JP2012076188A - Parallel link mechanism and driving stage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve position accuracy of a table of a parallel link mechanism.SOLUTION: The parallel link mechanism 1 is provided with: a base 2; a table 3 having six degrees of freedom for the base 2 and arranged to face the base 2 ; a plurality of connection parts 10 having an expandable rod 4 whose one end is attached to the base 2 and the other end is attached to the table 3; and a plurality of sensor parts 14 used for calculating the position of the table 3. The sensor part 14 has a wire 12 whose one end is attached to the base 2 and the other end is attached to the table 3 and a sensor 13 for measuring the length of the wire 12.

Description

  The present invention relates to a technique effective when applied to a parallel link mechanism and a drive stage including the parallel link mechanism.

  A link mechanism in which six rods are connected by a joint, which is a closed link connected by a joint, is called a six-axis parallel link mechanism. Japanese Patent No. 4519941 (Patent Document 1) describes a technique related to a 6-axis parallel link mechanism.

  Japanese Patent Application Laid-Open No. 10-180674 (Patent Document 2) describes a technique related to feedback control of a 6-axis parallel link mechanism. The parallel link mechanism of Patent Document 2 performs feedback control of an actuator (rod) so that the position and posture of an end effector detected by a sensor coincide with a command value. Thereby, it is supposed that the position and posture of the end effector can be accurately controlled (paragraph [0110] of the specification of Patent Document 2).

  Japanese Patent Laid-Open No. 11-10575 (Patent Document 3) describes a technique related to feedback control of a three-axis parallel link mechanism. In the parallel link mechanism of Patent Document 3, feedback control that incorporates detected values of the amount of axial movement and the tilt angle around two axes of one end connected to the center of the end plate and the other end connected to the center of the base plate. Is done. Thereby, it is supposed that the position accuracy of the end effector can be accurately controlled (paragraph [0015] in the specification of Patent Document 3). However, the three-axis parallel link mechanism is different in configuration from the six-axis parallel link mechanism and cannot be easily applied to the six-axis parallel link mechanism.

Japanese Patent No. 4519941 Japanese Patent Laid-Open No. 10-180674 JP-A-11-10575

  The inventors of the present invention have a stage (hereinafter referred to as 6-axis driving) driven by a total of 6 axes including 3 axes of an orthogonal coordinate system (X axis, Y axis, Z axis) and 3 axes of a polar coordinate system (θx, θy, θz). We are studying the application of a parallel link mechanism. This 6-axis drive stage can be applied to, for example, a microscope stage and a precision processing machine.

  Since the conventional 6-axis drive stage is a combination of, for example, a 1-axis drive stage, the size is large and the cost is high. On the other hand, if a parallel link mechanism can be applied as a drive mechanism, a 6-axis drive stage can be provided compactly and at a low price. Further, by applying a parallel link mechanism to the drive stage, the stage can be a fine movement stage that can be driven with high resolution and high accuracy of, for example, 1 μm or less.

  FIG. 1 is a side view schematically showing a parallel link mechanism 101 studied by the present inventors. The parallel link mechanism 101 has 6 degrees of freedom with respect to the base 2, the base 2, and a plurality of parallel-arranged tables 3 that connect the table 3 and the base 2 to each other. The connection part 10 is provided. When the parallel link mechanism 101 is provided as a drive stage, the table 3 corresponds to the stage.

  Six connecting portions 10 are arranged so that the table 3 has six degrees of freedom. In the parallel link mechanism 101, the connection part 10 is arrange | positioned symmetrically about the axis | shaft A (one-dot chain line) which divided the base 2 and the table 3 into every 120 degrees (refer FIG. 3).

  The connecting portion 10 has a telescopic rod 4 having one end attached to the base 2 and the other end attached to the table 3. That is, the connecting portion 10 is provided on the extendable rod 4 and the table 3, the multi-degree-of-freedom joint 5 to which one end of the rod 4 is attached, and the base 2, and the other end of the rod 4 is attached. And a joint 6 with a degree of freedom. Here, the joint 5 is attached to the side surface of the table 3. The joint 6 is attached to the base via a block that stands up from the base 2.

