JP7157548B2 - Screw tightening robot - Google Patents

Description

TECHNICAL FIELD The present invention relates to a screw tightening robot that suppresses an axial impact load generated when the tip of a screw to be fastened comes into contact with a work.

As shown in Patent Document 1, a conventional screw-tightening robot consists of a driver unit capable of rotationally driving a bit, an articulated arm movably supporting the driver unit, and the articulated arm and driver unit. a force sensor interposed therebetween for detecting an axial load applied to the driver unit; and a control unit configured to control the articulated arm.

The driver unit disclosed in Patent Document 1 is configured without an elastic member such as a spring that bends in its axial direction. a motor; The control unit is configured to compare the load detected by the force sensor and the pressing force to control the force of the articulated arm.

In other words, since the conventional screw-tightening robot is configured to directly transmit the axial load applied to the bit by the force sensor, the movement of the bit can be controlled by an appropriate pressing force, and the elastic member is not provided. It has the feature that a simple device configuration can be realized.

Patent No. 5565550

However, conventional screw-fastening robots that do not have the above-described elastic member have the problem of generating a high impact load when the tip of the screw contacts the workpiece. Moreover, in order to solve this problem, the moving speed of the bit is lowered before contact, but there is also the problem that the screw tightening time increases with this countermeasure.

The present invention includes a driver unit that includes a bit that can be engaged with a screw to be screwed into a workpiece and that drives the bit to rotate, a force sensor that detects an axial load applied to the bit, and a driver unit that supports the driver unit. In a screw fastening robot comprising an articulated arm movable to a predetermined position and control means for controlling the driving of the articulated arm based on the load detected by the force sensor, the driver unit is a rotary drive source. A cushion spring is provided on a drive transmission path for transmitting the rotational drive to the bit, and the cushion spring bends when the screw engaged with the bit comes into contact with the work, and immediately before the screw is completely tightened. is set so that the bit and the screw are kept in close contact with each other without bending even when a pressing force that does not cause cam-out required for .

The control means comprises a target pressing force lower than the pressing force exerted when the cushion spring begins to compress, a target moving speed determined by the lead of the screw to be screwed in and the number of revolutions of the bit, and a predetermined The target pressing force is a set value for force-controlling the articulated arm from the tip of the screw contacting the workpiece to the completion of fastening, and The target moving speed is a reference value for moving the multi-joint arm in the screwing direction from the tip of the screw coming into contact with the workpiece to the completion of fastening. It is preferable to be controlled to exert. Further, the control means includes a storage section for pre-storing the length under neck of the screw to be fastened to the work, and a judgment section for judging the floating state of the screw after fastening. The screwing start position of the multi-joint arm when the detected load reaches the target pressing force and the fastening completion position of the multi-joint arm when fastening is completed are read, and the difference between the read screwing start position and the fastening completion position and the under-neck length.

Since the screw tightening robot according to the present invention includes the cushioning member, it is possible to greatly reduce the impact load applied to the bit engaged with the screw when the tip of the screw to be screwed comes into contact with the work. As a result, since a strong impact is not applied to the workpiece when the screw is tightened, there is an advantage that it is possible to screw a substrate, which is easily damaged, for example. Also, as described above, the impact when the tip of the screw comes into contact with the work can be suppressed, so there is no need to switch the moving speed of the articulated arm from high to low just before the tip of the screw comes into contact with the work. Therefore, the screw tightening robot according to the present invention also has the advantage of being able to shorten the working time of one cycle from the start of screw tightening to the completion of screw tightening.

In addition, since the screw tightening robot according to the present invention is provided with a cushion spring that always biases the bit in the direction of drawing it out, the structure of the cushioning member can be made relatively simple. As a result, there is also the advantage that the cost can be reduced compared to a complicated mechanism having a large number of parts such as a cylinder type shock absorber.

Further, in the screw tightening robot according to the present invention, the cushioning force of the cushion spring is set to a high thrust rather than a low thrust to cam out. As a result, when the tip of the screw comes into contact with the work, the bit is drawn in with the deflection of the cushion spring and moves relatively. When it is finished, the cushion spring returns to its original position and the state of relative movement is eliminated. In other words, just before the screw starts to be screwed in, the bit is retracted to reduce the impact, while after the impact has been reduced, the bit reliably returns from the relative movement state to the initial pushed-out position. Therefore, screw tightening can be completed without changing the deflection amount of the cushion spring. Therefore, the screw tightening robot according to the present invention also has the advantage that the position information of the articulated arm can be used by replacing it with the tip position of the bit. Specifically, a deflection detection means for directly detecting the deflection amount of the cushion spring is separately provided, and the tip position of the bit is calculated in consideration of the detection result of this deflection detection means and the positional information of the articulated arm. There is no such need.

Further, in the screw-tightening robot according to the present invention, the force of the articulated arm is controlled based on a target pressing force lower than the set load, so that the screw being screwed into the work can be smoothly screwed inward. There is also the advantage of

Furthermore, the screw tightening robot according to the present invention can recognize that the tip of the screw has come into contact with the workpiece when the load detected by the force sensor reaches the set load. In addition, the distance that the multi-joint arm moves from the position where this abutment is recognized until the completion of fastening is compared with the length under the neck of the screw that has been stored in advance, and the screw after fastening is seated on the work and fastened normally. It is possible to determine whether or not Therefore, the screw tightening robot according to the present invention also has the advantage that it is not necessary to store in advance the position, which is the criterion for determining screw floating, by teaching or the like.

