A tool relocation device and a screw tightening device equipped with the same.

Abstract

The present invention provides a tool moving device that can impart a desired thrust to a tool unit. [Solution] The tool moving device 20 comprises a reciprocating movement unit 40 that moves a tool unit 50 that performs a predetermined operation closer to and further away from a workpiece, a moving motor that drives the reciprocating movement unit 40, and a control device capable of controlling the drive of the moving motor. The control device has a torque command unit that controls the value of the current supplied to the moving motor so that the moving motor outputs a predetermined command torque. The command torque is created by a drive load estimation step of estimating a drive load offset torque, a self-weight load estimation step of estimating a self-weight load offset torque, and a calculation step of adding the drive load offset torque and the self-weight load offset torque to a desired torque corresponding to a desired thrust applied to the tool unit 50.

Description

Technical Field

[0001] The present invention relates to a tool moving device for moving a tool unit that performs a predetermined operation, and a screwing device provided with the same device.

Background Art

[0002] Conventionally, as an example of a tool moving device including a tool unit having a tool for performing a predetermined operation on a workpiece and a reciprocating moving unit for moving this tool unit, a screwing device disclosed in Patent Document 1 is known. This screwing device includes a screwing unit including a driver bit that fits with a screw and a tightening motor that rotationally drives the driver bit, and a tool moving device that reciprocates the screwing unit in the axial direction of the driver bit. The tool moving device includes a driver base that holds the screwing unit, a ball screw that approaches or separates the driver base from the workpiece, and a moving motor that drives the ball screw. The tool moving device of this screwing device is torque-limited so that the moving motor does not output a rotational torque of a predetermined limit torque abnormality, and is controlled so that the driver bit does not press the screw against the workpiece with an excessive thrust.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, since the conventional tool moving device has a configuration that limits the rotational torque of the moving motor as described above, the self-weight of the tool unit, the drive nut of the ball screw, etc. is transmitted to the screwing tool. For this reason, there are problems such as not being able to apply a low thrust below the self-weight.

[0005] Therefore, the present invention aims to provide a tool moving device that can impart a desired thrust to a tool unit.

[0006] To achieve this objective, the present invention provides a tool moving device for moving a tool unit that performs a predetermined operation on a workpiece, comprising: a reciprocating moving unit for moving the tool unit closer to or further away from the workpiece; a moving motor for driving the reciprocating moving unit; and a control device capable of controlling the driving of the moving motor, wherein the control device has a torque command unit that controls the torque so that the moving motor outputs a desired command torque, and the command torque is created from a drive load estimation step of estimating a drive load offset torque that offsets the drive load of the reciprocating moving unit; a self-weight load estimation step of estimating a self-weight load offset torque that offsets the self-weight load generated by the self-weight of the tool unit; and a calculation step of adding the drive load offset torque and the self-weight load offset torque to a desired torque that is set in advance to correspond to a desired thrust applied to the tool unit. In addition, it is preferable that in the drive load estimation step, the entire range of motion of the reciprocating movement unit is divided into a number of minute sections, and the drive load offsetting torque is estimated for each of these minute sections. Furthermore, it is preferable that the drive load estimation step involves the reciprocating movement unit moving the tool unit back and forth, acquiring the load torque for each minute interval during forward and reverse movement, and estimating the drive load from the load torque during forward and reverse movement. Furthermore, in the self-weight load estimation step, it is preferable that the reciprocating movement unit reciprocates the tool unit in the forward and backward directions, and that the load torque immediately before movement begins is obtained at both the front and rear ends of the reciprocating movement, and that the self-weight of the tool unit is calculated from the load torques obtained at the front and rear ends. Furthermore, it is preferable that the reciprocating movement unit is equipped with an articulated robot capable of moving it to any position and orientation, and that the control device controls the reciprocating movement unit to perform the self-weight load estimation process when the articulated robot is driven.

[0007] Furthermore, a second object of the present invention is to provide a screw tightening device that can impart a desired thrust to a tool unit. To achieve this objective, the present invention provides a screw tightening device comprising: a screw tightening tool that can engage with a screw; a tool unit having a tightening motor for rotationally driving the screw tightening tool; a reciprocating movement unit for moving the tool unit closer to or away from a workpiece; a movement motor for driving the reciprocating movement unit; and a control device capable of controlling the drive of the movement motor, wherein the control device includes a torque command unit that controls the torque so that the movement motor outputs a desired command torque, characterized in that the command torque is created from a drive load estimation step of estimating a drive load offset torque that offsets the drive load of the reciprocating movement unit; a self-weight load estimation step of estimating a self-weight load offset torque that offsets the self-weight of the tool unit; and a calculation step of adding the drive load offset torque and the self-weight load offset torque to a desired torque that is set in advance to correspond to a desired thrust applied to the tool unit. [Effects of the Invention]

