JP7808522B2 - Electric press equipment - Google Patents

Description

The present invention relates to an electric press device.

An electric press device is known that uses an electric motor such as a servo motor as a drive source to move a ram up and down and press an object with the ram (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2022-33563

In electric presses, a drive stop mode such as "load stop" is set. In "load stop," the drive command is stopped when the set "target stop load value" is detected, but at this time, the ram may overshoot from the position where it should stop. The ram moves forward the overshoot distance and stops, and the load accordingly exceeds the set "target stop load value." The distance of the overshoot generally depends on the drive speed of the ram, and the higher the drive speed, the greater the distance of the overshoot.

To reduce this overshoot phenomenon, a method is provided in which, when the "deceleration start load value" is detected, the pressure is applied by decelerating to a preset value or a fixed value, the "set speed VL." This method does not directly specify the "deceleration start load value," but rather sets the "deceleration start load value" by setting a "deceleration load rate" expressed as a percentage of the "target stop load value." In other words, the "deceleration start load value" can be expressed as "target stop load value x deceleration load rate."

Ideally, it would be sufficient if the ram could be decelerated quickly to the set deceleration speed VL when the set value for the "deceleration start load value," i.e., the "target stopping load value x deceleration load rate," reaches a predetermined set value. However, in reality, it takes a certain amount of time to decelerate the ram. Therefore, if the set value for the "deceleration load rate" is inappropriate, the ram speed will reach the "target stopping load value" before it reaches the set deceleration speed VL, resulting in variation in the ram speed when the drive command is stopped. This variation leads to variation in the overshoot distance, which in turn leads to variation in the overshoot load, which ultimately leads to unnecessary variation in the ram stopping position and load value.

The "deceleration load rate," which is set to reduce work time and reduce overshoot, has an appropriate value that varies depending on the workpiece and press environment. Even if you are operating with a "deceleration load rate" set that allows for a certain degree of acceptable variation, adding equipment or making small changes to the workpiece can increase the variation and exceed the allowable range. Press operation can occur without checking that the deceleration load rate is outside the allowable range, resulting in greater variation in the ram stopping position and load.

In consideration of the above issues, the present invention provides an electric press device that can optimize the deceleration load rate and reduce variations in the ram stopping position and load when stopped, even when differences in the workpiece or press environment occur.

In order to solve the above problem, one embodiment of the present invention provides an electric press apparatus comprising: a ram that applies pressure to a workpiece; a load detection unit that detects the load on the ram; a target stopping load memory unit that stores a target stopping load value for the ram; a deceleration load rate memory unit that stores a deceleration load rate, expressed as a percentage of the target stopping load value, at which the ram begins to decelerate just before the target stopping load value is reached; a speed control unit that controls the ram speed to decelerate to a set speed from the time the load detection unit detects a load value obtained by multiplying the deceleration load rate and the target stopping load value; and a determination unit that determines whether the deceleration load rate is appropriate based on the results of a comparison between the ram speed at the target stopping load value and the set speed.

The present invention provides an electric press device that can optimize the deceleration load rate and reduce variations in the ram stopping position and load when stopped, even when differences in the workpiece or press environment occur.

1 is a perspective view showing an example of an electric press apparatus according to an embodiment of the present invention; 1 is a cross-sectional view showing a configuration of a mechanical portion of an electric press apparatus according to an embodiment of the present invention. 1 is a block diagram showing a configuration example of a controller portion and its peripheral portion of an electric press apparatus according to an embodiment of the present invention. FIG. 10 is a graph showing an example of the relationship between the load and speed of a ram when the deceleration load rate is appropriate. 10 is a graph showing an example of the relationship between the load and speed of a ram when the deceleration load rate is not appropriate. 10 is a graph showing the variation in the load of the ram when the deceleration load rate is not appropriate. 4 is a flowchart showing a first example (automatic setting method) of a method for calculating a deceleration load rate of an electric press apparatus according to an embodiment of the present invention. 8 is a graph showing an example of the results when the end condition δ is set to 2 and the deceleration load rate is calculated according to the flowchart of FIG. 7. 8 is a graph showing an example of the results when the end condition δ is set to 4 and the deceleration load rate is calculated according to the flowchart of FIG. 7. 10 is a flowchart showing a second example (semi-automatic setting method) of a method for calculating a deceleration load rate of an electric press apparatus according to an embodiment of the present invention. 1 is a graph showing an example of the relationship between the load and speed of a ram when the speed of the ram is calculated based on equation (1). 10 is a graph showing an example of the relationship between the load and speed of a ram when the speed of the ram is calculated using the least squares method. 10 is a graph showing an example of the relationship between load and speed when operation is performed multiple times under the same conditions.