1 is an overall view showing an outline of a screw tightening robot according to the present invention; FIG. 4 is a block diagram showing control means according to the present invention; FIG.

A screw tightening robot 1 according to the present invention will be described with reference to FIGS. 1 and 2. FIG. As shown in FIG. 1, a screw tightening robot 1 according to the present invention is configured such that a screw S, which is an example of a fastening part, can be fastened to a work W. , a force sensor 20 arranged at the tip of the multi-joint arm 30 for detecting the load applied to the tip of the multi-joint arm 30; a driver tool 10 attached to the force sensor 20; The sensor 20 and the multi-joint arm 30 are connected by wiring, and a control means 40 capable of inputting/outputting signals is provided.

The driver tool 10 comprises a bit B that can be engaged with the screw S, a bit rotating motor BM that imparts rotation to the bit B, and a torque sensor TS that can detect the torque applied to the bit B. , the bit rotation motor BM and the torque sensor TS are connected to the control means 40 .

The bit rotation motor BM is a so-called AC servomotor, which is configured to be able to transmit a rotation signal of an encoder built therein to the control means 40, and can rotate the output shaft 11 by electric power supplied from the control means 40. is configured to

The bit B has an engaging portion on its tip side that fits into a cross hole formed in the head of the screw S, and its rear end side is configured to rotate integrally with the output shaft 11 of the bit rotation motor BM. It is Further, the bit B and the bit rotation motor BM are connected via a buffer member that can expand and contract in the direction in which the bit B extends.

The cushioning member always urges the bit B in the direction of protruding toward the work W, and the bit B is positioned by a stopper 16 so as to have a predetermined protruding margin. Further, when an axial pressing force acts from the tip side of the bit B toward the bit rotating motor BM side, the cushioning member bends according to this pressing force. Therefore, the bit B is normally urged with a predetermined force by the elastic force of the buffer member, and rotates integrally with the output shaft 11 while maintaining the protrusion defined by the stopper 16 . That is, the bit B moves relative to the bit rotating motor BM when the pressing force is applied, but can rotate integrally with the output shaft 11 .

The axial force of the bit urged by the elastic force of the cushioning member described above will be described below as a set load. It is set in advance so that the force does not separate.

Further, in this embodiment, the cushioning member is the cushion spring 15 formed in a helical shape that bends in the compression direction shown in FIG. 1, but is not limited to this. It is sufficient that the bit B can be relatively moved in the axial direction and that the axial impact received by the bit B can be reduced by the relative movement.

The force sensor 20 has the driver tool 10 mounted thereon, can detect a load including the weight of the driver tool 10 applied thereto, and appropriately transmits the detected load to the control means 40 .

The multi-joint arm 30 is formed by connecting a plurality of arms in series so as to be freely rotatable, and a rotary drive source is arranged at this connection point. All of the rotary drive sources arranged at the plurality of connection points are connected to the control means 40 and driven and controlled. The multi-joint arm 30 has the force sensor 20 attached to its tip, and supports the driver tool 10 movably.

The control means 40 includes, as shown in FIG. 30 and a control section 42 that drives and controls the driver unit 10 .

The storage unit 41 stores the target tightening torque of the screw S, the target pressing force of the bit B, the target moving speed for moving the bit B toward the work W, and the tightening completion position of the screw S to the work W, which are the setting conditions. Numerical values such as the target position, the target rotation speed for rotating the bit B in the screwing direction, and the neck length of the screw S to be fastened to the work W are stored in advance.

The target pressing force is set to a value exceeding zero and lower than the set load, and is set to a value that does not cause the bit B to come out of the screw S, like the set load.

A plurality of target moving speeds are set. For example, a first target moving speed at which the tip of the screw S engaged with the bit B comes into contact with the internal thread W1 provided on the workpiece W, and a fastening speed after the tip of the screw S starts screwing into the internal thread W1. It is set such that it is divided into the second target movement speed until completion. In the case of these two target moving speeds, the first target moving speed is higher than the second target moving speed, and the second target moving speed is calculated based on the lead of the screw S and the rotational speed of the bit B. set to a value.

The control unit 42 is configured to send an operation command to the bit rotating motor BM and the rotary drive source of the articulated arm 30, and to receive detection signals transmitted from the force sensor 20 and the torque sensor TS. Configured. The operation command is a supply current or the like determined based on the setting conditions, and the detection signal is an axial detected load applied to the bit B transmitted from the force sensor 20 or a bit transmitted from the torque sensor TS. Detected torque applied to B and the like. The control unit 42 is configured to be able to read the value stored in the storage unit 41, and includes a determination unit 43 that compares the read value with the detection signal for determination processing.

The determination unit 43 is configured to perform various determinations such as whether or not the head of the screw S fastened to the work W is floating from the surface of the work W.