[0008] According to the above invention, since the motor that moves the tool unit is feedback controlled to output a predetermined command torque, a desired thrust can be applied to the tool unit. Moreover, since the command torque is set to a value that is the sum of the desired thrust, the thrust that offsets the drive load of the reciprocating movement unit, and the thrust that offsets the weight of the tool unit, when the command torque is output, the weight of the tool unit is not applied to the workpiece, which has advantages such as preventing damage to the workpiece. Similarly, since there is no torque loss due to the drive load, there are advantages such as not having insufficient thrust. Furthermore, since the command torque is obtained by dividing the stroke of the ball screw into minute sections and acquiring the drive load for each minute section, it can also respond to changes in the drive load at each position. Therefore, it is possible to precisely apply only the desired thrust to the tool unit. Furthermore, the control unit has a position command unit and an operation command unit, and the operation command unit switches between position control that enables high-speed movement of the tool unit and torque control that enables the application of a desired thrust to the tool unit at the switching position. This offers advantages such as a shorter cycle time and the ability to apply a desired thrust. Furthermore, since it has a multi-joint robot and the reciprocating movement unit performs the self-weight load estimation process when the multi-joint robot is driven, it has advantages such as being able to move the tool unit to any position and orientation, and being able to immediately set an appropriate command torque regardless of the position and orientation it is moved to.

[0009] Furthermore, according to the second invention described above, the thrust force applied by the screw tightening tool to the screw and workpiece can be reduced, which has advantages such as preventing damage to the screw and workpiece. [Brief explanation of the drawing]

[0010] [Figure 1] This is a front view showing the structure of a screw tightening device according to the present invention. [Figure 2] This is a front view showing the structure of a screw tightening device according to the present invention. [Figure 3] This is a side view showing the structure of a screw tightening device according to the present invention. [Figure 4] This is a partial cross-sectional side view showing the structure of a screw tightening device according to the present invention. [Figure 5] This is a block diagram showing the configuration of the control device for a screw tightening device according to the present invention. [Figure 6] This graph shows the changes in various parameters of the screw tightening device according to the present invention. [Figure 7] This is an enlarged, partially cutaway cross-sectional view illustrating the operation of the screw tightening device according to the present invention. [Figure 8] This is a schematic diagram illustrating the command torque table for the screw tightening device according to the present invention. [Modes for carrying out the invention]

[0011] Embodiments of the present invention will now be described with reference to the drawings. In Figure 1, 10 is a screw tightening device for fastening a screw S to a workpiece 90. This screw tightening device 10 includes a tool moving device 20, a tool unit 50 that moves in response to the drive of the tool moving device 20, and a control device 80 that controls the drive of these. In this embodiment, the screw S is a general screw S in which a head with a Phillips-shaped drive hole and a shaft portion with screw threads formed on its outer circumference are integrally formed, and is configured to be screwed into an internal thread 91 formed in the workpiece 90.

[0012] The tool moving device 20 consists of a multi-joint robot 30 and a reciprocating movement unit 40 fixed to the tip of the multi-joint robot 30. The multi-joint robot 30 is equipped with a plurality of arms 31 and a plurality of joints 32 connecting these arms 31. Each joint 32 is provided with an arm swing drive source (not shown) that swings the arm 31 around the joint 32 and an arm rotation drive source (not shown) that rotates the arm 31 around the joint 32. These drive sources are connected to the control device 80, and their drive is controlled by the control device 80. With this structure, the multi-joint robot 30 can arbitrarily move the position and orientation of the reciprocating movement unit 40 attached to the tip arm 31.

[0013] As shown in Figure 4, the reciprocating movement unit 40 includes a base 41 fixed to the tip of the articulated robot 30. This base 41 extends in the front-rear direction, with a motor base 42 fixed to its rear end and a chuck base 43 fixed to its front end. A guide rod 44 is provided between the motor base 42 and the chuck base 43, and a driver base 45 is guided on this guide rod 44 so as to be slidable in the front-rear direction. A drive nut 46 is fixed to the driver base 45, and a ball screw 47 extending parallel to the guide rod 44 is screwed onto this drive nut 46. This ball screw 47 is rotatably held by the motor base 42 and the chuck base 43, and an AC servo motor 48 (hereinafter referred to as the movement motor 48) that rotates the ball screw 47 is mounted on the motor base 42. With this structure, when the movement motor 48 is driven, the drive nut 46 and the driver base 45 move in the front-rear direction along the ball screw 47. Furthermore, the moving motor 48 has an encoder 49 that can emit pulse signals corresponding to the rotation angle of the output shaft of the moving motor 48, and this encoder 49 is connected to the control device 80.