Embodiments of the present invention will be described below with reference to the drawings. In the following description of the drawings, identical or similar parts are designated by identical or similar reference numerals. Note that the embodiments shown below are examples of devices and methods that embody the technical concept of this invention, and the technical concept of this invention does not limit the structure, arrangement, etc. of component parts to those described below.

<Structure of electric press device>
An electric press apparatus according to an embodiment of the present invention comprises a main body mechanism portion as shown in Figures 1 and 2 and a controller portion as shown in Figure 3. The main body mechanism portion comprises a conversion mechanism that converts rotational force into linear motion of a press ram 1 using a screw mechanism. As shown in Figure 2, for example, the conversion mechanism comprises the press ram 1 that applies a desired pressure to a workpiece W (workpiece) by linear motion, and a ball screw 2 that applies linear motion to the ram 1, and these are provided inside the upper body 4 of the press apparatus.

The ram 1 is located inside the upper body 4. The upper body 4 also contains a servo motor 3, which serves as an electric motor that powers the ram 1. The drive of the servo motor 3 is transmitted to the ball screw 2 via a pulley and belt. The upper body 4 is fixed to a support 7 located at the bottom of the upper body 4, and the support 7 is fixed to a base 8. The base 8 is made of a material such as aluminum or iron, and the workpiece W to be pressed is placed on this base 8. The guide section 6 extends axially adjacent to the ram 1 and is configured to guide the ram 1 along the axial direction. Switches 9a and 9b are connected to the ends of the base 8 and are operated by the operator when starting or stopping the pressing operation of the workpiece W.

The ram 1 has a hollow portion formed along the axial direction inside its cylindrical body, and the screw shaft 2a of the ball screw 2 can be inserted into this hollow portion. The nut body 2b of the ball screw 2 is fixed to the axial end of the cylindrical body of the ram 1. The tip of the cylindrical body is configured so that a strain-flexible pillar 1b can be freely attached. The strain-flexible pillar 1b abuts against the workpiece W and applies an appropriate pressure. A strain gauge is attached to the strain-flexible pillar 1b, and this strain gauge can detect the load value applied to the workpiece W.

Figure 3 is a schematic diagram of the controller (control mechanism) and its surroundings that controls the main body mechanical parts of Figures 1 and 2. The controller includes a processor (CPU) 20. Connected to the processor 20 are a control program memory unit 11, a display unit 12, an operation unit 13, a primary memory unit 14, a target stopping load memory unit 15, and a deceleration load rate memory unit 16.

The control program storage unit 11 stores various control programs that control the processor 20. The display unit 12 displays processing results, such as graphs shown in Figures 4 to 6, which show the relationship between the speed of the ram 1 and the detection results of the load on the ram 1. The operation unit 13 is composed of a mouse, keyboard, etc., which can be used to input the operating conditions of the ram 1 and various parameters required for pressing the workpiece W. The primary storage unit 14 is composed of memory, etc., which can store temporary data used in the calculation process.

The target stopping load memory unit 15 stores the target stopping load value (Load of Target) LT [N], which is the target load when stopping the press operation of the ram 1. The deceleration load rate memory unit 16 stores the deceleration load rate (Ratio) R [%], which is expressed as a percentage (%) of the target stopping load value, when deceleration of the ram 1 begins just before the target stopping load value.

The processor 20 is further connected to a load detection unit 31, a command pulse generator 32, a servo motor driver 33, and an encoder position counter 35, all connected to the strain column 1b. The load detection unit 31 amplifies the signal corresponding to the resistance change of the strain gauge attached to the strain column 1b, converts the analog signal to a digital signal through A/D conversion processing, and outputs the converted signal to the processor 20. The command pulse generator 32 generates the desired drive command pulse based on a command from the processor 20, and outputs the generated drive command pulse signal via the processor 20 to the servo motor driver 33. The servo motor driver 33 then controls the servo motor 3 to drive the ram 1, thereby moving the ram 1 up and down.

