensors.

[0056] ΔT=|T1-T2|=K*θ (1)

[0057] in:

[0058] K is the torsional stiffness of the beam component, which can be obtained through calculation or simulation;

[0059] θ is the angular deviation caused by the asynchronous movement of the beam components. When the two axes move synchronously, θ = 0.

[0060] According to the above formula, another method for measuring the dual-axis torque difference is provided:

[0061] S00 sets a zero point position at the same starting point on the first rotating shaft 11 and the second rotating shaft 21;

[0062] S10 obtains the distance value data from the two ends of the beam to the zero point position;

[0063] S20 calculates and obtains the difference data of the distance from the two ends of the beam to the zero point position;

[0064] S30 calculates and obtains the angle between the moving path of the beam after the beam is twisted and the moving path of the beam before the beam is twisted based on the difference data of S20 and the distance between the first rotating shaft 11 and the second rotating shaft 21;

[0065] S40 calculates the value of θ based on the fact that the moving path of the beam after the beam is twisted is still perpendicular to the beam;

[0066] S50 calculates the torque difference according to formula (1).

[0067] Example 4

[0068] The dual-axis synchronous control device of the present invention comprises:

[0069] The torque data acquisition module is used to obtain the torque data of the first rotating shaft 11 and the second rotating shaft 21 respectively; specifically, the movement of the first rotating shaft 11 and the second rotating shaft 21 adopts a coupled connection, which can dynamically detect the speed difference and torque value between the two shafts in real time, and is suitable for low-speed and heavy-load occasions.

[0070] a torque difference data acquisition module, which is used to calculate and obtain torque difference data of the first motor 12 and the second motor 22 connected to the first rotating shaft 11 and the second rotating shaft 21 respectively based on the torque data;

[0071] The motor control module is used to control the target operating parameters of the first motor 12 and / or the second motor 22 according to the torque difference data, so that the torque difference between the first motor 12 and the second motor 22 meets a preset condition.

[0072] Specifically, this control device can adopt a master-slave synchronous control strategy, or other synchronous control strategies, such as serial synchronous motion control strategy, parallel synchronous motion control strategy, virtual electronic spindle synchronous motion control strategy, etc., providing a platform for verifying complex multi-axis control strategies.

[0073] Example 5

[0074] The dual-axis synchronous motion device of the present invention includes: a drive assembly including a first drive unit and a second drive unit, the first drive unit including a first rotating shaft 11 and a first motor 12 connected to each other, and the second drive unit including a second rotating shaft 21 and a second motor 22 connected to each other;

[0075] The torque detection assembly includes a first torque sensor 13 and a second torque sensor 23 respectively provided on the first rotating shaft 11 and the second rotating shaft 21;

[0076] The motor drive assembly includes a first driver and a second driver respectively provided on the first motor 12 and the second motor 22 . The motor drive assembly is used to drive the motor to operate according to target operating parameters determined by the torque data obtained by the torque detection assembly.

[0077] Specifically, the structures of the first drive component and the second drive component are consistent, and the first drive component is now explained: the first drive includes a first motor 12, a first motor 12 bracket, a first coupling, a first torque sensor 13 bracket, a first torque sensor 13, a second coupling, a first bearing seat, and a first ball screw pair connected in sequence. Linear guides are provided on both sides of the first ball screw pair, and sliders are provided on the linear guides. A crossbeam is provided on the ball screw, and one end of the crossbeam is fixed on the slider; the first motor 12 drives the ball screw through the first coupling, and the first motor 12 is connected to the first torque sensor 13 through the first coupling, and the first torque sensor 13 is connected to the ball screw through the second coupling.

[0078] Specifically, the first motor 12 and the second motor 22 are both servo motors, and are 1.3 kW AC servo motors produced by Yaskawa Corporation of Japan, and the model of the servo motor is SGM7G-13AFC61.

[0079] The first and second rotating shafts 11, 21 are arranged parallel to each other and form a ball screw pair. The ends of the crossbeam are mounted on the first and second rotating shafts 11, 21. A linear guide is provided on the outer sides of each of the first and second rotating shafts 11, 21, respectively, to guide and limit the movement path of the crossbeam. The ball screw pair utilizes a Taiwan HIWIN precision ball screw, model R25, equipped with a standard ball screw nut. The ball screw support components are all machined parts, and the bearings are NSK 20TAC47 bearings, specifically designed for ball screw pair supports.

[0080] The linear guide uses Taiwan HIWIN's heavy-duty ball linear guide, model HGH25CA2R1000, with a guide rail width W1 of 23mm, an assembly height H of 40mm, a guide rail length L of 1000mm, and is equipped with a standard slider.

[0081] The first torque sensor 13 is connected to the first motor 12 and the first rotating shaft 11 via couplings. The second torque sensor 23 is also connected to the second rotating shaft 21 via the second motor 22. The coupling can be an R+W precision coupling model BK3 bellows elastic coupling.