[0014] As shown in FIG. 4, the tool unit 50 has an AC servo motor 51 (hereinafter referred to as the tightening motor 51) placed on the driver base 45. The output shaft of the tightening motor 51 is provided to penetrate the driver base 45. The tightening motor 51 has a measuring means (not shown) capable of measuring the rotational torque output by the tightening motor 51, and this measuring means is connected to the control device 80. Also, a driver bit 55, which is an example of a tool, is connected to the output shaft of the tightening motor 51 via a shaft coupling 52. A fitting portion 56 that can be fitted into the drive hole of the screw S is formed at the tip of the driver bit 55. The shaft coupling 52 has an insertion hole 53 into which the base end portion of the driver bit 55 is inserted, and a cushion spring 54 that constantly biases the driver bit 55 forward is enclosed in the insertion hole 53. Therefore, when the driver bit 55 is biased toward the tightening motor 51 side, it can move relative to the tightening motor 51 and the shaft coupling 52 in the axial direction while bending the cushion spring 54.

[0015] Also, the tool unit 50 has a holding sleeve 61 fixed to the front surface of the driver base 45. A hollow cylindrical screw guide 62 that rotatably houses the driver bit 55 is inserted into the holding sleeve 61 so as to be axially relatively movable. A hose coupling 63 is attached to the screw guide 62. An intake hose (not shown) is connected to the hose coupling 63, and an intake means such as an external vacuum generator is connected to the other end of the intake hose. Therefore, when the intake means is driven, the inside of the screw guide 62 becomes a negative pressure, and the screw S can be adsorbed and held at the front end opening of the screw guide 62. The screw guide 62 is constantly biased forward by a guide spring 64 enclosed therein, and is configured to be axially relatively movable with respect to the holding sleeve 61 and the driver bit 55 while bending the guide spring 64.

[0016] Furthermore, as shown in FIGS. 2 and 3, the tool unit 50 has a cable carrier 58. One end of this cable carrier 58 is fixed to the driver base 45, while the other end is fixed to the base 41. Inside it, wiring connecting the tightening motor 51 and the control device 80, an intake hose, and the like are inserted. As the tool unit 50 moves forward, the cable carrier 58 deforms as shown by the two-dot chain line in FIG. 3. Since wiring and an intake hose are inserted into this cable carrier 58, the postures of the wiring and the intake hose become constant each time the tool unit 50 moves forward and backward. As a result, the loads on the wiring and the intake hose caused when the tool unit 50 moves forward and backward can be made constant each time.

[0017] Moreover, in front of the tool unit 50, a chuck unit 70 capable of holding a screw S pumped from an external component supply device is provided. This chuck unit 70 has a chuck body 71 fixed on the moving paths of the screw guide 62 and the driver bit 55. In this chuck body 71, a guide hole 72 that encloses the tip of the screw guide 62 is formed through. Also, a pair of chuck jaws 73, 73 are swingably attached to the chuck body 71. On the opposing surfaces of these chuck jaws 73, 73, holding holes 74 capable of holding the screw S and located on the extension line of the guide hole 72 are formed in a divided manner. Furthermore, a supply pipe 75 swingable in a direction orthogonal to the swing surfaces of the chuck jaws 73, 73 is provided on the chuck body 71. The tip of this supply pipe 75 is configured to be continuous with the holding hole 74 and block the opening of the guide hole 72. On the other hand, on the base end side, a screw supply hose joint 76 to which a screw supply hose (not shown) is connected is continuous, and the screw supply hose is continuous to a component supply device (not shown). For this reason, the screw S pumped from the component supply device is configured to be supplied to the holding hole 74 through the screw supply hose and the supply pipe 75.

[0018] The chuck body 71 is fitted with a regulating plate 77 that can swing in conjunction with the supply pipe 75. The tip of the regulating plate 77 is provided with regulating claws 78, 78 that contact the outer surfaces of the chuck jaws 73, 73 when closed, and restrict the swinging of the chuck jaws 73, 73. These regulating claws 78, 78 swing in accordance with the supply pipe 75, gradually moving away from the chuck jaws 73, 73, and are set to completely move away from the chuck jaws 73, 73 before the screw guide 62 begins to push the chuck jaws 73, 73 open. Furthermore, the supply pipe 75 and the regulating plate 77 are constantly biased toward the chuck jaws 73, 73 by a torsion coil spring 79, and the torsion coil spring 79 elastically deforms in accordance with the swinging of the supply pipe 75 and the regulating plate 77.

[0019] As shown in Figure 5, the control device 80 consists of a drive control unit 81 that outputs various signals, a robot control unit 82 that controls the drive of the articulated robot 30, a mobile motor control unit 83 that controls the drive of the mobile motor 48, and a tightening motor control unit 87 that controls the drive of the tightening motor 51 of the tool unit 50.