The servo motor 3 is connected to an encoder 34. The encoder 34 detects the rotation angle of the servo motor and functions as a position detector that detects the position of the ram 1. The information from the encoder 34 provides position information to the servo motor driver 33 for feedback control. The position information from the encoder 34 is also output to the processor 20 via an encoder position counter 35, allowing the position of the ram 1 to be detected.

The processor 20 includes a stop unit 21, a speed control unit 22, a determination unit 23, a search unit 24, and a notification unit 25. When the load detection unit 31 detects a target stopping load value LT for stopping the pressing operation of the ram 1, the stop unit 21 outputs a control signal to the servo motor 3, which is an electric motor, to stop the servo motor 3, thereby stopping the ram 1. The speed control unit 22 controls the speed of the ram 1, and when the load detection unit 31 detects a deceleration start load value, which is a load value obtained by multiplying the deceleration load rate R and the target stopping load value LT, controls the speed of the ram 1 at the target stopping load value LT to be decelerated to a set speed (Velocity of Low) VL [mm/sec] that is slower than a preset pressing speed (Velocity of Pressing) VP [mm/sec].

The judgment unit 23 compares the speed of the ram 1 at the target stopping load value LT with the set speed VL during deceleration, and based on the comparison result, judges whether the deceleration load rate R is appropriate, i.e., whether the speed control unit 22 is correctly decelerating the ram 1. If the speed of the ram 1 at the target stopping load value LT is equal to or less than the set speed VL, the judgment unit 23 judges that the deceleration load rate R is appropriate. On the other hand, if the speed of the ram 1 at the target stopping load value LT is greater than the set speed VL during deceleration, the judgment unit 23 judges that the deceleration load rate R is inappropriate.

If the deceleration load rate R is inappropriate, the ram 1 will overshoot from the position where it should stop, resulting in variations in the stopping position of the ram 1 and the load at the time of stopping. When the speed of the ram 1 at the target stopping load value LT is greater than the set speed VL during deceleration, the search unit 24 gradually changes the value of the deceleration load rate R and performs a test in which the ram 1 press operation is performed at the changed deceleration load rate R, thereby searching for and finding the appropriate deceleration load rate R for proper deceleration just before the stopping position of the ram 1.

If the speed of the ram 1 at the target stopping load value LT is greater than the set speed VL, the notification unit 25 notifies the operator, for example via the display unit 12, that the deceleration load rate R is inappropriate. This encourages the operator to optimize the deceleration load rate R, allowing for early response to variations in the stopping position of the ram 1 and the load at the time of stopping, even when differences arise in the workpiece W or press environment.

When ram 1 is in operation, a control program stored in control program memory unit 11 issues a drive command to servo motor driver 33, causing ram 1 to drive at speed VP (also called "pressurization speed"). When the load value detected by load detection unit 31 reaches a deceleration load value, which is the product of deceleration load rate R and target stopping load value LT, deceleration begins so that ram 1 speed VP reaches set speed VL. Thereafter, when the load value detected by load detection unit 31 reaches target stopping load value LT, stopping unit 21 stops servo motor 3, thereby halting the drive of ram 1.

Figure 4 is a graph showing the relationship between the load value (detected load) of ram 1 and speed when ram 1 is decelerated and stopped appropriately. Here, an example is shown where the set conditions are ram 1 speed (pressure speed) Vp = 5 mm/sec, set speed during deceleration VL = 1 mm/sec, target stopping load value LT = 10,000 N, and deceleration load rate R = 90%. In the example shown in Figure 4, as expected, the load reaches 10,000 N after decelerating to 1 mm/sec and stops. In the example of Figure 4, it can be evaluated that an appropriate deceleration load rate R is set.

In contrast, Figure 5 shows an example in which the deceleration load rate R is inappropriate. The setting conditions are the same as in the example in Figure 4. In Figure 5, deceleration of the ram 1 speed begins when the deceleration load rate R multiplied by the target stopping load value LT is 9,000 N, but the target stopping load value of 10,000 N is reached before the set speed during deceleration, VL = 1 mm/sec, is reached. In reality, in Figure 5, the target stopping load value LT is reached when the ram 1 is decelerated to 3 mm/sec. When the drive of the ram 1 is stopped, an overshoot occurs, and it stops at a load value of 10,300 N.