  As the rod 4 that can expand and contract in one direction, for example, it is conceivable to use an actuator 4 (electric cylinder) having a ball screw, a linear guide, and a motor. This actuator 4 converts the rotation of the motor into a linear motion using a ball screw. Control of the actuator 4 can be performed by the parallel link mechanism 101 or an arithmetic processing device provided in a casing provided with the parallel link mechanism 101. FIG. 1 shows a case where the arithmetic processing device 7 is provided on the lower surface of the base 2.

  As the joints 5 and 6, for example, it is conceivable to use spherical bearings that hold steel balls in a spherical shape and can move with multiple degrees of freedom. When a spherical bearing is used, steel balls are connected to both ends of the actuator 4, and a race (receiving portion) is formed so as to wrap the steel balls.

  In the parallel link mechanism 101 having such a configuration, the position (attitude including tilt) of the table 3 can be determined by the six connecting portions 10. Even if the length of each connecting portion 10 (length of the actuator 4) is expanded or contracted, the position of the table 3 can be determined by stopping the operation of the actuator 4. That is, the parallel link mechanism 101 can freely move the posture (position) of the table 3 by controlling the length of the six actuators 4 to expand and contract in the axial direction (one direction). From this, the some connection part 10 functions also as a drive part of the parallel link mechanism 101. FIG.

  However, the present inventors have found that the position of the table 3 of the parallel link mechanism 101 is not fixed. For example, when an object is mounted on the table 3 and driven, a load is applied to the table 3 from the outside, and the force is applied to each of the six actuators 4 and the upper and lower joints 5 and 6 that connect the actuators 4. It will take. For this reason, the actuator 4 is deformed (for example, deflection) or the joints 5 and 6 are deformed (for example, crushed) due to external factors such as compression load or tensile load. Therefore, it is considered that the position of the table 3 is not fixed when the connecting portion 10 that connects the base 2 and the table 3 is deformed.

  It is also conceivable that the position of the table 3 is not fixed due to the backlash of the ball screw of the actuator 4. Further, it is conceivable that the spherical bearings used as the joints 5 and 6 have a gap between the steel balls and the race, and thus play occurs and the position of the table 3 is not fixed. Even if a high performance actuator with reduced backlash is used as the actuator 4, it is considered that backlash cannot be completely eliminated. Further, even if a high-performance spherical bearing with reduced backlash is used, it is considered that the backlash cannot be completely eliminated.

  The objective of this invention is providing the technique which can improve the position accuracy of the table of a parallel link mechanism. The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  Of the inventions disclosed in the present application, the outline of typical ones will be briefly described as follows. A parallel link mechanism according to an embodiment of the present invention has a base, a table having six degrees of freedom with respect to the base, a table arranged opposite to the base, one end attached to the base, and the other end A plurality of connecting portions having extendable rods attached to the table; and a plurality of sensor portions used for calculating the position of the table. Here, the sensor unit includes a wire having one end attached to the table and the other end attached to the base, and a sensor for measuring the length of the wire.

  Of the inventions disclosed in the present application, effects obtained by typical ones will be briefly described as follows. The position accuracy of the table of the parallel link mechanism can be improved.

It is a side view which shows typically the parallel link mechanism which the present inventors are examining. It is a side view which shows typically the parallel link mechanism in one Embodiment of this invention. FIG. 3 is a top view schematically showing the parallel link mechanism shown in FIG. 2. It is a block diagram which shows the control system of the parallel link mechanism shown in FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiments, and the repetitive description thereof may be omitted.

  First, the configuration of the parallel link mechanism 1 in the embodiment of the present invention will be described with reference to the drawings. FIG. 2 schematically shows a side surface of the parallel link mechanism 1, and FIG. 3 schematically shows an upper surface thereof. When the parallel link mechanism 1 is provided as a drive stage, the table 3 corresponds to the stage. Since the basic configuration of the parallel link mechanism 1 is the same as that of the parallel link mechanism 101 described with reference to FIG. 1, the same reference numerals are given to the same and the description thereof is omitted.