[0020] The drive control unit 81 is connected to the robot control unit 82, the tightening motor control unit 87, and the moving motor control unit 83, as well as to external devices such as the parts supply device, the intake means, and input devices capable of receiving various data. It is configured to control the drive by inputting and outputting various signals to and from these connected devices. The drive control unit 81 also stores an operation program and various control parameters.

[0021] The robot control unit 82 is connected to the arm swing drive source and the arm rotation drive source of the articulated robot 30, and by controlling these drives, the reciprocating movement unit 40 can be moved to any position and orientation.

[0022] The moving motor control unit 83 includes an operation command unit 84 for driving the moving motor 48, and a position command unit 85 and a torque command unit 86 provided between the operation command unit 84 and the moving motor 48. The operation command unit 84 controls the driving of the moving motor 48 using the position command unit 85 and the torque command unit 86. The encoder 49 of the moving motor 48 is connected to the operation command unit 84, and the amount of movement of the driver base 45, i.e., the movement position of the tool unit 50, can be determined from the pulse signal output by the encoder 49 (rotation angle of the moving motor 48) and the lead of the ball screw 47. The operation command unit 84 is also configured to detect the load current value supplied to the moving motor 48 and to control the current value supplied to the moving motor 48. By controlling the current value supplied to the moving motor 48 in this way, the output torque of the moving motor 48, i.e., the thrust applied to the tool unit 50 as it moves with the rotation of the ball screw 47, can be controlled.

[0023] Furthermore, the operation command unit 84 is configured to control the drive of the tightening motor 51 via the position command unit 85 while the tool unit 50 moves from the rear end of the ball screw 47 as shown in Figure 2 to position Z1 (hereinafter referred to as the switching position Z1) just before the tip of the screw guide 62 shown in (Z1) of Figure 7 collides with the workpiece 90, and to control the drive of the tightening motor 51 via the torque command unit 86 while the tool unit 50 moves from the switching position Z1 to a stop position Z4 set a predetermined dimension forward from the position where the screw S shown in (Z3) of Figure 7 sits (hereinafter referred to as the seating position Z3).

[0024] The position command unit 85 controls the position of the driver stand 45 by controlling the amount of rotation of the moving motor 48, and is configured to move the driver stand 45 at high speed from the standby position toward the target position Z1b which is set toward the stop position Z4 from the switching position Z1. The position command unit 85 limits the current value supplied to the moving motor 48 so that the output torque of the moving motor 48 is less than or equal to a preset upper limit torque. The position command unit 85 also monitors the position of the tool unit 50 throughout the entire movable range of the ball screw 47, and is configured to stop the drive of the moving motor 48 when the tool unit 50 moves forward to the stop position Z4, as shown in (Z4) of Figure 7. This prevents the tool unit 50 from moving outside the preset movable range.

[0025] The position command unit 85 is configured to gradually reduce the movement speed of the tool unit 50 from a deceleration start position Z1a, which is set behind the target position Z1b as shown in the upper part of Figure 6, to the target position Z1b, according to a predetermined deceleration rate, in order to stop the tool unit 50 at the target position Z1b. The deceleration start position Z1a and the target position Z1b are positioned such that when the tool unit 50 reaches the switching position Z1, the movement speed of the tool unit 50 has been reduced to the speed limit value of the torque command unit 86, which will be described later. In this way, since the target position Z1b and the deceleration start position Z1a are set, when the tool unit 50 reaches the switching position Z1, the control of the movement motor 48 can be switched from the position command unit 85 to the torque command unit 86 without stopping the tool unit 50. As a result, the tool unit 50 can be moved faster by the hatched region H compared to a control method in which the tool unit 50 is stopped at the switching position Z1, shown by the dashed line in the upper part of Figure 6, and then switched from position control to torque control. This shortens the cycle time.

[0026] The torque command unit 86 controls the current supplied to the moving motor 48 according to a pre-generated command torque table so that the moving motor 48 outputs a command torque Tsn, which will be described later, and is configured to move the driver stand 45 to the target position Z1b with a desired thrust. In addition, the torque command unit 86 limits the rotational speed of the moving motor 48 so that the tool unit 50 does not move at excessively high speeds.

[0027] The tightening motor control unit 87 is connected to the tightening motor 51 and is configured to switch between driving and stopping the tightening motor 51 according to the load current value of the tightening motor 51. In other words, when tightening a screw, the tightening motor control unit 87 determines whether the screw S has been tightened to a predetermined tightening torque based on the load current value of the tightening motor 51, which increases in proportion to the increase in tightening torque, and is configured to stop driving the tightening motor 51 when the load current reaches a predetermined value set in advance.