The problem in Figure 5 is not simply that the overshoot load is getting larger. Differences in the workpiece and press environment change the speed at which the target stop load value LT is reached, which can ultimately cause variations in the pressure application speed. Variations in the pressure application speed then cause variations in the overshoot distance, which ultimately manifests as variations in the load overshoot.

Figure 6 shows an example where overshoot load variations occur due to an inappropriate setting of the deceleration load rate R. The graph in Figure 6 shows three example operating results. The solid line indicates the same results as the operating operation in Figure 5. In the example shown by the dotted line above the solid line, the ram 1 speed is high at 4 mm/sec when the target stopping load value LT of 10,000 N is detected. As a result, both the overshoot distance and overshoot load when ram 1 stops are large, and the load exceeds by approximately 400 N. In the example shown by the dashed line below the solid line, the speed is low at 2 mm/sec when the target stopping load value LT of 10,000 N is reached, and the overshoot load is also small, staying at around 200 N.

The problem with Figure 6 is that deceleration begins at 9000 N, and the target stopping load value LT of 10,000 N is reached before the speed drops to 1 mm/sec, resulting in variable load overshoot.

When the phenomenon shown in Figure 6 is occurring, the problem can be resolved by lowering the deceleration load rate R. If the deceleration load rate R is lowered, for example from R = 90% to R = 80%, deceleration will begin at 10,000 N x 80% = 8,000 N, which is earlier than the stopping position of the ram 1 than in the case of 9,000 N. This increases the time it takes to reach the target stopping load value LT = 10,000 N, so it becomes possible to decelerate to the set speed VL for deceleration at the target stopping load value LT, which is 1 mm/sec, before reaching the target stopping load value LT.

The appropriateness of the deceleration load rate R can be determined by checking the speed of ram 1 when it reaches the target stopping load value LT = 10,000 N. In other words, if the speed of ram 1 is the set speed during deceleration VL = 1 mm/sec when it reaches the target stopping load value LT, then the deceleration load rate R is appropriate; if it is greater than 1 mm/sec, then the deceleration load rate R can be determined to be inappropriate.

Generally, reducing the deceleration load rate R increases the reliability of decelerating ram 1 to the set deceleration speed VL by the time ram 1 stops, but it also increases the distance it must be driven while decelerating, which increases the pressurization time, takt time, and productivity. Currently, the deceleration load rate R is set based on the experience and intuition of experienced workers, and there is no established method for appropriately setting the deceleration load rate R.

One tool for setting the deceleration load rate R to an appropriate value is, for example, PC application software that analyzes time-series data. Time-series data is a sequence of position and detected load values sampled at regular time intervals, for example, 1 msec intervals. The PC application software has a function that allows test pressure processing work to be performed during the setup stage, imports the time-series data from that time, and displays it as a position-load graph. It is primarily used to verify the validity of the judgment function and judgment values. Here, the judgment function refers to a function that specifies the position range and upper and lower load limits as set values, and detects whether the position and load during actual processing work pass within this judgment frame, and outputs an error if they go outside the judgment frame.

However, this type of PC application software is difficult to use for verifying the validity of the set value for the deceleration load rate R. As a result, it has become necessary for an experienced person to use a spreadsheet program or similar to find a valid value based on this time-series data.

On the other hand, the electric press device according to the embodiment of the present invention is equipped with a judgment unit 23 that judges whether the deceleration load rate R is appropriate based on the results of comparing the ram speed at the target stopping load value LT with the set speed VL. This makes it possible to optimize the deceleration load rate R even when differences arise in the workpiece W or press environment, thereby providing an electric press device that can reduce variation in the stopping position of the ram 1 and the load when stopped.

<Method for automatically searching for deceleration load rate R by search unit 24>
A specific example of an algorithm for searching for the deceleration load rate R is shown in the flowchart of Fig. 7. This algorithm is based on a dichotomous approach. Here, a method will be described in which the deceleration load rate R% is increased or decreased by a deceleration load rate adjustment range ΔR% and the deceleration load rate adjustment range ΔR% is halved.