  In addition to the basic configuration, the parallel link mechanism 1 includes a plurality of sensor units 14 that use the position of the table 3 for calculation. The parallel link mechanism 1 is a six-axis parallel link mechanism, and six sensor units 14 are arranged to calculate the position of the table 3.

  In this embodiment, the sensor part 14 is arrange | positioned symmetrically about the axis | shaft B (two-dot chain line) which divided the base 2 and the table 3 every 120 degrees (refer FIG. 3). Further, six sensor portions 14 are arranged adjacent to each of the six connecting portions 10. For this reason, the expansion / contraction amount of the connecting part 10 is measured by the sensor part 14 corresponding to the connecting part 10. In other words, the sensor unit 14 also measures the distance between the base 2 and the table 3 at predetermined six locations. In the parallel link mechanism 1, the position of the table 3 can be calculated with reference to the measurement value of the sensor unit 14. Note that the arrangement position of the sensor unit 14 is not limited to this, and may be any arrangement that can accurately obtain the measurement value for calculating the position of the table 3.

  Each of the six sensor units 14 includes a wire 12 having one end attached to the base 2 and the other end attached to the table 3, and a sensor 13 that measures the length of the wire 12. One end of the wire 12 is attached to the table 2 via a sensor 13 fixed to the base 2. The other end of the wire 12 is fixed by the wire fixing portion 11 and attached to the side surface of the table 3. The wire 12 is attached with a minimum tension that does not sag.

  In the parallel link mechanism 1, the length of the six wires 12 can be measured, and the position of the table 3 can be calculated by referring to the length. As described above, the position of the table 3 can be set by controlling the length of the connecting portion 10. The position of this table 3 is a set value. On the other hand, the actual position of the table 3 can be grasped by calculating from the measurement value of the sensor unit 14. The position of this table 3 is an actual measurement value.

  In this embodiment, one end of the wire 12 is attached to the base 2 and the other end is attached to the table 3. Since the wire 12 has flexibility, it is considered that each attached end itself functions as a bearing having multiple degrees of freedom. For this reason, there is no play like a spherical bearing used as joints 5 and 6.

  Therefore, the position of the table 3 can be accurately calculated by measuring the length of the wire 12. In addition, since the moving range of the table 3 is fixed with respect to the base 2 by the connecting portion 10, the tensile load on the wire 12 is small within the range, and there is no fear that the wire 12 extends.

  The parallel link mechanism 1 in the present embodiment includes a sensor unit 14 having a wire 12 coupled to the base 2 and the table 3 even when the coupling unit 10 that couples the base 2 and the table 3 is deformed due to an external cause. Thus, the actual position of the table 3 can be grasped. Further, if the actual position of the table 3 can be grasped, the position of the table 3 of the parallel link mechanism 1 can be corrected, so that the position accuracy of the table 3 can be improved.

  In the present embodiment, as the wire 12 and the sensor 13, a wire type linear encoder fixedly attached to the base 2 is used. In this wire type linear encoder, a wire is wound around a drum, the amount of rotation of the drum when the wire is pulled out is detected by a rotary encoder, and the amount of wire drawn is measured.

  The linear encoder (sensor 13) side is one end of the wire 12, and the other end of the wire 12 extending from the linear encoder is attached to the table 3. The wire-type linear encoder has a mechanism for winding the wire 12 while pulling it, and includes a sensor 13 for measuring the length of the wire 12. With this winding mechanism, the wire 12 is subjected to a minimum tension that does not sag. The winding mechanism can be pulled out in addition to winding the wire 12.

  By using the wire type linear encoder, the length of the wire 12 directly, that is, the distance from the wire fixing part 11 fixed to the table 3 to the wire type linear scale (sensor 13) fixed to the base 2 can be accurately determined. It can be measured. Thus, accurately measuring the length of the wire 12 is an important factor in improving the positional accuracy of the table 3 of the parallel link mechanism 1.