[0028] The command torque table will be described below. The command torque table is one of the control parameters, and divides the movable range of the ball screw 47 into minute intervals In, and sets a rotational torque Tsn (hereinafter referred to as command torque Tsn) to be output by the moving motor 48 for each minute interval In. This command torque Tsn is set to a value obtained by summing a desired torque Ton corresponding to a desired thrust, a drive load offset torque Trn that offsets the reaction force (hereinafter referred to as drive load Rn) generated by dynamic friction and springs when driving the minute interval In, and a self-weight load offset torque Tw that offsets the load Rw (hereinafter referred to as self-weight load Rw) generated by the self-weight W of the tool unit 50 and driver stand 45 etc. that hinders or enhances the driving of the moving motor 48.

[0029] Next, the method for setting the command torque Tsn will be explained. The command torque Tsn is created by a drive load estimation step for estimating the drive load offset torque Trn, a self-weight load estimation step for estimating the self-weight load offset torque Tw, and a calculation step for calculating the command torque Tsn by summing the drive load offset torque Trn and self-weight load offset torque Tw obtained in these steps with the desired torque Ton.

[0030] The desired torque Ton is set to the value obtained by dividing the product of the lead of the ball screw 47 and the desired thrust by the product of 2π and the efficiency of the ball screw 47, and is expressed as desired torque Ton = (lead of ball screw 47 × desired thrust) / (2π × torque transmission efficiency of ball screw 47). This desired thrust is set to gradually increase from the switching position Z1 as shown in the lower part of Figure 6, outputting excessive rotational torque immediately after switching with the position command unit 85, and preventing the forward speed of the tool unit 50 from exceeding the speed limit shown in the upper part. Furthermore, the maximum value of the desired thrust is set to a value at which the driver bit 55 does not cam out from the screw S when tightening the screw.

[0031] Next, the drive load estimation process will be described. First, the control device 80 drives the moving motor 48 to reciprocate the tool unit 50 from the standby position to the stopping position Z4 at a constant speed. During this reciprocating drive, the operation command unit 84 divides the movement range of the tool unit 50 into a number of minute sections In, and acquires the current value supplied to the moving motor 48 for each of these minute sections In, i.e., the load torque T1n, T2n output by the moving motor 48 (hereinafter referred to as the load torque T1n during forward movement and the load torque T2n during reverse movement).

[0032] The load torque T1n during forward movement and the load torque T2n during reverse movement are equal to the resultant force of the load Wn in the axial direction of the ball screw 47 due to the weight of the tool unit 50 and the drive load Rn between the various parts acting in the opposite direction to the direction of movement in the minute section In. These can be expressed mathematically as follows: T1n = Wn - Rn T2n = Wn + Rn This is the result. Furthermore, by eliminating Wn from these equations using the following procedure, the value of the drive load Rn can be estimated. T1n - T2n = (Fn - Rn) - (Fn - Rn) = -2Rn Rn = -(T1n - T2n) / 2 ····Equation 1 In other words, by substituting the forward load torque T1n and reverse load torque T2n obtained into Equation 1, the drive load Rn in the minute interval In can be estimated. Then, the drive load offsetting torque Trn is a value that offsets the drive load Rn estimated as described above, so a value is set that reverses the direction (positive or negative) of the drive load Rn.

[0033] When acquiring the drive load Rn, the difference in the rate of change between the load torque T1n during forward movement and the load torque T2n during reverse movement is large at locations where a load is applied only during forward movement, such as when the screw guide 62 pushes the chuck jaws 73, 73 apart or when the guide spring 64 is compressed. In such locations where the difference in the rate of change between the load torque T1n during forward movement and the load torque T2n during reverse movement is large and exceeds a preset threshold, the value of the load torque T1n during forward movement is adopted as the drive load Rn.

[0034] Next, the process of estimating the self-weight load will be explained. The operation command unit 84 drives the ball screw 47 while the tool unit 50 is waiting in a predetermined standby position, causing the tool unit 50 to reciprocate within a very small width of 1 mm or less. At this time, when the tool unit 50 begins to move toward the opposite end at the front and rear ends of the reciprocating movement, the operation command unit 84 monitors the current value supplied to the movement motor 48, calculates the difference between the current value supplied when stopped and the maximum value of the regenerative current, and obtains the load torques T3 and T4 (hereinafter referred to as the load torque T3 when moving forward and the load torque T4 when moving backward) output by the movement motor 48 at the start of movement from this difference.