In step 71, the search unit 24 sets an initial value for the deceleration load rate adjustment range ΔR [%]. The initial value can be, for example, a negative value, such as -16 [%]. Next, in step 72, the search unit 24 sets an initial value for the deceleration load rate R [%]. The initial value can be, for example, 84 [%]. Next, in step 73, the press process operation of the ram 1 is performed using the initial values set in steps 71 and 72. In step 74, from the data on the ram 1 position and ram 1 load detected by the encoder position counter 35 and the load detection unit 31, the search unit 24 calculates the speed of the ram 1 when the ram 1 load reaches the target stop load value LT.

In step 75, the judgment unit 73 determines whether the calculated speed of ram 1 is greater than the set speed VL. If the calculated speed of ram 1 is greater than the set speed VL, the judgment unit 73 determines that the deceleration load rate R is not an appropriate value and proceeds to step 76. In step 76, the search unit 24 updates the deceleration load rate R so that R becomes R + ΔR, and the process returns to step 73. As mentioned above, ΔR is a negative value. Here, the deceleration load rate R is gradually reduced until it becomes an appropriate value within the deceleration load rate adjustment range ΔR.

In step 75, if the calculated speed of ram 1 is equal to or less than the set speed VL, this indicates that ram 1 has been decelerated appropriately and the deceleration load rate R is an appropriate value. In this case, proceed to step 77. In step 77, the search unit 24 sets the deceleration load rate adjustment width ΔR to 1/2 and to a positive value.

In step 78, the search unit 24 updates the deceleration load rate R so that the deceleration load rate R becomes R + ΔR, and the process proceeds to step 79, where the ram 1 press process is performed using the updated deceleration load rate R. In step 80, the search unit 24 calculates the speed of ram 1 when the ram 1 load reaches the target stop load value LT from the data on the ram 1 position and ram 1 load detected by the encoder position counter 35 and the load detection unit 31.

In step 81, the judgment unit 73 determines whether the calculated speed of ram 1 is greater than the set speed VL. If the calculated speed of ram 1 is greater than the set speed VL, the judgment unit 73 determines that the deceleration load rate R is not a valid value (inappropriate), and proceeds to step 82. In step 82, the deceleration load rate adjustment width ΔR is halved to make it negative. In step 83, the judgment unit 73 determines whether the absolute value of the deceleration load rate adjustment width ΔR is smaller than the preset termination condition width δ. If the absolute value of the deceleration load rate adjustment width ΔR is not smaller than the termination condition width δ, the process returns to step 73. If the absolute value of the deceleration load rate adjustment width ΔR is smaller than the termination condition width δ, the process returns to step 84. The termination condition width δ [%] is the preset value of ΔR at the time of termination. If the absolute value of ΔR becomes smaller than δ, the process proceeds to step 84. Next, in step 84, the deceleration load rate R is determined to be an inappropriate value, so it is returned to the previous valid value. Here, ΔR is half, making it negative, so by doubling it and adding it, the deceleration load rate R is reset to a reasonable value, and the process proceeds to step 87 and ends.

On the other hand, if the calculated speed of ram 1 is not greater than the set speed VL, the deceleration load rate R is determined to be appropriate (suitable), and the process proceeds to step 85. In step 85, the search unit 24 halves the deceleration load rate adjustment range ΔR to make it positive. In step 86, the determination unit 73 determines whether the absolute value of the deceleration load rate adjustment range ΔR is less than the termination condition range δ. If the absolute value of the deceleration load rate adjustment range ΔR is not less than the termination condition range δ, the process returns to step 78. If the absolute value of the deceleration load rate adjustment range ΔR is less than the termination condition range δ, the process proceeds to step 87 and ends.

Figure 8 is a table showing the results of the automatic search for the deceleration load rate R when the termination condition width δ is set to 2 in the flowchart shown in Figure 7. In No. 1, when the initial conditions R = 84 and ΔR = -16 were used, the driving results were inappropriate, so in step 76 the value of the deceleration load rate R was updated to R + ΔR, resulting in the deceleration load rate R being updated to 76%. In No. 2, if the execution with the deceleration load rate R = 68 [%] was deemed appropriate, ΔR and R are updated in steps 77 and 78. In No. 3, ΔR becomes a positive value of 8, and the deceleration load rate R = 76%. If the driving results under these conditions are deemed appropriate, the values are updated in steps 85 and 78. Here, in step 86, the absolute values of the termination condition width δ = 2 and ΔR = 8 are compared, and it is determined that the termination conditions have not yet been met. No. In No. 4, if ΔR = 4 and deceleration load rate R = 80% and operation is deemed inappropriate, the values are updated in steps 82 and 78. In No. 5, if ΔR = -2 and deceleration load rate R = 78% and operation is deemed appropriate, then when ΔR is halved in step 85, the termination condition in step 86 is met and operation ends in step 87. In the example in Figure 8, when No. 6 ended, the deceleration load rate R = 78%.