  Next, the control operation of the parallel link mechanism 1 will be described with reference to the drawings. FIG. 4 shows a flow of control operation of the parallel link mechanism 1. The parallel link mechanism 1 includes the sensor unit 14 so that the position of the table 3 calculated from the measured value of the sensor unit 14 is compared with the position of the table 3 determined from the length of the rod 4 (actuator 4). Control can be performed.

  First, the arithmetic processing unit 7 that receives the position command (S1) of the table 3 with the six-axis parameters as inputs calculates the expansion / contraction amount (movement amount) of each actuator 4 (S2). Since the position of the table 3 is determined from the six-axis parameters, the length (expansion / contraction amount) of the actuator 4 is calculated so as to be at this position.

  Subsequently, the arithmetic processing unit 7 outputs the calculated amount of expansion / contraction and drives each actuator 4 (S3). The posture of the table 3 changes due to the expansion and contraction of the actuator 4, and this change is measured by the sensor 13 (linear encoder). The position of the table 3 is acquired from the measured value by the arithmetic processing unit 7 (S4).

  Here, the position of the table 3 that has been commanded is compared with the actual position of the table 3 (S5). Specifically, the 6-axis parameters for which the position is commanded are compared with the 6-axis parameters calculated from the actual position of the table 3. If the commanded position is different from the actual position, the position of the table 3 is corrected by the difference so that the commanded position is obtained. In this way, feedback control is performed in which the position of the table 3 calculated from the measurement value of the sensor unit 14 is compared with the position of the table 3 determined from the length of the actuator 4.

  It is generally known that closed link kinematics can be analyzed by iterative processing (feedback control). In the present embodiment, the accurate position of the table 3 relative to the base 2 can be derived by calculation by providing the sensor unit 14 and measuring six distances between the base 2 and the table 3. That is, in the parallel link mechanism 1 including the sensor unit 14, the position accuracy of the table 3 can be improved.

  In the technique of Patent Document 2, a distance sensor and an angle sensor are embedded in an actuator and bearing unit as a feedback control sensor. For this reason, an error factor outside the sensor (for example, deformation or backlash of the bearing) cannot be corrected. On the other hand, in the parallel link mechanism 1, the coordinates of the table 3 are acquired from the measurement values of the sensor unit 14 which is another configuration that is not affected by the deformation of the rod 4 and the joints 5 and 6, and the posture of the table 3 is changed. It can be corrected. Therefore, according to the present invention, the positional accuracy of the table 3 can be improved as compared with the technique of Patent Document 2.

  Although the present invention has been specifically described above based on the embodiments, it is needless to say that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention.

  For example, in the above-described embodiment, the case where an actuator (for example, an electric cylinder) constituting the plurality of connecting portions 10 is applied as the driving portion of the table 3 of the parallel link mechanism 1 has been described. May be. This is because the position accuracy of the table 3 of the parallel link mechanism 1 can be improved by applying a plurality of sensor units 14 having a different configuration from the drive unit.

1, 101 Parallel link mechanism (drive stage)
2 base 3 table (stage)
4 Rod (actuator)
5, 6 Joint 7 Arithmetic processing device 10 Connecting portion 11 Wire fixing portion 12 Wire 13 Sensor (linear encoder)
14 Sensor part

Claims (4)

Base and
A table having six degrees of freedom with respect to the base and disposed opposite the base;
A plurality of connecting portions having extendable rods having one end attached to the base and the other end attached to the table;
A parallel link mechanism comprising a plurality of sensor units used for calculating the position of the table,
The sensor unit includes a wire having one end attached to the base and the other end attached to the table, and a sensor for measuring the length of the wire. The parallel link mechanism according to claim 1, wherein
A parallel link mechanism that performs feedback control for comparing the position of the table calculated from the measurement value of the sensor unit with respect to the position of the table determined from the length of the rod. The parallel link mechanism according to claim 1 or 2,
The sensor unit is a linear encoder attached to the base,
The parallel link mechanism, wherein the wire extends from the linear encoder and has one end attached to the table.   A drive stage comprising the parallel link mechanism according to claim 1, 2 or 3.

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