[0035] The load torque T3 during forward movement and the load torque T4 during reverse movement are equal to the resultant force of the self-weight load Rw that constantly acts in the direction that lowers the tool unit 50, the maximum static friction force K between the various parts that acts in the opposite direction to the direction of tool movement, and a disturbance that is negligibly small compared to these. These can be expressed mathematically as follows: T3 ≈ Rw-K T4 ≈ Rw + K This is the result. Furthermore, the value of the self-weight load Rw can be estimated by eliminating K from the formula using the following procedure. T3 + T4 ≈ (Rw - K) + (Rw + K) = 2Rw Rw ≈ (T3 + T4) / 2 ... Formula 2 In other words, the self-weight load Rw can be estimated by substituting the load torque T3 during forward movement and the load torque T4 during reverse movement into Equation 2. Then, the self-weight load offsetting torque Tw is the value that offsets the self-weight load Rw estimated as described above, so it is set to a value that reverses the direction (positive or negative) of the self-weight load Rw.

[0036] Furthermore, during the self-weight load estimation process, the maximum static friction force K can also be estimated using the following procedure. The method for estimating the maximum static friction force K is described below. T3-T4≈(Rw-K)-(Rw+K)=-2K K ≈ -(T3 - T4) / 2 ····Equation 3 In other words, the maximum static friction force K can be estimated by substituting the load torque T3 during forward movement and the load torque T4 during reverse movement into Equation 3. The desired torque Ton and the drive load offsetting torque Trn are set so that their sum is greater than or equal to the maximum static friction force K in any minute interval In, thus ensuring that the tool unit 50 is always subjected to a thrust force greater than or equal to the maximum static friction force K. This allows the drive to be restarted from the position even if it stops midway through the drive.

[0037] In the calculation step, the desired torque Ton obtained in the above step, the drive load offset torque Trn for each minute interval In, and the self-weight load offset torque Tw are added together to calculate the command torque Tsn for each minute interval In.

[0038] Next, we will explain how to teach the screw tightening position to the moving motor control unit 83. During teaching, the motion command unit 84 controls the drive of the movement motor 48 via the torque command unit 86 over the entire range of motion of the ball screw 47, and is configured to set the desired torque Ton in the command torque table to 0. In this state, the articulated robot 30 is driven to move the reciprocating movement unit 40 to a predetermined position and orientation. At this time, the torque command unit 86 causes the reciprocating movement unit 40 to perform the self-weight load estimation process, obtains the self-weight load offset torque Tw immediately after the articulated robot 30 stops, and calculates the command torque Tsn from the self-weight load offset torque Tw. At this time, since the desired torque Ton is set to 0, the calculated command torque Tsn balances the self-weight load Rw and the drive load Rn. As a result, the tool unit 50 remains stationary until it is biased from the outside by an operator, etc., while sliding in the direction of bias when an operator biases it in any direction. As a result, the operator can move the tool unit 50 to the designated position with minimal force and teach the screw tightening position. Furthermore, since the tool unit 50 does not freefall even when the operator releases it, collisions with the workpiece 90 are prevented.

[0039] Next, the screw tightening process using the screw tightening device 10 configured as described above will be explained. In the screw tightening device 10, which is waiting with the desired torque Ton and drive load offset torque Trn input into the command torque table after the drive load estimation process has been performed in advance, when a drive signal is input to the articulated robot 30 moves the reciprocating unit 40 to a predetermined position and orientation. At this time, the reciprocating unit 40 performs a self-weight load estimation process, and when the articulated robot 30 stops, it acquires the self-weight load offset torque Tw. By performing the self-weight load estimation process while the articulated robot 30 is in motion, the self-weight load offset torque Tw can be immediately estimated regardless of the posture of the reciprocating unit 40, and the command torque Tsn suitable for the posture of the reciprocating unit 40 can be generated from the self-weight load offset torque Tw.

[0040] As described above, after the articulated robot 30 stops, the control device 80 drives the parts supply device to pressurize the screw S to the chuck unit 70. When the screw S is pressurized into the chuck unit 70, the motion command unit 84 drives the movement motor 48 via the position command unit 85, causing the tool unit 50 to move forward toward the target position Z1b. The control unit 80 also drives the tightening motor 51 simultaneously with the movement motor 48 to rotate the driver bit 55 and drives the vacuum generator to suck air from inside the screw guide 62. As a result, when the front end of the screw guide 62 enters between the chuck jaws 73, 73, the screw S held by these chuck jaws 73, 73 is held in place by suction inside the screw guide 62. At this time, as the driver bit 55 rotates, the fitting portion 56 of the driver bit 55 engages with the head of the screw S.