The operation of the screw tightening robot 1 according to the present invention configured in this manner will be described below. First, the control means 40 controls the movement of the articulated arm 30 based on the target position and the first target movement speed stored in the storage unit 41, and at the same time, controls the bit rotation motor BM based on the target rotation speed. to rotate. As a result, the bit B engages with the screw S and begins to descend at high speed while rotating.

Further, when the bit B is lowered at high speed at the first target moving speed, the control section 42 always receives the load detected by the force sensor 20, and the determination section 43 determines the difference between the detected load and the target pressing force. are compared.

When the tip of the screw S comes into contact with the inlet of the female screw W1, the load in the axial direction is transmitted to the bit B via the screw S, so the load detected by the force sensor 20 gradually increases. When the load detected by the force sensor 20 eventually rises to the target pressing force, the judging section 43 judges that the tip of the screw S has come into contact with the female screw W1. In addition, the control unit 42 that has received this determination switches the multi-joint arm 30 from speed control to force control to perform position control. Furthermore, the control unit 42 acquires the position of the bit B at the time of switching to the force control based on the position information of the articulated arm 30, and stores this in the storage unit 41 as the screwing start position.

In this way, when the tip of the screw S comes into contact with the internal thread W1, a load exceeding the set load may be applied to the bit B in some cases. However, since the bit B is always urged by the cushion spring 15, it can move relative to the axial direction even during such contact. Therefore, the screw tightening robot 1 according to the present invention greatly reduces the instantaneous axial impact force generated when the screw S and the work W come into contact with each other, compared to the conventional screw tightening robot that does not have the cushion spring 15. It has the advantage that it can be mitigated.

The force control is to position-control the articulated arm 30 so that the detected load matches the target pressing force. to drive and control the articulated arm 30 . In addition, since this force control is performed from the tip of the screw S coming into contact with the workpiece W until the screw S reaches the target tightening torque and the tightening is completed, the bit B maintains a constant target pressing force during this period. will perform. Moreover, since this target pressing force is a value that does not come out as described above, the bit B will not come out from the tightened screw S after switching to force control.

Further, since the target pressing force is set lower than the set load, the cushion spring 15 will not bend again during the force control. That is, while the screw S is being screwed in and tightened to the target tightening torque, the bit B maintains the initially set protruding margin. There is also the advantage that position information can be used as the tip position of bit B.

The determination unit 43 compares the detected torque sent from the torque sensor TS with the target tightening torque, and sends a tightening completion signal to the control unit 42 when the detected torque reaches the target tightening torque. Upon receiving this fastening completion signal, the control unit 42 sends a rotation stop command to the bit rotation motor BM to stop the rotation of the bit B, and determines the position of the bit B at this time based on the position information of the articulated arm 30. to get. The position of the bit B at the completion of fastening is stored in the storage unit 41 as the fastening completion position.

The determination unit 43 reads the tightening completion position and the screwing start position from the storage unit 41, calculates the difference between them, and stores the difference and the neck length of the screw S stored in advance in the storage unit 41. By comparison, it is determined whether or not the head of the screw S is lifted from the surface of the work W.

Reference Signs List 1... Screw tightening robot 10... Driver unit 11... Output shaft 15... Cushion spring 20... Force sensor 30... Articulated arm 40... Control means B... Bit BM... Bit rotating motor S... Screw TS... Torque sensor W... Work W1... female thread

Claims (3)

A driver unit having a bit that can be engaged with a screw to be screwed into a workpiece and rotatingly driving the bit, a force sensor that detects an axial load applied to the bit, and a driver unit that supports and moves to a predetermined position. A screw tightening robot comprising a flexible articulated arm and control means for controlling the drive of the articulated arm based on the load detected by the force sensor,
The driver unit is provided with a rotational drive source that rotationally drives the bit and a cushion spring that biases the bit toward the workpiece between the bit,
The screw tightening robot , wherein the cushion spring is set to start compressing when a load exceeding a required pressing force is applied when fastening is completed . The control means comprises a target pressing force set lower than the pressing force exerted when the cushion spring begins to compress, a target moving speed determined by the lead of the threaded screw and the number of revolutions of the bit, and a predetermined speed of the screw. A target position to finish fastening with a target tightening torque is stored in advance,
The target pressing force is a set value for force-controlling the multi-joint arm from the tip of the screw contacting the workpiece to the completion of fastening,
The target movement speed is a reference value for moving the multi-joint arm in the screwing direction from the tip of the screw coming into contact with the workpiece to the completion of fastening,
2. The screw tightening robot according to claim 1, wherein said articulated arm is controlled to exert said target pressing force toward said target position. The control means includes a storage unit that stores in advance the length under neck of the screw to be fastened to the work, and a determination unit that determines the floating state of the screw after fastening,
The determination unit reads a screwing start position of the multi-joint arm when the load detected by the force sensor reaches the target pressing force and a fastening completion position of the multi-joint arm when fastening is completed, and reads these read screws. 3. The screw tightening robot according to claim 2, wherein the presence or absence of screw floating is determined based on the difference between the engagement start position and the tightening completion position and the neck length.

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