stepper acceleration

#include <StepperDriver.h>  //https://github.com/xxxooo/StepperDriver/blob/master/StepperDriver.h

int motor_steps = 200;  //
int step_divisition = 16;
int en_pin = 6; //enable
int cw_pin = 5; // dir
int clk_pin = 2; //step

StepperDriver ss(motor_steps, step_divisition, en_pin, cw_pin, clk_pin);

void setup() {

    Serial.begin(115200);
	ss.setSpeed(160);
	ss.powerEnable(true);
	ss.positioning();
	delay(1600);
}

void loop() {
	ss.setSpeed(80); //160 werkt niet
	ss.step(400);
   Serial.println("1");
   delay(1000);


	ss.step(-400);
  Serial.println("2");
   delay(1000);


    ss.setSpeed(40);
	ss.step(1200, 144, 160);
  Serial.println("3");
   delay(1000);

	ss.step(-1200, 144, 160);
	  Serial.println("4");
   delay(1000);


	ss.setSpeed(200);
	ss.step(400, 32, 40);
  Serial.println("5");
   delay(1000);

	ss.step(-400, 32, 40);
  Serial.println("6");
   delay(1000);

}