[0041] As described above, when the tool unit 50, which holds the screw S by suction, moves further forward, the screw guide 62 protrudes from the chuck unit 70. Subsequently, when the tool unit 50 reaches the deceleration start position Z1a, the reciprocating movement unit 40 gradually reduces the forward speed of the tool unit 50. When this decelerated tool unit 50 reaches the switching position Z1, the operation command unit 84 switches the control of the movement motor 48 from the position command unit 85 to the torque command unit 86. At this time, since the speed of the tool unit 50 has been reduced to below the speed limit of the torque command unit 86 before reaching the switching position Z1, there is no sudden braking immediately after the switch, and the movement speed of the tool unit 50 is not reduced to below the speed limit set by the torque command unit 86. On the other hand, since the torque command unit 86 is configured to gradually increase the desired thrust after the switch, there is no sudden acceleration immediately after the switch. As a result, the control of the movement motor 48 can be smoothly switched from the position command unit 85 to the torque command unit 86, preventing the tool unit 50 from colliding with the workpiece 90, etc.

[0042] Subsequently, as the tool unit 50 moves further forward, the tip of the screw guide 62 comes into contact with the workpiece 90, as shown in (Z2) of Figure 7, at which point only the screw guide 62 stops moving forward. As a result, the driver bit 55 moves forward inside the screw guide 62, bending the guide spring 64, and presses the screw S toward the workpiece 90. The screw S then comes into contact with the workpiece 90 and rotates integrally with the driver bit 55 to fasten to the workpiece 90.

[0043] During the aforementioned screw tightening, the moving motor 48 is feedback controlled to output the command torque Tsn stored in the command torque table. At this time, as described above, the command torque Tsn is set to the resultant force of the desired torque Ton, the drive load offsetting torque Trn, and the self-weight load offsetting torque Tw, and the self-weight load Rw and drive load Rn are offset, so the driver bit 55 can be biased with the desired torque Ton. In this way, the self-weight of the tool unit 50 is prevented from being applied to the screw S, thus preventing damage to the screw S or the threads of the workpiece 90. In addition, excessive thrust such as the self-weight of the tool unit 50 is applied to the screw S via the driver bit 55 immediately after the screw S and the workpiece 90 begin to screw together, which can prevent the screw S from moving diagonally. Furthermore, since the drive load due to dynamic friction force and spring reaction force is also offset, it is prevented that the thrust applied to the screw S will not change due to fluctuations in such loads. Furthermore, the wiring and intake hose connecting the mobile motor 48 and the control device 80 are housed in the cable carrier 58 and are configured to bend as a single unit, so the reaction force from the wiring and intake hose does not change with each tightening. As a result, the driver bit 55 does not cam out from the screw S, and the screw can be tightened smoothly with an appropriate desired torque Ton without damaging the workpiece 90 or the screw S. In addition, since the tool unit 50 is set to be able to move forward to a stopping position Z4 located in front of the seating position Z3, the screw can be tightened without any problems regardless of whether the workpiece 90 is curved in the front or back direction.

[0044] Subsequently, when the screw S is seated on the workpiece 90, the tightening torque of the tightening motor 51 reaches a predetermined value. Upon determining that the screw tightening is complete, the operation command unit 84 uses the torque command unit 86 to reverse-drive the movement motor 48, moving the tool unit 50 back to the switching position Z1. Once the tool unit 50 has moved back to the switching position Z1, the operation command unit 84 switches control of the movement motor 48 from the torque command unit 86 to the position command unit 85, moving the tool unit 50 back to the standby position. Note that if the workpiece 90 is not positioned as predetermined, as shown in (Z4) of Figure 7, and the tool unit 50 moves forward to the stopping position Z4, the position command unit 85 stops the movement motor 48. The position command unit 85 then reverse-drives the movement motor 48, moving the tool unit 50 back to the standby position.

[0045] As described above, the screw tightening device 10 divides the command torque Tsn of the moving motor 48 into a drive load offset torque Trn, whose value changes depending on the part of the ball screw 47; a self-weight load offset torque Tw, whose value differs depending on the posture of the reciprocating movement unit 40; and a desired torque Ton. The drive load offset torque Trn is estimated in the drive load estimation step, and the self-weight load offset torque Tw is estimated in the self-weight load estimation step. Therefore, the appropriate command torque Tsn can be calculated immediately regardless of the posture in which the articulated robot 30 moves the reciprocating movement unit 40. As a result, even if there are multiple tightening positions, it is not necessary to create separate command torque tables for each, reducing the burden on the operator. Furthermore, by performing the drive load estimation step at predetermined intervals, changes in the coefficient of friction due to lubricant deterioration or dust can be reflected in the drive load offset torque Trn. Thus, the present invention estimates the self-weight load offset torque Tw, which changes each time the posture of the reciprocating movement unit 40 changes, and the drive load offset torque Trn, which hardly changes in the short term, in separate processes, and determines the command torque Tsn from these values, thereby enabling the application of a desired thrust to the tool unit 50.