Figure 9 is a table showing the results of the automatic search for the deceleration load rate when the termination condition width δ is set to 4 in the flowchart shown in Figure 7. Since the operation result of No. 4 is inappropriate, the value is returned in step 84, and the process ends with the deceleration load rate R = 76%.

In an electric press device according to an embodiment of the present invention, the search unit 24 determines an appropriate deceleration load rate R under specified conditions, for example, based on the flowchart in Figure 7, and then repeats press process operation execution tests using the determined deceleration load rate R, thereby searching for the appropriate deceleration load rate R. This makes it possible to provide an electric press device that can reduce variations in the stopping position of the ram 1 and the load at the time of stopping, even when differences arise in the workpiece or press environment.

<Semi-automatic search method for deceleration load rate R using notification unit 25>
10 is a flowchart showing a modified example of the method for searching for the deceleration load rate R. After starting in step 90, in step 91, the operator inputs and sets the deceleration load rate R via the operation unit 13. In step 92, the operation of the press process of the ram 1 is executed. This operation may also be initiated by the operator. In step 93, the judgment unit 23 calculates the speed of the ram 1 at the target stopping load value LT. In step 94, the judgment unit 23 compares the calculated speed of the ram 1 at the target stopping load value LT with the set speed VL. If the calculated speed is greater than the set speed VL, the judgment unit 23 determines that the deceleration load rate R is inappropriate, and the process proceeds to step 95. The notification unit 25 notifies the operator via the display unit 12 that the deceleration load rate R is inappropriate, and the process returns to step 91. On the other hand, if the calculated speed is equal to or less than the set speed VL, the judgment unit 23 judges that the deceleration load rate R is appropriate, and in step 96, the notification unit 25 notifies the operator via the display unit 12 that the deceleration load rate R is appropriate, and the process returns to step 91.

In step 95, the notification unit 25 may not only notify the operator via the display unit 12 that the deceleration load rate R is inappropriate, but also display a graph of time-series data showing the relationship between the speed of the ram 1 and the load (detected load) applied to the ram 1, as shown in Figures 4 and 5, for example. By referring to the displayed graph, the operator can adjust the value of the deceleration load rate R entered in step 91, thereby more quickly obtaining an appropriate value for the deceleration load rate R.

The calculated speed of ram 1 at the target stopping load value LT calculated in steps 74 and 80 of Figure 7 and step 93 of Figure 10 can be calculated using the following calculation method.

The velocity can be calculated from the position of the ram 1 observed at regular time intervals. For example, assume that position information for positions P1, P2, ... is detected at a certain time Tc. At this time, the instantaneous velocities V2, V3, and VN of the ram 1 are expressed by equation (1):
V2=(P2-P1)/Tc
V3=(P3-P2)/Tc
VN=(PN-P(N-1))/Tc...Formula (1)

Figure 11 shows a graph plotting the relationship between speed and detected load calculated based on equation (1). Here, the pressure application speed VP of ram 1 is set to 5 mm/sec, and the set speed VL during deceleration is set to 1 mm/sec.

When calculating speed by simply taking the difference as shown in equation (1), the value fluctuates, as shown in Figure 11. In reality, the speed does not fluctuate; it is merely a phenomenon that appears to occur in the calculation, and it is thought that this is due to errors associated with the quantization of the position of RAM 1. Alternatively, this fluctuating calculation occurs because the sampling time interval Tc is not completely constant. Incidentally, the sampling time interval Tc in Figure 11 is 5 msec.

The speed calculated as the slope of the linear regression using the least squares method is shown in the graph in Figure 12. Figure 12 shows that the speed values are relatively stable. Figure 12 also shows that at the target stopping load value of 10,000 N, the speed has not yet dropped to 1 mm/sec, remaining at around 2 mm/sec.