[0082] Example 6

[0083] The dual-axis synchronous motion device of the present invention further includes a main controller, which is electrically connected to the torque sensor in the torque detection component and the driver in the motor control component.

[0084] It also includes a signal converter assembly, which includes a first signal converter arranged on the electrical connection circuit between the first torque sensor 13 and the main controller, and a second signal converter arranged on the electrical connection circuit between the second torque sensor 23 and the main controller.

[0085] The system further includes an encoder assembly, which includes a first encoder and a second encoder respectively disposed on the first motor 12 and the second motor 22 .

[0086] Specifically, the controller is an industrial control computer, the first signal converter and the second signal converter of the signal conversion component are the first A / D conversion card and the second A / D conversion card respectively, and the first encoder and the second encoder of the encoder component are the photoelectric encoders of the first motor 12 and the second motor 22 respectively.

[0087] In the description of the present invention, it should be understood that the terms "upper", "lower", "bottom", "top", "front", "back", "inside", "outside", "left", "right", etc., indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention.

[0088] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely illustrative of the principles and applications of the invention. It should be understood that many modifications may be made to the illustrative embodiments, and that other arrangements may be devised, without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in ways other than those described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be employed in conjunction with other described embodiments.

Claims

1. A dual-axis synchronous control method, characterized in that: The steps include: respectively obtaining torque data of the first motor and the second motor and providing feedback; Calculating and obtaining torque difference data between the first motor and the second motor; The step of obtaining the torque difference data between the first motor and the second motor includes: S00 sets a zero point position at the same starting point on the first rotating shaft and the second rotating shaft; S10 obtains the distance value data from the two ends of the beam to the zero point position; S20 calculates and obtains the difference data of the distance from the two ends of the beam to the zero point position; S30 calculates and obtains an angle between a moving path of the beam after the beam is twisted and a moving path of the beam before the beam is twisted based on the difference data of S20 and the distance between the first rotation axis and the second rotation axis; S40 calculates the value of θ based on the fact that the moving path of the beam after the beam is twisted is still perpendicular to the beam; S50 calculates the torque difference according to the formula ΔT=K*θ, where ΔT is the torque difference and K is the torsional stiffness of the beam component; if the torque difference data does not meet the preset conditions, then according to the torque difference data, control the first motor and / or the second motor to operate with target operating parameters so that the torque difference between the first motor and the second motor meets the preset conditions.

2. The dual-axis synchronous control method according to claim 1, characterized in that: Also includes: Before controlling the first motor and / or the second motor with target operating parameters, the rotation angle and speed of the first motor and the rotation angle and speed of the second motor are respectively obtained, and the rotation angle and speed of the first motor and the rotation angle and speed of the second motor are respectively adjusted to the target parameters based on the torque difference data.

3. The dual-axis synchronous control method according to claim 1, characterized in that: The target operating parameter includes at least the rotational speed.

4. The dual-axis synchronous control method according to claim 1, characterized in that: The preset condition is that the torque difference between the first motor and the second motor is zero.

5. The dual-axis synchronous control method according to claim 1, characterized in that: The steps include: A pulse control signal is generated according to the torque difference data to control the first motor and / or the second motor to operate at the target operating parameters.

6. A dual-axis synchronous control device, characterized in that: It can execute the dual-axis synchronous control method according to claim 1, which includes: a torque data acquisition module, configured to acquire torque data of the first rotating shaft and the second rotating shaft respectively; a torque difference data determination module, configured to calculate, based on the torque data, torque difference data of a first motor and a second motor connected to the first rotating shaft and the second rotating shaft, respectively; A motor control module is used to control target operating parameters of the first motor and / or the second motor according to the torque difference data so that the torque difference between the first motor and the second motor meets a preset condition.

7. A dual-axis synchronous motion device, characterized in that: It can execute the dual-axis synchronous control method according to claim 1, which includes: a drive assembly comprising a first drive unit and a second drive unit, wherein the first drive unit comprises a first rotating shaft and a first motor connected to each other, and the second drive unit comprises a second rotating shaft and a second motor connected to each other; a torque detection assembly comprising a first torque sensor and a second torque sensor respectively disposed on the first rotating shaft and the second rotating shaft; The motor drive component includes a first driver and a second driver respectively provided on the first motor and the second motor. The motor drive component is used to drive the motor to operate according to target operating parameters determined by the torque data obtained by the torque detection component.

8. The dual-axis synchronous motion device according to claim 7, characterized in that: It also includes a main controller, which is electrically connected to the torque sensor in the torque detection component and the driver in the motor control component.

9. The dual-axis synchronous motion device according to claim 8, characterized in that: It also includes a signal converter assembly, which includes a first signal converter arranged on the electrical connection circuit between the first torque sensor and the main controller, and a second signal converter arranged on the electrical connection circuit between the second torque sensor and the main controller.

10. The dual-axis synchronous motion device according to claim 7, characterized in that: An encoder assembly is also included, which includes a first encoder and a second encoder respectively arranged on the first motor and the second motor.

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