[0046] As described above, the screw tightening device 10 is configured such that the position of the moving motor 48 is controlled by the position command unit 85 until the tool unit 50 reaches the switching position Z1, and then the torque command unit 86 switches the moving motor 48 to torque control once the tool unit 50 reaches the switching position Z1. Therefore, since torque control, which is generally slower than position control, is only applied in the vicinity of the workpiece 90, the cycle time is shortened and it is possible to press the workpiece 90 with an appropriate thrust. Moreover, since these are performed solely by controlling the moving motor 48, it is more energy-efficient than systems that combine multiple drive sources.

[0047] It should be noted that the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. For example, the tool unit 50 is not limited to one that fastens screws as described above, but may be equipped with a drill that forms an internal thread 91 in the workpiece 90, or it may be one that inserts a pin into a hole formed in the workpiece 90.

[0048] Furthermore, the estimation method for the command torque Tsn, drive load offset torque Trn, and self-weight load offset torque Tw in the above embodiment is merely an example, and other methods are perfectly acceptable. For example, in the self-weight load estimation step, the self-weight load Rw was estimated by excluding the value of the maximum static friction force K from the load torque T3 (≒Rw-K) during forward movement and the load torque T4 (≒Rw+K) during reverse movement. However, there is no problem with a method in which the value of the maximum static friction force K is calculated first, as shown in the following procedure, and then Rw is calculated by substituting the maximum static friction force K into either T3 or T4. T3-T4≈(Rw-K)-(Rw+K)=-2K K ≈ -(T3-T4) / 2 Rw ≈ T3 + K Furthermore, just like with Rw, there is no problem regardless of the procedure used to estimate Rn, etc. [Explanation of Symbols]

[0049] 10 ... Screw tightening device 20... Tool moving device 30… Multi-joint robot 40… Reciprocating movement unit 45… Driver stand 47… Ball screw 48… Mobile motor 49… Encoder 50… Tool Unit 51… Tightening motor 55 ... Driver bit 58… Cable carrier 70 ... Chuck unit 80 ... Control device 81 ... Drive control unit 82… Robot Control Unit 83 ... Motor control unit for movement 84 … Operation command section 85 … Position command section 86... Torque command unit 87 ... Tightening motor control unit 90… Work 91… Female thread

Claims

1. In a tool moving device that moves a tool unit to perform a predetermined operation on a workpiece, The tool unit is a reciprocating movement unit that moves the tool unit closer to or further away from the workpiece, A motor for driving the aforementioned reciprocating movement unit, The system includes a control device capable of controlling the drive of the aforementioned moving motor, The control device includes a torque command unit that controls the torque so that the moving motor outputs a desired command torque. The command torque is A drive load estimation step for estimating a drive load offsetting torque that offsets the drive load of the reciprocating movement unit, A self-weight load estimation step for estimating a self-weight load offsetting torque that offsets the self-weight load generated by the self-weight of the tool unit, A tool moving device characterized by being created by a calculation step of adding the drive load offset torque and the self-weight load offset torque to a desired torque that is set in advance to correspond to a desired thrust applied to the tool unit.

2. The tool moving device according to claim 1, characterized in that the drive load estimation step divides the entire range of motion of the reciprocating moving unit into a number of minute sections and estimates the drive load offsetting torque for each minute section.

3. The tool moving device according to claim 2, characterized in that the drive load estimation step involves the reciprocating movement unit moving the tool unit back and forth in the forward and backward directions, acquiring the load torque for each minute interval during forward and backward movement, and estimating the drive load from the load torque during forward and backward movement.

4. The tool moving device according to claim 1, characterized in that the self-weight load estimation step involves the reciprocating movement unit moving the tool unit back and forth in the forward and backward directions, acquiring the load torque immediately before movement begins at both the front and rear ends of the reciprocating movement, and calculating the self-weight of the tool unit from the load torque acquired at the front and rear ends.

5. The reciprocating movement unit is equipped with a multi-joint robot capable of moving it to any position and orientation. The tool moving device according to claim 1, characterized in that the control device controls the reciprocating movement unit to perform the self-weight load estimation process when the articulated robot is driven.

6. A tool unit having a screw tightening tool that can engage with a screw, and a tightening motor that rotates the screw tightening tool, The tool unit is a reciprocating movement unit that moves the tool unit closer to or further away from the workpiece, A motor for driving the aforementioned reciprocating movement unit, The system includes a control device capable of controlling the drive of the aforementioned moving motor, The control device is a screw tightening device having a torque command unit that controls the torque so that the moving motor outputs a desired command torque, The command torque is A drive load estimation step for estimating a drive load offsetting torque that offsets the drive load of the reciprocating movement unit, A self-weight load estimation step for estimating a self-weight load offsetting torque that offsets the self-weight of the tool unit, A screw tightening device characterized by being created by a calculation step of adding the drive load offset torque and the self-weight load offset torque to a desired torque that is set in advance to correspond to a desired thrust applied to the tool unit.

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