To calculate the speed of ram 1, instead of using a calculation method based on two points like equation (1), we can use m pieces of data (here, m = 6) as shown in equation (2), assume that these m pieces of data lie on a straight line, and find the slope of this line using the least squares method. The calculation formula is shown below in equation (2).

(Here, Tk indicates time, Pk indicates position, and m indicates the number of data (m=6 in FIG. 12)).

Since the sampling time interval Tc is 5 msec, when m = 6, it becomes 5 msec x (6 - 1) = 25 msec, and 6 points will fall on a straight line. The number of data points m can be fixed, but as the speed slows, the amount of movement decreases, so a small number of points will result in larger errors. On the other hand, if m is made too large, the assumption that the points fall on a straight line will be incorrect. Also, if m is large, tracking will be poor when the speed fluctuates.

The number of data points m may be variable depending on the speed. First, calculate the approximate speed using equation (1), then determine the number of data points m based on that speed, and calculate the slope of the line using equation (2), thereby calculating the speed of ram 1.

Figure 13 shows a load-speed graph obtained when an operation is performed multiple times (three times) under the same conditions. Even under the same conditions, the graph results will vary depending on factors such as workpiece variations. When automatically finding the deceleration load rate, as shown in the flow chart in Figure 7, the calculated speed used for judgment may actually vary as a result of the operations performed in steps 73 and 79. Therefore, to determine whether the deceleration load rate R is "appropriate," it is necessary to perform the operation multiple times (for example, 10 times) without changing the deceleration load rate R, and only judge it to be appropriate if all of the operations are appropriate. If it is judged to be inappropriate, a single occurrence is sufficient to make the judgment. This makes it possible to determine a deceleration load rate R [%] that is reliably appropriate.

The present invention has been described using the above embodiments, but the descriptions and drawings that form part of this disclosure should not be understood as limiting the present invention, and various modifications are possible. For example, while "load stop" has been described in the embodiments of the present invention, "load gradient stop" processing, which monitors the amount of load change, particularly the amount of load change per unit distance, and stops when a certain set value is exceeded, can also be considered in the same way as the present invention. In other words, by applying the above embodiments to a function that sets a percentage of a set load gradient value and decelerates when this value is exceeded, an appropriate "deceleration load gradient rate" can be automatically calculated.

DESCRIPTION OF SYMBOLS 1...ram 1b...strain-generating column 2...ball screw 2a...screw shaft 2b...nut body 3...servo motor 6...guide section 7...support column 8...base 9a, 9b...switch 10...casing 11...control program memory section 12...display section 13...operation section 14...primary memory section 15...target stopping load memory section 16...deceleration load rate memory section 20...processor 21...stop section 22...speed control section 23...judgment section 24...search section 25...alarm section 31...load detection section 32...command pulse generator 33...servo motor driver 34...encoder 35...encoder position counter

Claims (5)

A ram that applies pressure to the workpiece;
a load detection unit that detects a load applied to the ram;
a target stopping load memory unit that stores a target stopping load value when the pressurizing operation of the ram is stopped;
a deceleration load rate storage unit configured to store a deceleration load rate, which is indicated as a ratio to the target stopping load value, when deceleration of the ram is started just before the target stopping load value is reached;
a speed control unit that controls the speed of the ram to be decelerated to a set speed from when the load detection unit detects a load value obtained by multiplying the deceleration load rate and the target stop load value;
an electric press apparatus comprising: a determination unit that determines whether the deceleration load rate is appropriate based on a result of comparing the ram speed at the target stopping load value with the set speed. 2. The electric press apparatus according to claim 1, further comprising a search unit that searches for an appropriate deceleration load rate when the speed of the ram at the target stopping load value is greater than the set speed. 3. The electric press apparatus according to claim 1, further comprising a notification unit that notifies the user that the deceleration load rate is inappropriate when the speed of the ram at the target stopping load value is greater than the set speed. 3. The electric press apparatus according to claim 1, further comprising an operation unit that allows input of a set value for the deceleration load rate based on time-series data that represents a relationship between the speed of the ram and a detection result of the load acting on the ram. 3. The electric press apparatus according to claim 1, further comprising: calculating the speed of the ram at the target stopping load value by finding a slope by applying a least squares method to time-series data representing a relationship between the speed of the ram and a detection result of the load acting on the ram.